Sam's Laser FAQ, Copyright © 1994-2013, Samuel M. Goldwasser, All Rights Reserved.
I may be contacted via the
Sci.Electronics.Repair FAQ Email Links Page.

Care and Feeding of the Climet 9048 One-Brewster HeNe Laser Head

The following summary is written specifically for those who have acquired a Climet 9048 one-Brewster HeNe laser head possibly with the Melles Griot 05-LPM-379 brick power supply. Note that much more general info on one-Brewster HeNe lasers and this laser head in particular - including possible mirror mount designs and mounting arrangements - may be found in the chapters: Helium-Neon Lasers and Home-Built Helium-Neon (HeNe) Laser.

One-Brewster HeNe Laser Head with Very Simple Mirror Mount should look similar to the unit as shipped.

  1. Safety: This is potentially a Class IIIb laser (though I've never actually gotten 5 mW) and the power supply is also capable of a painful (if not lethal) shock. Once the wiring is complete, the electrical hazards are minimal as all the exposed surfaces are at ground potential (assuming the ballast resistor is double insulated as suggested below). Although the circulating photons inside the resonator can possibly exceed 1 watt with a super HR, the output beam is likely to be in the 2 to 3 mW range with an optimal OC - about the intensity of a decent laser pointer. So, reasonable precautions should suffice - don't stare into the beam with your remaining good eye. :) For additional safety information, see the chapter: Laser Safety.

  2. Powering the Climet laser head: This is a hard-seal wide bore HeNe tube (actually a Melles Griot 05-LHB-570). A 05-LPM-379 power supply works fine for up to almost 6.5 mA (though some of the tubes take awhile to start but always do eventually). To set it (or another power supply), put a DC milliameter in between the thin black HV return wire (negative of meter) and the HeNe tube exhaust tip-off (positive of meter); adjust for 6.5 mA after warmup. (The -379 may only go to 6.25 mA or so but that's fine. Even running at lower current will cause no problems as long as the discharge is stable - the output power will just be a bit lower.) The operating voltage is around 1,500 VDC with the included 75K ballast resistor. It is possible to run the tube at over 6.5 mA (at least for short periods of time) using a power supply that goes higher. I've found that the output power peaks at around 7.5 to 8 mA for at least one sample I tried but don't know if this is true in general. However, Melles Griot recommends 6.5 mA. I do know that the ballast resistor will likely overheat if run much above 6.5 mA for any length of time.

    Note that the Alden connector/cable is a bit funny. The high voltage lead goes to a clip that attaches to the anode-end (HR) mirror mount inside the end of the laser head. That area is actually plastic so the HV won't arc to it. But the thin black high voltage return/ground has to attach to the gas exhaust tip-off on the cathode end-cap of the actual tube (as provided - double check that the connection is secure). It is also a good idea to ground the case if the return of your power supply is also grounded (as it is with the 05-LPM-379). However, the case and tube are NOT connected together internally and the cable shield doesn't go inside the head at all.

  3. Wiring up the Melles Griot 05-LPM-379 power supply: If your unit came with this power supply, you need to provide a 3 wire grounded line cord for 115 VAC and 1/2 to 1 amp fuse or circuit breaker. THIS IS CRITICAL as I've heard of power supply bricks from various manufacturers exploding if there is an internal fault and no current limiting! A sticker on the power supply shows the wiring color code. With the CDRH loop (if present) intact, there will be a 3 to 4 second delay from application of AC power to startup. Cut the loop to disable this delay. A power switch, power-on indicator, and fancy box are optional. :)

    Once the wiring is complete and power is applied, the unit should lase. If the tube doesn't light after a few seconds (there is a 3 to 4 second delay built in to the power supply - cut the CDRH loop wire to disable this), check the wiring and that your outlet is powered. (The discharge can be seen via several small holes in the cylinder or by looking at the Brewster window area.) Assuming the tube lights but there is no red beam, gently dust off the Brewster window with a new Q-tip (cotton swab). If there is still no lasing, the 900 pound Gorillas must have gotten to it - Gently press on the mirror mount to see if alignment might have gotten altered somehow.

    WARNING: DO NOT disconnect the Alden connectors while the unit is running! If you disconnect it just after powering down, there may still be some residual charge on the male Alden pins attached to the laser head due to stray capacitance. Don't jump too high. :)

  4. Mounting: Use the holes in the flange (front and back) or provide clamps (not too tight) to hold the head in place. DO NOT use any of the other threaded or non-threaded holes for ANYTHING! The glass HeNe tube is in there! It's all too easy to tighten screws too much. Crunch. :(

    It's a good idea to arrange the ballast resistor away from wandering fingers, metal brackets, or materials like plastics since it has the high voltage on it (and the insulation may not be that great) and it gets hot enough to melt bubble wrap!

    Although the diagrams photos show the B-window facing up and this is the most convenient orientation for display and cleaning, it is also the one that collects dust quickest. Facing it to the side or down will result in a much longer running/storage time between cleanings.

  5. Mirrors: The first thing you will probably want to do is throw away the barcode scanner mirror chip and fabulous mirror mount I provided. :) (Well, OK, don't throw them away but store the mirror in a plastic bag or pill bottle. For your sanity, if the other mirrors you have refuse to cooperate, the lowly barcode scanner mirror chip can be installed to confirm that the laser still works.) The Radius of Curvature (RoC), reflectivity (R), and quality of your mirror will determine what's possible:

    High quality laser mirrors are best though dichroic mirrors from HeNe laser based barcode scanners work quite well as HRs. Even some protected aluminum mirrors have high enough reflectivity for lasing - barely: it will be weak and nothing to write home about. (There will, of course, be no output beam with these since aluminum is quite opaque.) However, aluminum mirrors are not all created equal and many won't work at all due to low reflectivity or poor quality or both.

    The RoC of the mirror will determine what range of locations are result in a stable resonator (and thus lasing). These can be found from the equations involving g1 and g2. See the section: Resonator Stability. Planar mirrors will work almost up to a distance of 60 cm from the internal HR (which has its RoC equal to 60 cm). Mirrors with very small RoCs (e.g., from short barcode scanner HeNe tubes) will have a very limited range of acceptable positions - a typical RoC for these which is 26 cm won't work at all close to the Brewster window. I recommend 60 cm if you have a choice. This arrangement will lase anywhere from the mirror next to the Brewster window out to almost a meter away with changing mode structure as this distance is varied! There is at least one most interesting singularity along the way (you find it!). Mounting the mirror assembly on an optical rail will allow you to easily experiment with mirror placement. A confocal cavity will result using this mirror at a distance of about 34 cm from the Brewster window.

  6. Optics cleaning: Your output and circulating power will be a strong function of the cleanliness of the Brewster window and external mirror. The Brewster can be cleaned with alcohol. Spectroscopic grade isopropyl or methanol alcohol is best but drugstore rubbing alcohol (70 percent isopropyl) or medicinal alcohol (91 percent isopropyl) will work just fine as long as it doesn't contain any ingredients other than alcohol and water. Use a fresh Q-tip (cotton swab) or lens tissue. Once the window has been cleaned, all you should have to do is dust it off from time-to-time with a new (clean) Q-tip. Break a new Q-tip in half, use each part exactly once, then discard it. With the laser lasing, dust and other debris will light up like a beacon so it is easy to see what is there. It will never be perfect - and will degrade in anything but a clean room environment. (And, some tubes may have a speck inside which can't be removed. If anyone has a suggestion on cleaning the inside surface of a Brewster window, please contact me via the Sci.Electronics.Repair FAQ Email Links Page.) Accept this as a fact of life! With the relatively high gain of this tube (at least relative to a one-Brewster tube that does green!), the laser will still work quite well after a week in a dusty basement environment though its output power will be way down if measured on a power meter.

    As for the mirror, if you start with a nice clean mirror, it will likely stay fairly clean as long as (1) you don't put your grubby fingers on its surface and (2) your environment doesn't have any tobacco smoke or cooking grease vapors. :) I have found that in my dry, but somewhat dusty basement lab, mirror cleaning isn't needed for months with only some plastic bubble wrap for covers - dust doesn't tend to collect on the vertical mirror surfaces. If you must clean the mirror, use the "drop and drag" method as described in the section: Cleaning of Laser Optics.

  7. Solar cell sensor: I have not tested this and don't even know for sure what it was intended to monitor. The waste beam from the internal HR is pretty weak and it would appear as though the sensor would be overwhelmed with just the glow of the discharge.

  8. Initial alignment: Once you are ready with a real mirror and mount, the easiest way to do the alignment if the mirror is located fairly close to the Brewster window is to view the reflection of the bore light on the Brewster window. When it is approximately centered, there should be flashes. This works best if the mirror is behind an aperture of about 6 mm. An alignment jig using a separate HeNe laser will also work but is overkill for this wide bore multimode tube. Really. :)

    If the mirror is a half meter away, good luck. :)

  9. Maintenance: No routine maintenance is required. The laser head does NOT need to be run periodically. Since it uses a hard-seal HeNe tube, it can sit on the shelf unpowered for as long as you like without any ill effects. It should operate for several thousand hours with at most a slight decrease in possible output power. I would recommend that the laser be covered or stored in a dust proof box when not in use but that's just to protect it and help to keep the Brewster window and external mirror as clean as possible. Unless fully enclosed and sealed, cleaning of the Brewster window will be required more or less frequently depending on environmental conditions. (The mirror generally remains quite clean even after long a period.)

  10. Electrical troubleshooting: The HeNe tube inside the Climet 9048 one-Brewster laser head is much like any other modern hard-seal HeNe tube except that its bore is quite wide (more along the lines of a multimode tube) and thus the operating voltage is relatively low for its length (just over 1 kV not including the ballast resistor). Unless it is abused (e.g., run on a power supply putting out way too much current or with reverse polarity), almost any amount of hobbyist running time shouldn't hurt it or use up a substantial portion of its life expectancy. About the only other way to cause damage is to drop the tube on a concrete floor!

    I've seen two sorts of problems with a few samples of these tubes, both related to starting:

  11. Lasing troubleshooting: Problems obtaining a beam are most likely related to mirror reflectivity or radius of curvature, mirror alignment, or the cleanliness of the mirror or Brewster window. A scratched mirror or one that is damaged in some other way may lase erratically depending on its X-Y position and/or behave strangely with alignment. Sometimes an almost invisible speck of dust or fiber will land in a strategic location on the Brewster window and totally inhibit lasing. However, this laser head really loves to lase given half a chance!

CLIMET 9048 with Home-Built Mirror Mount and 05-LPM-379 HeNe Laser Power Supply

Here are some relevant diagrams and photos:

Here are some of the relavent sections to start reading:

Have fun!


Sam's Laser FAQ, Copyright © 1994-2013, Samuel M. Goldwasser, All Rights Reserved.
I may be contacted via the
Sci.Electronics.Repair FAQ Email Links Page.