Direct Emissivity Measurements of Painted Metals for Improved Temperature Estimation During Laser Damage Testing

A database of spectral, temperature dependent emissivities was created for a range of painted aluminum laser damage testing targets with the purpose of improving accuracy in temperature estimates on front and back target surfaces during laser damage tests. Previous temperature estimations were made by fitting an assumed graybody radiance curve to the radiance measured from the back surface via a Telops imaging Fourier transform spectrometer. In this work, spectral emissivity measurements were made using an SOC-100 hemispherical directional reflectometer and Nicolet Fourier transform infrared spectrometer. Of particular interest was a high temperature matte black enamel paint used to coat the rear surfaces of the aluminum samples. Previously, the paint was assumed to have a spectrally at and temperature- invariant emissivity. Collected data showed spectral variance and temperature dependence. Back-surface temperature estimations of laser damage test samples were improved from 25 C to 5 C away from the beam center. At beam center, temperatures exceeded the capabilities of the reflectometer, so a new method was developed using a mid-infrared laser probe to measure temperature dependent reflectance. The new method may be used in future laser damage tests to estimate single-wavelength temperatures up to the target melting point. Accurate temperature measurements in laser damage testing will be helpful in informing a predictive model for future high energy laser weapon engagements