This bit of hardware is just overflowing the todo list...
First, read Sam's Laser FAQ.
The laser head is a cylinder about 3 inches in diameter and a foot or so long. The data sheet says that to cool it, one connects a blower to the open end, and pulls a vacuum. The laser requires between 65 and 150 cubic feet per minute of air. Unfortunately my exact head isn't actually described on the data sheet, thus the range.
It is apparently possible to overcool a head. You want to avoid too great of a thermal gradient. I don't have any good information on that issue though...
The advice of Usenet is to pressurize the head, instead of pulling the vacuum. I don't have much wisdom on this, so I took the suggestion. Dealing with pressure is easer than vacuum too.
I have, in the heap of stuff, two squirrel cage blowers. They were pulled from some large computer equipment we got at a surplus auction to disassemble. The gray one played a rather important role when Graysoul and I tried to strip some paint in the basement, and nearly gassed ourselves. (we eventually got a Bigger Fan (tm) It was a thing to behold... I have pictures...)
Anyway, one of the two fans is now going to be on cooling detail.
I went to Home Despot, and got some dryer vent plumbing, and some drain plumbing. Then I went back and tried again. Important note: pipes are described by their inside diameter, not their outside. No one seems to actually think about wall thicknesses either. According to the label, the metal dryer tubing is apparently good for 6 inches of water of pressure, positive or negative. Which is pretty cool, but I'm doing it positive, and using the plastic kind since its more flexible.
Then I fabricated some plexiglas adapter plates, to put round 4 inch dryer couplers onto the outputs of the blowers. The couplers were attached to the plates with electrical tape, then the plates electrical taped to the blowers. While they leaked a little it was not significant. I then attached the dryer tube by putting it over the coupler and using a monster cable tie.
For the other end, the 4 inch dryer tube doesn't attach to the 3 inch laser head very well... So I got a 3 inch to 2 inch PVC pipe adapter. (and put the 4 to 3 adapter on the shelf.) The 4 inch dryer tube went over the outside of the 3 inch end of the PVC perfectly (with another monster cable tie), and the outside diameter of the 2 inch end matched the outside of the laser head close enough to apply some 2 inch wide masking tape.
So now, the question is how warm is the laser tube running? I had an old indoor/outdoor thermometer. I stuffed its temperature probe into the laser head, between the two sets of fins on the tube itself.
I set the power supply to light regulated, and all the knobs to lowest setting. I then turned on the fan and power supply for one minute. At t+ 1 minute, I turned the key to turn on the laser itself. Twenty seconds or so later (nominal) the filament got to operating temp, the arc was struck and the tube started lasing. I then recorded the temperature every ten seconds. If the tube temperature passed 120 degrees, I turned off the arc (but obviously left all the fans on)
The X scale is time, in tens of seconds. The Y scale is degrees Fahrenheit.
I suppose you're wondering why the gray fan has two lumps. The first one was with the power supply at minimum output. After the temperature stabilized the first time (91 degrees) I turned the power supply up to about 8.9 amps of tube current (which I think is a little high for this tube). The temp then went up again, and re-stabilized at 110 degrees.
Obviously, the black fan moves much less air than the gray one. But is it safe? I turned it off at 120, before it had stabilized... looking at the gray fan's curve, it would probably stabilize at 130 or so. The data sheet says the operating temperature of the laser is 10 to 40 degrees Celsius. Thats probably ambient air, not tube temp. So its debatable, but probably safe on the black fan. The black fan is much less of a vibration source... (and my vague goal is doing some more holography)
Another interesting observation is that at greater power levels, the laser no longer generates fringes in an interferometer. Graysoul's theory was that the tube went multi-mode.
The Bernoulli effect is that air which is moving has a lower preassure than air which is not moving. Thus wings and venturi work... Take a piece of paper, hold one edge horizontally directly below your mouth (against your lip) so it hangs down in front of your chin. Then blow straight forward, along the top surface of the paper. The paper will lift up.
Thats the boring demonstration.
The other demonstration is to take (say for example...) a blower connected to a dryer tube. Hold the tube so the air is blowing straight up. Then balance a beach ball on the stream of air. The air in the center of the stream is moving faster than on the edges, the ball will be sucked towards the center, and thus stay balanced on the stream.
The black fan could barely get the ball off the end of the tube.
The gray fan had problems with the ceiling... Which brings us to the second part of the demonstration. The suction towards the center of the air stream can be stronger than gravity. Hold the tube at an angle, the ball will stay stuck in it. I had the ball hovering a good three or four feet away.
Mpeg file of the beach ball This is an anaglyphic 3D mpeg, red lens on your left eye. I'm still working on the colors though.
The laser normaly stablizes at about 155 degrees, running about 5 amps through the tube, and a runtime of 15 to 30 minutes. 5 amps seems like a sustainable power output. One interesting result of playing with "turning it to eleven" is that my thermometer fails at 160 degrees. It was intended for weather, so I guess it has a point.
Currently, I have the laser head mounted on a pair of steel bars with tapped holes in the ends for leveling screws.