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Astronomy and Orion Skyview 8 Pro EQ Review
Hobby Electronics and My Projects
Miscellaneous Laser Pictures
Increasing The Output Of The Leadlight Green DPSS Laser Pointer
There are links to relevant websites throughout this narrative, so please check them out! This webpage details my experiments with increasing power output of a green laser pointer and should not be attempted by those not experienced with electronics and laser technology. I removed a limiting resistor in mine, which *could* conceivably cause thermal runaway in some pointers, although this one seems to be just fine. Also, you do any modifications to your own or others laser equipment under your own risk; this page is for educational reference ONLY.
Click here to watch a video of the laser in action! This was filmed from a cold start, and allowed to warm until the output was at maximum and stable. Notice that the background does not change in brightness; the beam really is getting that much brighter! The occasional flickers along the beam are random dust particles drifting in the air, no steps were taken to enhance the beam visibility other than lowering the room lighting.
On January 9, 2003, I purchased a green DPSS (diode pumped solid state) laser pointer from
Extreme Lasers. It took me quite some time to decide
which pointer to buy, but knowing little about DPSS lasers, I finally opted for the rather expensive GP-Series Extreme, which was supposedly modified for greater power output and lifespan. Had I to do it again, I'd probably just go with the regular GP-Series pointer, or
save up and get the 15mW Class IIIb green pointer from Megalaser. Why? Because even taking into account my limited experience, I have reason to believe that I *might* have been able to do the "Extreme" modifications myself, thus saving $100 US, and the "Extreme" model certainly is NOT a 15mW laser. Hindsight, you know.
Anyways, I got my laser, a Leadlight model, a mere two business days after ordering, and had oodles of fun with it
before losing all control and drilling a hole in the casing to turn up the power via the very small and delicate internal trimmer potentiometer. You'll probably notice that I kinda squashed the pot doing this hehe. Mind you, it took me 2 whole days to get to the point of justifying voiding the warranty :-)
I *did* increase the power... but only very slightly, and it was really only noticeable as a current drain increase on my BK Precision digital multimeter, which by the way I dearly love. Anyways, the battery drain before turning up to full output was 280mA, and 320mA afterwards; a mere 40mA increase. Irritated, I studied some postings on the Alt.Lasers newsgroup, and posted some queries there also. A member named Fleetie was very helpful, and with his assistance, I managed to fairly easily disassemble my laser and do some extensive testing on it.
Here you see the disassembled pointer. Note that I did not disassemble the optical assembly at this time, as I saw no need. What I really wanted to get at was that driver board, since that is where the power input is controlled at. The internal parts consist of simply the driver board/diode/crystals/optics assembly, and a piece of molded black plastic that serves as a support for the driver board and a lever for the power switch. A very Mickey Mouse style pushbutton switch consists of nothing more than an oval shaped plastic tab stuck to the rest of the molded black plastic piece via contact adhesive, and it popped off when I pried the internal parts out of the body tube. It sticks back together easily enough.
I then rigged up a rather simple mess to supply power to the diode assembly while still free of the body tube, which allowed me full access to all of the electronics even with the laser running. This must be what my college education was really for. Had I not attended those courses, I might never have known how to turn a Dorcy flashlight into a AA battery holder, haha! Anyways, I did everything I could think to do, from reading current drain while turning the trim pot, to actually replacing some of the chip resistors, all the time observing the effect on beam brightness.
Here are the top and bottom sides of the driver board. On the topside (first photgraph), note the two chip resistors flanking the trim pot. The one marked "102" is a 1K resistor and does nothing magical when replaced with even a 100 ohm. The one marked "202" (2k), however, serves as a minimum limit for the trim pot, and when removed the driver circuit will go as high as it can. With this unit, that meant a battery drain of 400mA, from the original of 280mA. Now that's more like it! To power the unit up, one only needs to clamp a 3V+ supply line to the brass body of the diode assy, and the negative line to the plated through hole on the top left corner of the driver board in the first photo.
Now here's the funny part... When I removed the 2K resistor described above, I did note that it fixed the unit into maximum output given the rest of the circuit was left as is. I noted that my digital meter showed battery drain now at 400mA. As almost an afterthought, I put the pointer back together and left that resistor out. The beam wasn't that much brighter, but I thought it might have gained just a tiny bit of brightness and might be useful. Here is what I did NOT expect:
After much shining of the beam at various walls and objects, suddenly the beam got MUCH brighter. By "much" I mean AT LEAST 50% brighter and quite likely as much as a 10mW increase, landing me around 15mW give or take. Then it went away. Then it came back. I assumed the obvious in electronics; the switch contacts must be dirty. I clicked and clicked until the beam stayed that ghastly bright green, clearly visible throughout the house, even in fairly bright light. The first picture shows the beam as it always looked after I turned up the trim pot. The second shows the dramatic increase in brightness after all the manic clicking and pressing on the body tube to eliminate bad power contact.
Laser Extreme, baby!!
The difference was spooky. In a low light level room, the beam had become a thick, grass-green line extending out to the dot no matter how many dozens of feet I could manage in the house. The dot was a fierce, angry little green sun glaring at me in a rage on a wall ten feet away. Within a minute or so, it was apparant that the tube was growing warm, but not overly so. I'd guestimate about 105 degrees farenheit after a minute of running time. Battery drain was much stronger, sucking down batteries much more quickly. The more I used it, the more it seemed like the odd flickering increase in brightness occurred each and every time the pointer was operated from a cold start. I still suspect, even now, that the switch is a bit gritty, but I no longer believe it is mostly to blame. I built a very quick and dirty photocell voltage devider circuit to connect to my homebuilt MAX187 based paralell port ADC, and set my copy of Radio Skypipe to work graphing the relative brightness of the scattered light from the laser starting with the pointer cooled to room temperature and a mostly charged up pair of AAA NiMH batteries. Striking results! At 34 seconds of run time, give or take a second, the pointer begins to flicker and go into "superbright mode". To the eye it appears quite stable after it settles in for a few seconds. To the ADC, however, the output is quite noisy, wavering up and down considerably. I did this same test many times, and found that even more surprisingly, much of the wavering is nearly identical from test to test, only varying slightly in timing of occurrences.Please note that I had the graph running slightly faster in the second image, accunting for the somewhat expanded nature of the events.
Observe these two screen captures. They appear almost identical, with differences very few. One would think, at first glance, that these are the same event from different sensors, but they are not. They are two events monitored just over an hour apart.
It would *appear* that the huge jump in power at 34 seconds is in relation to either heat or the charge or discharge of one of the driver circuit's chip capacitors. I am betting it's a heat issue, but why that would be I have no idea. Whatever the case, it does happen; the brightness jumps by an apparant factor of 20 during the higher spikes. I don't yet have a method to do real time current draw graphing, but I suspect the drain looks very similar to the brightness.
Where does it end?
Now that I have a laser, it has taken a painfully short time to become maddened with the whole idea. This pointer has already been taken apart, and the warranty is of course null and void as a result. Should this pointer prove to fail due to switch contact issues, it already has a destiny, and that destiny may come to pass even if it functions well from here on out. I envision a small black handheld box, just big enough to fit two C cell batteries, the guts of the laser, and some simple support items. I envision this box having a power toggle switch, a power pushbutton, a TTL modulation input, an analog modulation input, and a zero to max power output control. During testing, I was able to ascertain that the last two items are indeed possible, as that 2K ohm fixed chip resistor was the only thing holding the unit back from using the trim pot to reduce output power to zero. Substitute the pot/resistor combo with a transistor, et voila, a simple analog input that varies the laser output. This gives one the ability to send any analog signal such as audio, video, or other analog data, to a distant receiver. How distant depends on beam power and environmental conditions, but I feel that even a mile or more should be easily attainable. Beam power could be adjusted by the output power control to suit whatever application, from short distance of only a couple of feet, to full range of thousands of feet. A TTL input would grant the ability to send digital data, the C cell battery supply would allow much longer peak power running times, and the choice of power switches would allow either momentary or hands free operation. One could even add a jack and regulator circuit for use with an AC power adapter for serious, long term applications. Why not even abandon all control and replace the pump diode with a 500mW unit, heatsink and TEC the diode assembly, and totally rework the driver board to really whomp ass with a variable output from 0 to 100 milliwatts sustained?!
Links To Relevant Pages
Sam's Laser FAQ -
Fleetie's Laser Pointer Dissection Pictures -
MegaGreen Green Lasers; Future Power! -
Radio Skypipe Data Aquisition for the PC. Very cool, very affordable! -