Results and Discussions The laser pulse characteristics are investigated using a pump pulse width of 7.5 μs, repetition frequency of 40 kHz, and pump power of 6 W. When the 1065 nm output mirror tilt angle is approximately 0.02°and the 1063 nm output mirror tilt angle is 0°, the laser achieves dual-wavelength pulse synchronization with a repetition rate of 40 kHz. The pulse widths at 1063 nm and 1065 nm are 120 ns and 150 ns, and the output powers are 143 mW and 96 mW, respectively. The pulse repetition frequency fluctuations are both less than 2%. By tuning the pump pulse repetition frequency, dual-wavelength synchronized pulse signals with a pulse repetition frequency of 30.7-100.0 kHz are realized. When the pump pulse repetition frequency lies between 30.7 kHz and 45.0 kHz, the average power of the dual-wavelength laser increases linearly with an increase in the pump repetition frequency, and the peak power of the dual-wavelength pulse remains unchanged. When the pump repetition rate lies between 45 kHz and 100 kHz, the average output power of the 1063 nm laser decreases with a rate of 0.8 mW/kHz, and the pulse peak power decreases with a rate of 0.25 W/kHz. The average output power of the 1065 nm laser decreases with a rate of 1.27 mW/kHz, and the pulse peak power decreases with a rate of 0.07 W/kHz. When the pump repetition rate is 100 kHz, the average output powers at 1063 nm and 1065 nm reach their highest values of 215 mW and 176 mW, respectively, and the total average output power is 391 mW.
Dual-wavelength synchronous pulsed lasers have important practical applications in fields including precision metrology, holographic interferometry, lidar, and coherent terahertz (THz) wave generation. One approach to obtain dual-wavelength synchronized pulsed lasers is based on a Y-type-cavity dual-crystal laser combined with a saturable absorber, which achieves power balance by adjusting the pumping power of the respective laser crystals. Another approach is based on a linear laser cavity combined with a saturable absorber and dual-gain-peak laser crystal, which achieves power balance by means of birefringent elements, etalons, or stress-induced birefringence. Passive Q-switched pulse mechanism often leads to time jitter between the dual-wavelength laser pulses, owing to the nonlinear characteristics of the saturable absorbers, and dual-wavelength pulse synchronization is difficult to achieve using conventional means. In this paper, a gain-switched dual-wavelength pulsed laser based on a Nd∶GdVO4 crystal is proposed. By adjusting the misalignment of the Y-type cavity to change the dual-wavelength laser thresholds, synchronized pulse outputs at 1063 nm and 1065 nm are obtained. The gain-switching mechanism simplifies the laser resonator structure and flexibly controls the laser pulse parameters, including the pulse repetition frequency and the peak power, by adjusting the pump parameters. Currently, there are no studies on gain-switched synchronous dual-wavelength pulsed lasers, and obtaining dual-wavelength synchronous pulsed output by employing a gain-switching mechanism is challenging.
First, a simulation model of a gain-switched dual-wavelength pulsed laser is established based on the four-level rate equation. Through model simulation, it is found that the laser thresholds have an important influence on the time-domain characteristics of dual-wavelength pulses, and changing the loss of the output mirrors can control the dual-wavelength thresholds. Therefore, it is inferred that the reasonable output mirror loss can realize time synchronization of dual-wavelength laser pulses. The effect of the pump parameters on the repetition rate of the dual-wavelength pulse and the characteristics of the single laser pulse are also studied, which provides a reference for further design and experiments on dual-wavelength lasers.
In summary, a gain-switched dual-wavelength synchronous pulsed laser is proposed. Based on the simulation analysis of the four-level rate equation, a Nd∶GdVO4 crystal with a high emission cross-section and a Y-shaped cavity design are employed, and the laser thresholds of the dual-wavelength signals are changed by adjusting the misalignment of the laser cavities. Finally, dual-wavelength pulse time synchronization is realized. By changing the repetition frequency of the pump pulses, dual-wavelength synchronous pulses of up to 100 kHz, pulse widths of 120 ns and 150 ns, and peak powers of 29.85 W and 15.10 W, respectively, are realized. Compared with the passive Q-switching mechanism, the gain-switched dual-wavelength synchronous pulse laser has a simple structure, good time synchronization characteristics, and a high pulse repetition frequency, which can be applied to the generation of terahertz wave signals.
