Research on photothermal gas detection based on miniature fiber Fabry-Perot Cavities

• Applicant: Professor Sebastian Hofferberth, Ph.D.
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 544894227

The primary focus of this project centers on laser-based gas sensing and micro-optics, particularly miniature fiber Fabry-Perot cavities. The overarching objective is to assemble an interdisciplinary team of researchers to address the challenge of enhancing spectroscopic signal extraction in photothermal gas spectroscopy. Our approach involves the utilization of custom-designed miniature fiber Fabry-Perot cavities (FFPCs) to investigate the amplitude of spectroscopic signals. We plan to evaluate the performance of this signal extraction technique through a series of experiments. The FFPCs will be incorporated into a specially designed chamber filled with the gas sample. Excitation of gas molecules will occur through an auxiliary pump laser, inducing refractive index modulation. The pump laser will be focused in the middle of the FFPC, leading to a refractive index modulation causing a phase change in the probe beam within the Fabry-Perot cavity. This change will be observable as an amplitude variation in the probe laser reflected from the cavity. Throughout the project, we will design FFPCs in various geometries and optimize their parameters to enhance their applications in gas sensing. Key aspects include redesigning FFPCs to operate at 1550 nm, allowing the use of telecom wavelength lasers and fiber components, thereby expanding the current operational range of FFPCs at 780 nm. In addition, improvements in cavity Finesse, mirror separation, and the exploration of novel designs such as three-port cavities and crossed-cavity configurations will be pursued. Furthermore, the project aims to develop fiber-based pump laser beam delivery to enhance sensor stability. Signal processing techniques, such as wavelength modulation spectroscopy and boxcar averaging, will be evaluated to improve the signal-to-noise ratio of gas detectors. The project will also explore frequency division multiplexing and time division multiplexing to experimentally validate the multi-gas detection capabilities of the proposed sensors.

• DFG Programme: Research Grants
• International Connection: Poland
• Co-Investigators: Professor Dr. Dieter Meschede; Dr. Hannes Pfeifer
• Cooperation Partner: Professor Dr. Karol Krzempek