New laser amplifier improves laser Doppler interferometry

The design of a laser light amplifier developed to improve the ability of a laser Doppler interferometry system to measure the high velocities of explosion-driven objects or targets is described. The amplifier increases the laser light intensity and S/N ratio. A green coumarin dye is utilized as if the lasing medium for an argon-ion laser and a blue dye as the frequency shifter to improve coupling between the light-pump power source and lasing medium. The arrangement of amplifier components and the frequency characteristics of the flash lamps and dyes are examined. The design requirements for eliminating chirping and achieving acoustic isolation are discussed. The control of the thermal gradients which produce lens effect is analyzed. The selection of a proper dye concentration for uniform excitation across the active volume of the amplifier is studied; an excitation absorption length of three diameters of active cross section is utilized. In order to increase the amount of pumping light reaching the laser dye and to reduce the number of unwanted wavelengths a optical frequency shifter is employed. The amplifier produces enough light to observe two or more spots on the target, record data for up to 12 microsec, and have an accuracy of 0.5 pct.