| 题名 | 全固态拉曼激光技术研究 |
| 作者 | 陈俊驰 |
| 文献子类 | 博士 |
| 导师 | 冷雨欣 |
| 关键词 | 受激拉曼散射 Stimulated Raman scattering 受激拉曼放大 Raman amplification 大能量1064nm泵浦源 high energy 1064nm pumping laser 高功率皮秒短脉冲泵浦源 high power picosecond pumping laser KGW晶体 KGW crystal Ba(NO3)2晶体 Ba(NO3)2 crystal |
| 其他题名 | Study on the all solid state Raman laser |
| 英文摘要 | 受激拉曼散射(SRS)属于三阶非线性过程，是一种有效实现频率转换的技术，并且具有净化光束、窄化脉冲宽度、高度相干性和大范围的频率转换等特点。目前，基于受激拉曼散射技术的拉曼激光器，可获得激光光谱范围已经从紫外波段涵盖到中红外波段，极大地丰富了激光工作光谱波段。同气体和液体拉曼激光器相比，固态拉曼激光器具有热导性好、散射粒子浓度高、拉曼散射截面大、拉曼增益系数大、良好的机械性能和小体积等特点；同光纤拉曼激光器相比，固体拉曼激光器更适合发展短脉冲拉曼激光。因此，固态拉曼激光器已经成为现在研究拉曼激光技术的重要选择之一。全固态拉曼激光器输出的斯托克斯光谱范围很大，决定了其有广泛的用途，比如基于通用的1064nm激光进行拉曼频移，可以获得用于探测生物组织的1197nm激光；获得的1178nm激光倍频后为589nm，可以用于产生人工钠导星；拉曼频移获得1.5μm三阶斯托克斯光属于人眼安全波段，还可作为中红外光学参量振荡器的泵浦光。因此，开展全固态拉曼激光技术研究具有非常重要的研究意义和应用价值。 本论文选择Ba(NO3)2和KGd(WO4)2（KGW）晶体作为拉曼介质，对全固态拉曼激光以及相关泵浦源技术等开展了研究工作，取得的主要创新点和研究成果包括： 1.发展了大能量的纳秒脉宽拉曼泵浦源。选用能量为400mJ的商业化闪光灯泵浦激光器作为种子源，经过三级基于Nd:YAG晶体的闪光灯泵浦放大模块，将1064nm激光的单脉冲能量提高到7.3J，重复频率为1Hz。为克服增益饱和导致的窄化效应，提出采用偏振合束结构来改变注入种子脉冲时域波形，特别是种子光的脉冲前后沿强度比值的技术，使得放大输出激光的脉冲宽度在7~20ns内可调，脉冲波形也在一定的范围内可控。 2.在高功率短脉冲拉曼泵浦源技术研究方面，发明了一种基于全内反射的板条皮秒激光放大器结构。无需额外反射镜，仅依靠板条自身的结构可实现种子激光在板条内的多程放大。当泵浦功率为25W，100ps脉冲宽度种子激光功率为4W时，放大后输出最高功率为6.6W，光-光转换效率为10.9%，快轴和慢轴的光束质量M2因子分别为1.7和2.47。 3.发展了基于新型Nd,Y:SrF2晶体的皮秒再生放大激光器技术。Nd,Y:SrF2晶体具有较宽的光谱、大的发射截面以及良好的热导性。利用该晶体应用于再生放大激光器中，实现了脉冲宽度为1.6ps，重复频率为5Hz，压缩后能量为3.7mJ的激光输出。 4.对偏振合束技术抑制斯托克光脉冲宽度窄化技术进行了理论和实验研究。通过研究泵浦光能量对输出的斯托克斯光的脉冲波形的影响，发现斯托克斯光脉冲窄化的主要原因是泵浦光的脉冲前沿部分用于激活拉曼晶体，泵浦光的脉冲后沿部分实际产生斯托克斯光。为此，提出采用偏振合束的结构来抑制时域脉冲窄化的技术，通过产生一个预脉冲来激发拉曼晶体，使得在受激拉曼散射过程中主泵浦脉冲可以直接用于产生斯托克斯光，从而保证斯托克斯光的波形和泵浦光的脉冲波形一致。 5.基于大能量的纳秒脉宽拉曼泵浦源，开展拉曼振荡器技术研究，实现大能量斯托克斯光的输出。主要研究了两种形式的KGW拉曼激光振荡器：外腔拉曼振荡器和单程拉曼发生器。当泵浦能量为1.8J时，外腔拉曼振荡器输出的斯托克斯光最高输出能量为448mJ，相应的光-光转换效率为25%。对于单程拉曼发生器，当泵浦能量为2.8J时，单程拉曼振荡器输出的斯托克斯光的最高能量为676mJ，相应的光-光转换效率为24%，是目前所知全固态拉曼振荡器输出的最高能量。 6.在此基础上，进一步发展了拉曼放大器技术，实现大能量斯托克斯光的放大输出。通过延时优化等，当泵浦能量为3.9J时，输出的斯托克斯光的最高能量为800mJ，首次接近1J量级，总体光-光转换效率为22.6%。 7.通过级联光学参量振荡器与拉曼激光器，获得1.88μm波段的纳秒激光脉冲输出，该激光工作波段在探测卷积云等方面具有重要应用价值。我们先利用130mJ能量的 1064nm纳秒激光泵浦基于KTP晶体的OPO，实现40mJ 的1.57μm激光输出；再将1.57μm激光作为Ba(NO3)2晶体拉曼激光器的泵浦源，经拉曼频移获得了7.5mJ能量的1.88μm波段激光输出，总体光-光转换效率为5.8%，脉冲宽度为5.4ns，相应的峰值功率为1.4MW。 8.提出了基于KGW晶体和Ba(NO3)2晶体的拉曼频移以及和频技术获得可用于纳导星的589nm激光输出的新技术。将1064nm泵浦激光分为两部分，一部分用于泵浦KGW晶体获得1156.8nm的斯托克斯光输出，输出能量为400mJ；另外同步泵浦Ba(NO3)2晶体获得1197.8nm的斯托克斯光激光输出，输出能量为200mJ。两束斯托克斯激光的部分能量同时入射到KDP晶体中通过和频后获得589nm激光，输出能量为31mJ。; Stimulated Raman scattering (SRS), belonging to the third order nonlinear process, is one of the effective techniques to realize frequency shifter, and it is characterized with beam clean up effect for improving the beam quality, pulse narrowing effect, high coherence and large frequency shifter. So far, the wavelength of the output Stokes lasers have covered from ultraviolet to mid-infrared wavebands, largely fulfilling the optical spectrum. The properties of the all solid state Raman laser overcome these possessed by the gas and liquid Raman lasers, such as high concentration of scattering centers, large emission area, large gain coefficient, high thermal conduction, small volume and well mechanical property; compared with the fiber Raman laser, the all solid state Raman laser is more suitable to develop short pulse laser. The excellent properties of the all solid state SRS laser decide its wide applications, for example, 1197nm laser obtained through SRS frequency conversion from the 1064nm can be used to detect the biological tissue; 1178nm can be obtained by SRS process, the second harmonic wavelength can be used for generating the sodium laser star; third order Stokes laser around 1.5μm is belonging to the eye-safe wavelength. In conclusion, the all solid-state SRS laser is significantly worth of studying. In this dissertation, the all solid state Raman laser and the relative pumping source is experimentally and theoretically studied based on the Ba(NO3)2 and KGd(WO4)2 (KGW) crystals. The main work is presented as the following: 1. The high energy nanosecond pumping laser system is developed and studied. The steady commercial product is employed as the seeder laser source. The single pulse energy can be boosted to 7.3J operated at repetition rate of 1 Hz after being amplified in three Nd:YAG crystals based flash lamps pumped amplification modules. This pumping laser system sets the basement for achieving high energy Stokes laser. However, due to the gain saturation effect, the obtained amplified laser pulse width will become narrow compared with that of the original seeder laser. A simple and cheap polarization beam combination technique is proposed for reshaping the temporal waveform of the seeder laser, especially the intensity distribution between the front and rear edge of the seeder laser pulses. It is experimentally and theoretically demonstrated that the output amplified pulse shape can be achieved with tunable pulse width of 7~20ns and tunable waveform. 2. In terms of the high power picosecond pumping sources for Raman lasers, an all–internal reflection small-sized slab picosecond amplifier is proposed. Without the additional mirror, the seeder and pumping lasers are reflected and propagate several passing depending on the slab structure itself. When the 4W 100ps seeder laser is injected into the slab, the maximum output power of 6.6W is achieved, and the corresponding optical efficiency is 10.9% under the pumper power of 25W. The measured M2 factors are 1.7 and 2.47 respectively along the fast and slow axes. 3. Research on the picosecond amplifier laser based on new material-Nd,Y:SrF2 crystal is carried out, which is characterized with wide spectrum width, large emission area and high thermal conduction coefficient. The picosecond regenerative system is capable delivering pulse energy of 3.7mJ, pulse with of 1.6ps operated at the repetition rates of 5 Hz. 4. Theoretical and experimental research on reducing the pulse with narrowing using the polarization beam combination techniques. Firstly, the influences of the pumping laser energy on the Stokes pulse waveforms are investigated. The reasons for the pulse compression effect is due to that the front part of the pumping laser is used for exciting the crystal and the rear part of the pumping laser is used to generate the Stokes laser. In our work, the polarization beam combination structure is proposed for eliminating the pulse compression effect, the main principles for preserving the temporal waveform of the Stokes lasers is as following: the pre-pulse pumping laser is firstly generated to excite the crystal and the main pulse is used for generating the Stokes laser. 5. Studying on the single pass Raman oscillator and extra-cavity Raman oscillator is carried out. The aforementioned high energy nanosecond laser system is employed for pumping the KGW crystal. Under the pumping energy of 1.8J, the maximum output energy of 448mJ is achieved and the corresponding optics efficiency is 25% for the extra-cavity oscillator. For the single passing Raman generator, the maximum energy of 676mJ is obtained and the corresponding optical efficiency is 24% with the pumping energy of 2.8J. As far as we know, the 676mJ is the highest energy based on the all solid-state Raman oscillator. 6. The Raman laser is further studied by developing the Raman amplifier. The 7.3J 1064nm nanosecond laser is divided into two parts, one part is as the pumping source for the Raman oscillator to generate the Stokes seeder laser; and the other part is used for pumping the Raman amplification medium. The delay time between the two parts of 1064nm pumping laser is firstly investigated to obtain the maximum energy of amplified Stokes laser, and the optimized delay time is about 1.89ns. Under the pumping energy of 3.9J, the output power of Stokes laser can reach 800mJ, and the total optical efficiency is 22.6% when the polarized direction of the 1064nm laser is parallel to the Nm optical axis of the crystal. As far as we know, this energy is the highest based on the all solid state Raman laser. 7. The combination of optical parametric oscillator (OPO) and Raman laser is used for obtaining 1.88μm laser. It is demonstrated that 1.88μm laser is effective wave band for detecting the circus cloud. In our work, 130mJ 1064nm laser is used for pumping the OPO laser based on the KTP crystal, and 40mJ 1.57μm laser is achieved. Then the 1.57μm laser is selected as the pumping source for the Raman laser based on the Ba(NO3)2 crystal, and the wavelength will be converted to 1.88μm laser with energy of 7.5mJ, and the total optical efficiency is 5.8%. The pulse width of the 1.88μm laser is about 5.4ns, the corresponding peak intensity is 1.4MW. 8. Newly technique for generating 589nm laser is proposed based on the KGW crystal and Ba(NO3)2 crystal. The 1064nm laser is divided into two part, one is for pumping the KGW crystal and the other is for pumping the Ba(NO3)2 crystal. The 1064nm laser can be converted to 400mJ 1156.8nm through the KGW crystal; The 1064nm laser can be converted to 200mJ 1197.8nm through the Ba(NO3)2 crystal. 1156.8nm and 1197.8nm lasers are turned into 589nm through sum harmonics process in KDP crystal. The obtained energy of 589nm laser is about 31mJ. |
| 学科主题 | 光学 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/30933]  |
| 专题 | 中国科学院上海光学精密机械研究所 |
| 作者单位 | 中国科学院上海光学精密机械研究所 |
| 推荐引用方式 GB/T 7714 | 陈俊驰. 全固态拉曼激光技术研究[D]. |
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