Narrowband diamond Raman lasers for remote sensing of trace gases

晶体固体中的受激拉曼散射(SRS)可以将激光辐射有效地转换到使用传统激光增益介质无法直接访问的光谱区域。该过程涉及强抽运光与振动模(声子)的非线性相互作用，产生波长相对于抽运波长上移(斯托克斯)或下移(反斯托克斯拉曼散射)的离散发射线。将拉曼活性介质集成到具有适当规格的光学谐振器(拉曼激光器)中，可以选择性地放大单线，从而产生特定的激光波长。这对于利用在近红外光谱范围内发射的强大激光对大气痕量气体进行遥感特别有意义。在这里，必须满足对空间和光谱辐射特性的严格要求。在他以前的科学工作的框架内，申请人研究了20多个拉曼活性晶体关于受激拉曼促进振动模的激发，并量化了它们的相互作用强度。在选择合适的材料后，研制了一套复杂的拉曼激光系统，并将其用于实验室条件下的二氧化碳检测。在这些研究的基础上，计划中的项目重点放在拉曼活性材料金刚石上，由于其特殊的热和光学性质，特别适合于转换高功率激光辐射，近年来在激光物理领域经历了迅速的发展。为了将金刚石拉曼激光器应用于痕量气体检测，需要利用现代测量技术对这些光源的光谱特性进行分析。该项目的主要目标是开发一种波长可调谐的窄线宽钻石拉曼激光器。为此，将研究一种针对激光发射的光谱控制的新概念。其可行性将通过对氨的吸收测量来评估。这项研究为证明(钻石)拉曼激光器在光谱应用中的潜力，特别是刺激其在遥感方面的进一步发展提供了原理证明。此外，该项目旨在提供专业知识的协同，因为悉尼麦格理大学的R.P.米尔德伦教授团队是高功率钻石拉曼激光器方面的领先团队之一，而申请者在稳频技术和用于痕量气体检测的固态激光器方面都有经验。申请者方法范围的扩大将使他能够为未来的气候和环境研究做出重要贡献。

Stimulated Raman scattering (SRS) in crystalline solids allows for efficient frequency conversion of laser radiation to spectral regions which are not directly accessible using conventional laser gain media. The process involves the nonlinear interaction of intense pump radiation with vibrational modes (phonons), producing discrete emission lines whose wavelengths are up- (Stokes) or down-shifted (anti-Stokes Raman scattering) with respect to the pump wavelength. Integration of a Raman-active medium into an optical resonator with appropriate specifications (Raman laser) enables selective amplification of single lines and thus the generation of specific laser wavelengths. This is of particular interest for remote sensing of atmospheric trace gases by means of powerful lasers emitting in the near infrared spectral range. Here, strict requirements regarding the spatial and spectral radiation characteristics have to be met. In the framework of his previous scientific work the applicant has investigated more than 20 Raman-active crystals with regard to the excitation of SRS-promoting vibrational modes and has quantified their interaction strengths. After selection of a suitable material a complex Raman laser system has been developed and employed for carbon dioxide detection under laboratory conditions. Based on these studies the planned project focuses on the Raman-active material diamond which is especially well-suited to converting high power laser radiation due to its exceptional thermal and optical properties and which has experienced a rapid upswing in the field of laser physics in recent years. With a view to the application of diamond Raman lasers for trace gas detection, the spectral properties of these laser sources should be analyzed using modern measurement techniques. The major goal of the project is the development of a wavelength tunable diamond Raman laser with narrow linewidth. For this purpose, a novel concept aiming at the spectral control of the laser emission will be studied. Its feasibility will be evaluated by absorption measurements of ammonia. The research serves as proof-of-principle to demonstrate the potential of (diamond) Raman lasers for spectroscopic applications and especially to stimulate their further development for remote sensing. Moreover, the project is meant to provide a synergy of expertise since the group of Prof. R. P. Mildren at Macquarie University in Sydney is one of the leading groups in terms of high power diamond Raman lasers, while the applicant has experience in both frequency stabilization techniques and solid-state lasers for trace gas detection. Expansion of the applicant's spectrum of methods will enable him to provide important contributions to the climate and environmental research in the future.