Highly Precise Measurement And Experimental Research Of Thermal Focal Length Of Thin-disk Laser

The thin-disk laser design is a concept for diode-pumped solid-state lasers which allows the realization of lasers with high output power,highest efficiency and good beam quality,simultaneously.The advantages of the thin-disk laser benefit from the large surface-to-volume ratio of thin-disk and lower quantum defect Yb:YAG crystals,which can realize efficient cooling and very weak thermal aberration.However,the fraction of absorbed power deposited as heat generates a radial temperature gradient inside the crystal,which induces thermal lensing effect.Therefore,a thin-disk laser resonator can be considered as a resonator containing an internal lens.The precise measurement of dioptric power of thin-disk laser becomes more important to design dynamically stable resonators,especially for thin-disk laser operating in fundamental mode.Based on the analytical model of the thermal effect,the distribution of temperature,stress,and strain can be derived using different super-Gaussian form pumping spot.The total OPD caused by temperature gradient,axial thermal strain,thermal strain-induced birefringence,and deformation of the thin-disk crystal is discussed and the practical meaning of measuring the spherical OPD(equivalent focal length)is emphasized.Then the method oftwo-step translation of stability zone to measure the equivalent thermal focal length of thin-disk laser is concluded.Several resonators with different fundamental spot radius on disk are designed,of which the stability zones are shrinked centering on the measured focal length.The impact of the fundamental spot radius to pump spot radius ratio on the beam quality is discussed.The experiments are carried out to measure the dioptric power of thin-disk crystal.Based on the measured results,the beam quality is concluded that becomes better at first but becomes worse afterwords with the increase of the fundamental spot radius on disk to pump spot radius ratio.Output of 125 W near fundamental mode laser generation with optical efficiency 40% and M2 1.5is reached.At last,the experiment is carried out based on the dual V-shaped resonators and the concept is proved feasible.And good beam quality under all pump power can be acquired based on dual V-shaped resonators when the pump spot size is bigger or the range of pump power is bigger(the range of dioptric power is bigger).