Filtered rayleigh scattering and dispersion filters in between 380 to 420 nm for atmospheric temperature profiling

The use of ultra violet LIDAR for look-down atmospheric profiling is attractive because of the increased Rayleigh cross section and reduced retinal eye hazard compared to conventional 532 nm frequency doubled Nd:YAG laser look-down LIDAR systems. Incorporation of an atomic filter cell into the detection system enables the suppression of particulate scattering and provides the potential for high resolution Rayleigh Brillouin Spectroscopy (RBS) through atomic filter prism concepts. This paper presents a study of possible atomic transitions, the cell temperature ranges and optical path lengths required for atomic vapor filters in the 380 nm-420 nm range. This frequency range is chosen since it is accessible with a frequency-doubled Ti:sapphire laser operating in the 760 nm-840 nm region. Number density (N), oscillator strength (F) and optical path length (L) of the cell determine the extinction and index of refraction. The number density is a function of the cell side arm temperature, which determines the vapor pressure, and the cell wall temperature. Based on the modeling of ground state transitions for candidate atomic species, a NFL parameter is derived to compare different options. From this analysis we see that cesium at 387.6 nm and potassium at 404.4 nm are the best performing transitions at relatively low side arm temperatures. A model for transmission and refractive index is developed for these two transitions. The refractive index gradient is of interest for prism vapor cell dispersion spectroscopy of the RBS LIDAR return. Simulations are run for different cell parameters to understand the trade-offs associated with maximum achievable refractive index gradient while maintaining reasonable transmission through the vapor cell. Models of RBS lineshapes are shown for the standard atmospheric profile from 15 km altitude to the ground. To determine the potential for the measurement of the atmospheric temperature, density and wind velocity profiles, a sensitivity analysis is performed on these lineshapes by perturbing the temperature and pressure.