Gas-Phase Plume from Laser-Irradiated Fiberglass-Reinforced Polymers via Imaging Fourier Transform Spectroscopy

Abstract

Emissive plumes from laser-irradiated fiberglass-reinforced polymers (FRP) were investigated using a mid-infrared imaging Fourier transform spectrometer, operating at fast framing rates (50 kHz imagery and 2.5 Hz hyperspectral imagery) with adequate spatial (0.81 mm2 per pixel) and spectral resolution (2 cm−1). Fiberglass-reinforced polymer targets were irradiated with a 1064 nm continuous wave neodymium-doped yttrium aluminum garnet (Nd:YAG) laser for 60 s at 100 W in air. Strong emissions from H2O, CO, CO2, and hydrocarbons were observed between 1800 and 5000 cm−1. A single-layer radiative transfer model was developed for the spectral region from 2000 to 2400 cm−1 to estimate spatial maps of temperature and column densities of CO and CO2 from the hyperspectral imagery. The spectral model was used to compute the absorption cross sections of CO and CO2 using spectral line parameters from the high-temperature extension of the HITRAN. The analysis of pre-combustion spectra yields effective temperatures rising from ambient to 1200 K and suddenly increasing to 1515 K upon combustion. The peak signal-to-noise ratio for a single spectrum exceeds 60:1, enabling temperature and column density determinations with low statistical error. For example, the spectral analysis for a single pixel within a single frame yields an effective temperature of 1019 ± 6 K, and CO and CO2 column densities of 1.14 ± 0.05 and 1.11 ± 0.03 × 1018 molec/cm2, respectively. Systematic errors associated with the radiative transfer model dominate, yielding effective temperatures with uncertainties of > 100 K and column densities to within a factor of 2–3. Hydrocarbon emission at 2800 to 3200 cm−1 is well correlated with CO column density.