【摘要】 报道了基于保偏光纤结构的窄线宽窄脉宽高重复频率光纤激光器。采用主振荡器功率放大器（MOPA），主放大级采用芯径为40μm的光子晶体光纤（PCF），获得了重复频率为10 kHz、脉宽为1.34 ns、光谱宽度为0.05 nm、脉冲能量为298μJ的稳定激光输出。通过腔外倍频的方式，使用长度为40 mm的温度匹配型三硼酸锂（LBO）晶体，获得了能量为155.5μJ的532 nm激光输出，倍频效率为52%，横向和纵向光束质量分别为M_x~2=1.28和M_y~2=1.26。该激光器可应用于基于单光子探测技术的空间激光探测雷达。更多还原

【Abstract】 Objective With the development of single-photon detection technology,human exploration of Earth and space has enhanced the study of Earth s surface changes,such as those in ice,terrain,and vegetation,and improved the understanding of the impact of glaciers on sea level change.These detections have led to new requirements for the light source of LiDAR technology,including lasers with high repetition rates,narrow pulse widths,and narrow linewidths for improved detection distance and accuracy,enabling better observations of changes in surface characteristics.Lasers with all-fiber structures are more compact and stable,which have higher photoelectric conversion efficiency and longer lifespan.The optical fiber structure is more conducive to the multi-beam ground detection.This is because a certain detection blind zone between the beams exists,and the detection of multiple beams reduces the distance interval between the beams,resulting in a certain degree of gridded high-precision detection.All-fiber lasers are expected to enable thousand-beam laser ground detection and direct ground measurement.Methods In this study,a continuous seed light of 62.6 mW is used,which is modulated into pulsed light by an electro-optical modulator through a rectangular pulse signal from a signal generator.First,the pulsed seed light is amplified by a gain optical fiber to obtain pulsed light with a wavelength of 1064.43 nm,a linewidth of 0.037 nm,and a peak power of approximately 9.33 W.Then,through a gain fiber for two-stage two-pass amplification,the pulsed light with a linewidth of 0.037 nm and a peak power of approximately 383.5 W is obtained.After the first two-stage amplification,an acousto-optic modulator (AOM) is connected to filter out the continuous wave components of the front stage and improve the contrast of the pulsed light.The third-stage amplification is done through a PLMA-YDF-15/130 double-clad gain fiber to obtain pulsed light with a linewidth of 0.046 nm and a peak power of7.11 kW.The main amplification stage uses the PLMA-YDF-25/250 and photonic crystal fiber (PCF) for amplification effect comparison.The PCF amplified linewidth is smaller than that of the PLMA-YDF-25/250,with no spontaneous radiation,stimulated Raman scattering,or other nonlinear effects.It obtains a wavelength of 1064.44 nm,pulse energy of 298μJ,and pulse width of1.34 ns for lasers with a linewidth of 0.05 nm.The corresponding maximum peak power of the laser is approximately 223 kW.The temperature-matched lithium triborate (LBO) is used for the frequency doubling of fundamental frequency light at an energy of 298μJ,resulting in a green light output of 155.5μJ.The frequency doubling conversion efficiency is 52%,and a beam quality of M_x~2=1.28and M_y~2=1.26 are also obtained.Results and Discussions To simplify the optical path and maintain the stability of the output,the forward amplification method is selected (Fig.1).The main amplification stage uses the PLMA-YDF-25/250 and PCF for comparison.Under varying pump currents(Fig.6),the former exhibits slightly higher optical conversion efficiency than the latter.At a current of 5.6 A,the PLMA-YDF-25/250 exhibits self-phase modulation effects,as shown by the spectral comparison (Fig.7).Because the mode field area of the PCF is larger than that of PLMA-YDF-25/250,the threshold of nonlinear effects is increased,and other nonlinear effects,such as amplified spontaneous radiation and stimulated Raman scattering,are not observed at 298μJ (Fig.8).The optical path design uses a temperature-matched LBO crystal for frequency doubling on fundamental frequency light of 1064 nm,resulting in 155.5μJ green light output with a frequency doubling conversion efficiency of 52%(Fig.9).Conclusions In this study,a master oscillator power amplifier (MOPA) structure combined with photonic crystal fiber is used to obtain stable fundamental frequency light with a repetition rate of 10 kHz,a wavelength of 1064.44 nm,a linewidth of 0.05 nm,an energy of 298μJ,and a peak power of approximately 223 kW.After the temperature-matched LBO frequency doubling,the resulting155.5μJ green light with a frequency doubling efficiency of 52%and beam quality of M_x~2=1.28 and M_y~2=1.26 can be used as a light source for space detection lidar.更多还原