Tm doped crystals embrace several attractive features that nominate them as the material of choice for solid-state laser sources with emission wavelength tunable around 2um. It was demonstrated that Tm:YAG laser can be tuned from 1.91 up to 2.15um. Similarly,Tm:YAP laser can tuning range from 1.85 to 2.03 um.The quasi-three level system of Tm:doped crystals requires appropriate pumping geometry and good heat extraction from the active media.On the other hand,Tm doped materials benefit from a long fluorescence life time,which is attractive for high-energy Q-Switched operation.Also,the efficient cross-relaxation with neighbouring Tm3+ ions produces two excitation photons in upper laser level for one absorbed pump photon.This makes the laser very efficient with quantum efficiency approaching two and reduces thermal loading.
Tm:YAG and Tm:YAP found their application in medical lasers, radars and atmospheric sensing.
Properties of Tm:YAP depends on crystals orientation.Crystals cut along the ‘a’ or ‘b’ axis are mostly used.
Advantages of Tm:YAP Crysta:
Higher efficiency at 2μm range compared to Tm:YAG
Linearly polarized output beam
Wide absorption band of 4nm compared to Tm:YAG
More accessible to 795nm with AlGaAs diode than the adsorption peak of Tm:YAG at 785nm