Real-time DIAL measurement using 1-kHz-repetition-rate tunable laser

LIDAR using DIAL is a very attractive method to measure impurities in atmosphere. So far, it is difficult to realize realtime detection because of the low pulse repetition rate of tunable laser used. For the realtime detection of impurities, a LIDAR using a laser with the repetition rate of 1 kHz is constructed. The system consists of a laser transmitter and a receiver. The laser is a tunable dye laser pumped by a LD-pumped Nd:YAG laser with the pulse repetition rate of 1 kHz. The diameter of the receiver is 200 mm. A backscattered radiation collected by the receiver is transmitted to a monochromator through a fiber of which transmittance is around 80 %. Then the signal is detected by a photomultiplier tube. With this system, detection characteristics of iodine and aerosol has been studied. The iodine in a glass cell is placed around 100 m from the system and the absorption is measured with DIAL method. The wavelength of the laser is around 585 nm and pulse duration 30 ns. Number of laser shots accumulated is 1000 shots, that is, the duration of the measurement is only one second. The concentration of the iodine measured by the method agrees well with the concentration calculated from the vapor pressure at the temperature. As the pulse repetition rate is around 100 times higher compared with typical DIAL system, it can be used to detect other gases with realtime bases.