Study Of The Self-Optical Parametric Oscillator Based On Nd:MgO:PPLN By High Power Multi-Point Coupling Pumping

Because the 1.5μm laser is in the atmospheric transmission window and is called eye-safe laser,it is widely used in many fields such as military confrontation,medical diagnosis,atmospheric environment monitoring,and space ranging.At present,in order to solve the problems of large size and poor portability of lasers,we can use Nd:MgO:PPLN crystals that can generate self-frequency-conversion based on the theory of quasi-phase matching to form self-optical parametric oscillators,and then achieve high integration 1.5μm all-solid-state laser.However,due to the doping of Nd³⁺,the thermal effect of Nd:MgO:PPLN crystal is significantly enhanced.In this paper,multi-point coupling pump Nd:MgO:PPLN crystal is used to carry out orthogonal polarization fundamental frequency optical experiments,fundamental frequency optical passive Q-switching experiments and1.5μm self-frequency-conversion experiments.Finally,a high repetition rate 1.5μm self-frequency-conversion signal light was obtained.In terms of theoretical simulation,at first,according to the doping properties,physicochemical properties and optical properties of Nd:MgO:LN crystal,its properties are introduced in detail,and the gain competition relationship betweenπ-polarized 1084 nm andσ-polarized 1093 nm and the reason ofσ-polarized 1093 nm are expounded.And based on the quasi-phase matching theory,two tuning methods for controlling the output wavelength of parametric light of Nd:MgO:PPLN crystal are simulated.Secondly,the internal thermal effect model of Nd:MgO:PPLN crystal under multi-point pumping is established,and the changes of the temperature field distribution,thermal stress field distribution and thermal lens focal length inside the Nd:MgO:PPLN crystal are elaborated.In addition,based on the multi-point coupling pumping method,the coupling system and the self-optical parametric oscillator resonator structure which are different from the traditional single-point pumping are optimized and designed,and the specific parameters of the final experiment are determined,and the specific parameters of the final experiment are determined.In terms of experimental setup,the orthogonal polarization fundamental frequency optical experiments,fundamental frequency optical passively Q-switching experiments and1.5μm self-frequency-conversion experiments under the multi-point coupling pumping mode are respectively studied.In the orthogonal polarization fundamental frequency optical experiments,there is no difference in output wavelengths and simultaneous output of two wavelengths under double-point pumping and three-point pumping,respectively.π-polarized 1084 nm laser of 4.3 W and 5.5 W were obtained,respectively.In the fundamental-frequency optical passively Q-switching experiments,a fundamental-frequency optical pulse output with the repetition rate of 5.1 k Hz,the pulse width of 19.6 ns,and the maximum single-pulse energy of 266.0μJ can be obtained under double-point pumping.In the 1.5μm self-frequency-conversion experiments,under the condition of double-point pumping,the highest average output power is 183 m W,the maximum single-pulse energy is 33.9μJ and the peak power is 5.0 k W when the repetition rate is 5.4k Hz and the pulse width is 6.8 ns.The center wavelength of signal light is 1514 nm.It is verified experimentally that the multi-point coupling pumping mode can effectively realize the thermal management of Nd:MgO:PPLN.Finally,a single-wavelength and high-efficiency laser is obtained.