Powering down a newwish greenie

Ok, so I got me a 5mW newwish laser (the one called "true green" on DX), it's really cool, the weight is right, the size is right — well, I like it. There's one problem though: it's too bright. I'm going to use it as, well, laser pointer on a white screen several meters from away, and right now the spot rather uncomfortable to look at.

So I want to power it down.

I disassembled it and tried to turning that resistor, but ended up increasing the power a bit — the current was ~280mA initially, now it's around ~350mA, and I can't get it back down for some reason. Ok, I have no reliable 3V source right now, I guess I'll try tuning it again once I'll get something to power it from without the need to hold the module, the probes and the batteries with only two hands.

Anyway, before I do that: does anyone know if it's possible to reduce power of these things? And how much? Maybe changing the resistors on the board etc?

If you want it to be less powerful, try an IR filter, it would step down the power a bit. More if it's an inefficient light transfer.

Ugh, correct me if I'm wrong but filtering out invisible IR shouldn't affect visual brightness of the beam. A piece of (visible-)colored not-exactly-green glass would be a better choice I guess.

My initial idea was to reduce diode current, I assume it's easier to do than altering laser's optical components.

The pot (or "resistor" as you put it) doesn't work any more?

Use different batteries. I find nimh AAA's don't work nearly as well for my pens... but they do provide better run time.

Got a suitable 3V source today and did some testing.

The pot (or "resistor" as you put it) doesn't work any more?

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It does, I was wrong initially. Tried turning it carefully with the power on, and yes, the effect is clearly visible.
Maximum current I can get is ~420mA (leftmost (ccw) position), minimum current at which laser beam is still there is ~140mA; at ~130mA it cuts off (that's close to rightmost (cw) position). Currents around 160..180mA seem to give me the brightness I like.

Now there's another problem. The laser beam is quite unstable at those currents. I can set it to 160mA, turn it off, let it cool down, turn it on and get no beam at all. At higher settings, it will start with a faint beam and will slowly gain power in 10 seconds or so. Left it set to 200mA for now, looks like the laser at least turns on consistently at this setting.

Use different batteries

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Yeah, that was the first thing I tried. I didn't notice any change in brightness at all with NiMH instead of alkaline cells.

With batteries the instabilities will only be worse. I'd go for a cheap ND filter, with some some luck this would also attenuate the IR. Turning down the pot won't lower the IR output accordingly. Adding an IR filter would be an idea anyway.

The instabilities cannot be overcome, i'm affraid. The problem is that you want to operate the laser at the point where in barely produces green light. The required current to do that is very dependent on temperature. This gives the problem that it does what you want when the laser is warm, but after you switch it off and let it cool down, it doesnt produce any green light, then starts to flicker until its warmed through.

The only way would be to rework the driver, either to use PWM to control the average brightness, or you need to include some sort of optical feedback that 'reads' the amount of green light produced.

The latter approach was used in an early generation of newwish pointers, but i have never seen it since.