Narrow-line-width pulsed solid-state lasers in the 2 μm eye-safe spectral region are usually used as the lidar emitter in coherent Doppler lidars for wind field measurement or in differential absorption lidars (DIALs) for monitoring the concentrations of gases such as CO2 and H2O[1–4]. A lidar configuration requires an emitter with high energy to increase the detection range, a long pulse width to improve the spectrum resolution and a narrow line width to enhance the spectral purity. A critical technique for obtaining a narrow-line-width pulsed laser is the injection of a single-frequency continuous-wave (CW) laser into a Q-switched slave laser[6,7]. In addition, there are two ways to obtain a long pulse width: one is to increase the cavity length of the Q-switched slave laser; and the other is to ensure that the slave laser operates at a lower energy. Increasing the cavity length, however, leads to difficulties with the cavity design, a complex structure and a large laser volume. Compared with a longer resonator, it is an effective approach for realizing a pulsed laser with narrow line width, long pulse width and high energy, by making the Q-switched slave laser operate at a lower energy and then increasing the output energy through an amplifier system.
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