Lasers
Well, my dad did make a simulated ruby laser with a little bit of my help in second grade for the science fair, but this was my first opportunity to own a laboratory-grade Spectra-Physics 124 laser for the low price of $80 from HGR Industrial Surplus. This Helium-Neon laser isn't well represented on the web, but estimates as to its power hover above 15 mW. Garden-variety laser pointers only simmer above a milliwatt or so, and most of the legal bright green ones are below 5 mW. To set things on fire at a distance, you'll really need something above 250mW.Don't lase me, bro!
Had I looked at Sam's Laser FAQ, I would have known that laser tubes age, with the slippery noble Helium escaping from the tube over time. This having been said, my beloved laser started but did not lase, providing a neat light show but no actual laser beam. As I wrote this I wondered if I shouldn't keep the useless beauty around, but I had to remind myself to carefully ration my toys budget and resolve to take it back. HGR's excellent return policy as well as their endless flow of fascinating new stock are reasons enough to make me return and pick some other cool thing off the floor, take it home, and learn more stuff. The laser beam in the picture diverges, but that's not how it is in real life. A lens of short focal length was used to take the picture, and that's just how optics work at large apertures; things diverge. If you want to see some great wide-aperture work, check out Liz's site. With respect to the beam of the laser in the picture, the beam is a needle when seen in smoke or haze.
As for reviving the laser, I read about such elaborate schemes as soaking the tube in a garbage bag filled with helium, baking the tube in the sun, or even microwaving the tube, but I thought there were ways my time and $80 would be better spent. If you are interested in lasers, I strongly suggest, as does any search engine, that you check out Sam's Laser FAQ.
Sure, I've always been into lasers, what nerd hasn't? The thought of vaporizing a playground bully at 100 meters has always been my secret fantasy. I've hung out with laser people from Centrak, who created the laser show for last century's post-restoration unveiling of the Sphinx, and recently toyed around with an astronomer's green laser pointer for hours, marvelling at the capillary beam of coherent light that seemed to go on forever. The 124 would have been something truly special, especially when deployed in working order in a residential setting. The power supply, a Spectra-Physics 255, makes you turn a key to turn on the laser, and it offers a friendly dry-contact terminal pair for remote operation. The unit ships with the contacts soldered together.
I no longer care about the schoolyard bully. After all, who's the cool one now? :)
Rebirth (added 5-24-09)
I am really surprised to be writing this, as I was already over the disappointment surrounding the laser and ready to move on to other projects. About a week ago I opened the power supply, in hopes a single a current-adjustment trimmer might push things over the edge and elicit a laser beam. I found a schematic for the Spectra-Physics 255 on my favorite laser FAQ, and this strategy was my last hope, as well as Big Dog's. After all, this laser is about a meter long, and I wanted it in my family so badly.
It was easy to find the trimmer, as it was one of the smallest components on the board, at the left edge of a prehistoric forest of giant passive components and heat sinks. Slowly turning the dial with a screwdriver had an obvious dimming function on the tube, as well as a slight color shift, but no laser beam. I tried restarting the tube again with the trimmer at various positions, but there was no output. I did notice that the violet-colored light coming from the output end had become strong enough to project a wide spot on the wall, and that was somewhat encouraging.For some mundane reason, I had to leave the laser, and didn't think about it for I'd say, 15 minutes. Going about some other task, I absently flipped the keyswitch as I had been doing over the couple of previous days, cycling the power. Next I uttered a phrase best reserved for the most important of scientific discoveries. "Oh my God..."
To my amazement, there was a bright red spot on the wall, a pinpoint of glowing cherry-liquer purity that could not have been mistaken for anything other than a laser beam. "Cool..." I thought, "I have a friggen laser!"
But the beam soon faded away, replaced by the diffuse violet circle projected onto the wall. Returning quickly to the trimpot, I made slight adjustments and experimented with power cycling, increasing the duration of the period between firings. The beam reappeared and was sustained somewhat with higher current. I found I could turn the current down while the tube was lasing, and this extinguished the beam at the low settings. Now we were getting somewhere.
I began to notice a consistent curve, like that of a capacitor discharging, that the laser was following between starting and the disappearance of the output. I am a photographer, and have a small Speedotron flash setup, so I'm somewhat familiar with the care and feeding of big power supplies. With power equipment that has banks of capacitors, it's a good idea to keep them in good health by energizing them from time to time, say every few months. What if the capacitors in the laser exciter needed re-forming? The power supply probably hadn't been used in some time, and maybe needed to get used to doing some real work again. The solution turned out to be exactly this. Fast-forward to the present day.
Now, the laser starts about a second after throwing the switch and remains stable until I get tired of having a distractingly-bright red spot on the wall. I began at some point to worry about the specularity of the paint used on my wall, so I've since mounted a matte white card as a target. I don't have a means of measuring power yet, but with continued use, the spot has become absurdly bright, and the discharge color in the tube bore has changed to a red-orange glow, replacing the purple that was there for so long. Yes, I have a friggen laser. With a little bit of work, a seemingly-dead laser can be brought back to life. All that's left is to figure out what to do with it, but that's for another page.
A little brother... (added 6-1-09)
This past weekend I visited HGR again, with the express mission of rescuing "Little Dog," the Spectra-Physics 120S. I had seen it there several times, but the $299 price tag and a broken power supply key had dissuaded me. When I plugged it in there was no laser beam, so I figured it was junk, not knowing yet that with a little work, a seemingly-dead laser tube might be brought back to life.
The price had dropped since my last visit, and that Saturday's discount helped too: the laser head and exciter unit came to $107. The 120S is a 15mW unit, 10 milliwatts more than Uncle Sam's rating, and it came alive within the span of an hour. Today's lesson: tube lasers and power supplies need a little warmup time after long periods of inactivity. At first, there was the waste glow that's not a laser beam, and then a faint pinprick, and then a pure needle of concentrated coherent light.You can get a laser pointer today that has decent output, but such a device wasn't meant to be left on for long periods of time. Temperature effects are eventually going to change the beam characteristics and output power during a run. Having a lab laser is much better for experiments, and having two is twice as better.
The laser's output continues to increase, a fact that is apparent through the appearance of a secondary output spot, off-axis to the main output TEM-00 circle. I am not a laser scientist, but I've read enough to know that this laser is gradually returning to what it was made to do, cooking away and producing "a splendid light for man's use." (National Geographic, March, 1984).
