Laser Polarimetric Apparatus for Rapid Emissivity Measurements on Pulse-Heated Materials

Laser polarimetric/ellipsometric methods have been employed in our laboratory for the measurement of the normal spectral emissivities of solid and liquid materials at elevated temperatures. In this approach, a polarized light source is incident on the surface of interest at oblique incidence, and the reflected polarization state is measured in about 0.5 ms. The optical properties of the surface, including athe normal spectral emissivity are then derived. Recently, we have developed a laser polarimetric appartus using this approach and have achieved 1-3% accuracy in emissivity measurements on solid and liquid materials pulseheated over a 0.5 s time period. These successful efforts form the basis of this proposal which seeks to extend the laser polarimetric approach to be capable of 1 MHz measurement bandwidth for application to very rapid pulse-heating experiments which last 50-100 us. The Phase I work will be aimed at establishing: (i) detector and electronics capable of 10 MHz bandwidth, (ii) design of the optics to accommodate specimen motion which occurs during the rapid pulse, (iii) methods to eliminate or minimize the incandescent background from interfering with the laser signal, (iv) methods to accurately measure the magnitude of the laser signal, and (v) testing of the proposed methods at the pulse-heating facility. These key design problems will be investigated, both analytically and experimentally during the Phase I effort. During Phase II, a prototype instrument will be constructed and delivered to NIST for experimentation on pulse-heated materials.