Theoretical analysis of wavelength switchable diode-side-pumped Tm:YAG laser

Abstract

In the Tm³⁺ doped YAG crystal, the Tm³⁺ ions are excited into the ³H₄ state from ³H₆ state by absorbing pump radiation at ~ 785 nm, and the ions then relax down to the upper lasing level ³F₄. The laser radiation takes place between the lower Stark level of ³F₄ and the higher Stark level of ³H₆. The considerable phonon broadening and high multiplicity of the Stark levels of the 4f electron provides tunability from 1.87 to 2.16 μm. We presented an analysis for the performance of side pumped quasi-three-level laser oscillators. Taking into account reabsorption loss, we present a theoretical model studies of quasi-three-level laser with particular attention given to the Tm:YAG laser. Equation for Tm:YAG quasi three-level laser system is founded, and a formula of the threshold pump power of the laser is described. The threshold pump power with different emission wavelengths versus the transmission of the output coupler is discussed, and we also analysis the influence on the threshold pump power with different emission wavelengths affected by the crystal length. With the same pump power, a lower transmission of the output coupler would result in a higher intracavity intensity. As a result, the lower laser sub-level within ³H₆ ground state manifold has higher reabsorption loss and therefore, the higher Stark sub-level within ³H₆ ground state manifold has a lower laser threshold and longer laser wavelength.