Can someone help me tune my green laser?

[Things]

I am having a few problems with the green laser in my laser projector. Originally it was starting off with a nice high power, but soon after would drop right down to around 60mW or so. I then tuned it myself and it was doing about 150mW stable. Although, I didn't do it while the laser was being modulated, so now when I modulate it, it becomes unstable and flickers between power levels quite a bit. I have a thermopile based meter. The laser driver has 3 potentiometers, and I have found the pot that controls the diode current, however I'm not sure what the other 2 do, and whether there is 2 TEC's in this head or just 1.

The module is rated for 150mW, however I have even seen it do up to 240mW on startup meaning there is a fair bit more power to be had, however I can't figure out how to do that whilst keeping the damn thing stable. There is even a certain range on the 2 potentiometers that makes the laser flicker so badly it's a strobe light!

It's a laser century laser, and if anyone knows about the potentiometer config I'd appreciate it

Otherwise, what would be the best way to go tuning this to perform the best with modulation?

If I can't figure it out, I may need to find someone to send the laser to and have them tune it for me, since I get easily frustrated and run out of time

Cheers,
Dan

[-bart-]

Surely you have marked the original setpoints of the pots, haven't you ?

Post a picture of the driver, maybe someone will recognize it.
One of the pots should be for temp setpoint, the other might be for feedback gain.
Are there any test points on the driver? Then one is likely to be correlated to the thermistor.
If so, this makes tuning a lot easier.

[Things]

No reason to mark a set point, I believe this driver has already been adjusted before. However, I have accidently maxed out the pots a few times and nothing bad has happened, so I'm fairly confident I can fix this without breaking it.

I'll take some pics, and look for test points.

Whats strange about it's stability is it seems to flicker, not slowly change powers. Has me wondering whether the driver is doing something too.

[Things]

Here we go:

http://dl.dropbox.com/u/203420/IMG_2481.jpg

Put it in a URL link otherwise it'd be too large for this page.

[Doc]

The flickering is very likely mode hopping, the three pots are probably diode bias current, diode max current and diode tec control.

Sorry I can't help you with the arrangement of the pots but it should be very easy to find out with a DMM.

[Things]

Sorry for the late reply, had to deal with my Laser-wave 640nm red which seems to have died!

It's on it's way back to China for repair now.

Anyway, back to the green. I tried tuning it with modulation, however it's hard to tell what power its doing, as some frames have more or less green than others. Is there any specific frames I need to use or something?

EDIT: Bah, no matter how much I try I just can't get it tuned

Is there anyone here that would be willing to tune it for me? I'd pay shipping of course I just don't have the time or patience to do it properly myself

[Things]

I got it doing this without any modulation:


But as soon as I start modulating it, I set it on the ILDA test pattern for a few seconds, then switch it back to the lasermedia pattern (Barely any, if any blanking), and it takes a few seconds for it to stop flickering and settle down again.

[Doc]

Dan

You don't need to be projecting a show, just project a circle and minimise the size, the laser is still being modulated; even when projecting a circle.

Now you have a stable start point for tuning.

1. First set the laser running CW, find the diode current pot and set your maximum current, once done; apply some ink correction fluid or your mum's nail varnish to the adjuster screw - now you can forget this pot.

2. Turn CW of and find the zero bias turn it up very slowly until the laser outputs green photons, turn it back until it stops lasing, then a further quarter turn.

3. Project a full power circle and minmise the size.

4. Turn the diode tec almost off (check with a meter as clockwise isn't always up!).

5. Start turning up the diode tec very slowly until you see the power start to increase, wait five minutes.

6. Turn it back one eighth of a turn; you may have already overshot!

7. Make a nice cup of tea.

8. Turn it back a further one sixteenth of a turn, wait several minutes - if power increases; turn a tiny amount further in that direction (by tiny I mean "did that move then or did I imagine it?), if the power fell then turn the other way a tiny amount.

9. Wait at least 5 minutes between tweaks and keep edging towards the increased power until it peaks, then keep going in that direction until it starts to fall again - mark this point on the pot.

10. Work your way back down again past the peak and mark that point - the sweet spot is there, between those points.

Note: This does require patience; out of the 10 or 20 turn pot the actual zone were the power is is probably one eighth of a turn and the sweet spot is probably with one sixteenth of a turn, but if I can do it with my "Mars Bar fingers" then so can you.

Ian

[Things]

Thanks for the tips Doc.

The problem is, I only know which potentiometer is diode current, the other 2 I don't know. The pot above the diode current seems to affect the stability, and the one off to the right also seems to effect the stability even more!

If I turn the pot on the right far enough, the laser turns into a strobe light!

Dave has reassured me there is only 1 TEC in the laser. If it was the diode bias pot, it wouldn't have any effect on the stability (Once it's actually stable), right?

The laser head has 7 wires coming from it, I don't know the pinout though, which makes it hard to find which to measure for the TEC etc. He reckons the 7 wires are for: LD, Thermistor, TEC and fan.

One pot is obviously the TEC, but I can't seem to figure out what the other one does.



EDIT: Would a graph of the laser output while I adjust both of the pots help figure out what each pot is for?

[Doc]

Have you checked your power supply, maybe it is collapsing under load and the strobing is caused by the duty cycle of the tec current draw?