Investigation Of Continuous-wave And Passively Q-switched Dual-wavelength Laser Performance With Combined Gain Medium

Dual-wavelength laser based on combined gain medium have shown great development potential in obtaining high-purity and stable terahertz waves at beat note.Compared to the dual-wavelength laser with single gain medium,the conversion efficiency is significantly improved with this configuration and the dimension of the laser resonator can be more compact if a single output coupler is used.In addition,there is flexibility to choose the emission wavelengths by utilizing different gain medium as long as the threshold conditions are met.This paper starts with the factors affecting the stable operation of neodymium-doped combined crystal dual-wavelength continuous laser and passively Q-switched pulsed laser,and explores the methods of obtaining stable dual-wavelength beat signal.Firstly,by analizing the characteristics of typical neodymium-doped crystals,a combined gain medium that can achieve stable output is designed.According to the different modes of the laser,the specific factors affecting the output characteristics are analyzed.For continuous laser,the influence of pump waist position and crystal temperature on balance of output power is explored according to the four-level rate equation;for pulsed laser,the influence of passive Q-switched pulses of different wavelengths on the time synchronization of dual-wavelength pulses is explored according to the passive Q-switched rate equation.The output characteristics of the power-balanced Nd:YVO₄/Nd:Gd VO₄ combined gain medium dual-wavelength laser(DWL)under different pumping conditions is investigated.The experimental results show for power-balanced Nd:YVO₄/Nd:Gd VO₄ DWL,the heat sink temperature needs reduce when the pumping power increases,and the ratio of temperature decreasing versus pumping power increasing is 11.23?/W.The output power of the power-balanced DWL increases with the pumping power increasing.The fitted slope efficiency is 8.7%.With the change of pumping power and heat sink temperature,the DWL wavelengths shift slightly.When the pumping power increases,the DWL left wavelength blue-shifting rate is 0.056 nm/W,and the right wavelength one is 0.054 nm/W.Based on the research of Nd:YVO₄/Nd:Gd VO₄combined gain medium continuous wave(CW)laser,the pulse synchronization of dual wavelength pulse laser are explored by employing the pulse width modulated LD for pumping and Cr⁴⁺:YAG crystal for passive Q-switching.The experimental results show that the output of 1063 nm and 1064 nm pulses is synchronous by using passive Q-switching mechanism and self-triggering mechanism,and the time jitter between different wavelength pulses is less than laser pulse width about 0.01 times.Finally,the high-efficiency frequency separations tuning is realized by temperature control,and the tuning range is 305.99 GHz?344.11 GHz.In order to obtain a dual-wavelength pulsed laser signal with greater frequency separations,higher output power and time synchronization,a passively Q-switched dual-wavelength pulsed laser based on Nd:YVO₄/Nd:YLF combined gain medium is designed.The output wavelengths are 1047nm and 1064 nm,and the frequency separations is 4.31 THz.Based on the pulse synchronization mechanism,the effects of different pump mode,pump power and crystal temperature on the time synchronous are explored.The experimental results show,comparing with the CW pumping condition,the pulsed pumping can realize the dual-wavelength pulses with controllable repetition frequency,and the pulse time width stability also reaches 97%.