Experimental and analytical evaluation of an active barium vapor notch filter functioning at 355  nm

This work presents an experimental and theoretical study of the 6s²¹S₀→6s6p³P10 (791 nm) and 5s5d³D₂→6s5f³F20 (355 nm) transitions within a low vapor pressure barium vapor in the absence of a buffer gas. To the authors' knowledge, this is the first measurement of the latter absorption feature. The study is motivated by the development of an optically controlled atomic vapor notch filter functioning at the third harmonic of the commonly used Nd:YAG laser at 355 nm. The low-pressure environment within the vapor source has enabled a deeper understanding of barium vapor collisional and velocity changing properties with a simple pump-probe spectroscopy measurement. The results demonstrate depletion of the ground state and subsequent population of the 5s5d³D₂ level. Most notably, the 5s5d³D₂→6s5f³F20 transition displays a non-thermal, cusped absorption curve. An analysis of this line shape in the context of existing analytical collisional kernels is presented. Additionally, a six-level kinetic model of the low-lying energy levels, incorporating spatial diffusion and collisional and radiative transitions, is introduced and compared to the measured level populations for the barium ground state and excited 5s5d³D₂ state.