Narrowband diamond Raman lasers for remote sensing of trace gases

• Applicant: Dr. Oliver Lux
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2014 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 267204784

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.

• DFG Programme: Research Fellowships
• International Connection: Australia
• Host: Professor Dr. Richard Mildren