Direct laser diode blanking versus PCAOM or multiple AOM's?

[LaserLover]

I was thinking about blanking speed versus efficiency and comparing direct laser diode (TTL or analogue) versus using a PCAOM to do the job.
The problem with direct laser diode blanking is power loss versus recovery time, specially with higher power laser diodes. The faster you switch them the less average power output you get and I'm not happy with the speed when I push to 30 KPPS or faster I see tails on some frames.
If you are able to combine all 3 solid state laser outputs ( RGB ) and rotate their polarity so they all match and the beam spot size is small enough you can use a PCAOM (a NEOS 8 channel synthesized RF driver unit will allow fine tuning of wavelengths and optimize efficiency).
Using a PCAOM would allow full power output (mins the 10% losses of the PCAOM) and unmatched switching speeds plus better color mixing.
The other benefit of using a PCAOM is that you would be running your laser diodes CW which would extend their lifetimes instead of switching at 10 to 30 KHz. Running laser CW would also stabilise them better (reduce chirping ).
Has anyone ever see a solid state RGB laser diode based projector using a PCAOM or multiple AOM's to switch instead of direct blanking ?

Rick

[buffo]

I've never heard of it, but my experience is quite limited so I may well have mised it. Still, I think there is another, more fundamental issue to consider. Namely, how many DPSS lasers have sufficient polarization stability such that you could use an AOM (or PCAOM) with them?

I was always under the impression that the vast majority of DPSS lasers emitted a beam that was randomly polarized. While I'm sure that you could purchase a high-end unit that had good polarization specs, I wonder what the price premium would be?

Does anyone know of a reasonably priced DPSS laser (blue or green) that produces a beam with at least 100:1 stable polarization ratio?

Adam

[LaserLover]

I think you might be right when it comes to cost versus good polarity and also has to be TEM00.
It may also be possible to combine lower quality RGB DPSS based lasers and diodes and pass the beam through a AR coated brewster window (made of quartz to polarize the output) but I think they would all need to be aligned for best polarity match to maximize efficiency before you add the brewster window. I don't know enough but someday will find time to experiment just to satisfy my curiosity.
With that in mind I may just keep the 8 channel NEOS PCAOM I have until I can test my theory.
Anyone have a high quality optically flat broadband AR coated quartz plate I can setup at brewster angle to test things ?
Rick

[aijii]

I think you might be right when it comes to cost versus good polarity and also has to be TEM00.
It may also be possible to combine lower quality RGB DPSS based lasers and diodes and pass the beam through a AR coated brewster window (made of quartz to polarize the output) but I think they would all need to be aligned for best polarity match to maximize efficiency before you add the brewster window. I don't know enough but someday will find time to experiment just to satisfy my curiosity.
With that in mind I may just keep the 8 channel NEOS PCAOM I have until I can test my theory.
Anyone have a high quality optically flat broadband AR coated quartz plate I can setup at brewster angle to test things ?
Rick

wow.. what a headache. why not just replace the diodes with an ar/kr tube. would be easier to align

[buffo]

I think I would hang on to the 8 channel NEOS PCAOM as an investment, if nothing else! Those things are like gold.

Besides, ion lasers just keep getting cheaper and cheaper. Who knows, before long it might not be all that uncommon for a hobbyist to own a Kr/Ar whitelight rig. (Of course, poviding power and cooling water is always going to be a pain in the ass.)

Adam

[chad]

Theoretically you could do this but there are some problems.
First- beam quality unless you have a very low divergence, perfect beam and good mode, forget it, you will loose way too much.
Second- polarization. Ion's are typically 1000:1. Dpss arn't, usually 100:1. Big loss. You can't just put a quarts window in front of a beam and polarize it. That trick only works intracavity. If you figure out how to do that let me know ( we will make millions!! )

pcaom's are finicky beasts. It is possible to do what you want to do but it would cost you more in high quality dpss units that it would be for a ion.
90% is almost impossible to do, figure a really well tuned pcaom and a ion putting around 80%. most cases the levels are much less.


Chad

[LaserLover]

Hi Chad,

You're correct about the efficiency of the NEOS PCAOM being 80% for all wavelengths but another manufacturer in France called AA Optoelectronic claim > 90% diffraction efficiency. I think Yaddatrance has one of their PCAOM's so he can vouch for them.

If I ever get a chance to experiment with various quality DPSS lasers and my NEOS PCAOM I'll post the results here.

TTYL
Rick

[yaddatrance]

The efficiency stated is based on total usable power, unfortunately a lot of that "usable" power is dumped as the waste beam so I'd actually rate PCAOMs as 66% efficient in the sense that you were thinking. Less if you use a higher order for easier line control. The main problem
you'll run into with diodes into a pcaom is the aperture, 2.5mm is not much room to work with
even on big whitelight gas lasers. The 90% ratings which are given are for single color line lasers with the driver tuned for it. When you use a PCAOM with say 8 lines, then it's a matter of finding an acceptable compromise.