面向DIAL应用的单频光纤激光的稳频与放大技术

This research project plans to find new solutions to the laser source "bottlenecks" obstructs hindering the current differential absorption lidar(DIAL) systems for atmospheric molecule exploration applications by utilizing the rich wavelength resources of near-infrared region fiber laser techniques. By studying the influences of the specifications of the hollow-core photonic crystal fiber (HC-PCF) on the saturable absorption characteristics of the gas filled in the HC-PCF, we can obtain the optimized specifications of the HC-PCF for developing the gas-filled HC-PCF cell with very narrow saturable absorption spectrum, and achieve the high-precision frequency stabilization for the single-frequency fiber laser by using the narrow absorption peak of the developed the all-fiber low-pressure gas-filled HC-PCF cell as the frequency reference. A high power single-frequency laser fiber amplifier system may be developed by having suppressed the stimulated Brillouin scattering (SBS) effect in the single-frequency light signal fiber amplification, weakened the waveform distortion caused by the gain dynamics of rare-earth doped fibers and decreased the amplified spontaneous emission (ASE) noise accumulation generated in the low duty cycle pulse fiber amplification. Finally, a maser -oscillator power-amplifier (MOPA) fiber laser system may be constructed with the developed high-precision frequency-stabilized single-frequency fiber laser and high power single-frequency laser fiber amplifier system required for the demands in DIAL applications. Obiously, executing this project plan will definitely establish a solid theoretical and technical foundation for the development of new generation of DIAL laser source system, and thus, holds an remarkable significance in both scientific research and technological progress.

本项目拟利用光纤激光器在近红外波段的丰富波长资源，发展满足DIAL大气分子探测要求的新型激光系统，以解决制约DIAL技术发展光源瓶颈问题。通过研究HC-PCF吸收池的气体饱和吸收特性及其影响因素，提出能改善稳频精度的HC-PCF优化设计参数，解决全光纤型低压HC-PCF气体腔的研制技术问题，实现对单频光纤激光器的高精度稳频；通过抑制SBS效应对单频高功率光纤放大器输出功率的影响，解决低占空比单频脉冲光纤放大过程中的波形失真与噪声积累问题，构建满足DIAL系统应用要求的光纤型MOPA激光光源系统。通过本项研究，将为新型实用化DIAL光纤激光光源系统的发展奠定理论与技术基础，具有极其重要的科学意义和实用价值。

光纤激光器和半导体激光器体积小、重量轻、近红外波段波长资源丰富，并且，稀土掺杂光纤放大器不仅带宽宽、散热性能好，而且输出激光光斑小、亮度高、光束质量好。但是却存在着输出功率低，单频运转时频率漂移量大等缺点，并且当采用传统气体吸收池进行单频激光稳频时存在系统过于庞大等缺点，单频激光放大过程中出现非线性和ASE噪声积累等问题。本项目中提出利用全光纤型HC-PCF低压气体腔构建小型化激光稳频系统，并通过优化放大器结构方案，进行增益合理分配和采用ASE滤波器等方式抑制单频激光放大过程中的非线性效应，提高信噪比，降低噪声积累等。.理论研究了HC-PCF吸收池的吸收特性及其影响因素，提出能改善稳频精度的HC-PCF优化设计参数，通过理论研究HC-PCF低压气体填充与泄漏过程的动力学行为，掌握了HC-PCF内部气压分布及其演变控制技术，成功研制了基于HC-PCF的全光纤型低压气体腔，并进而构建了基于HC-PCF吸收池激光稳频实验系统，稳频系统中HC-PCF低压气体腔内填充CO2气体分子，腔压为50 mbar，将单频激光频率稳定在CO2气体吸收线上，稳频精度达50MHz；通过理论研究高功率光纤放大器的输出特性及其影响因素，提出高功率单频光纤激光器放大优化设计方案，通过种子注入调Q方案，获得了重频80kHz线宽约1.5MHz的窄线宽脉冲激光输出，并采用级联放大方案，实验研究了其高功率放大特性，实验结果表明，当采用级联放大方案时，可获得信噪比约65dB的放大激光脉冲输出，且保持良好的单纵模特性，并且，实验还发现，放大器输出激光线宽与种子激光线宽相比展宽较少，通过优化光纤掺杂浓度、结构参数和长度，可提高非线性效应的阈值，抑制了SBS，通过ASE滤波器可降低了ASE噪声的积累，最终我们构建了光纤型MOPA单频激光光源系统，并初步进行了SO2气体浓度检测应用研究实验。通过本项研究，将为新型实用化DIAL光纤激光光源系统的发展奠定理论与技术基础。