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    Home-Built Dye Laser

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  • Back to Home-Built Dye Laser Sub-Table of Contents.

    Basic Home-Built Dye Laser Information

    Introduction to Home-Built Dye Laser

    Dye lasers are unique in that they are a class of lasers whose lasing medium is a liquid. Depending on the particular dye used, output can be at a wide range of wavelengths spanning the visible spectrum and beyond.

    Commercial dye lasers are often pumped by other lasers. For example, Rhodamine-B, a common dye used in dye lasers for the red region, is often pumped with an argon ion laser at 514 nm for CW operation or a doubled YAG laser at 532 nm when pulsed. A suitable flashlamp can also be used as a pump source (but not just any old electronic flash - it needs to be very intense with a fast rise-time). As it turns out, this can easily be home-made.

    In fact, the overall construction of a flashlamp pumped dye laser is quite simple and straightforward, at least compared to nearly all of the other lasers discussed in this chapter. At most, a minimal vacuum system is required (for the home-made flashlamp) and there is absolutely no special glass work or need for exotic gases (though finding the highly pure dyes may require a little finger-work).

    The hazards are also relatively moderate - some of the organic dye materials are toxic and a high voltage power supply (low current but a BIG energy storage capacitor) is needed to fire the flashlamp.

    Home-Built Dye Laser Safety

    There are three areas of safety considerations for the home-built HeHg laser (and other similar lasers, for that matter): Provide proper warning signs for both the laser radiation and high voltage. Keep pets and small children out of the area and make sure everyone present is instructed as to the dangers. The use of proper laser safety goggles for the specific wavelength(s) of your laser are highly recommended.

    For more information, see the chapter: Laser Safety. Sample safety labels which can be edited for this laser can be found in the section: Laser Safety Labels and Signs.

    Dye Laser Construction References and Links

    In addition to the article in: "Light and its Uses", there is also a fine article on the operation of organic dye lasers in the February 1969 issue of Scientific American. (This also happens to be the same issue that features plans for the home-built argon ion laser.). The following should also be of interest:

    Some Photos of Home-Built Dye Lasers

    (From: Chris Chagaris (pyro@grolen.com).)

    Home-Built Dye Laser Description

    The dye laser can be constructed without any requiring any glass working, and only a minimal vacuum capability (none if you use a commercial xenon flashlamp instead of the home-built variety). However, the power supply can be lethal and of course, liquids and HV do not mix!

    Refer to Typical Home-Built Dye Laser Assembly for a simplified diagram of the overall glasswork and power supply electronics.

    To totally eliminate ANY need for a vacuum system, a conventional xenon flash lamp and power supply can be substituted for the home-made variety. See the document: Notes on the Troubleshooting and Repair of Electronic Flash Units and Strobe Lights and Design Guidelines, Useful Circuits, and Schematics. However, simply substituting a xenon flashlamp for the air flashlamp without modifying the circuit will likely not work (at least, not more than once!) and common (relatively) low voltage photographic type strobes may be inadequate in terms of peak intensity to efficiently pump the dye lasing medium.

    (From: Chris Chagaris (pyro@grolen.com).)

    Using a 15 uF, 5 kV capacitor without any inductor would likely cause catastrophic failure at the first attempt to fire the xenon flashlamp. An inductor would save the lamp but cause a great lengthening of the pulse width which would not produce the needed flux density to excite the dye to laser threshold. There are methods sometimes used to enable one to utilize xenon flashlamps but these employ very high overvoltages (typically .3 uF at 20 kV for this size lamp) and triggered spark gaps for firing. This will usually keep the risetime of the lamp fast enough for success.

    Guidelines to Assure a Successful Home-Built Dye Laser

    These set of guidelines should be followed during construction of your first home-built dye laser. The factors below will greatly influence the ultimate output power, beam quality, and whether it produces any coherent light at all! Once you have a working laser, feel free to make modifications - one at a time.

    Where to Obtain Dye Laser Dyes

    Although you are welcome to try virtually any colored compound in your laser chamber to see if it will lase, sticking with what is known to work (at least in the beginning) is probably the wisest choice. In that regard, the following advice probably applies in general to dyes other than the one mentioned:

    (From: Chris Chagaris (pyro@grolen.com).)

    Fluorescein (Uranin) or more specifically disodium fluorescein can be purchased from a number of chemical houses. If you plan to use this compound in a dye laser, it must be of a very pure grade. If this is the case, I would suggest that you purchase it from one of the companies who specialize in laser dyes such as Lambda Physik at 1-800-EXCIMER, or Exciton at 1-937-252-2989. This is one of the least expensive laser dyes that can be purchased and has good efficiency in the green wavelengths.

    Also see the section: Laser and Optics Manufacturers and Suppliers.

    (From: Jon Singer, of the Joss Research Institute.)

    Conditions being what they are these days, an individual can't generally buy things from a chemical company. While it is possible to find Fluorescein on eBay (and also some scintillators -- my first UV dye laser was PPO that I got on eBay, pumped with a nitrogen laser), you can't just go there and expect to find a gram of laser-grade R6G.

    I've been looking into reasonable things for DIY laser folks, and so far I have two cheap and easy candidates, which I describe on Inexpensive Laser Dyes for the Do-It-Yourselfer. In case you want a quick precis, they are:

    1. "Highlight" fluorescent markers. I've lased 2 or 3 of the available colors. The Sharpie "Accent" yellow-barrel marker (makes a yellow-green highlight) is probably the best I've found so far.

    2. Several of the brighteners used in laundry detergents are good blue or indigo laser dyes. It is possible to use some liquid laundry detergents directly. I lased All “Free Clear” in 2000, using a low-pressure nitrogen laser; and Jarrod Kinsey has recently been getting very nice results with Arm and Hammer 2x liquid concentrate, pumping it with a TEA nitrogen laser.

      If you try this, remember to use detergents that are listed as “No Dyes, No Perfumes”, and are as close to water-clear as possible: murky blue gunk is obviously not going to work. A few of the better organic detergents actually are free of dyes, including optical brighteners, so it’s a good idea to test for fluorescence before you buy, or look for the word “brightener” in the ingredient list. OTOH, most or all of the major brands, at least the ones that are transparent, appear to be good candidates.

      You can, alternatively, make an alcohol extract of a dry powder detergent (I have gotten my best results with Arm and Hammer). This works extremely well, provided you can filter or centrifuge the extract to remove the remaining dusty bits of detergent. I believe that this method works best with 91% pure (or higher) isopropyl alcohol or 95% ethanol, but it may be possible to do it with 70% isopropyl rubbing alcohol.

      Far and away, however, the best thing I've found along these lines so far is “Optic Whitener”, from Dharma Trading Co. A very small amount of this, diluted with isopropyl alcohol (70% rubbing alcohol from the drugstore seems to be just about ideal) or ethanol, will fill a dye cuvette that is pumped by a nitrogen laser; and the bottle contains 8 ounces, so it will last several lifetimes. I have also lased this stuff in the "Minimalist" flashlamp-pumped dye laser that I mention below, which stores only a dozen joules in its capacitor bank.

    I mention all of this because Jarrod, in an email message, pointed out that these things should be really well known, because people need the info, but they aren't — they seem to be hiding under everybody's radar. I thought it would be a good idea to alert you, because you are a major hub of information for DIY people.

    I should note, btw, that I have been getting 99+% iso at a local electronics supply house. It is somewhat expensive, but it works extremely well.

    Also see the section: Jarrod Kinsey's Dye Laser.

    Anthony's Comments on the Home-Built Dye Laser and Parts Sources

    (From: Anthony Paolini (apaolini@cros.net).)

    The SciAm/Lankard dye laser design is indeed a worthwhile project for a hobbyist. Its specifications, optical requirements, and adjustments are far less demanding than most of the other SciAm lasers. Plus, the design lends itself to experimentation with a variety of modifications. The output is extremely powerful. (While adjusting mine for peak power, it generated a beam of sufficient intensity to vaporize the aluminum coating on my less than perfect cavity mirrors.) Most of the parts are available from North Country Scientific, RFD1, Plymouth, NH 03264. (I recommend all their parts EXCEPT the mirrors.) The most costly part will be the capacitor. Condenser Product in Florida can make one. Do not go over 15 to 20 uF or flashlamps will shatter. Also, do not substitute anything else for the quartz parts. I also recommend the electronic trigger circuit. Use only ultra pure solvents (i.e., distilled in glass methanol). Dyes are available from Exciton Corp in Dayton, OH. Also, read the sections describing the modifications to this laser that other people have made. When I get back to that project I plan to add a water jacket which should improve beam quality by reducing thermal gradients.



  • Back to Home-Built Dye Laser Sub-Table of Contents.

    Other Examples of Home-Built Dye Lasers

    Jon's Dye Laser and General Comments

    (From: Jon Singer, of the Joss Research Institute.)

    An LC inversion circuit, frequently (and incorrectly) called a Blumlein, consists of a pair of capacitors and a fast switch, connected essentially as follows:

    
                      R1                L1
              - o----/\/\------+------^^^^^^------+--------+
                               |                  |        |
                               +------->  <-------+        |
                HV         C1 _|_   Flashlamp    _|_ C2    v SG1
                              ---                ---       ^ Spark Gap
                               |                  |        |
              + o--------------+------------------+--------+
    
    
    (For more on these circuits, see the chapter: Home-Built Nitrogen (N2) Laser.)

    The following things occurred to me, after I considered that picture for a while:

    1. If you switch with a spark gap, you need at least 10 amps going through it for some ns to develop a good conductive channel & make the switch close smoothly & thoroughly.

    2. There is no earthly reason why this device has to be balanced. That is, the cap on the left can have an entirely different value from the cap on the right.

    What I did was to use an old Maxwell low-inductance cap with stripline termination as the one on the left, and a pair of barium titanate "doorknob" caps, each of 3600 pF, in series as the cap on the right. (I had to put them in series because their voltage rating was not high enough.)

    The Maxwell is rated 0.089 uF at 75 kV; I've never taken it over about 35, partly because I do not care to X-ray myself too heavily. See: Jon's Lamp Driver.

    How it works: When I trigger the spark gap (an old EG&G device that is designed to work when there's anything from 25 to 69 kV across it), the cap on the right promptly discharges through it, causing many amps to flow & closing the switch rather firmly. I haven't actually been able to measure this, but it seems likely that this creates a tank circuit that rings down to perhaps minus half of the initial charging voltage, V. (A proper LC inversion circuit, BTW, probably rings down to at least -0.8V. I doubt that my thing is anywhere near that good.)

    One way or the other, this doesn't take very long, because the capacitance & inductance are both very low. My first guess is that it's no more than 50 ns. At the end of this time the switch is shut very firmly, and there's a HUGE voltage across the flashlamp. Overvolting the lamp fast & heavily is a good way to accomplish two things: (1) it turns the lamp on much better than a slow rise in voltage, and (2) as I learned to my regret, it has a much better chance of blowing the lamp to hell.

    The first two lamps I tried in this thing were beautiful things. They had 6" arc length, and were 5 mm ID, 7 mm OD. They were brand spanking new. I got 'em surplus, for $15 apiece, after which the place that was selling them raised the price to $50 and I could no longer afford them. Sigh.

    Anyway, at 23 kV (below the actual lowest rated voltage for the switch), it took just 3 pulses to blow up each of my nice lamps. I then switched to an old capillary-bore lamp with only 4" of arc length and about a 1 mm or maybe 2 mm bore. I have several of these and I figured I could blow a few up & still have a laser. It turns out that this lamp holds things back enough that it is stable even as high as about 35 kV. (At 1/2 * C * V2, with C in farads and V in volts, that's right around 40 joules at 30 kV or 54.5 joules at 35 kV, unless I have my head on backwards tonight.)

    With this lamp, and running at 30 kV if I recall correctly, the driver was able to threshold a dye cell without any mirrors. It's a well-aligned cell, of course -- the end windows are serving as the mirrors -- but that's not a whole lot of feedback, and you can demonstrate for yourself that it isn't all that easy to threshold a naked cell: just try it. I only did it with fluorescein and with Rhodamine-6G, near as I recall, though I bet I could have done it with Rhodamine-B in glycerol as well -- Rhodamine-B is a very reasonable dye in glycerol or plastic, much better than it is in water or isopropanol. (For whatever reason, it has very high fluorescence quantum efficiency in solvents with very high viscosity.) Believe I tried with 7-diethylamino- 4-methyl Coumarin & failed, no real surprise -- that's a harder dye to work with than fluorescein or R6G, by a fair margin.

    (I should mention that I just wrap aluminum foil around the lamp & dye cell - close-coupling of this sort is a win as far as I'm concerned. MUCH easier than trying to make one of those fancy ellipsoidal reflector things and probably at least as effective - not so much room for light to fall out the ends!)

    Jarrod Kinsey's Dye Laser

    Jarrod now has his own Web site at Jarrod Kinsey including information on this dye laser.

    (From: Jarrod Kinsey.)

    I finally succeeded in lasing my first dye laser. See the results here:

    The first top photo shows some R6G, lasing with an orange output. The other photo shows some 4MU lasing with an intense blue output. I really like the color in the output from the 4MU.

    Many thanks to Jon Singer and Milan Karakas for helping me to do this.

    Here are some videos of one of my dye lasers, with the output passing through some water vapor. It's noisy, because the entire setup is powered with a mechanical generator and a spark gap switch. The dye is R6G, which produces a yellow-orange laser output.

    Also, here is a comparison between low frequency and high frequency HV sparks from my Wimshurst Machine. As with electronic circuitry, the capacitors control the frequency. The size of the capacitors also determine the current (and thickness) of the HV sparks, as well.

    Here are some pics of my more recent work. These are very 'scratchy' and 'DIY' approaches; some using common household supplies for dyes.

    Dye from fluorescent yellow markers:

    Coumarin or 4MU (can't remember which):

    More laundry detergent:

    R6G:

    Examples of Wimshurst Machine power supply:

    Dye pumping diagram:



  • Back to Home-Built Dye Laser Sub-Table of Contents.

    Additional Information on Home-Built Dye Lasers

    More on the Air Flashlamp

    (From: Chris Chagaris (pyro@grolen.com).)

    The article in "Light and its Uses" claims that this flashlamp will fire at about 60 Torr using the recommended capacitor of 15 uF at 3 kV. This is not true (not even close). The actual pressure that will cause discharge of this capacitor is more like 8 to 9 Torr.

    A way to calculate this is found in: X. M. Zaho, J-C-Diels, C.Y. Wang, and J.M. Elizondo, IEEE Journal Quantum Electronics, vol. 31, pp. 599-612 (1995):

                                  V
                        Pd = -----------   or   Vb = P * (d * Esb)
                               d * Esb
    
    where:

    For the flashlamp suggested for the dye laser with approximately 82 mm between electrodes, one can calculate a breakdown pressure of 8.8 Torr, NOT 60 Torr! Thus, either the vacuum system will need to be somewhat better or the flashlamp dimensions adjusted accordingly.

    Using a Xenon Flashlamp

    I don't know whether the approach described below can be made to work without extraordinary effort (or for other types of laser dyes) but it would certainly appear that the electronics at least would be a nice challenge! His not very special energy storage capacitor and not very high voltage must not have been that mundane to produce 6 J in a 2 us pulse!

    (From: fatusa@netscape.net.)

    Lasing of Rhodamine-6G can be done with a regular garbage strobe tube (glass of linear dimensions - without crazing in glass) by attention to several points including: very tight coupling of strobe/cell, use of confocal cavity with HeNe laser mirrors, and a fairly strong molar dye solution. But the most important thing to do is a prepulse technique - to first hit the tube with a pulse of low energy (say 10 amps) and then hit it harder 5 to 10 us after the prepulse. Do not expect much output. For mine (done a while ago) with a prepulse of 0.5 J and main input pulse of 6 J, lasing broad band was achieved reliably and repeatably at a low rep rate in a portable system. The main pulse had a rise time of approximately 200 ns and was 2 us wide. Better results can be achieved if a triplet quencher is used as well. The main cap was not a "special" and the voltages were mild (relatively), but the electronics, etc. are not trivial.

    Discussion on Dye Laser Construction

    (From: Jacob Conner (jake@westplainsonline.com).)

    If I use the OC/HR (Output Coupler/High Reflector mirrors) from a HeNe and a dye that peaks around 630 nm would I get any amplification? I have Kiton-red and Rhodamine-B both of which should peak around the HeNe red line.

    (From: Jon Singer, of the Joss Research Institute.)

    If you pump correctly, either of these should lase; but because HeNe has much lower gain than dyes, the HeNe output coupler is seriously not the right tool for the job. Dye laser output couplers often pass as much as 25 or even 50% of the light that hits them. If you intend to lase Rhodamine B, BTW, use a viscous solvent if you can; from what I've read it has lousy fluorescence efficiency in methanol (0.43), but by the time you get to glycerol it is highly efficient (0.96 or so). The problem with glycerol is getting the solution out of the dye cell after you pulse it; maybe propylene glycol is a reasonable compromise, or a mixture of glycerol and water...

    (From: Jacob Conner (jake@westplainsonline.com).)

    The OC/HR are from a Hughes HeNe. I believe they are dielectric (look blue when you look through them) and the optical resonator will be external to the dye cell which is a quartz glass tube with quartz ground glass windows (not sure if I should place at the Brewster angle) and there are 2 "T"'s coming out of the cell for dye circulation

    
               ||          ||  
      |     .--''----------''--.
      |    /                  /  =====>
      |   '-----------------'
            ________________
           |________________|
              Halogen Lamp
    
    

    Excuse the crude drawing. :-)

    The quartz tube is cemented to two brass T pipe fittings using Epoxy. The pump lamps are going to be either a pair of 300 W halogens or 2 xenon flash lamps. I hope this will work. if so i will invest in some other optics so I can go tuneable since the HeNe mirrors do have a small bandwidth I can probably insert a prism in the cavity for "some" tuneability

    (From: PandaSnax (pandasnax@aol.com).)

    It sounds like you are going in the right direction so far. I'd lean more toward the Xenon flash tubes myself because they tend to put out a lot of UV and their use is highly documented. Unfortunately unless you build them yourself they tend to be pretty pricey. However two that flash alternately can give you a pretty high flash rate and some specialized tubes working together can give you continuous operation. The next question to ask is how are you going to flow the dye through the dye cell?

    (From: Dan Mills (Dmills@abcde.demon.co.uk).)

    Forget the TH lamps! You will not get enough light. I would go for the Xe flashlamps and would probably use a pair. It is worth getting a copy of the EG+G Electro optics catalog as this gives lots of detail on the design of flashlamp circuitry.

    Note that even if you could get sufficient optical power from the halogen lamps your design will probably not lase continuously. I do not think that a liner flow dye cell is capable of a high enough flow rate. I attempted to build a dye laser similar to your design using a continuously burning SBA Xenon lamp in a old projector lamp house as the pump source. It was not enough! This was running 900W at 2-3 times the efficiency of a TH lamp.

    I have considered attempting to use a DC arc welder to power a carbon arc lamp as a pump. Anyone else attempted this?

    (From: Jacob Conner (jake@westplainsonline.com).)

    The Scientific American dye laser lamp talked of getting 5 kW output from the laser. Is this possible with a home made flashlamp? The airport here has some hefty xenon strobes :) I want brick busting performance here ;)

    (From: Dan Mills (Dmills@abcde.demon.co.uk).)

    Yea you can get 5kW output pulses. (Not 5 KJ) The pulse duration is really short and the PRF is fairly low. Average *INPUT* power in the scientific American design is around 70W, at 1 PPS Average output is probably in the order of milliwatts.

    It is probably not possible to obtain more then a watt average output from a home made dye laser. I would recommend you consider a liquid cooled pulsed YAG. This will give your 'brick busting performance' especially if you can get the local radar tech to get you some of the caps they use in the pulse forming network for the radar! You can make a suitably cooled yag lase continuously. Pulsed would probably be better for you.

    (From: Dan Mills (Dmills@abcde.demon.co.uk).)

    I have considered attempting to use a DC arc welder to power a carbon arc lamp as a pump. Anyone else attempted this?

    (From: Heath Edwards (heathe@citi.w1.com).)

    I use my Lincoln AC arc welder with a twin-carbon arc torch. The carbons are 3/8" diameter and copper plated for strength. I wouldn't recommend this type of torch because the carbons burn down fairly rapid. Just having done some light brazing with the torch the rods have shortened several inches. Which means you would need to have an automatic rod adjuster.

    Now if you used larger diameter rods, they might run longer. But they'll require more current.

    The light intensity is certainly high! You HAVE to wear welding goggles with a dark lens of #8 or better.

    (From: Mike Poulton (tjpoulton@aol.com).)

    I would like to build a dye laser for use in light shows and classroom demonstrations. I have built several lasers, but never completely from scratch. My question is about an interesting phenomenon which was referred to in a small piece of literature about dye lasers. It seemed to imply that if you direct the beam of a nitrogen laser through a chamber containing a dye used in dye lasers, it will cause the dye to lase along the path of the nitrogen laser beam, and where the beam exits the other side of the chamber, it will have been converted to a visible beam from the dye. No resonant optics involved. If this works and is true, please tell me, because that means that I don't have to align any resonant optics! If this does not work, please inform me of that, too. Any other information on dye lasers would be appreciated.

    (From: PandaSnax (pandasnax@aol.com).)

    I read in one of Jeff Hecht's (sorry if misspelled) books that this is a viable technique but that for most applications the dye is contained in an optical chamber that is semi-resonant, i.e. one partially reflective output mirror.

    (From: Charles Nelson (cnelso01@merit.edu).)

    The reason is similar to why Nitrogens don't really need mirrors, or if any are used that only as a high reflector and not an output coupler. The gain is very high with using a nitrogen as a pump so you get a very large population inversion. Try also using some Day-Glo plastics such as those used in rulers and the like.

    (From: somebody (p.g@worldnet.att.net).)

    I have built a variety of flashlamp pumped dye lasers including the one in Scientific American.

    The only way I have gotten them to work is to pump a huge amount of energy in to a two mm bore dye tube. I had to use two 150 uf, 1000 V capacitors with two xenon flashlamps with the proper inductors. I also had to experiment with different dye/solvent mix ratios. the easiest dye to get to lase is Rhodamine-6G. these type of dye laser are to say the least, a pain in the a** and not much worth the effort. the best way I have found to make a dye laser, is to pump it with an UV laser.

    I made the nitrogen laser in from Scientific American but scaled it up to one meter in length. it uses no mirrors and it will operate with ordinary air at about one torr. all though using pure nitrogen will give much better performance. I simply focused the beam onto the surface of the dye with a cylindrical lens and got fantastic results. no mirrors required but using one mirror at one end will get you twice the output.

    (From: Jon Singer, of the Joss Research Institute.)

    The reason lamp-pumped dye lasers generally can't be made to lase continuously is strictly a thermal issue, not a matter of self terminating population inversion. Dye is NOT self terminating; the lower laser levels (of which there are lots, not just one) are essentially thermally excited levels of the ground electronic state, which depopulate (to a Boltzmann distribution) in about 10-12 seconds. In support of this, I offer the fact that CW dye lasers not only exist, they have been commercially available for more than 3 decades.

    The reason why a flashlamp-pumped dye laser has to be allowed to relax between pulses or after a few pulses is that the dye solution gets hot when you lase it, and develops refractive index irregularities (these are called "Schlieren"), just like the wiggles you can see in the shadow of the exhaust from a bus or a truck on a sunny day, or so-called "heat waves" over an asphalt road in the summer. These irregularities prevent the light from passing straight through the dye. You either have to allow the temperature to achieve a smooth profile in the cell, or you have to move fresh dye solution into the cell to replace the hot stuff.

    (From: Jon Singer, of the Joss Research Institute.)

    I'm afraid this is a sad example of a fundamental fact about capacitors:

     
         Energy = 0.5 C * V2
    

    A thousand volts just isn't the way you want to run a lamp driver for a dye laser. 300 uf at 1,000 V stores 150 joules; at 20 kV it takes less than 1 uf! The much smaller cap will discharge much faster, especially if it's a design that has low Effective Series Inductance (ESL) - 20 nH or less seems to be quite decent.

    Notice that you had trouble lasing anything, even with 150 J into the flashlamp, whereas a driver that ran at high voltage, used a fast 0.1 uf cap, and was constructed with reasonably low inductance had absolutely no trouble lasing any of several dyes with 25 joules or less, in a tube with 4 mm bore. In other words, far from being a pain in the butt, this type of dye laser is actually quite easy to build and work with, provided that you are willing to run at 20 kV instead of 1 kV.

    I ended up tight-wrapping the lamp and the dye cell with aluminum foil, the way I always do, because the white reflective material in the head was nonviable. (I don't use ellipsoidal reflectors for lamp- pumped dye lasers -- they are much more trouble than they're worth. Aluminum foil is cheap and easy, and it works just fine. Remember, shiny side in! Remember, also, that both the flashlamp and the dye cell have to be made of fused silica, else you are looking for severely reduced efficiency if you actually get lasing at all.)

    For some info about my setups, see Jon's "eBay Head" Dye Laser Page and Jon's "Minimalist" Dye Laser Pages.

    The "eBay Head" laser was quite crude, but it worked very well even so. (I took it out of service so I could work on one of the nitrogen lasers, which is why I speak of it in the past tense.)

    BTW, there is what I hope is an amusing "photographic tuning curve" for Rhodamine 6G toward the bottom of that page -- I didn't have the monochromator running at that point, and I figured that if I could get the camera to show the colors even moderately well, it would make a cute set of pictures.

    The newer "Minimalist" laser stores only 12 Joules in its capacitor bank, but lases the usual dyes quite handily. So far, it has succeeded in thresholding Rhodamine 640, Rhodamine 6G, Fluorescein, Fluorol 555, Coumarin 1 (7-Diethylamino-4-Methyl-Coumarin), 4-Methyl-Umbelliferone, and two handy DIY laser dyes: Dharma Trading Company's "Optic Whitener" (which is mentioned elsewhere on this page with a link, and is particularly nice for nitrogen laser pumping) and an isopropyl alcohol extract from a Sharpie "Accent" yellow-green highlighter marker.

    In Its current incarnation (as of early February, 2010), it uses a single-stage Marx generator built from a pair of 30-nf Maxwell capacitors that I got on eBay, charged to 20 kV, running a flashlamp that I bought for $16 from the Electronic Goldmine. (Search for "Large High Power Xenon Strobe Tube". It isn't actually large; the arclength is only about 4".)

    This laser is a fine demonstration of what I pointed out above, about small capacitors at high voltages. I was actually able to threshold R640 with only 6 J in a single 30 nf Maxwell, before I shifted to the Marx generator design.

    Dave's Comments and Improvements on Dye Laser

    (From: Dave (skeeve@excellentproducts.com).)

    On the issue of mirrors, I suggest that for the total reflector, a person use a first surface mirror, which can be very easily obtained from an old photocopier, laser printer or wholesale place like Edmund Scientific. For the output coupler, on low power dye lasers, a piece of Mirro-Pane, which is used for two way mirrors will work nicely. Normally, a local glass shop will give you a sample for nothing. :-) The transmittance is about 30 percent or so, which works well for the small laser.

    Next, the question of pumping a dye laser with 300 watt halogens is a waste of effort. Organic dye requires a far, far more intense light source than that to reach threshold. Even the airport runway lamps are not quite right for a dye laser. Xenon flashlamps have to be specially designed to be driven to extremely high current levels to pump dye lasers efficiently. Normally, this is combined with high current simmer to ensure long lamp life. The ablative wall lamp, as described in the article, is really the best source of light for the homebuilder! This type of lamp can easily be scale up to any size desired. Furthermore, it is very inexpensive and simple to construct. The pumping cavity design is important as is a reasonably fast discharge circuit.

    The one, single most important thing that was not used in the Scientific American laser, is an infrared filter of some sort, between the flashlamp an the dye cell! For a flash pumped laser, this will make the difference between a working or non working laser. The reason is this: When the flashlamp fires, it produces a very intense pulse of light throughout the ultraviolet, visible and infrared spectrum. The dye solution, whether alcohol or water based, has very strong absorption lines in the mid infrared. If the dye is allowed to absorb this radiation, a VERY strong shock wave appears at the edge of the dye cell wall and travels in toward the center of the dye solution. This shock wave completely destroys the optical homogeneity of the dye solution and terminates the laser pulse almost as fast as it can begin! (less than one microsecond) Lankard was not aware of this effect, as it had not been detected at the time that the article was written. For the folks out there who have gotten this laser to work, I would bet that you got a very divergent laser beam. As opposed to the tight beam of say a HeNe, right? This was caused by the infrared shock wave! If a filter is used, the laser will produce a much nicer beam and will lase for quite a bit longer. This translates into more energy out. For an infrared filter, I suggest that a second tube be placed around the flashlamp and water flowed though the annular space between the two tubes. That way, the water jacket absorbs this infrared radiation before it can get to the dye cell and ruin the performance of your laser. Of course, the water jacket must not be extended to the electrodes of the flashlamp or the water will short the lamp out. (unless deionized water is used)

    There is a very good paper that was published in Applied Optics Vol 13, No. 2, 1974, by Fisher and Ganiel in which they describe the shock wave problem and even photograph the shock waves.

    Finally, the amount of pump energy in the Lankard laser is somewhat low for the design. If a person were to scale the laser dye cell to say 6 mm bore with a length of 5 or six inches, they would be better off. For the matching lamp to go with that, I would suggest a lamp of 6 mm bore and arc length equal to the dye cell length pumped by capacitor of maybe 5 microfarads at 10 kv. (Low inductance and high current discharge capability should be specified to the cap manufacturer) This would give an energy storage capacity of 250 joules which should be plenty to reach laser threshold. Also, dropping the lamp pressure to just a couple of torr and firing the lamp by use of a simple spark gap will make the rise time of the lamp faster and really help in the efficiency of the laser.

    This only touches on the improvements that are possible with the dye laser. :-)

    Also see the section: Using a Copper Vapor (or CuCl/CuBr) Laser to Pump a Dye Laser as an alternative if you happen to have a Cu vapor laser laying around or in your future!

    As to potential output of the dye laser. For the Scientific American laser, 5 kW would be "maybe". ;-) As to the output that can be had from a homemade dye laser, the last one that I built produced 5 joules in a 3 microsecond pulse with a peak beam intensity of well over a megawatt. The beam diameter was 1 cm and divergence was about 1 mr, a nice clean beam. The one that I am building now should easily do 9 joules in about 2 to 3 microseconds.

    One thing that should be touched on again, is that it only takes less than 25 MICRO joules of energy at the Rhodamine-6G wavelength of 590 nm. to do permanent damage to the eye. These lasers must be used with great care to prevent serious injury!

    Also, the energy discharge circuit for the flashlamp is potentially LETHAL if you are careless! All it take is once!

    Comments on Dye Laser Dye Concentration

    (From: Chris Chagaris (pyro@grolen.com).)

    As you will discover, there is no absolute 'best' dye concentration to be used in these types of lasers. There are certain parameters to which one may adhere in order to produce desired results regarding the peak wavelength emission within the tuning curve of each dye. Different dye concentrations as well as the choice of solvent will affect the output wavelength to some extent, with higher concentrations shifting the output toward the longer wavelengths. In general, laser-pumped dye cavities usually contain higher dye concentrations than are commonly employed in flashlamp-pumped dye cells.

    A concentration like 0.8 g/l Coumarin 460 in pure ethanol is common for N2 laser-pumped dye lasers and should perform as expected if all other conditions are met including sufficient pump power and proper focusing of the pump beam. The Coumarin derivatives will likely 'lase' superradiantly (without need for a resonant cavity) if the pump flux density is adequate.

    Common concentrations of Rhodamine 6G in ethanol for a N2 laser pumped dye laser application are usually in the 1 to 2 g/l range. This appears as a yellow/orange fluorescent liquid.

    Incandescent Lamps or Other Light Sources to Pump Dye Laser?

    In order for a dye laser to be pumped successfully, the light source must produce an extremely high peak intensity in a short period of time. This greatly limits your options. About the only approach that might have any chance of working is something like a mercury discharge lamp or solar furnace. See the section: Mercury Vapor Lamps to Pump Dye Laser? but your probability of success isn't very high.

    And the answer to your next question is: No, you can't pump a conventional dye laser with the laserdiode out of your CD player or likely even a high power laser diode for that matter. :-) However, a different sort of design might work. See the section: Diode Laser to Pump Dye Laser.

    A typical question goes like:

    "Say I took a 100 W light bulb and surrounded it by a sphere that was coated inside with a 100% reflective mirror and made a little hole in a place on one side of the sphere. Then, in time all the light would come out of that hole. Would the power of the beam be 100 W or would there be no beam because it's a multiple wave length light?

    Just wondering"

    The short answer is: Forget it. Despite how bright a large incandescent (even a halogen) bulb appears, it converts only a few percent of electrical power to light output. And, even less of it is going to be at the absorption band of the laser dye.

    (From: Terry Greene (xray@cstel.net).)

    What you will get is one very hot globe.

    1. No reflector is 100 % efficient. After dozens of bounces most of the optical energy coming from the bulb will become heat.

    2. Power ratings on light bulbs is a measurement of INPUT power. Incandescent light bulbs are very inefficient converting only a few percent (can't recall average number, anyone?) of input power into optical energy. A 100 watt light bulb will only have several watts of optical output.

    (From Steve Roberts.)

    There has only ever been one non-laser pumped or non-flashlamp pumped dye laser experiment that I have seen documented and that used 7 huge custom made CW xenon arcs to pump a IR dye. The input power was far greater then required for even a small ion laser. The lamps were driven beyond their specified maximum power and lasted about a hour.

    The particular dye was chosen because it is one of the few that wouldn't fall pray to triplet state quenching. It did 15 mW in the IR at 1100 nm or so. No currently known dye that can lase in the visible can hold up to continuous lasing because it will be overpumped into the next nonlasing level in something far less then a microsecond. This is why CW dye lasers all have flowing jets and even rapidly pulsed dye lasers of any significant power have fast flows. You have to get the old still somewhat excited dye out of the lasing path as it then has a high adsorption and will literally turn itself off. Those well funded researchers were looking for a easier way to get laser emission - for years - and that was the best they could come up with.

    You're not going to get anywhere near the pump threshold with a sun pumped dye, yet a simple home made nitrogen laser will do it, the wonders of quantum mechanics. :-)

    (From: Jon Singer, of the Joss Research Institute.)

    I had no idea that anyone had ever successfully pumped a CW dye laser of any sort with lamps, and was astounded to see mention of it. Wow! No surprise they had to exceed the ratings on the lamps.

    Hmmm — it turns out that there has been at least one other instance. It used Rhodamine 6G, and it was published in 1988 (!). Here is the reference:

    Continuous-Wave Dye Laser Pumped by a High-Pressure Argon Arc
    E. Thiel, C. Zander, and K. H. Drexhage
    Optics Letters, Vol. 13 (1988), Issue 11, pp. 973-974.

    Abstract: Continuous-wave operation of a Rhodamine 6G dye laser, incoherently pumped by a high-pressure argon arc, has been achieved. A special electrode design reduces melting of the electrode tips, and thus the arc provides the necessary brightness for periods of the order of hours.

    (I believe they had to push 8.8 kW through the arc lamp, so this is not exactly a DIY project.)

    A Townes-Schawlow calculation will tell you that for a reasonable solution of R6G, you need about 5 kW per cubic cm of dye to bring the thing to threshold if your active region is maybe 10 cm long.

    If memory serves, the Townes-Schawlow criterion (which gives you the number of excited centers per cubic cm that you need in order to reach threshold) is pretty simple:

    N0 = 8π n2 (1-R1R2) τ Δν / λ2 L φ

    Where:

    Remember, this calculation ignores all loss sources other than the output of the laser, so it is wildly optimistic. At the very least, you should double or quadruple the number it gives you.

    Here's a sample calculation, for Rhodamine 590 in ethanol:

    The numerator evaluates to something so close to 7.35 that I'm just going to stay with that. The denominator evaluates to 3.34x10-8. Putting them together gives us 2.2x1013; that’s 2.2x1016 per liter, which is approximately 3.6x10-8 molar, actually only about a factor of 5 low. Not bad, all things considered. Remember, for any real system, you need to use more dye and push harder.

    Now: how much power do we need to apply?

    Let’s assume that the dye cell holds 1 cubic cm of solution, just for convenience. That takes 2.2x1013 photons.

    2.2x1013 photons, however, is only part of the story. We can’t dump them all in at once, and the dye is fluorescing while we try to pump it, so I am arbitrarily going to say that we take one fluorescence lifetime, give or take a little, and we use twice the calculated number of photons to compensate for the fluorescence loss. That is, 4.4x1013 photons over 5 ns.

    I'm also going to say that the average energy of a pumping photon is 3.5 eV, which (if I am not miscalculating) corresponds to a wavelength of just over 350 nm. This is probably fairly reasonable.

    1 eV = 1.602x10-19 joule, so 3.5 eV times 4.4x1013 photons is about 25 microjoule. If we apply that in 5 nsec, the resulting average power is just under 5 kW. Q. E. D., kids: the absolute minimum you could ever hope to run a Rhodamine 590 dye laser with, in a 10 cm dye cell with a 95% reflective output coupler, is 5 kW... but there's something you have to remember: that 5 kW is the actual amount of power absorbed by the dye. Anything the dye fails to pick up doesn't count. In order to put 5 kW into 1 cc of R590 at usable wavelengths you have to put well over a megawatt of electrical power into a flashlamp, and that ignores all of the other possible losses that can drive up the threshold.

    I hope you now see why only two or three groups have ever produced a fully CW lamp-pumped dye laser. Very few CW lamps are capable of this level of service; that 5 kW is the actual power absorbed by the dye solution, so the input power to the lamp is ridiculous. It is also difficult to move the dye fast enough to keep it from developing significant optical inhomogeneities, which ruin the optical path and cause lasing to cease. (The first laser-pumped CW dye laser needed to have its dye solution move through the dye cell at 2 meters per second, and that was just to get the dye past a "hot spot" a few microns across.)

    I do like the idea of doing it with laser diodes; they are getting cheaper and cheaper, even with reasonable output power. A DiY diode-laser-pumped CW dye laser would be quite something.

    Mercury Vapor Lamps to Pump Dye Laser?

    "Does anyone here know if any of the organic dyes can be optically pumped to lasing with a mercury vapor light of sufficient power? If so, what is the minimum wattage needed?"
    (From: Don Klipstein (don@donklipstein.com).)

    Organic dye lasers tend to require much higher degree of pumping than a mercury arc can provide. This is due to the short lifetime of the desired excited state of organic dye molecules (typically around a nanosecond or a few nanoseconds). You have to have a light intense enough to achieve the necessary population inversion in about this amount of time.

    (Since these lasers are usually 4-level lasers, you don't actually have to excite a majority of all dye molecules within a nanosecond. However, what you have to do is still a tall order.)

    In fact, plain ordinary xenon flash tubes often have difficulty achieving the necessary light intensity. You may need extra-intense flash tubes with somewhat unusual circuitry, voltages, etc. to get a dye laser working.

    For some xenon flash tube stuff including stuff that may help getting a dye laser to lase, try these web pages of mine:

  • Xenon Flash Design Guidelines (including a bit of info for laser pumping)
  • Don's Xenon Strobe Index
  • Don's Lighting Home Page

    As of several years ago, the dye I have heard of as most suitable for a do-it-yourself dye laser is Rhodamine-6G. The more available Rhodamine-B and Uranine (or Fluorescein in alkaline solution) can work, but generally not as well. Adding glycerin or the like to make the solution more viscous is said to have a beneficial effect, but probably makes little difference in the extreme pumping requirements of aqueous (or alcohol) dye solution lasers.

    For a similar type of laser construction that has a much lower pumping requirement, use an appropriate compound or chelate of europium. I have heard of this being capable of king a "dye" type laser that can be pumped from the intense light of a solar furnace, and this may work from an intense enough mercury arc.

    (From: Thomas A Suit (tsuit@osf1.gmu.edu).)

    Solar furnace?? Yeow!! The dye laser I saw in operation up at LLE was pumped via YAG light frequency doubled to green. I put my hand in the green beam and it felt like a candle flame. I rapidly pulled my hand out. :-) The KTP frequency doubler was said to be 20% efficient. No way was my hand going into the IR beam. A solar furnace would be much hotter than a candle flame.

    (From: Don Klipstein (don@donklipstein.com).)

    The working europium compounds emit a highly visible orange-ish red wavelength in the low 600's of nm wavelength. Any europium based stuff that will work will have at least some visible reddish, orange-reddish or pinkish fluorescence in ordinary daylight or most high-pressure mercury light.

    Please note that most fluorescent inorganic and inorganic-based substances fluoresce only or mainly from shorter UV wavelengths that damage many organic substances (including chelates?). It may be a bit tricky getting an europium based substance that can be pumped from wavelengths that don't harm it.

    What I have seen (several years ago) seems to discourage europium based liquid lasing medium lasers as having the disadvantages of both inorganic and dye lasers.

    (I suspect conspiracy mode)

    I wonder if this is to discourage the obvious hazards of telling anyone how to make a Class IV laser that hobbyists can make in their basements. (Minor remote accidental fire-starting hazards, moderate skin burn hazards, and extreme hazards of accidentally causing permanent eye damage in milliseconds.)()

    Anyone who knows how to get this to work, or names/sources of appropriate dyes or euoropium compounds, please post and/or email to don@donklipstein.com.

    (From: Joshua B. Halpern (jbh@ILP.Physik.Uni-Essen.DE).)

    Lamps are not, in general, intense enough unless you pulse them with a powerful fast current (flashlamp pumped dye lasers) Mercury lamps are a bad choice because the UV (253.6 nm??) light tears the dye molecules apart. If you are looking for a pump laser that you can build yourself (you assume all risk, etc.) There are several designs for simple nitrogen lasers (337 nm) that can be found in the journal: Review of Scientific Instruments (late 1970s and early 1980s) and one design was published in the Amateur Scientist section of Scientific American.

    These can easily pump a small dye laser.

    (From: Michael Solonenko (misha@vm.temple.edu).)

    You need high pump power densities to get anything out of the dye. At the same time, the dye gets easily destroyed if continuously irradiated with powers much less than the one necessary for lasing. Hence, the dye flow, cooling and filtering should be set up. In the industrial lasers (Coherent), ~6 W of an argon ion laser (~448 and/or 514 nm) is focused, as noted before, in ~30 micrometer spot on a dye jet to get the job done. See if the total power of your lamp in the absorption region of the dye you are going to use can provide comparable power densities (take 6 W/30 um as a total power density for a laser).

    You just might get lucky if you:

    But, I'd warn you, the wavelength of such a laser will be extremely unstable, shifting randomly in the region of 10 to 20 nm around the dye's emission maximum with the increments of intermodal spacing.

    (From: Jens Decker (dej05093@rchsg6.chemie.uni-regensburg.de).)

    I don't think it is possible to get a CW laser running with any lamp. Even a standing wave laser need's about a Watt focused into a very small (about 30 microns) spot of a thin dye jet. You can't focus the light of your street lamp (a really nice tool for photochemistry!) to such a small spot. Dielectric mirrors are essential too.

    Maybe it would be possible to pump a standing wave dye with a telescope using a single mode fiber to couple the moving telescope with the laser?

    Building a small N2-laser or using flashlamps for pumping a self made pulsed dye laser should be possible. In two resent papers in the journal: Review of Scientific Instruments, bright blue LEDs have been used as pulsed UV sources which might be useful as a pumping source.

    (From: Joshua Halpern (jbh@IDT.NET).)

    The strongest lines from the mercury vapor lamp are in the UV (the intercombination 253 nm line, and if you contact the lamp directly to the dye cuvette, the resonance 186 nm line. By the way it is the latter which photodissociates oxygen leading to the formation of ozone that you should be smelling if you operate this lamp in the air). These emissions have a high enough energy to break R6G apart. That is a bad idea if you want to build a dye laser. The peak of the R6G absorption is in the green. You would be better off with a strong green or white light, with a UV filter on it.

    You would also have to have a huge CW lamp. AFAIK, it has not been done, but rather one uses Ar-ion lasers, or pulsed lasers or flashlamps to pump dye lasers. There is a report of a sun pumped dye laser (Israeli?) in the last few years, but how big the collector is I do not know.

    (From: Dave (skeeve@excellentproducts.com).)

    I believe that you will not be able to reach lasing threshold of R6G with a mercury vapor lamp unless you do some fancy trickery.

    The output of a 1000 watt mercury vapor lamp is at lease 25 times too low to lase organic dye, however, one research team found that if they set up a mercury vapor lamp with a special power supply which could run the lamp at about half power continuously and then discharge an energy storage capacitor through it, they could reach the intensity level that was needed to pump a dye laser. The pulsed light of the lamp was about 100 times brighter than the cw emission of the lamp. Of course this laser operated in a pulsed manner. What was really interesting, though is that the mercury vapor lamp which was operated in this way, altered from the normal emission spectrum of the mercury vapor lamp so that the emission spectrum matched really well to the absorption curve of R6G and other dyes.

    Indeed, it was compared to a xenon flashlamp at the same discharge energy and the comparison indicated that the pulsed mercury lamp should be a much better pump source for visible spectrum organic dyes - especially those in the blue.

    The articles quoted are:

    If you are determined to try a mercury vapor lamp, be sure to check out these papers, as they have lots of good info in them!

    Diode Laser to Pump Dye Laser

    No, you can't just replace the flashlamp in your home-built dye laser with a bunch of salvaged laser diodes out of old CD player or laser pointers! (From: A.E. Siegman (siegman@ee.stanford.edu).) Anyone wanting to play with home-made dye lasers might look at an article by Richard Scheps, "Low threshold visible dye laser pumped by visible laser diodes", IEEE Photonics Technology Letters, vol 5, 1156 (October 1993). Experiments were done using two 10 mW visible diode lasers (a.k.a. "super laser pointers") as pumps; the threshold was 5.6 mW. The dye was actually in a 100 micron thick jet, which is not all that easy to make; but I'd bet that with some care it could be done with a thin dye cell. Also, laser wavelength was 758 nm, which is not really visible. But also, this was 6 years ago - with some ingenuity an experimentalist might be able to something similar "at home". (From: Joshua Halpern (jbh@IDT.NET).) You can do it using razor blades, or smooth glass plates to form the jet. It takes a bunch of fussing, and can be pretty messy learning how to do it, but it works. OTOH, just use the EtGlycol without the dye until the jet is working. Thin cells will probably have too much reflective loss to work. You might look in RSI between bout 1974 and 1980 for jet designs. An interesting idea.

    Coaxial Dye Laser

    For optimal pumping efficiency, consider placing the flashlamp *inside* a coaxial dye chamber (this could also be applied to other types of optically pumped lasers). Surround the entire affair with a cylindrical reflector. In this way, one would think that virtually 100 percent of the optical energy from the flashlamp will be absorbed by the lasing medium as it bounces around inside the cylindrical reflector. However, at high current densities, the plasma in the flashlamp will not be transparent so you might only really get two passes - out and back.

    The laser output will be ring shaped rather than Gaussian and there could be some unusual mode structure depending you your resonator optics, but for maximum power and efficiency, this should be unbeatable.

    (From: Dave (skeeve@excellentproducts.com).)

    Yes, to find a very efficient pumping scheme was the motivation for this unique pumping idea. If the lamp were in the center of the lasing medium, (organic dye solution in the case of the article that I refer too), and the pump light could be completely absorbed in two passes through the dye , from the lamp out to the reflector and back, then it should be possible to realize extremely high pumping efficiency. Of course, the output of the laser would be a ring, and there is the problem of getting the electricity to the lamp, in the center of the dye cell, but perhaps these obstacles might be overcome. At any rate, I did not see any further work done in this area, and as I recall, the author did not build a working model.

    I have constructed several standard coaxial flashlamps , but they suffer from the problem of having half of the output wasted, because it is emitted to the outer wall of the lamp. In pumping a solid state laser, this might not be a problem, as the lamp could be driven at a low enough current level that it is a grey body and the reflector would send at least some of the light back through the plasma to the lasing medium. In pumping a dye laser though, the lamp is driven at a high current level which is needed to reach lasing threshold, (80,000 to 160,000 amps per sq. cm) and the lamp is a true black body radiator. The reflector that you see around a coaxial lamp is just for a current return. It does lengthen the pump pulse marginally, but at peak output, when the plasma is "black", it contributes nothing to the pump light that gets to the dye cell.

    In a later test, Baltakov and the gang went one better and achieved 400 joules per pulse from a coaxial dye laser. Now that is one mean dye laser! :-)

    Operation Manual for a Real Dye Laser

    Photon Technology International provides on-line manuals for some of their products. Here is the operation manual for their Model GL-302 Dye Laser. Maybe it will provide some ideas for your dye laser!

    Jon's Comments on Some Dye Laser Issues

    (From: Jon Singer, of the Joss Research Institute.)

    1. Length of dye cell versus flashlamp

      1. Dyes are 4-level lasers, so having a dye cell that is much longer than the active length of the flashlamp shouldn't be much of an issue. This is true of all regular dyes. (There may be some truly squirrely weird stuff that behaves differently, but there's some question as to whether such a thing could properly be described as a dye laser.) This is a fundamental property that has to do with the quantum mechanics involved in dye fluorescence. I can probably find a diagram - there are several on the Web, but one I just ran into is in German and is in a discussion of scintillators, not dye lasers, so it's a bit difficult to follow. ;o)

      2. That said, however, there is always (at reasonable temperatures, anyway) some thermal population in the lower laser level (which is actually the rovibronic manifold above the ground singlet electronic state, but let's not get too involved), and you can excite molecules out of that population into the first excited singlet, so there actually *is* a bit of absorption.

        This effect is fairly small; but if you take a dye laser running, as an example, Rhodamine B, and put a cuvette of Rhodamine 6G into the cavity, you'll probably find that the R6G flashes yellow when you pulse the laser and orange light from the RB goes through it. (This also happens if you use the same dye that you're lasing, but because the color is about the same as the laser's output, it's harder to see the effect.)

        This shows that unexcited dye almost certainly causes the threshold to be *slightly* higher; but again, the effect is pretty small, and I wouldn't be too worried about it.

        (I showed this effect to a bunch of people in 1971, BTW, using the red light from a HeNe to pump Rhodamine B (which emits in the orange) dissolved in glycerol, and told them it was a quantum-mechanical refrigerator. Cute joke; I didn't think about doing it with a high-powered pump because there weren't any at the time, and I failed to think about future developments. Sigh. This refrigerator was patented within the last few years - needless to say, *not* by me. Argh!)

      3. The absorption spectrum of a dye almost always overlaps the emission spectrum. This is one way you can tune an organic dye laser: if you increase the dye concentration, you push the output toward longer wavelengths. Unexcited dye in the cavity will have the same effect. This effect is generally larger than the "B" effect.

        If you want to see it, take a dye laser with any handy dye, and run the output through a monochromator so you know what the wavelength is. Now put a cuvette of the same dye into the cavity. As you increase the concentration of the dye in the cuvette (or use a longer & longer cuvette), so that there are more dye molecules in the path, the effect on the wavelength should also increase. If you increase the concentration too much, you may find that the extra dye begins to interfere with lasing; but that's probably a different effect.

    2. Capacitor size and speed, and relation to dye lasing threshold

      1. Dye laser threshold, for pump pulses that have duration a lot longer than the fluorescence lifetime, is perhaps best addressed as a power issue (rather than an energy issue). Basically, because a lamp pulse is always more than an order of magnitude longer than the fluorescence lifetime of any dye, you can pretend that you're dealing with a CW laser. (The lifetime of R6G is about 4.1 ns, and that's not terribly unusual.)

        Assuming that there are no particular problems with things like Triplet-Triplet Absorption, a given volume of dye solution at a specified active length, with specified mirrors, requires a certain level of absorbed power to reach threshold.

        You can make a rough calculation of this (see the discussion of the Townes-Schawlow criterion in the section: Incandescent Lamps or Other Light Sources to Pump Dye Laser?. For R6G in a cell that has 10 cm pumped length, with a "perfect" max-ref rear reflector and a highly reflective OC (optimized for low threshold rather than output), you find that the dye has to absorb 10 to 20 kW per cubic centimeter during the pulse, in order to reach threshold.

        Note that I said that R6G takes 10 to 20 kW per cc, which is higher than what I arrived at earlier. There's a reason for that: When I redid the calculation few months ago, I used the actual bandwidth as shown on an excellent Web site: PhotochemCAD Spectra by Category. So the power I got is higher because I underestimated the bandwidth a few years ago.

        If you translate this back to actual electrical power in the lamp it comes to about 50 MWE, give or take. Depends on how efficient the lamp is, how much of its output is at wavelengths that the dye can absorb, and how well the light is coupled from the lamp into the dye cell. (Also on how much dirt there is in the dye solution and on the windows and mirrors, but let's not even go there.)

        The bottom line can be stated about as follows:

        If you can put greater than 5 J into a good xenon lamp with 5" or 6" arclength in less than 100 nsec, if you can get a good chunk of the resulting light into the dye cell, if the dye solution actually absorbs a goodly amount of that light, and if it's a nice friendly efficient dye (like R6G or Fluorescein), you probably have a chance. ...But if the pulse isn't fast enough, or if *anything* else is less than optimal, your chance fades away like the dew on the grass. Thus the Lankard laser from SciAm, which uses a slow capacitor, an air flashlamp, and a big lossy reflector, usually takes greater than 100 J per pulse.

        (I've said this before, but maybe it's worth repeating: I have a lamp with 38 cm arclength; my capacitor is 0.1 uF and fairly fast; I'm charging it to 18 to 24 kV, and switching it with a reasonably fast triggered spark gap. The pulse is a few hundred ns long. As a result I can threshold R6G with about 20 J into the lamp, possibly even less.)

      2. It has been pointed out that large capacitors are inherently slow; but small capacitors are not necessarily all that much faster. You have to design and build them correctly, and you need interconnections with very low inductance. (This argues in favor of the TEA-nitrogen-laser style of construction, which *is* fast. OTOH, it's not necessarily easy to make a transversely-pumped flashlamp, and it's not necessarily easy to make a structure of this sort that couples nicely into a regular linear lamp.)

        There may also be some afterglow from the lamp, light that doesn't get released quickly; this effectively spreads out the pulse. (I recently saw something suggesting that an air-spark quenches faster than a xenon lamp. Speaking of which, see the next item.)

    3. Spark versus lamp pumping of dye laser?

      Then there is the question of pumping with an air-spark, which has been raised by several people. That can certainly work. The lowest threshold I think I've ever heard of was something on the order of 5 mJ into the "lamp", which suggests that if you want to use something like the circuit that drives a TEA nitrogen laser, a structure that stores relatively small amounts of energy, a spark may be a good bet.

      The trick, I guess, is twofold: 1) keeping the spark confined to a straight line, and 2) getting as much of the light as possible from the spark into the dye.

    4. Mercury lamp pumping of dye laser?

      I think this has been done. They only got "quasi-CW" operation, IIRC, and they had to pour a lot of juice into the lamps. (See the two dal Pozzo articles that are cited elsewhere on this page.)

      One thing: I'd expect considerable afterglow at some wavelengths, and I'm not 100% sure which ones are most likely to display the effect. Perhaps we get to find out.

    5. Efficiency of dye lasers

      Someone said, "I am beginning to understand 'why' dye lasers are less efficient than common solid state lasers like ruby."

      Actually, ruby is awful. Besides, it's a 3-level laser, and it isn't really comparable to dyes.

      Nd+++, in glass, YAG, or YVO4 (or whatever host you happen to like) is a better example of a solid-state laser with reasonable efficiency (if it's done well; anything can be built and/or operated poorly).

      In any case, if you are pumping a dye laser with another laser, and you have things optimized and adjusted carefully, it can be quite efficient -- I think I've seen listed conversion efficiencies on the order of 35 or more percent. (Even a good lamp-pumped dye laser isn't *too* bad, though it clearly isn't likely to reach the 35% level.)

    6. Photochemical effects in laser dyes

      Here's an odd sidelight, for whatever it's worth, described in the paper: "Photochemical effects in a high-power flashlamp-pumped laser utilizing solutions of rhodamine 6G in isopropyl alcohol", B. A. Knyazev et. al., 1979, Sov. J. Quantum Electron. 9 1191-1193.

      Abstract:. The energy and shape of the output pulses from flashlamp-pumped solutions of rhodamine 6G in isopropyl alcohol were investigated experimentally as a function of the serial number of a pulse. The output energy obtained on excitation via a glass filter first increased from one pulse to another and then began to fall. When the pump energy was 10 kJ per pulse, the output energy increased by a factor of 1.52 by the eighth pulse, whereas in the case of ethyl alcohol solutions the output energy fell monotonically to zero in four pulses. The stability of rhodamine 6G solutions in isopropyl alcohol exposed to light was an order of magnitude higher than in ethyl alcohol.

    White Light Dye Laser?

    (From: Jon Singer of the Joss Research Institute.)

    I decided to make RGB "white" light from a single cuvette of dye, pumped by a nitrogen laser. This is kind of pointless, because you can't get much power out of it, but I had an interesting time doing it. See: RGB "White" Dye Laser Light from a Single Cuvette.



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    Dye Laser Tid-Bits

    The Jello Laser Legend

    Whether you can take any currently available flavor of off-the-shelf Jello(tm) brand dessert mix and build a working laser using it as the lasing medium is unknown. However, clear gelatin can certainly be doped with a variety of dyes to create some sort of a dye laser. But, it might not be tasty to eat. :-)

    The seminal paper on this work (I'm serious!) is: "Laser Action of Dyes in Gelatin", T. W. Hansch, M. Pernier, A. L. Schawlow, IEEE Journal of Quantum Electronics, January 1971, pp. 45-6. (Thanks to: Jon Singer, of the Joss Research Institute, for tracking down the reference.) The authors tried various types of materials for the lasing medium using a nitrogen laser pump source including:

    For a watered down version :) which covers the lasing of Scotch whiskey fumes and dyed gelatin, see: Schawlow, A. L., "Lasers: The Practical and the Possible", The Stanford Magazine, Stanford Alumni Association, Stanford, CA, pp. 24-29, Spring/Summer 1979.

    The definitive general article may be at Edible Lasers and Other Delights.

    Here are some additional comments:

    A normal dye laser was also used successfully as the pump source with some of these concoctions.

    One interesting characteristic of the gelatin medium was that if the incident pump laser remained stationary, lasing action faded after 100 or so shots. Some movement was needed, even if quite small, to maintain the response. Jiggling the Jello was sufficient. :)

    The paper is a worth-read. :)

    (From: Leonard Migliore (lm@laserk.com).)

    According to A. E. Siegman in his book, "Lasers", A. L. Schawlow (who got a Nobel Prize for his more mainstream laser work) put fluorescein dye in Knox gelatin and pumped it with a nitrogen laser. After observing laser emission from this medium, he ate it. It is my understanding that Dr. Schawlow is alive today despite this activity. (That was in 1998; he died of unrelated causes in 1999. --- Sam.)

    (From: Chris Chagaris (pyro@grolen.com).)

    Disodium Fluorescein is one of the few laser dyes that could be ingested without any ill effects. This chemical is routinely injected into the bloodstream of patients who undergo fluorescein angiography.

    (From: Dave (dyelaser@my-dejanews.com).)

    Kiton-Red-S a.k.a. Sulforhodamine-B a.k.a. Acid-Red-52 is another dye that might be used as well. It is not a legal food coloring in the USA, but it is used for coloring food in other parts of the world. It is also one of the more efficient laser dyes. Some of the laser dyes are extremely toxic, but many others are just slightly toxic or not at all.

    (From: Steve Quest (Squest@galileo.cris.com).)

    This I did not know. I think it was Red 12 or similar, I know it wasn't Red 52 that was banned in foods and cosmetics. Is this dye transparent, translucent, or opaque? The banned dye was opaque.

    (From: Steve Roberts.)

    Yeah, Jello will lase. I saw the original paper about it at one time. They used a orange Jello - the dye in it was later pulled by the FDA as a toxin.

    (From: Steve Quest (Squest@galileo.cris.com).)

    Ahh, I don't buy that. I recall lipstick had a dangerous red dye, so did red M&M's, but I don't recall Jello having the same problem. The dye in question was a coal-tar dye, opaque, and not fluorescent.

    (From: Steve Roberts.)

    The walls of the glass cell were the cavity and it was superradient when pumped by N2. Otherwise attempts to lase it were with it seeded with Rhodamine-6G.

    (From: Steve Quest (Squest@galileo.cris.com).)

    Any transparent thick substance when doped with neodymium, chromium, etc., will lase. The first Nd lasers (as in Nd:YAG) were actually Nd:Glass, plain SiO2 glass doped with neodymium. Thus you could Nd dope clear Jello and I'd bet it would lase when pumped by ruby laser.

    (From: Steve Roberts.)

    Certain types of DayGlo(tm) plastics will lase with a nitrogen laser pump as well. I personally can attest that Bud Light(tm) nailed hard with a excimer lases in the yellow in a dye cavity.

    (From: Steve Quest (Squest@galileo.cris.com).)

    So will Prestone anti-freeze, when pumped with an excimer. :) The stuff in Prestone antifreeze that makes it fluoresce is (TaDa!) Fluorescein. :) Take the stuff under a blacklight sometime. :) Ethylene Glycol (the active agent) is water clear, the fluorescein is added so you can see the stuff (glowing greenish yellow).

    Fluorescein isn't toxic, but I bet unflavored Jello doped with fluorescein would not taste good!

    You could also dope clear Jello with Nd and pump with ruby. It would lase in the IR. Given the amount of of Nd required, you could probably eat *it* as well, without much harm.

    (From: Sam.)

    So add some suger to the unflavored gelatin. It might even improve lasing! Then add KTP to the Nd doped Jello laser and get some green light. :)

    (From: Matt Polak (skandranon@avians.net).)

    In my readings, if I remember correctly, the experiments done with Jello typically incorporated 'non-toxic' fluorescein dye suspended into the gelatin in order to actually make it 'lase' when pumped.

    I have also heard about beer lasing from multiple sources, usually when pumped with a nitrogen laser I believe. (vodka also reportedly lases in the violet region). I've been joking at work (SeaWorld of Ohio - we're owned by Anheuser Busch beer company) that we should get some money from Corporate to develop a beer laser for our shows, and run it off kegs of the corporate product. Of course, there'd have to be extremely strict quality-control on the lasing medium, which would come in the form of a spigot in-line with the keg's output flow-lines to allow constant sampling... err.... testing. :)

    Hey L. M. Roberts, how about for this year's LaserF/X technical workshops we try to get sponsoring for doing demonstrations of which items in the patented 'Canadian Optics Cleaning Kit(tm)' (i.e., liquor cabinet) will lase, and their multiple uses for entertainment purposes?

    (From: Wes Delaney blkstr@zwallet.com).)

    My plan would be to try different kinds, of soft drinks, fruit drinks, and so on. Although probably not all will work, some might, and some might work better than others. It is worth pouring a few things from the refrigerator through the laser cavity. My guess is that some of the fluorescent dyed Gatorade and Power Ade drinks would probably lase. When I get a dye laser up and running I intend to do this. You can try anything but, drinks are fluid so it is easier to pass them through the cavity, and they widely available.

    Whiskey Dye Laser?

    (From: Doug Dulmage.)

    This is probably 100% urban legend, but what I heard as the discovery of the first dye laser went something like this:

    Back in the early 70's or so, remember when everyone had blacklights and Hedrix posters all over the place? Well, there were some guys that were working for IBM or some big company that was out in the Boston area somewhere, and it was late at night and they decided to go out for a drink while they talked over making a liquid laser. They got into some "blacklight bar" back then, probably a bit of stuff wisping about in the air, etc., and a noisy band, etc. But, they being good white shirt and blue tie guys, ordered a round of Martini's. When the martinin's arrived, the first thing they noticed was the they were glowing?! This had them a bit stumped as they had been trying a lot of different dyes and not seeing that much fluorescence with so little pump source energy like all these blacklights. So, they went to the bar and asked the bartender to take all the ingredients of a martini and pour them out into separate shot glasses, well, before it even got poured, they could tell exactly what it was, it was the gin! So, they bought a fifth of gin and took it back to their lab and I guess the rest as they say, is history. Or probably UL, but still, it would be fun to think that's how it happened. I did hear that from a good source back in the mid 70's while I was still a kid that had gotten my first HeNe courtesy of a very wealthy uncle who lived in Missasauga Ontario from a neighbor who had the first laser company in Canada, a fellow named White if I remember. And they gave me this militarized monster that he yanked off their line and gave it to me for my 10th birthday. And yes, I still have it, the uncle passed away on Salt Spring Island BC a few years back, all those stories and use of gin caught up with him, but having a few millions tucked away never made his life miserable.. And I even remember when we could take pictures of the beam and the photo shop would give us the prints for free as they thought that the red blotch on the print was a mistake they made in their lab, now that's old. In fact, they even had a monster CO2 laser at the Ontario Science center that they would blow up stuff with twice a day I think, I only saw it once, but it was COOOOOOL.

    Ah, the fun days of youth.. :)

    Perspex as a Dye Laser Medium?

    Well, not quite a liquid but similar idea. :)

    "I have been experimenting with some green fluorescent Perspex pieces that I obtained a long time ago as samples from a perspex shop. I found that when I placed them alongside a blue fluoro tube, the ends lit up *very* brightly. Adding a reflector improved output even more. Now, I have never been able to coax this stuff into lasing as I cannot organize appropriate mirrors, however, the ease with which this material fluoresces make me wonder whether it could be a possible laser medium. The furthest I got was polishing the ends, wrapping some flashlamps around the pieces and dumping about 10,000 uF at 350 V into them. What excited me was that under these conditions, the light emanating from the ends of these rods is by far the most beautiful and powerful green light I have *ever* seen (and I've seen a fair bit of it!). Your thoughts?"

    (From: Chris Chagaris (pyro@grolen.com).)

    Your idea of building a Perspex laser is not too far-fetched at all. There is one company that I know of (A HREF="http://www.dnlabs.com/">DN Labs Laser Technology) that is manufacturing a high temperature cross-linked, polymeric solid-state dye laser material. More simply stated: Organic dye doped plastic laser rods. The Perspex samples that you have may or may not be doped with an organic dye that would be capable of characteristics as a liquid organic dye contained in a quartz cell. The mirrors required would not be terribly specialized and most likely a good quality aluminized high reflector and a simple partially transmitting aluminized output mirror with about a 70% reflectance would suffice, if properly aligned. The flashlamp pumping of this material would be possible if the proper conditions were meant. Organic dyes require very short and intense pump light pulses to overcome losses due to molecules that are accumulated in the triplet state. Flashlamp rise-times in the (hundreds or less) nanoseconds regime are common in practical systems. This is usually achieved with commercial xenon flashlamps by using a very high voltage (many times higher than the self-firing voltage) low capacitance firing circuit with a triggered spark gap in series with the lamp. Your present low-voltage high capacitance circuit would create very long pump-light pulses which would not be suitable in such a laser system.



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