5mW - inconsistant brightness

[mikeage]

Hi,

I have a 5mW DX green pointer, which lately has started behaving rather weirdly. When I first press the button, it outputs a quite bright spot for about half a second, and then it drops significantly. The output then remains constant for at least 30 seconds (I'm not sure how long I can leave it running for without a short cool down break).

I've opened it up to check for anything obvious (like a short or bad solder joint), but I didn't see anything significant.


The switch seems OK, as well.

Any ideas?

Thanks

 

[Hemlock Mike]

A half second ?? Seems too fast to be thermal. What are you using for cells to power this ?? The "lately" statement tells me to check the cells.

Mike

 

[mikeage]

standard AAA alkalines (can't get the E2 lithiums here). I've tried replacing them -- no noticeable improvement.

FWIW, I measured current when I had it disassembled, and it was drawing about 250mA (in the steady state). Is that reasonable?

 

[Corona]

That's a reasonable current draw.

I've seen this effect on several green pointers; it could be any number of things related to the laser "chain".

The 808nm IR laser diode can shift in output wavelength slightly with temperature. And the laser die heats up almost instantaneously when power is applied, from ambient to at least tens of degrees above ambient.

Understand that the following stage, the Nd:YVO4 crystal, is "pumped" by the 808nm laser energy, and re-emits laser energy at 1064nm. This is then doubled in the KTP crystal and becomes green at 532nm.

The Nd:YVO4 absorption wavelength is critical and any shift in either the diode output or the crystal characteristics from the peak efficiency ("center frequency") will result in greatly reduced pump efficiency (and 1064nm output).

Heating of the Nd:YVO4 laser material will alter it's properties slightly as well. The absorption wavelength is determined by the doping of the crystal at the time of manufacture, and this is subject to variances as well. Especially when cost is the driving factor...

The "overlap" between the 808nm pump laser output wavelength and the Nd:YVO4 laser peak absorption wavelength is important and this tolerance is what determines if the laser chain drifts outside an acceptable pump efficiency.

 

[mikeage]

Could it be a problem from heat, then? The laser diode and optics are encased in the normal copper cylinder, but there's nothing that helps conduct heat between there and the metal case of the pointer.

Should I add a very thin coating of thermal grease?

I'm unable to feel any noticeable change in temperature in the case, even after a few minutes of operation. Hopefully that's a good thing... but maybe not.

 

[Comidt]

I just got a DX 10mW laser last night and there were some americans school kids who were here (my uncle takes kids out to South Africa every year) and they had it on for a long time. I would say maybe even 5 minutes without turnning it off, (yes, I know I'm an idiot to let them do that) Now, it is bright, like it was when I first got it, then it drops visible power by like a half... As in the brightness halves at least.

What do you think the problem could be?
I left it for like two hours after they fiddled with it, and it was okay for a few minutes, then it just dropped again.

What can I do?
My other problem is that I'm sending it to a shop in another city so that they can have a look at it, because they want to buy some, so I'm not to sure what to do then.... (you can;t get them anywhere in South Africa)

Thanks and I appreciate any help I can get...
Jonno