Scaling Cr:LiSAF to high average power

Abstract

We report on the status of an experimental activity to scale Cr:LiSAF to high average power using a unique zig-zag optical cavity design.KEYWORDS: Cr:LiSAF, slab laser, zig-zag laser. INTRODUCTIONOver the past several years, we have been developing zig-zag optical cavities for a variety of lasers. This development has been successful in the performance of high power dye lasers using this new design. In brief, we have demonstrated single mode, 7 J per pulse, 10 Hz, near diffraction limited operation of a laser pumped liquid dye laser. 1,2 When compared to the operation of a comparable power dye laser which used a more conventional optical cavity, we achieved an improvement in beam quality of about an order of magnitude and a comparable improvement in RMS jitter performance. We have also demonstrated that this laser can be operated virtually chirp free.3 More recently, we have applied some of the design approaches used for the liquid dye laser to the design of a solid state plastic dye laser. The resulting laser pumped plastic dye laser operated near the diffraction limit with a beam quality about an order of magnitude improvement over plastic dye lasers which use more conventional optical cavities.4'5 This plastic host device also achieved record energy output for a plastic dye of about 1 J. EXPERIMENTWe are now in the process of applying this approach to the operation of more standard solid state materials. In particular, we report in this paper some initial experiments that were performed lasing Cr:LiSAF, an interesting new crystal which lases over a broad wavelength range about 250 nm wide centered at about 850 nm. Cr:LiSAF has a 67 jis storage time and so can be efficiently laser diode or flashlamp pumped. A flashlamp pumped dye laser was used as the pump source for this study. Some of the key features of this design have been confirmed. However, because of a fabrication error, the crystal that was tested operated below optimum.The key to scaling lasers to high average power while maintaining good optical quality is the thermal control of the lasing medium. As with many solid state crystals, Cr:LiSAF has poor thermal properties. Our approach is to use thin, 1.5 mm, slabs of the crystals immersed in a flowing index matched fluid which acts as a thermal reservoir. A schematic diagram illustrating the design approach is shown in Figure 1. A simple stable optical cavity is pictured. The cell is made of fused quartz with a 4 mm wide flow channel that is 20 mm high and 165 mm long. Two 1.5 mm X 110 mm slabs are positioned in Dimethylacetamide (DMA) which has an index of refraction, n = 1.43, a good match to quartz (n = 1.46) and Cr:LiSAF (n = 1.40). Laser flux is coupled into and out of the cavity through quartz prisms. Single sided optical pumping is used.The dye laser pump source operated at 590 nm with Rhodamine-590 dye and is capable of single pulse energies up to 12 J with an 3 .ts pulse length. The pump laser output is passed through an optical 56 SPJE Vol. 3092 • 0277-786X1971$10.00 Downloaded From: h...