It has been proven that the focal length of the thermal lens in the crystal depends on the temperature itself. This is why we need to maintain the crystal in a cold head that allows the fastest extraction of the heat.

In fact, both techniques are appropriate for cooling a crystal. They can both efficiently dissipate the heat caused by the green light pumping. The choice of cryogenic cooling must not be made because it could be a more efficient cooling technique but because this technique is the only one for keeping optimal 800 nm beam quality when very high pumping power (high stress) is applied to the crystal. Basically, the stress brought to the crystal with high average power is such that it induces a thermal lens by modifying the structure of the crystal.


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