Hardware > Other Hardware
Analog laser shunt modulation
dtewksbury:
Hi everyone. I have been busy buying red and violet lasers off eBay. As a consequence, I have found that the LM317 laser supplies are fine for driving the lasers, but when it comes to blanking and ramps they are of course useless.
So, I am designing an analog shunt modulator for these supplies that has a fast response. I have simulated the circuit and it seems to have a delay of about 1 microsecond, and it is very linear with an expected input of 0-5 V (of course). You can adjust the maximum power and blanking points. The circuit is very simple and I will post it if anyone is interested (once I have determined that it doesn't destroy the laser diodes).
Anyway, I have tested it's blanking with my laser driver software and it is awesome (as far as blanking response anyway), I have attached an image of Quisp being scanned with a 650nm 200mW diode I bought from eBay.
I have to apologize about the laser spill, I had to focus the laser on the wall and that made the spot a little too large for the scanner mirrors, I will have to do something about the optics with these cheap lasers to get the spot smaller on the mirrors (maybe a beam expander will work), and this is with a glass collimating lens.
I will post some images with gradients as well when I get a chance.
So here it is, a $49 300mW laser diode (running at 200mW, measured with a coherent power meter). Plus about $10 worth of parts for the modulator.
Fanny Pack:
Good work. I used to use Norm's driver and it is a shunt type. It worked fine but was a bit bulky and needed a big heatsink since the driver was always allowing max current to flow. I ended up going with the tiny die4drive units and just being careful not to touch my diode cases while they were in use.
dtewksbury:
I have never heard of the Die4Drive units, but they look good. I am also curious about the ZVS unit that is mentioned on the site. I have smoked quite a few FETs while trying to build ZVS power supplies. Its all a learning process.
drlava:
Here is a high speed shunt driver schematic I posted back in 2008:
http://www.photonlexicon.com/forums/showthread.php?t=5428
Since that time, I've found the FlexMod more flexible, precise, and easier to use.
dtewksbury:
I didn't realize there were so many available. I did try to search for them before I decided to design one, but that's what seems to happen a lot. Anyway it is very simple and only uses two transistors, it is very linear as well, with a fast response time.
I am not sure about this linear thing though, the very low intensity end I think would benefit from a non linear response when you get down to near the laser threshold, then a sharp cutt off for blanking, I find it too 'steppy' at the lower end, even though the response is linear.
I have attached an image of the circuit so far.
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