Question for the DPSS experts.

[ElektroFreak]

I've got a ~350mW RGB scanner with all CNI modules. When I play certain frame sequences, my green laser loses power briefly. The weird part is that instead of being random, it always happens on the same sequences of frames and only those frames, no others. Also, it doesn't seem to happen quite as often when I use the projector in warmer environments.

Is this simply a temperature issue, or is there something else afoot here?

Thanks for any input you all may have..

[Laser Ben]

I would say that is it probably a program issue turning down the power too much, but the fact that it is dependant on temperature means that it is a stability issue with the laser or the driver. Can you check and make sure the module is not getting crazy hot?

[allthatwhichis]

Sounds like a jelly beaning issue or just a liniarity issue during modulation. (Which might be exactly what jelly beaning is... )

[ElektroFreak]

I'll check the module temp. tonight when I get home. I also should add that I'm using the built in DMX program board with this scanner.

[ElektroFreak]

The laser module is actually quite cool to the touch, and its fan is working properly. I don't know.. I've had it on for about 1/2 hour so far and it's displayed every frame perfectly. It seems like it happens completely randomly except for the fact that when it happens it only happens on specific frames.

[weartronics]

When I play certain frame sequences, my green laser loses power briefly.

Without a detailed analysis it is difficult to know the specific cause, but this is a common problem.

As you probably know, production of 532nm is a three-step process (808nm -> 1064nm -> 532nm). Even if the pump source is modulated cleanly, temperature and power fluctuations in the subsequent optics will cause mode hopping, non-linearities and other effects not seen with direct injection diodes commonly used for red and blue. These problems are exacerbated by wide modulation range and high modulation speed.

The simplest DPSS projectors typically ignore these problems, and the highest quality DPSS projectors overcome them by using a constant pump power and modulating the output with a separate AOM.

Best regards,

weartronics

[ElektroFreak]

Thanks for the replys, all! I know that DPSS is not a perfect technology (at least not when referring to lasers I can afford), and I can accept that this is inherent to the laser without issue.

An AOM would be ideal, but the scanner I'm referring to is what appears to be a very well-made Chinese unit from a company called LKI. There's really no room for AOMs. The construction is very clean, the lasers are up to (and above) spec before optics, and it typically puts on one hell of a show, even with just the DMX programs.. Just with certain DMX frames the green decides to show a little character. I was curious about the cause, and I came to the right place.

I guess I'll just leave it be for now. It's not even noticeable to the audience, anyway. Only folks who pay lots of $$ for lasers would notice it.

[shrad]

hi eletrofreak!

wouldn't any small AOM like those sold by meredith or small isomets fit inside?

I know that copier-oriented AOMs are easily modifiable to modulate 532nm if they don't, and meredith's ones simply modulate 532nm very well

what would be needed is in fact something like 3~4cm between the laser and the dichro/mirror, plus a little place for the modulator

[FourDee]

Shrad, do you happen to know if the meridith-AOM's handle 473 very well?

[shrad]

as they are designed for small argons at 488nm, they should accomodate pretty well

we tested one with a green DPSS at a laserfreak meeting in april, and it seemed to modulate easily (difracted spots moving with the output of a small FM modulator), so I'd say they can modulate 473nm which is more "argon-ish" than 532nm

but is has to be tested, though

all I can say is it is worth the try, as these AOMs are quite cheap!