Temporal Characterization Of Nd:GdVO₄ Gain-Switched Dual-Wavelength Pulsed Lasers

The research and application of the terahertz wave will play a key role in future national security and combat,and its application prospect is getting more and more attention.Lasers based on neodymium-doped gain media are capable of generating multiple wavelength signals with high correlation and stability in the cavity,showing great potential in obtaining stable terahertz bands at beat frequencies.The output time synchronization and high-power dual-wavelength pulses are important output characteristics of the laser to improve the efficiency of optical external aberration beat frequency,and the dual-wavelength pulses with controllable repetition frequency and adjustable pulse width can be applied to more scenarios.In this paper,we propose a gain-switched dual-frequency/dual-wavelength laser based on a neodymium-doped gain medium and investigate the mechanism of dual-wavelength pulse synchronization and the modulation mechanism of pump pulse parameters on the output of dual-wavelength pulses,and finally obtain a gain-switched laser with controllable repetition frequency and adjustable pulse width for dual-wavelength pulse synchronization.The main contents of the paper include the following three parts:First,the current status and direction of domestic and international research on Nd-doped dual-wavelength lasers are briefly introduced,the system composition of Nd-doped dual-wavelength gain-switched laser is analyzed in detail,the chirality oscillation process is qualitatively explained based on the four-energy level rate equation,and the working principle of gain-switching is further analyzed theoretically.Second,a gain-switched orthogonally polarized dual-wavelength synchronous pulsed laser based on Nd:GdVO₄ crystal is designed.The corresponding mathematical model of the rate equation is established,and the influence of the geometric loss in the gain-switched Nd:GdVO₄dual-wavelength synchronous pulse laser on the time-domain characteristics of the dual-wavelength pulse is analyzed.A dual-wavelength pulsed laser with a Y-cavity structure based on a Brewster polarizer was built for experimental verification,and gain switching was achieved by modulating the pumping source current.The experimental results show that the simultaneous output of dual-wavelength pulses can be achieved by adjusting the tilt angle of the output mirror.Finally,the highest average output powers of 215 m W and 176 m W of orthogonally polarized dual-wavelength1063 nm（π-polarized）and 1065 nm（σ-polarized）synchronous pulses were output experimentally when the pump power was 6 W.The experimental and theoretical results are in good agreement.Third,a dual-wavelength gain-switched Nd:GdVO₄ laser with adjustable output pulse parameters is proposed.Based on the study of the gain-switched dual-wavelength synchronous pulsed Nd:GdVO₄ laser,a simulation model of the effect of superimposed DC pumping and pulse modulation current on the output pulse modulation of the laser is established,and the effects of the pump pulse parameters on the output pulse width,repetition frequency and peak power of the gain-switched Nd:GdVO₄ dual-wavelength synchronous pulsed laser are analyzed.A high-power pump source is used,and a signal generator is used to modulate the pump pulse,which includes superimposed DC pumping and pulsed current modulation.The experimental results show that the dual-wavelength pulse width performance and peak power of the laser output can be improved by superimposing dc pumping and increasing the pump power.The gain-switched laser delivers 1063nm（π-polarized）and 1065 nm（σ-polarized）dual-wavelength synchronous pulses with peak powers of 23.5 W and 16.5 W and pulse widths of 85 ns and 90 ns respectively.In addition,the laser achieves controllable pulse repetition frequency from 40 k Hz to 200 k Hz and adjustable pulse widths from 85 ns to 109 ns and 90 ns to 136 ns for 1063 nm and 1065 nm,respectively.