Research On The Influence Of Laser Crystal Thermal Lens Effect In Resonant Cavity Dynamic Stability Zones

Because of its large output energy,high peak power,compact and durable structure,and a wide variety of crystal materials,solid-state lasers have a range of research prospects in laser rangefinder,atmospheric detection,and micro-machining of electronic devices.However,due to the thermal lens effect,the fundamental mode volume in laser crystal varies with the thermal focal length.This greatly affects the stability of solid-state laser output,thereby limiting its application.In order to reduce the sensitivity of fundamental mode volume in crystal to the change in the thermal lens focal length,the laser should be operated in the center of dynamic stable zones as far as possible.Since the range of resonant cavity dynamic stable zones is usually defined by the refractive power,the thermal lens effect has a great influence on it.It is also necessary to study and discuss the dynamic stability zones of the resonant cavity.In this paper,the influence of thermal lens effect on the dynamic stable zones is obtained through the comparison between experiments and theory.It provides a basis for the theoretical and experimental research of thermal lens and spherical aberration effect in solid-state laser.The inference is composed of two parts: research on the effect of pumping inhomogeneity factor on spherical aberration;investigation of spherical aberration effect caused by thermal on the dynamic stable zones in resonant cavity.Aimed at gaining the magnitude of the spherical aberration and the changing law of sign symbol,based on the heat conduction equation,a theoretical model for the influence of pumping inhomogeneity factor on spherical aberration is established.It is obtained that the pumping inhomogeneity factor is one of the main factors affecting the magnitude and sign symbol on spherical aberration.By fitting Zernike polynomials,a relationship model among the spherical aberration term,pumping inhomogeneity factor,spherical aberration factor and beam quality can be set up.Research experiments oon the effect of pumping inhomogeneity factor on spherical aberration at different crystal lengths and doping concentrations indicate that:the longer the crystal length or the higher the crystal doping concentration,the larger the factor and the maximum spherical aberration value generated in the cavity,with the lower the pump power at where spherical aberration is zero.Use the measured wavefront information to analyze the change law of beam quality factor,the best area where the spherical aberration zero point should exist should be given.Study of thermal lens effect on dynamic stable zones is an effective way to control the thermal effect of high-power and high-brightness solid-state lasers.The propagation circle method is used to analyze the width and position of the dynamic stable zones in cavity.A physical model of the relationship between the spherical aberration caused by thermal lens effect and the dynamic stable zones in resonant cavity is constructed based on the “effective” thermal lens focal length formula.The experimental study with the effect of the thermal lens effect on the dynamic stable zones shows that: there is a phenomenon called “transient variation” in spherical aberration exists at the boundaries of resonant cavity dynamic stability zones and the positions of where the mode separations occur.This phenomenon can be regarded as a significant principle for judging the location of dynamic stability zone boundaries and mode separations occuring.By calculating the measured wavefront information,which can be reversed that: the output oscillating beam radius overflows the critical spot size in some special locations leading to the beam quality deterioration.We define the area where this phenomenon exists as the “beam quality deterioration zones”,analyze its cause in conjunction with the related theory mentioned above in addition.