Formation of Low-Coherent Beams in Nd:YVO₄ and Nd:YAG Lasers

Abstract

Lasers with low-coherent radiation have attracted the attention since the first publications on this topic in the 1960s and up to the present time, thanks to their numerous applications. Compact lowcoherent lasers with a flow of the active medium through the pumped region can be done, using dense mixtures of solid particles and a liquid – slurry lasers. The preparation of slurry compositions based on particles like Nd :YVO₄ or Nd :YAG crystal granules meets certain difficulties associated with the use of liquids having high refractive indices, n ≈ 2. Here, we study the properties of a perspective Nd-doped slurry laser in model experiments, comparing parameters of Nd :YVO₄ and Nd :YAG slab lasers in compact plano-spherical resonators with and without a cuvette-diffuser on an immersion mixture of LiF crystal microparticles and isobutyl alcohol, n ≈ 1.39. At a laser diode pump power of 100 W, these lasers (without a cuvette) emit, in a quasicontinuous multimode regime, 1 ms pulses of low-coherent radiation (⋋ ≈ 1064 nm) with a divergence of 20 – 40 mrad and the 21 – 47 W power at the 10 Hz repetition rate. Under the same pumping conditions, we obtain a low-coherent radiation with the 1 – 6 W power and divergence up to 100 mrad in these lasers with a cuvette-diffuser. The spatial coherence of these lasers under changes in the pump current, pump spot sizes, and the state of immersion in the cuvette is estimated from the contrast C of the speckle patterns produced by the radiation. Also, we register C values in the region 0.02 − 0.04, comparable to the thermal sources contrast. The presented scheme demonstrates low-coherent Nd :YVO₄ and Nd :YAG lasers and show the feasibility of creating compact LD-pumped slurry lasers.