Measurement of Doppler effects in a cryogenic buffer-gas cell

Buffer-gas cooling is a universal cooling technique for molecules and used for various purposes. One of its applications is using molecules inside a buffer-gas cell for low-temperature spectroscopy. Although a high-intensity signal is expected in the cell, complex molecular dynamics is a drawback for precise spectroscopy. In this study, we performed high-resolution absorption spectroscopy of low-J transitions in the A2Π(0,0,0)-X2ς+(0,0,0) band of calcium monohydroxide (CaOH). CaOH molecules were produced by laser ablation in a copper cell and cooled to ∼5K using helium buffer gas. We probed the Doppler effects in a buffer-gas cell by injecting counterpropagating lasers inside the cell. The time evolutions of the Doppler width and shift were simulated using a dedicated Monte Carlo simulation and compared with data.