An instrument for measuring high-power laser beam profiles and beam attenuation

An instrument has been developed for measuring high-power laser beam profiles and the amount of beam attenuation during radiative ignition of solid propellants. The detector houses a 1.0 mm square PZT (lead-zirconate-titanate) sensing element that responds to changes in incident laser beam intensity. A chopper wheel with three slots was employed to produce the changes in beam intensity required by the element. The resultant output signal is a series of ''spikes'' whose height corresponds to the level of beam intensity. Profiles of a high-power CO2 laser beam were obtained by using the detector to acquire a series of radial data points which were then graphed to yield the beam profile. Experiments were also conducted to measure the amount of attenuation of the laser beam during the ignition of solid propellants. This was done by mounting a small sample of propellant on a thin plate above the detector, cutting a 1.5 mm hole through the propellant and the plate, and aligning the hole with the sensing element. The gases and particles evolved during ignition and subsequent combustion of the propellant attenuated the laser beam as it passed through the gaseous plume and the small hole in the sample before being measured by the sensor. The intensity measured by the sensor was then used to quantify the level of transmittance of the beam through the gaseous plume to the propellant sample surface. Results are presented and discussed for a beam profile test and two attenuation tests performed on different energetic materials