A Rayleigh lidar on rockets for studies of the middle atmosphere

Two new rocket-borne Rayleigh lidar experiments were developed at the Norwegian Defence Research Establishment and launched from Andøya Rocket Range in October 97 and January 98. The aim of the experiments were to measure the neutral atmosphere number density and to study the dynamics of the middle atmosphere. A simulation programme for calculation of Rayleigh-scattered signal, background level and noise was used to investigate the performance of the instrument. Various configurations of transmitters and receivers were evaluated. For the transmitter, laser diode arrays and solid state lasers were considered. The diode arrays were found suitable and two types of high power diode arrays were tested in the laboratory. A 20 bar array assembled using the bars-in-grooves technology was selected. It was operated in QCW mode with a pulse length of 450 μs, a pulse repetition rate of 135 Hz and an average optical power of 62 W at 805 ± 5 nm. It required a power supply giving 65 A at 42 V, active water cooling and a collimating lens. For the receiver, diodes and PMTs were considered. A large-area detector able to process photon rates of 106to 1010 s-1 was essential. An APD was selected due to the better quantum efficiency compared to the PMTs at 805 nm. It had a gain of 200 at 2.4 kV, and was cooled to -20°C to reduce the dark current to 1.5 nA and the rms-noise to 40 pA.