- 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:
- 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.
- 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. :)
- 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
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.
- 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:
- An HR (High Reflector, R approaches 100%) will result in maximum
circulating power (perhaps as much as a watt or more) but little or no
- An OC (Output Coupler) with R of around 99% will result in modest
circulation power and a strong (1.5 to 4 mW) output beam. I don't know
quite where output power peaks. A 98% mirror results in a lower output
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.
- 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
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.
- 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.
- 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. :)
- 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
- 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:
- On one of my tubes, the anode was arcing inside the head to the
cathode end-cap or case via the start-tape - there must have been
condensation or other contamination of some kind. Should this happen
(the symptoms will be an inability to start with periodic snapping
or sizzling sounds emanating from the laser head), just remove the start-tape
from the anode of the tube - I've never noticed any benefit from the
start-tape anyhow - on any HeNe laser head! To get inside, kill power (!!)
and disconnect the head from the power supply. (Discharge the tube
capacitance if you don't like getting shocked.) Then, remove the 4 cap
screws, carefully pull off the plastic plate (with the solar cell and its
coax), and then the anode clip. To gain better access to the start-tape,
loosen the 3 Allen setscrews holding the plastic barrel in place and remove
it. Cut or peel the start-tape away from the anode leaving at least a 1
inch gap. Reassemble in reverse order.
- Under certain conditions - perhaps high humidity, perhaps being ignored
for too long :), some of these tubes take awhile to start when cold, up to
a minute using the 05-LPM-379 power supply. However, they always do start
eventually and once they have started, restarts are virtually instantaneous.
I have not noticed any deterioration in this behavior with age or use, nor
does this correlate at all with performance.
- 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!