Technology Research Of Acquiring Smooth Time Domain Waveform And Single Longitudinal Mode Laser Based On Active And Passive Q-switching And Mode Selection

Traditional solid-state lasers show serious modulation in time domain due to multi-longitudinal mode operation,which inevitably limits the practical application of solid-state lasers.In this paper,the technology of active and passive Q-switching combined with resonant reflector and Twisted-mode cavity to obtain smooth Gauss pulse and single longitudinal mode?SLM?output laser is studied.Firstly,the development history of SLM lasers is reviewed,the methods of realizing SLM are summarized,and the research status of realizing SLM output in solid state lasers is analyzed.The research progress of double Q-switched laser is analyzed.The advantage of double Q-switched laser is to improve the symmetry of time-domain waveform and shorten the pulse width.Secondly,for the Q-switching rate equation,the transcendental equation satisfying the passive Q-switching rate equation is solved numerically by computer programming combined with the physical process of laser oscillation,and the relationship between the corresponding parameters?initial transmittance of passive Q-switching T₀,reflectivity of output coupling mirror R?and the output energy,pulse width and peak power is obtained.Then,when the mode difference is determined,the relationship between the SLM output and the number of laser oscillations is given.The principle of multi-longitudinal mode oscillation caused by spatial hole-burning effect in gain medium of solid-state laser is analyzed.The necessity of suppressing spatial hole-burning effect by SLM laser output and the principle of suppressing spatial hole-burning effect by Twisted-mode cavity are analyzed.In this paper,the longitudinal mode of resonant cavity is studied by using thin film theory when resonant reflector is used as mode selector and output coupling mirror.The factors affecting the envelope period of reflection spectrum and the fine structure period are studied.The influence of fine structure period on the output characteristics of SLM is given by combining the longitudinal mode spacing of resonant cavity.Finally,when the active Q-modulation waveform is given,the smooth symmetrical Gauss time-domain pulse obtained by active and passive Q-switching is compared experimentally with passive Q-switching time-domain pulse,and the factors affecting the time-domain pulse waveform are pointed out.Then the output parameters of active and passive Q-switching and passive Q-switching are compared and analyzed.The relationship between T₀ of Cr⁴⁺:YAG and the SLM output of the laser is obtained,and the influence of the angle between the fast axis of the two quarter-wave plates constituting the Twisted-mode cavity on the output waveform of the resonator in time domain is also obtained.Finally,the differences of laser output energy,pulse width and peak power parameters under different parameters are analyzed.Under active and passive Q-switching,combined with resonant reflector and Twisted-mode cavity technology.When the thickness of the mirror is 1.5 mm,the spacing L is 7.5 cm and the T₀ value is 6.23%,the SLM output rate of the laser reaches 92.6%.At this time,the energy is 11.39 mJ,the energy stability is 0.38 mJ,and the time-domain waveform Gauss fit is 0.9866.