Photothermal-induced Brillouin dynamics in CO₂-filled anti-resonant hollow-core fibers

Gas-filled anti-resonant hollow-core fibers (ARHCFs) provide a promising platform for enhancing Brillouin interactions in gases, enabling narrow linewidth and high Brillouin gain. However, at high pump powers, optical absorption induces a photothermal effect that dynamically perturbs the stimulated Brillouin scattering (SBS) process. Here, we investigate this effect in a CO₂-filled ARHCF using time-resolved and wavelength-dependent measurements. At 29 dBm, the Brillouin frequency shift (BFS) drifts by over 2 MHz, indicating an estimated average temperature rise of ~2°C based on the temperature calibration, and the linewidth broadens by approximately 0.6 MHz. The wavelength dependence further identifies gas absorption as the primary origin of these dynamics. These results demonstrate the significance of photothermal effects in high-power gas-based SBS systems, with direct implications for the design of Brillouin lasers and distributed sensing devices.