Determination of the Raman gain coefficient in leucosapphire

An experimental investigation was made of stimulated Raman scattering in leucosapphire (α-Al₂O₃) pumped at the wavelength λ = 532 nm by pulses of τ = 30 ps duration (the second harmonic of an Nd³⁺ : Y₃Al₅O₁₂ laser). The Raman gain coefficient was determined for the first vibrational Stokes component with the wavelength λ = 544 nm, corresponding to a Stokes shift of 419 cm^–1. This gain coefficient varied from 2.5 × 10^–10 to 4.6 × 10^–10 cm W^–1, depending on the relative orientation of the leucosapphire crystal axes relative to the plane of polarisation and to the axis of the pump beam. The energy conversion efficiency was η = 1% when the pump intensity was 100 GW cm^–2.