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

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.