Thermal Lens Determination of End-Pumped Solid-state Lasers by a Simple Direct Approach

The stability of linear planar resonators involved in solid-state lasers is entirely decided by the thermal lens of the laser crystal. There exists a critical point between stable state and unstable state at which the thermal focal length equals the distance from the center of the crystal to one end mirror. Based on this fact, a new method for measuring the thermal focal length of the laser crystal has been presented and applied to a Nd³⁺:YVO₄ crystal at various absorbed pump power levels up to 10 W. The results have shown to be in good agreement with theoretical calculation.