Laser-induced fluorescence of metastable helium for thermosphere studies

Our study focuses on the experimental research of the thermosphere, which significantly affects spacecraft operations. Metastable helium, a key component of the thermosphere, can characterize the coupling process between the neutral atmosphere and ionized components. We designed an optical system to detect stimulated fluorescence at the P-3(1,2,3)-S-3(1) transition of helium and tested it in a laboratory-created environment with metastable helium. By tuning the laser frequency around resonance, we measured the fluorescent spectrum and used fitting methods to estimate the temperature of metastable helium. Fluorescent intensity and temperature were systematically recorded under varying bias voltages and pressures, revealing a positive correlation between intensity and both parameters. The temperature displayed a linear increase with bias voltage at a slope of 2.1 +/- 0.4 K/V, while no discernible relationship was observed between temperature and pressure. Our experimental setup not only provides a robust platform for the optical diagnosis of thermosphere-like conditions in the laboratory but also serves as a validation tool for advancing helium lidar technologies. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International (CC BY-NC-ND) license (https://creativecommons.org/licenses/by-nc-nd/4.0/).