Research On Passively Q-switched Nd:YAG/Cr⁴⁺:YAG Microchip Laser And Amplifier

Diode-pumped all-solid-state lasers have the advantages of small volume,light weight,high efficiency,good beam quality,high reliability and long life.The output of short pulse width and high pulse energy laser has been widely applied in industrial processing,communication,medical,military,science research and so on.In particular,the all-solid-state lasers with high power,high beam quality and high stability have a broad range of applications.Combining Master Oscillator Power amplifier?MOPA?technique with passively Q-switched oscillator technology,the passively Q-switched pulse energy of high beam quality can be amplified,which makes up for the inadequacy of passively Q-switched oscillators.This paper designs a Nd:YAG/Cr⁴⁺:YAG passively Q-switched microchip laser with high repetition rate,high beam quality,and high stability,which can be used as the oscillation of the MOPA system.A grazing incidence Nd:YVO₄ slat with optical contacted sapphire laser amplifier is designed,which can achieve high efficiency and high beam quality amplification for high-repetition-rate passively Q-switched seeds.The main research contents of paper are as follows:1.Establish passively Q-switched rate equations to theoretically analyze the influence of reflectivity of the output coupling mirror on the characteristics of the output laser pulse.For a given initial transmission of Cr⁴⁺:YAG,the output mirror has an optimum reflectivity.The optimum reflectivity of output mirror is chosen through the experiment,which can obtain the optimum output pulse characteristics.2.The polarized pump beam is adopted to compare the output pulse time jitter,extinction ratio,beam quality,pulse width,pulse energy in different orientations of the Cr⁴⁺:YAG crystal.The results show that when the pump polarization direction is parallel to the crystallographic axis of Cr⁴⁺:YAG crystal,the best output laser performance can be obtained.When the repetition rate is 100 kHz,an output pulse timing jitter of 0.1?s,an instability of timing jitter of less than±0.5%,an amplitude instability of less than±0.67%,a pulse width of 2.6 ns,a single pulse energy of 4.8?J,a beam quality M² of 1.17,and an extinction ratio of 300:1 is obtained.3.We use COMSOL software to simulate the temperature field distribution of the Nd:YVO₄ slab with optical contacted sapphire and the Nd:YVO₄ slab without optical contacted sapphire.We also calculate the thermal distortions of the two crystals.Through the comparison and analysis,it is found that the temperature of the slab with optical contacted sapphire is obviously reduced,and the thermal distortions in the horizontal and vertical directions are also significantly reduced.4.Experimental study is carried out on the Nd:YVO₄ slab with optical contacted sapphire and the Nd:YVO₄ slab without optical contacted sapphire.The experiments show that both optical convension efficiency and beam quality of the amplified laser output have improved through the Nd:YVO₄ slab with optical contacted sapphire.When the pump power is 45 W,average output power of 10.2 W,pulse width of 2.5 ns,beam quality of M_x²=1.32,M_y²=1.27 is achieved at a light-to-light conversion efficiency of 22%.