Novel method for thermal lensing measurement applying in a Tm:Yap crystal

Tm:YAP crystal uses has grown rapidly in recent years due to the growing development of 2&mu;m lasers. Its optical and mechanical properties, make it suitable for a wide range of applications. He has a high absorption coefficient of around 793nm, allowing for efficient laser diode pumping. Large wavelength tunability can be achieved due to the large emission cross section (1900nm&#8211;1960nm) and the significant Stark splitting of the energy levels. Tm:YAP has great efficiency by the cross-relaxation process which makes it have quantum efficiency greater than 1 (1.8 approximately). It is a polarized crystal with high LIDT. One of its biggest disadvantages is related to its relatively high thermal lensing effect, making it harder to use in high-energy lasers. A better understanding of the thermal lensing effect with a novel method to measure it will enable us to use it in higher-energy lasers. The conventional thermal lensing measurements using a He-Ne laser through a pumped crystal seem to be insufficient, so we apply to use of the laser beam itself. By building a laser cavity using two exit mirrors one can measure the beam quality (<i>M</i>²) using one arm and the beam divergence by the other, by matching the two parameters (using the ABCD matrix system) one can extricate the focal length caused by the thermal effect in a more accurate method. Using this method of measurements, we found that the laser efficiency has a great impact on the crystal's thermal lensing due to the changes in the heat absorption in the crystal. Using this understanding we have recalculated the fractional thermal loading concerning the laser efficiency.