just how do laser crystals "burn out"?

[ixfd64]

It is my understanding that DPSS laser crystals will burn out if they are pumped with a higher output than they are designed to handle. However, I'm a little confused as to what actually happens.

For example, from what I've read, the melting and decomposition temperatures of KTP crystals (in the case of green lasers) are well above 1,000° C. However, hobbyist lasers are unlikely to heat a crystal to such high temperatures, so melting and chemical changes seem out of the question.

So what actually happens? Does the crystal give in to thermal stress?

 

[kiyoukan]

from what i have understood the crystal is undamaged but it become unaligned. due to heat and warping of its metal.

 

[dnar]

I also believe the facet facing the pump diode can burn, I have seen this 1st hand from over-clocking (pot modding)... Just don't do it with cheap modules...

 

[Things]

Yes, the face of the crystals burn

 

[dnar]

I can try a macro shot of a burnt crystal facet if your interested. The coating is clearly burnt.

 

[bbshamsa]

Be great to see that ^^^

 

[dnar]

Be great to see that ^^^

Here you go. This is the facet facing the IR pump diode. It is a dealextreme.com 200mW module that I pot moded too far. You can clearly see the carnage. Considering the rating, these crystal sets are very small.

I blew a 100mW module the other night due to a slip with the meter probe. The IR pump diode is still working, the crystals look fine so it must be an alignment issue.

 

[ElektroFreak]

Another major failure that can occur due to excessive pump energy is coating failure.. the HR and AR coatings found on many crystals often cannot handle nearly as much energy as the crystal itself can.

 

[HIMNL9]

^^ it looks almost "chipped" in the corner

What have you used, 2W IR ?

 

[ixfd64]

Thanks for the replies everyone.

That's a lot of useful information!

 

[Prototype]

Another problem can be thermal expansion, it's not technically 'burning' but if the crystal gets too hot in an improper mount it can crack in half. This happened to an old 5mW module I was messing with, I believe it's the Nd:YYVO4 that cracked but it's a very obvious diagonal line from on corner to the opposite.