Thermal Conductivity and Lasers

[says]

Homework Statement

My textbook on lasers has mentioned thermal conductivity a few times, but hasn't specifically mentioned it's importance. I'm at a part talking about Nd:Glass lasers and it says that glass has a lower thermal conductivity than Nd:YAG lasers, which prohibits continuous wave (CW) operation and limits the pulse repetition frequency in pulsed operation to a few Hz.

My first idea was that low thermal conductivity would be bad for semiconductor and solid-state lasers because if the heat isn't spread out over the gain medium then it could cause stress/damage of that one part of the gain medium, and that it would be much harder to cool a certain area of the gain medium, whereas with higher thermal conductivity you could have a uniform cooling across the whole gain medium without having to worry about hotspots.

Am I missing something? I'm imagining thermal conductivity isn't really mentioned in regards to gas or dye lasers because it's so low, compared to that of solid-state and semiconductor lasers.

 

[Tom.G]

Yeah, steep thermal gradients can result in mechanical failure. Physical warpage of the medium is also a possibility. Then there is the change in optical and electrical characteristics with temperature. In gas Lasers there is at least a little convection flow which helps, and some gas Laser designs use continuous flow. A friend had an early design CO₂ infrared Laser that used a tank of CO₂ and vented it to the atmosphere after one pass thru the Laser cavity. Had to get a full tank now and then, but it was a neat toy. Probably others here can come up with some more 'explanations'.