I remember the first time I encountered one. It was (according to my fuzzy memory) a 4-Watt behemoth from Spectra-Physics, being incorporated into a prototype Fluorescence-Activated Cell Sorter in the lab at Becton-Dickinson.
The laser head was maybe 4 feet long; the power supply was a large box; and 3-phase power and water cooling were involved. The price was astronomical; the rated working life, brief.
Well... my blue laser module came in today's mail, one day behind the corresponding safety goggles. It's a bit less than an inch and a half long. The power supply for initial testing, being massively overkill, is a modest-sized bench unit with the current limit set to something safe for both diodes and (with some care) the eyes of bystanders.
OK, so the diode module is only rated 2 Watts, not 4. There are modules the same size rated up to 6 Watts, to my knowledge, but this one was cheap.
Not having bothered to set things up for safe testing at high power, but wanting to do a basic functional test, I stuck the module in a heatsink, hooked it up to the bench power supply, set the current limit to 200mA (being around 10% of rated operating current), and slowly cranked up the voltage.
Surprise! The threshold is quite low. Run a modest trickle of current through the critter, and a nice beam emerges, at roughly laser-pointer intensity. So, no need to use PWM for low-power alignment mode; just set the current limit way low, and run it CW. Win!
On the negative side, the supplied lens does not seem conducive to tight focus at close range, as would be needed for a laser cutter. It gives a nice tiny round dot on the wall a few feet away, but at sub-foot distances I get a greatly elongated dot. Well, if it's meant for a home-theater projector, focus a few feet out is a lot more interesting than focus close in.
Not sure what I'll end up using it for. Maybe I'll come up with a lens arrangement suitable for cutting plastic film (the short wavelength makes it more suitable than a CO2 laser for fine detail). Or maybe I'll build a ray gun for zapping spiders from a safe distance.
Update: The supplied lens can in fact focus to what appears to be a fairly tiny roundish spot at close range; I just hadn't been unscrewing it far enough. Determining the actual spot size and shape, well, that's another question entirely.
Those $40 goggles are very effective at this wavelength! If I crank the power up to a modest fraction of nominal, such that the diffuse reflection from the far wall is eye-hurtingly bright, then put on the goggles, all I see of the spot is a dim glow... which, curiously enough, appears orange, and as a ring around where the actual spot ought to be. Does the diode have some emissions on a secondary, longer wavelength?
Anyway, it may work for cutting plastic film. So now I need a supply of maybe 0.002" thick, orange-tinted polyester film... or a reddish / orangeish dye that'll work on regular clear film.
Or I could have OSH Stencils make my solder-paste stencils. Hm - they even offer stainless steel, at a price that could fit my budget for serious projects. Outsource the stencil-making, and use the laser for zapping bugs and lighting bonfires?
Maybe play with Fluorescence Photobleaching Recovery? That's another thing I was briefly involved in, as a teenager - may tell the story someday. Apparently it's called FRAP now; I thought that was Bostonian for milkshake. The experimental setup back then involved a CW, fixed-power (30mW?) argon-ion laser - my attempts to retrofit it for pulsed operation having been unproductive - with a high-speed shutter for pulsing the beam; a primitive MCU (8748?) programmed in old-school pencil-and-paper assembly language, controlling the timing of the shutter; a photodetector, the nature whereof I don't recall; a Berkeley Nucleonics pulse ADC to capture the output of the detector; and an LSI-11 to send the start command to the MCU, capture the numbers from the ADC, and do a little crunching in FORTRAN.
And... anyone else remember when a 30mW laser was considered worthy of signage? DANGER, and DO NOT ENTER WHILE LASER IS IN USE?
Comments