This study presents an eye-safe, single-mode, nanosecond-pulsed, and all-fiber laser source with masteroscillator-power-amplifier configuration at 1 550 nm that is suitable for high-resolution three-dimensional (3D) imaging light detection and ranging (LIDAR) system. The output peak power of 7.6 kW is obtained at the 1.2-ns pulse width and 50-kHz repetition rate. The single-mode pulse laser output ensures the range precision and imaging results of the LIDAR system. The laser is used as a transmitter for the 3D imaging LIDAR system. The detailed characteristics of the LIDAR system and the results of the 3D imaging are presented.OCIS codes: 140.3280, 140.3500, 110.6880. doi: 10.3788/COL201210.121402.The light detection and ranging (LIDAR) system has been proven to be a powerful tool for range finding, threedimensional (3D) imaging, wind sensing, and differential absorption LIDAR systems [1] . A laser source with excellent quality is a key requirement in LIDAR systems. Three kinds of laser sources are used for 3D imaging LIDAR systems. For example, the commercial diode laser, which has limited pulse width and peak power, is used as a laser source for short distance range and low precision [2] . On the other hand, the solid-state laser can produce high-energy and narrow-pulse-width output [3−5] and has become an important laser source for LIDAR applications. Fiber laser sources have several appealing properties for use in LIDAR systems, including good beam quality, narrow linewidth, and versatility that allow the independent optimization of pulse duration, repetition rate, and shape. The single-mode all-fiber pulsed lasers pumped by laser diodes have obtained much attention because of the various advantages, including good beam quality, high efficiency, lightweight, low power consumption, and reduced heat generation [6,7] . In highresolution 3D imaging LIDAR systems, the repetition rate of the laser sources decides the imaging speed, and the detectable distance precision depends on the peak power and the pulse width [2] . Therefore, this study develops a narrow-pulse, high-peak-power, single-mode, and all-fiber laser source to improve the performance of the LIDAR system. Philippov et al. reported an erbium-ytterbium codoped fiber (EYDF) master-oscillator-power-amplifier (MOPA) system for coherent LIDAR applications with a space-coupling power amplifier stage, and they obtained 0.29 mJ and 100 ns pulses with a repetition rate of 4 kHz [8] . Feng et al. introduced an all-fiber pulsed laser transmitter for space-based 3D imaging LIDAR system with a pulse repetition rate of 100 kHz and an amplified laser with output power of 2.3 W, in which a pulse width of 10 ns was generated [7] . Liu et al. developed an eye-safe, single-frequency pulsed all-fiber MOPA laser for a Doppler wind LIDAR system with repetition rate of 10 kHz and pulse duration of 500 ns [9] . They also presented another all-fiber laser with MOPA configuration [10−14] . The results show that both the pulse width and repetition rate are not optimized for...

We report a continuous-wave high-output power and narrow-linewidth all-fiber laser at 1550 nm with the master oscillator power amplifier (MOPA) configuration. An all-fiber distributed feedback seed laser was boosted by three cascaded fiber amplifiers. In the experiment, we adopted a large-mode-area (LMA) Er 3+ :Yb 3+-co-doped polarization-maintaining fiber to increase nonlinear thresholds and avoided the broadening of the laser linewidth. A linear-polarization fiber laser with average output power of 20 W, linewidth of 0.88 kHz, and power jitter less than 2% was finally achieved.

In this paper, we obtain target information about the distance between laser sources and targets based on the linear frequency modulated laser ranging system. We designed a specific experimental scheme for the ranging of linear frequency modulated semiconductor lasers based on heterodyne ranging experiment. Ranging precision can reach micron dimension and range resolution is about 0.002 m within the range of 1-40 m. The ranging method in this paper can apply to laser radars which could be used to capture target information, which is very helpful for tracking, identifying and extracting targets.

Experimental investigation of single and dual pulses in a passively Q-switched Nd:YAG microchip laser with a Cr4+:YAG saturable absorber has been reported. The dual pulses consist of a main and a satellite pulse with respective spectra, intensities, and durations. It is found that the preponderant oscillating mode gives birth to the main pulse, and the other oscillating mode corresponds to the satellite pulse. Our results demonstrate that the dual-pulse emission results from double-longitudinal-mode oscillation in high pump regime.