Diode-pumped Tm: YAG solid-state lasers with indirect and direct manifold pumping

Abstract

We study the continuous-wave (cw) characteristics of both two-manifold and three-manifold Tm: YAG laser pumped at λ_p ≈ 1.8 µm or λ_p = 0.785 µm and lasing at λ₁ = 2.02 µm. The three-manifold rate equations are adiabatically reduced to their two-manifold form. For each pumping scheme, the steady-state rate equations are combined with the cw differential equations for the forward- and reverse-lasing fields and the pump-depletion differential equation. These three coupled cw differential equations are solved analytically. This gives the linear flux-conservation law between the input pump and the laser output, the minimum crystal length, and optimal output couplings. We show that the major difference between these two pumping schemes is due to the different pump effective absorption cross sections and not the two-for-one cross relaxation. Our example shows that the minimum intensity threshold and optimal crystal length are smaller for pumping at λ_tp = 0.785 µm than pumping at λ_p ≈ 1.8 µm.