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Q-Switched YAG Question

Alaskan

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Does anyone here know if it is OK to turn a 100 ms pulsed ND:YAG into a 10 ns pulsed YAG by adding a Q-Switch, or would that likely cause the rod to have problems when the laser was designed for long pulse without a Q-Switch?

Edit: Adding this

 
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RedCowboy

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1 millisecond = 1,000,000 nanoseconds if that's what you are talking about.
So your turning 100 million nanoseconds into 10 nanoseconds, does that mean you are packing the same energy into 1/10,000,000 the time duration?
 

Alaskan

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Yes, but I don't know the design parameters for YAG rods to know if a shorter, but far higher peak power could be a problem for the rod or not, or whether the doping is different.
 

RedCowboy

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I had thought, and I could be wrong about this, but I thought that a Q switch allowed the FL pulse to bounce around through the crystal longer to build more energy, if that's correct then it would seem like the pulse width would longer, but I forgot most of what I read.
However the ratio of change would need a lot more than a timing switch, unless it could cause all that energy to exit in a much shorter but more energetic pulse, but 10,000,000 to 1 sounds like something more will be needed, some much thicker mirrors at the least.
 

ultimatekaiser

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Actually what it does is it keeps the cavity misaligned or blocked until the power peaks then releases it all at once, rather than letting it randomly cascade a pulse as the rod gets stimulated. If you don't have a Q switch you usually end up with a whole bunch of longer sloppy pulses of inconsistent power, where as with the q switch you would end up cleaning it up and obtain a shorter sharper and more consistent peak power per pulse. As for the rod it shouldn't care, but if you execute a pulse with a cavity that creates a concentration too strong in a particular part of the rod or too high a dopant, then you will damage it from too much light saturation.
 
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diachi

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Actually what it does is it keeps the cavity misaligned or blocked until the power peaks then releases it all at once, rather than letting it randomly cascade a pulse as the rod gets stimulated. If you don't have a Q switch you usually end up with a whole bunch of longer sloppy pulses of inconsistent power, where as with the q switch you would end up cleaning it up and obtain a shorter sharper and more consistent peak power per pulse. As for the rod it shouldn't care, but if you execute a pulse with a cavity that creates a concentration too strong in a particular part of the rod or too high a dopant, then you will damage it from too much light saturation.
Not to mention potentially burning mirrors or other optics with the increased peak power.
 

Alaskan

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I guess the simple question is can any ND:YAG rod be Q-Switched, even if it was purposed for use in a cavity without a Q-Switch before. I have a cavity which was used for long pulse, but want to insert a Q-Switch to make it short pulse.

I would have to either use different mirrors, or just move the original mirrors further out to make room for the Q-Switch to be inserted. Another question which just came to mind; do the distances between the back and front side mirror need to be symmetrical, or spaced the same amount? I see cavities with the mirrors spaced close to the rod, others far. If they are far from the rod there is more cavity gain, but do they need to be spaced the same distance on each side?

Here is the YAG I want to Q-Switch, although little room to fit one in, will need to mount it in a different rail for that. This is from a Unitek Miyachi ND:YAG long pulse seam welder:








 
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ultimatekaiser

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Mainly depends on how much dopant the rod has, and the curvature of the mirrors. These are quite hard to align as many of them are planar on all surfaces or very close. Adding a q switch would be potentially quite a challenge.

You would need to have that mounted on a very rigid surface to start with, and insert the Q switch at one end and then sync it with the lamp pulse. Very quick precise timing as required, as yags don't fluoresce for very long. You'd need some very fast electronics.
 

Alaskan

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Tks, maybe I will try.
 




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