Dye laser for lidar ozonometry

Abstract

Thus results have been published in Ref. 2 of observations of ozone in the lower layers of the atmosphere with the help of lidar, but the necessary measurement accuracy was not obtained due to insufficient energy of the laser pulses. A detailed analysis of the possibility of such measurements [3] has shown the need to use a dye laser with frequency doubling for these purposes which lases at two wavelengths in the 300-320 nm region with a radiation energy in the pulse of 5-10 mJ and a pulse duration of 1 t~sec. We set ourselves the goal, in performing these experimental investigations, of creating a laser whose parameters would satisfy most completely the conditions posed. In this connection the possibilities of increasing the efficiency and the generation energy of the second harmonic of dye laser radiation were investigated. A solution of 6J Rhodaminein ethanol, whose maximum radiation was located near 600 nm, was used as the active medium, which provided for the generation of a second harmonic with a wavelength of about 300 nm. An INP2-7/120 standard pulse lamp was mounted in a cylindrical single-unit condenser 40 mm in diameter and 120 mm in length with a diffusely reflecting coating of silicon monoxide on the outer surface. The discharge circuit of the laser consisted of two parallel-connect ed K-75-30 capacitors, a controllable discharger with a chamber filled with nitrogen, and a lamp. An IPI-1 power source provided for charging the accumulator up to the operating voltage of 20 kV, and the energy of the electric discharge was 190 J. The dye solution was pumped through a micron filter and a test cell 12 ram in diameter and 120 mm in length at a velocity of 2.5 liters/rain. The optical resonator of the laser was formed by plane dielectric mirrors with reflection coefficients of 0.99 and 0.4 in the wavelength range of rodamine 6J radiation. Polarizing quartz plane-parallel plates mounted at Brewster's angle to the resonator axis and elements to narrow and tune the radiation spectrum of the laser were placed in the laser resonator. Fabry-Perot interferometers in optical contact and an interference-pol arization filter (IPF) whose action is discussed in Ref. 4 were used as the discriminating elements. The reflection coefficients of the interferometer mirrors was 6070 in the wavelength region of the laser generation, and the baselines were 5 and 100 #m. The IPF was formed by two plates of crystalline quartz 1.5 and 3 mm thick mounted at Brewster's angle to the resonator axis between polarizing plates. The angle between the optical axis of each of them and the plane of the plate was 25 ~ A KDP crystal 40 mm long cut at the synchronism angle of 60 ~ for interaction of waves of type 00-e was used for doubling of the radiation frequency. The laser beam was focused inside the crystal by a spherical lens with an optimal focal length of 400 mm to increase the power density of the radiation.