Sodium Lidar


In order to investigate the night-time variability of Na concentration during normal and meteor shower times, formation of sodium layer, relation between sodium layer and field aligned irregularities through neutral ion coupling, wave motions and instabilities using sodium as a tracer, and to find the relation between sodium composition and sodium airglow intensity NARL has designed and developed Na Lidar. The broadband Na lidar system at Gadanki was setup as augmentation to Rayleigh lidar in a mono-static configuration with the power-aperture product of 0.35Wm2. The transmitter consists of a tunable pulsed dye laser pumped by a frequency-doubled Nd: YAG laser. The pulsed dye laser is tuned to the D2 resonant absorption line of Na at a wavelength near 589 nm. The dye laser employs a dual grating system that is controlled by a computer which enables a rapid selection of transmitted wavelength. The line width of the laser is about 2 pm. The dye laser is pumped with 200 mJ at 532 nm to obtain output pulse energy of 25 mJ at 589 nm. The dye laser uses Kiton Red as the laser medium. The laser beam is expanded and transmitted into the atmosphere using a steering mirror. The receiving system uses a 750-mm Newtonian telescope with field optics and an interference filter. A PMT is employed for photon detection. The output pulses of the PMT are amplified by a broadband amplifier and then fed into a PC-based photon counting multi-channel scalar (MCS). The MCS counts the pulses in successive time bins. Each time bin is set to 2μs, corresponding to a vertical resolution of 300 m. The photon counts are accumulated for predesignated shots, corresponding to its time resolution. The effective cross section of the Na atom, which is a function of the laser spectral width, is estimated and using this value sodium concentration profiles are derived.