Introduction to Thermal Effects in Solid-State Lasers Лекция

Introduction to Thermal Effects in Solid-State Lasers Лекция 4 1

Contents Introduction Heat release in lasers Temperature fields in laser rods Thermally-induced strains and stresses Thermal shock resistance of laser rods Thermally-induced optical path distortions (OPD) in lasers dn/d. T stress-induced birefringence in isotropic media thermal lensing depolarization of a polarised light OPD in anisotropic media Compensation for thermally-induced OPD Temperature influence on spectroscopic characteristics 2

Introduction: General Effects Change of ambient temperature Pump power Laser Head Heat release Heat removal Laser radiation Temperature drop δT strains and stresses δT Temperature drop destruction of laser rods optical path distortions Change of T change of multimode operation + width of spectral lines distortions in laser amplifiers laser gain output power 3

Contents Introduction Heat release in lasers Temperature fields in laser rods Thermally-induced strains and stresses Thermal shock resistance of laser rods Thermally-induced optical path distortions (OPD) in lasers dn/d. T stress-induced birefringence in isotropic media thermal lensing depolarization of a polarised light OPD in anisotropic media Compensation for thermally-induced OPD Temperature influence on spectroscopic characteristics 4

Balance of Energy: Lamp Pumping Power supply Heat exhaust 5

absorption pump spectrum Heat release in Laser Rods (Stokes Heat) hnpump-hnlas 6

Balance of Energy: LD Pumping pump emission Absorption spectrum (0. 3 – 1 m) for YAG: Nd, T=300 K 7

Contents Introduction Heat release in lasers Temperature fields in laser rods Thermally-induced strains and stresses Thermal shock resistance of laser rods Thermally-induced optical path distortions (OPD) in lasers dn/d. T stress-induced birefringence in isotropic media thermal lensing depolarization of a polarised light OPD in anisotropic media Compensation for thermally-induced OPD Temperature influence on spectroscopic characteristics 8

Temperature Field, General l d 9

Temperature Field, Single Pulse Regime l d In single pulse regime, the heat release and temperature distribution repeat the distribution of pump density 10

Temperature Field, Single Pulse Regime 11

Temperature Field, time interval between pulses is near the relaxation time 12

Time Buildup of the Temperature Field, CW or Repetitive Pulse Regime T(r=0) T(r) ΔT r In CW and repetitive pulse regimes, the temperature field is determined by a competition of the heating and the heat relaxation; the temperature drop is large (up to tens Centigrade) 13

Time Buildup of the Temperature Field, CW or Repetitive Pulse Regime 14

Temperature Fields @ Uniform Distribution of Pump Density T(r) ΔT δTcool r Tc 2 R=d For the uniform heat release, the temperature distribution is parabolic. If inhomogeneities of the heat release are small (less than ~10 -15%), the temperature distribution differs small from the case of uniform distribution 15

YAG: Nd Flash Lamp Pumped Liquid Cooled Laser : an Example of Temperature Distribution 16