Modulation efficiency

[ElektroFreak]

The TEC(s) already functions in that manner. They are there to hold the crystals (and diode) at their optimum temperature. Unless the second diode was focused precisely at the same spot in the crystal as the main pump diode, it's effects would likely be purely detrimental. There's also a possibility that another wavelength will cause thermal lensing on a different scale than the main pump diode.

I'm not trying to say that the idea wouldn't work, what I'm trying to say is that I think we're already seeing the best modulation response possible from a simple linear cavity. The better Chinese manufacturers are doing things about as well as can be done short of implementing optical feedback. As mentioned before, using feedback to stabilize direct modulation would require the system to run at reduced output compared to no feedback, so that's obviously going to cause issues for some people. These kinds of problems are why the world's major manufacturers of DPSS systems (whose engineers have forgotten more about DPSS technology than most of us will ever know) do not recommend direct modulation.

Far be it from me to stifle creativity or ingenuity, however. I believe we should look at each possibility presented here with an open mind. So far we've discussed optical feedback and the "danielbriggs" effect. One is plausible but at high cost in terms of output power, the other is a long-shot, and comes at high cost of design implementation.

Also, as I said previously in this thread, crystal suppliers are becoming very ingenious with their crystals. Using special optically bonded crystal stacks (not talking about hybrid DPMs here) rather than the typical single-gain-medium solution offers improved stability and reduced thermal lensing which would improve direct modulation response as well. IMO this is the best option presently available.

For more information, see here:
http://www.jiepu.com/en/2008/1017/article_2.html

[mccarrot]

What's the size of the power supply/ controller on those? Is it 'Lab' style or OEM?

Jem

Its the CNI OEM style version.

[-bart-]

@tocket
You are scanning at 30kpps, right?
When making a histogram like above, would it not make sense to use statistical buckets of 33uSec?
This significant spike 200uSec you encounter must be a 6points dot or line.
When looking at the histogram there should be no more then 5 discrete buckets on the left side of the 200uSec bucket. Really not wanting to split hairs, but a proper representation is half the conclusion, right ?

So if the scanspeed dictates the statistical distribution of the pulsewidth, in the end we might end up with modules that are tuned to a specific scanspeed ?

[ElektroFreak]

^So again, how do you propose that this "tuning" be accomplished? You're assuming such tuning methods exist or are even possible. All other data is moot without a way to "tune" the laser for modulation response. There are only so many adjustments possible with a linear-cavity DPSS laser, and none of them are guaranteed to even improve modulation response slightly, much less eliminate it. Why even worry about "splitting hairs" when the idea of "tuning" a DPSS laser to a specific modulation frequency range is likely impossible in the first place. That's not to say that the idea isn't a good one, it's just the implementation that I believe to be extremely difficult if not impossible with current technology and at the hobbyist price point.

Throughout this thread we've discussed the fact that linear-cavity DPSS technology is inherently unstable when under direct modulation. This instability varies in how it is manifested from one individual laser to another, even among the same model laser from the same factory line with sequential serial numbers. A method of tuning for modulation response would require some sort commonality in that response so that a tuning method can be developed. If each laser behaves differently, how would one tune them for specific performance along a specific frequency range? There might be slightly different factors contributing the instability in each laser, some of which are out of our control, such as the response of the crystal structure itself to heating.

[tocket]

@tocket
You are scanning at 30kpps, right?
When making a histogram like above, would it not make sense to use statistical buckets of 33uSec?
This significant spike 200uSec you encounter must be a 6points dot or line.
When looking at the histogram there should be no more then 5 discrete buckets on the left side of the 200uSec bucket. Really not wanting to split hairs, but a proper representation is half the conclusion, right ?

Oh, that makes sense. Hadn't thought about that. Actually I saw something in the data that I thought was odd, but now I see where it comes from. There are a lot of bins that have either 0 or very few pulses in them. In fact they occur in regular intervals, every 3rd-4th bin. Even if I bunched them together it would not make a huge difference and the 200µs peak would still be the largest by far.

Here's the fine structure around 0, quite interesting I think.

[ElektroFreak]

Now that we know the relative frequency and width of the pulses, and how often pulses of each pulse-width occur, what is to be done with this information in the absence of an ability to tune the lasers to a specific duty-cycle range? To me, it would seem wiser to establish a method for tuning the system, and then determine the range of duty-cycles to tune the laser to..

Only constructively commenting, however.. Improving modulation response is important to all of us, so I'll be watching closely what kinds of new innovations your graphing produces.

[sugeek]

http://www.photonlexicon.com/forums/...ead.php?t=9606

I have a similar one I am working on getting running right now, but the 28vdc supply is in the mail right now. I have purchased a crystalaser from gogu, it shipped promptly, and I even got extra goodies included. Once I get mine running I can run a few tests for you I do have a meter, a photodiode and a scope.

-Adam

[-bart-]

I got a aom from gogu too, (aside from the fact that I can't get my efficiency beyond 80%, probably due to poor polarisation of my source) from my first results it modulates bad-ass.

To improve modulation stability, I think some form of feed-forward of the input signal into the temperature control loop might help to anticipate heating effects. But that would mean that the thermal-mass attached to the shg crystal should be as small as possible, to make a fast tec response possible. But when improperly tuned a small thermal mass only adds to the instability.
I totally agree that without physically altering the optical/mechanical design huge improvements in modulating efficiency can't be expected.


@tocket

I think it's important to look at how much does a certain pulse-width does contribute to the total power of the show. It could be that a 200uSec pulse is very common, but a 2mSec pulse contributes a factor 10 to the show.

But hey, what if we compose one standard frame that has the same distribution of pulse widths as 'a large bunch' of shows. With this one standard frame one could compare modulation efficiency of modules side by side.

Another interesting experiment would be: If dpss modules like a consistent meal of pulses, could one create or modify a (beam)show that anticipates this and takes this diet into account.

[mixedgas]

We scan, scan, scan, scan, scan in our club the whole day through
To scan, scan, scan, scan, scan is what we really like to Do.
It ain't no trick to spend too much quick
Even if you could dig pure gold with a shovel or a Pick.
To Do lasers you need a mine, a mine, a mine.
Where a million OPSL shine.

AAA OH, AAA OH, AAAA OH, AAAAA OH, AO, and off to scan you go....

Apologies to the Seven Dwarfs.

Guys the solution is old technology, 20% loss and consistent brightness is LESS then 50-80% loss and semi randomized color.

Dont forget the 800 uS storage time in the yag.

I just observed a planetarium laser system that had a 200 mW CNI blue averaging about 10 mW off ADATs set up for a pcaom/Argon. Turnon was about the last .1V of the 0-5V range.

I'm gonna help them, I'll try DZs card, then I'm going AO next.

This wont work for the Europeans, but the real trick is perhaps to quadruple the pump power and pulse it in as constant pulses at a very high rate. Overdrive the crap out of the xtal till it heats up, then back off. This is going to need a heck of a adaptive loop control system, and frankly I cant see the Chinese doing it. It may self qswitch at that point.


Steve

[mccarrot]

Does someone know the price difference between a IRIS Color safe and a AOM.

http://www.eyemagic.gr/laser-iris-colorsafe.html