【作者】 姜培培；

【导师】 沈永行；

【作者基本信息】 浙江大学 ， 光学工程， 2009， 博士

【摘要】 高功率脉冲光纤激光器具有高光束质量、高转换效率、高脉冲能量、较低热效应等特点受到人们的广泛关注,最近几年来成为了国际科技界的研究热点。使用高功率脉冲光纤激光器作为泵源,泵浦基于PPMgLN晶体的光参量振荡器(OPO),可以产生高功率中红外激光输出,在光电对抗、红外干扰以及激光雷达等方面具有重要应用。本论文主要目的是研究高功率的脉冲光纤激光器,获得几十ns级的高功率脉冲激光输出,并以此作为泵源,泵浦PPMgLN晶体,获得高功率的中红外激光输出。本论文主要包括三个方面的内容,声光调Q光纤激光器研究、MOPA型脉冲光纤放大器研究以及光纤激光器泵浦的基于PPMgLN晶体的光参量振荡器研究。声光调Q光纤激光器采用法布里-珀罗谐振腔结构,以大直径双包层掺镱光纤作为增益介质,获得了稳定的高功率脉冲波形输出。系统地考虑了影响脉冲波形稳定性的因素,包括声光调Q开关(AOM)与反射镜之间的距离、光纤长度、泵浦功率以及重复频率等。使用自制光纤和Liekki公司的熊猫型保偏光纤,分别研制了随机偏振和线偏振光纤激光器,获得了脉冲激光输出功率分别为12W和10.5W,激光输出脉冲稳定,脉宽分别为45ns和33ns。分别采用固体激光器和全光纤型声光调Q光纤激光器作为种子源,研制了MOPA结构的高功率脉冲光纤激光器。固体激光器的光谱线宽较窄,在光纤放大器运行过程中极易产生SBS等非线性效应。调整种子激光的功率和重复频率,可以有效抑制非线性效应,提高光纤放大器输出功率,最终在泵浦功率达到30.4W时,获得线偏振输出功率20W,偏振抑制比大于14dB。全光纤型声光调Q光纤激光器结构紧凑、功率较高,而且具有较大的光谱宽度,可增加SBS等非线性效应的阈值,减少非线性效应的影响。使用这种种子源的光纤放大器可以产生更高的输出功率,在40W泵浦功率下,最终获得29.6W线偏振激光输出,偏振抑制比大于10dB。以MOPA型光纤激光器作为泵源,以PPMgLN晶体为非线性材料,运行光参量振荡器,获得了高功率中红外激光输出。首先,利用电光调Q固体激光器的高脉冲能量,研究了1mm厚度PPMgLN晶体的抗光损伤特性,得到其损伤阈值约为4.6J/cm~2,即460MW/cm~2。其次以固体激光器作为种子源的光纤放大器泵浦OPO,在泵浦功率为15.2W时,1602nm通道获得最高参量输出8W,对应3163nm的闲散光功率为2.5W,相应的斜效率约为69%,光光转换效率为54%。在泵浦功率增长的过程中,并没有发现功率饱和现象。再次,用全光纤结构的光纤放大器泵浦OPO,在泵浦功率为22.9W时,1602nm通道得到最大参量输出11.7W,其中闲散光3163nm功率为3.3W,光光转换效率为51.9%,其运行过程中出现一定的功率饱和现象。分析认为,闲散光吸收引起的热透镜效应是引起功率饱和现象的主要原因。腔镜结构、泵浦光光斑大小以及散热系统的设计,对谐振腔内的热透镜效应有明显的影响。更多还原

【Abstract】 High power pulsed fiber lasers, which draw a lot of attentions in recent years, have become the international research hotspot because of the advantages such as good beam quality, high efficiency, excellent heat dissipation capability, and compactness. Using the high power pulsed fiber laser as the pump source, the PPMgLN-based optical parametric oscillator can achieve high power output in mid-infrared waveband, which can be used in a wide variety of applications such as LIDAR, infrared jamming and optoelectronic countermeasure. In this thesis, the main work is on the development of the high power multi-10ns pulsed fiber lasers and their application on PPMgLN-based optical parametric oscillator. The thesis is composed of the following research work: acousto-optic(AO) Q-switched fiber laser, MOPA structured pulsed fiber amplifier and PPMgLN-based optical parametric oscillator.The AO Q-switched fiber laser was set up with Fabry-Perot cavity structure. Using a large mode area double-cladding fiber as the gain medium, stable Q-switched short pulse high power laser output was achieved. To maintain the laser pulse stable, many factors were considered such as the distance between the AO modulator and the reflect mirror, the length of the active fiber, the pump power and the repetition rate. Using the home-made fiber and the Panda PM fiber from Liekki, we obtained random polarized output power over 12W and linearly polarized output power over 10.5W with pulse duration of 45ns and 33ns respectively.We demonstrated two kinds MOPA structured fiber amplifier; one seeded by a solid state laser and another seeded by a Q-switched fiber laser. Because of the narrow linewidth of the solid state laser, serious nonlinear effect was observed in the fiber amplifier. By adjusting the output power and repetition rate of the seed source, the nonlinear effect could be suppressed. When the pump power exceeded 30.4W, a maximum linearly polarized output power of 20W was obtained. The measured polarization extinction ratio(PER) was greater than 14dB. The fiberized AO Q-switched seed laser has high output power and large linewidth, which is suitable for suppressing the nonlinear effect. This kind fiber amplifier has much higher output power. At the pump power of 40W, a maximum linearly polarized output power of 29.6W was obtained. The measured polarization extinction ratio(PER) was greater than 10dB.PPMgLN-based optical parametric oscillator pumped by MOPA structured fiber amplifier can achieve high output power. A high-energy PPMgLN optical parametric oscillator (OPO) pumped by a E-O Q-switched Nd:YAG laser working at 1.064μm was successfully illustrated. The damage to the input surface of PPMgLN crystal was carefully observed with a damage threshold of 4.6 J/cm~2. When pumped by the solid state laser seeded fiber amplifier, a maximum parametric output of over 8 W was obtained with 2.5 W at 3.16μm. The conversion efficiency of the OPO was computed to be 54% with a slope efficiency of 69%. No saturation phenomenon was observed in the experiment. When pumped by the fiber laser seeded fiber amplifier, a maximum parametric output of over 11.7 W was obtained with 3.3W at 3.16 urn. The conversion efficiency of the OPO was computed to be 51.9% . The saturation phenomenon was observed in this experiment. It is due to the absorption of PPMgLN within the idler wavelength band. To improve the performance of the OPO system, the cavity structure, beamwidth of the pump source and the design of the cooling system must be optimized.更多还原