The Big Green Thread (I'm gonna regret posting this in the morning)

[mixedgas]

Eric, wind your crystal heaters out of fine copper wire. Make sure the copper coil is all around the crystal and along its length. It has one heck of a positive tempco which helps stabilize the temperature. That is what eveyone does for etalons, and etalons need held to .001 degree some times.

Steve

[shrad]

wouldn't induction heating be useful in this case? something like a SP stabiliser circuit would be enough to stabilize it accurately, no?

[mixedgas]

If your clever, you sense the temperature with the same wire that heats it.

Yes, you can do induction, although I see no advantage unless you have a very tiny crystal mass.

Steve

[shrad]

I was talking about the mount or whatever it is in contact with, but a simple heater wire could be more effective in this case.. I wonder if it would be stable enough with a simple PID loop as the thing has to be very fast.. maybe PWM?

I know KTP usually likes to be hot in higher power or higher mode quality lasers, but is there a central source of information where you would find the different angle/temperature "standard" configurations with advantages and disadvantages? I guess I can't heat my generic KTP to 70°C and just get a better beam doing this... would it be that simple?

[planters]

Steve,

I'm a little confused here If your suggesting that the vanadate and or the KTP be wrapped in a fine strand of wire to provide a resistance element to heat them then the whole concept of low resistance, indium foil and copper mounting blocks would in fact interfere with the wire's ability to quickly make small correction adjustments in the in the crystal's temperature. Aside from the fact that your describing something I would consider robot level small scale work there is also the increased risk that I might damage or contaminate the crystal in the process.

I know KTP usually likes to be hot in higher power or higher mode quality lasers, but is there a central source of information where you would find the different angle/temperature "standard" configurations with advantages and disadvantages? I guess I can't heat my generic KTP to 70°C and just get a better beam doing this... would it be that simple?

I also was aware that running the KTP up around 70 C. decreased it's tendency to "grey track" which is a type of crystal damage that is seen at very high powers and I believe it is induced by UV or higher harmonic photon generation. But, what I recently learned is that if you plan to run your crystal this warm then it must be cut by the manufacturer to a different angle during manufacture. So unless you are using a high power 532 like the Q switched LS then 25 degrees is just fine. What is required, however is to hold this temperature very stable. Based on my experiments, a variation no greater than 0.1 degrees is probably about right.

[mixedgas]

Let me clarify. The Lexel etalons and Dpss crystal holders use a few hundred turns of copper wire wound on a thin aluminum tube that surrounds the crystal mount or etalon mount. They are wound on a simple lathe fixture by hand. So the coil forms a pretty solid thermal mass. The thermal mass + the positive tempco helps you.

The mount heats quickly till the whole assembly gets uniformly warm, then as the temperature rises, the copper starts to conduct less, forming a proportional term that helps level off the temperature changes.

I'll try to shoot a pic in the morning.



As for the KTP temperature, that gets modeled in something like SNLO software.

Steve

[Stiffler]

Any updates on this? I've been patiently waiting for the next season to start.

[planters]

Oh...Yesss. But in the very near term if Steve doesn't have anything to add (assuming he survived the pool party) I have been finishing up the orange laser and after that video then I'll present my version of the vanadate soon afterward. It is working well by the way.

[Stiffler]

I'm sure Steve survived, that 6-way looked well insulated by that pair of flip flops:-)

I'm glad to hear it's working; forgive me if you already posted numbers, but what kind of output and beam quality are you achieving. BTW, I enjoy your videos, they are both entertaining and educational.

[planters]

Thanks,

The limit to date has been the long wait for the second driver from Badpip, which finally did arrive. The last time I ran the output I was getting approx 1.5W @ 50% from one pump. The beam was TEM00 and a little under 2mm @ the focusing lens and 5mm in dia @ 9M.