Cheap green laser pointer immediately faints

I have recently bought a cheap green laser pointer from a Chinese guy selling them on the street. According to its label it was rated as <100mW. It was the one he was demonstrating. It worked well for some minutes and it produced a bright beam that reached about 2 kilometers. After that it started fainting immediately after the button was pressed. It does not take more than half a second to faint. If I release it and press it again it gives a good burst and faints again immediately. It is not temperature related as it does the same thing always no matter what. I have opened the case and removed the driver. It seems ok. I have tried the module directly on my lab power supply that I made myself and I know that it is LM317 based. I have set it to 2 Volts. Same thing happens. I will also post a video.

Anyone knows why does this happen?

I think that if I provide a 2 volt p-p square (90% on and 10% off) about 50 Hz signal it will work better than it does now!  

EDIT: Here is the video!

www . youtube . com/watch?v=8_zXOMb6abc (remove the spaces as I am a new member and not allowed to post links)

Hmm. That's odd.

I'm trying to guess why it would be doing that if it weren't heat or voltage related... If it does it instantly it shouldn't be a heat issue, and if you've replaced the driver it shouldn't be an issue with cheap batteries... I'm not immediately sure what's causing this, though be careful if you try pulsing it.

[edit]PS: Welcome to the forums![/edit]

Hi, not too sure what the problem is, I remmeber a cheap red 2mw laser I had would die like that but it was due to the button being a bit dodgy but I don't know if this will apply in your case. Sorry I can't be off much use but welcome to the forums

You need to put a 1ohm resistor between the power source and the driver, measure across the resistor in mv, It will be somewhere between 200 and 300mv.
Does the reading drop when the module dims?
If it keeps drawing current (mv=ma) at the same level or higher on either driver then there is something wrong with the LD and there is not much you can do.

Regards rog8811

I have an oscillloscope. Actually, it is the stand of the oscilloscope the one that I am aiming in at the end of the video. ;D

I will measure the current the way you suggested and I will post results. But I think that the current is stable because, as I said, I connected the module on my LM317 based power supply without a driver and it did the same thing...

Confirmed. The current is stable. There is no current drop... So the driver is ok. The laser absorbs the same amount of power but its efficiency drops down.

Isn't that odd? Have anyone met something like that?

Isn't that odd? Have anyone met something like that?

Click to expand...

Yes it is very odd, I would say duff LD I am afraid, you could try replacing it, but is it worth the hassle?

One other thing you could try, if you have a camera that will show up the IR emissions (or a night vision scope), see if the IR diminishes as the green fades, if it does then you know for sure it is the LD, if it stays the same it is the crystal set.

Regards rog8811