Beam profiles and radiation coherence at the output of solid-state and dye lasers with an intra-cavity immersion diffuser

Abstract

Lasers on mixtures of solid particles and liquids have long been an attractive subject of research as they can serve as sources of low-coherent radiation and provide a good thermal management using a medium flow. One of such schemes is a laser with an intra-cavity cuvette-diffuser filled by a dense immersion mixture of activated solid micro-particles and a liquid (slurry), similar to the known Christiansen filter. The properties of perspective slurry lasers and features of beams formation in such media were studied in model experiments on bulk Nd:YVO4 and Nd:YAG active elements pumped by 808 nm diodes in quasi-continuous (1 ms, 10 Hz) regime, and on a Rhodamine 101 dye laser pumped by 20 ns, 532 nm light pulses. Laser media were tested in compact (7–50 mm) resonators using a diffuser on a mixture of non-doped LiF micro-particles and isobutanol. The laser spatial coherence was estimated by the contrast C of speckle patterns or by the visibility of Young interferograms γ. Near the threshold separate deformed Laguerre-Gaussian modes and concentric rings were observed at lasers’ output, indicating radiation coherence of C=0.5−0.7. At 100 W pumping Nd:YVO4 and Nd:YAG lasers with diffusers in plano-spherical (PS) resonators provided 1 ms pulses of 1–6 W multimode 1064 nm generation with smoothed beam profiles, divergence up to 0.11 rad and C=0.02−0.1. For a dye laser with a diffuser in PS resonators, 17 ns pulses of 627 nm multimode radiation with 1–3.5 mJ energy, beam divergence 60–280 mrad, γ=0.01−0.05 and up to 30% optical efficiency were obtained. Thus, an intra-cavity diffuser with an immersion mixture is a convenient and simple device to reduce the laser coherence. C and γ values, close to those for thermal light sources make it possible to use the developed lasers for speckles suppression at laser projection, in speed photography, etc. Promising solid-state and dye slurry lasers are discussed. The obtained results show the specific of beam formation in slurry media and give grounds to expect successful development and applications of low-coherent solid-state and dye slurry lasers operating in the visible and infra-red spectral regions.