Analysis On Thermal Effects Of Large Size Nd:Glass Slab Laser Medium

Lasers with high pulse energy and high peak power have many applications suchas generating X ray, laser shock peening of metal, inertial confinement fusion, etc.Heat deposited in the laser medium may cause temperature gradient, stress anddeformation, thus distorts the wave front and causes depolarization, or even cracks inthe medium and serious problem of thermal effects. As thermal effects put limitationson key performances like output power, beam quality and stability, it is important forlasers with high pulse energy and high peak power to select proper lasing medium andreduce thermal effects.With a slab geometry, Nd:glass slab lasers have high heat elimination capabilitiesand can withstand higher pump power or pump energy; Stress induced birefringenceis eliminated by proper geometry; Thermal and Stress focusing of the first order areeliminated by zig zag optical path of full internal reflection; Wonderful energy storageand big energy storing volume are provided by Nd:glass. Large size Nd:glass slabemedium is a good selection for laser systems with high pulse energy and high peakpower.Thermal effects of large size Nd:glass slab medium for laser with high pulseenergy and high peak power are studied. Based on related theoretical principles, bothanalytical deduction and numerical simulation are used as methods to analyze thedistribution of pumping light, temperature, stress and deformation. Related optimizedparameters are concluded from results of analyses.With geometric properties like large size and large aspect ratio, research topics ofthermal effects of large slab laser medium can be categorized into uniformity of pump,side effects and end effects.Firstly, distributions of pump light in various cavity geometries are simulatedwith TracePro and compared with each other. A reflective object is selected to pumplarge size slab medium. Uniformity of pump is studied for various geometricparameters. The optimized positions of flash lamps in reflector are decided to achievea good pumping uniformity.Secondly, distributions of temperature, stress and deformation are simulated withAnsys. Analysis shows that even for a uniform pump and cooling, wave frontdistortion and depolarization may still be produced by side effect and end effect ofslab. Distributions of temperature, stress and deformation for slabs with differentaspect ratios are simulated, and a proper size is suggested according to therequirement on thermal effect and aperture. Lastly, a Matlab program is programmed to compute wave front distortion anddepolarization of slab medium. Influence of side effects and end effects are studied,and countermeasures are suggested. Influence of thermal induced wave frontdistortion and thermal induced depolarization of slab medium for non uniform pumpare simulated.