532nm modulation problem

[buffo]

As a general rule, the SHG crystal works better when it's warm. Example: Some high-power DPSS designs run the KTP at 60 C or higher. But I am not certain if that applies to all designs or not. It would probably be a good idea to shoot a PM to Planters (Eric) and see what he has to say, since he's done quite a bit of work with various dpss designs recently.

Adam

[epyn]

This one is a 2*2*5mm in dimensions and purchased from ebay snoctony.There's not available anymore from him.

The originally crystal mount also contained the same sHG ,but i cracked ,so i bougth a new one.

Everything was fine,until i made separated cooling one for the diode/vanadate and one for the SHG.

In the original setup the whole systems' temperature was around 25-27C° it contained a single TEC.

It was a DHOM 300mW model from Spacelas.

This is the original module inside,with single TEC

This one is the separeted cooling DPSS

And this one,you can see the SHG mount

I tried to cool down to 20-25C° and heat up by the pump power up to 40C° but no result.The jellybeaning is still present.

Might the ATX power supply voltage ripples causes the jellybeaning?

The IR diode runs from the 5V line(to prevent the unnecessary heat dissipation of the MosFET.)

BUT

the Red/Blue from the 12V line and as i said they're works properly,there's no the phenomenon.

And one more funny thing not all of the frames do that even at low power.

All ILDA test frames and some of the Quickshow's built-in frames are jellybeaning(what a word omg...)

The imported .ild files from my collection doesn't jellybeaning also.

I run to the wall i don't know what should i do.

Anyway not too disturbing Shall I leave it as is?

Best Regards: Ferenc
Merry Christmas all of you dear my photon lovers!

P.S.:Sorry for the grammatical mistakes

[-bart-]

I think the jellybeaning is inherent in your laser design.
I find it remarkable that you managed to add an extra temperature stage to the shg AND got it back to working again.
You should be able to find an optimum by *slowly* ramping it @ 1 degree per minute.
Keep in mind that temperature affects the optical properties of the crystal and is therefore an intricate way of angle-tuning or phase matching..

Brass is in fact a pretty bad material for an ktp/lbo holder, maybe ok for pointers, bad for good modulation response.
Heat should be conducted away as efficiently as possibly, as the crystal itself is a pretty good thermal insulator.

Be careful not to stress or press the crystal as it may (locally) change its Birefringence.

The difference you find between ilda frames is probably because they differ in average-on-times, or rms voltage

[epyn]

The best things i can do:

- throw out on the window,

- Leave it and whine along,

- Try to make a better solution or just recovery to the original single TEC stage(state ???)

[-bart-]

If you want a good laser, buy one! (no spacelas)

If you want to learn about lasers, fiddle around with it, until the day comes that you break it.

[planters]

If you want to learn about lasers, fiddle around with it, until the day comes that you break it.

I read through the later posts on this thread and I have some thoughts. DPSS laser have a tendency to produce fluctuating power output. On longer time scales ie seconds to hours this arises from the interaction of the crystals and pump diodes to small changes in temperature. These interactions are very complex. Warm the KTP and you change its optimum tuning angle which decreases the 532 output which increases the inter-cavity fundamental power which warms the vanidate which increases its thermal lensing which moves the fundamental focus point within the KTP and so on. There are many scenarios such as this that make very good thermal control of all the components including the pump diodes an ideal goal. But, a term is used to describe this instability on short time scales called "green noise". This is very common and it is a chaotic, irregular fluctuation that as I understand it arises from mode instability that becomes less significant in long cavities which highly discourage transient mode wandering. The jelly beaning you are demonstrating in your images looks very regular and stable, almost like the green laser is being modulated. From your image I would make an extremely rough guess that your "beans" are repeating at tens of kHz. This is typical Q switch territory and very low for mode locking.

You clearly have the ability to swap out crystals and TECs. What if you test the green independently? Put it on the bench and modulate it with a stable 0-5V source. How does the power ramp with input modulation? Place a photo diode on an oscilloscope ( at these frequencies even a small solar cell would probably work) and carefully position it relative to the beam. What happens?

[epyn]

Thank you for this explanation.

I have no scope :/

Without ilda modulation DC 0-5V on input (9V fully charged Li+ion cell + 5V voltage regulator +10kohm pot) so all of the blanking lines were visible


DC 0.7V * lasing started the green light has been emitted
.
.
.
.
DC 4.96V * full brightness (5.1A on the 5W 808nm diode)

There was NO jellybeaning in this CW modulation interval even at the lowest brightness.

Interesting.

I didn't adjust the TECs in this experiment at all.At full brighness the diode was 27°C SHG was 39°C after 5 minutes and i broke up powering of the driver.

I used the standard testframes scanspeed=continously increase from 5 to 30kpps Pango QS

I noticed that with ilda modulation on very low scanspeeds (1-5kpps) there is no jellybeaning at all.

Probably the problem is with my DIY driver.(LT1013/1014 opamps+IRFP mosFETs)

If anyone wants i'll take a sketch of the schematics.It's simply the basic opamp based constant current source.

If you want a good laser, buy one!

I'll do.Unfortunately , Santa Claus not brought for me

[planters]

Watson, I think you're on to something. I would pursue this lead for now.