NASA EPSCoR: R3 E-007: Optical Transmissivity of Windows Coated by Laser-Ablation Products

This project is for investigating the optical transmissivity of radiometer windows as pyrolysis and ablation products are deposited on their surfaces. NASA’s space mission vehicles such as Mars 2020 carry radiometers as part of their instrumentation suite. Due to high- temperature and low-pressure conditions during entry, pyrolysis and ablation products such as phenolic-impregnated carbon ablator (PICA) can be deposited on the radiometer windows, resulting in significantly reduced transmissivity. The reduction in transmissivity can lower the signal level reaching the radiometer sensing element. Hence, it is imperative to systematically investigate how optical transmissivity is affected as pyrolysis and ablation products are deposited. For example, some pyrolysis and ablation products may affect only a limited range of spectral wavelengths of optical windows, whereas other products may deteriorate the overall transmissivity. Using a pulsed laser ablation technique, we will evaporate samples such as PICA and collect their ablation product on optical windows. Compared to large-scale ArcJet or Plasma torch experiments, our table-top experimental approach can economically create pyrolysis and ablation products in systematically controlled high-temperature and low-pressure conditions. The outcome of this project will also help find technical solutions to prevent or mitigate the deposition problem of pyrolysis and ablation products. 1