Photonic Integrated Circuit TUned for Reconnaissance and Exploration (PICTURE)

The mid-infrared (MIR) spectral range (3-5 μm) is of particular interest for remotely sensing gaseous molecules such as H₂O, CO₂, CH₄, N₂O, CO, NH₃, and many other compounds. The infrared spectra of planets, moons, comets and asteroids are rich in information, including gas composition and surface mineralogy. For example, comets are generally thought to best preserve a compositional record of icy material dating to the formation epoch. Measuring the abundances of constituent ices in comets is inferred through spectroscopic sounding of the molecules released into their atmospheres (i.e., comae) through sublimation that results from solar heating. These molecules absorb incident solar photons and then emit at characteristic IR wavelengths, a process referred to as fluorescence. Planetary atmospheres, like those of comets, exhibit multiple overlapping MIR gas bands arising from molecular vibrations. For the inner planets such as Venus and Mars, atmospheres are dominated by the strong bands of CO₂, while many hydrocarbons are evident on the outer planets.

Under a recent awarded NASA PICASSO program, we are developing a mid-infrared (MIR) Photonic Integrated Circuit TUned for Reconnaissance and Exploration (PICTURE) spectrometer based on integrated photonics technologythat offers ultra-small size, weight and power with non-moving parts and low cost for future planetary missions.

We will describe our progress in developing the PICTURE instrument designed for CO spectroscopic measurements near 4.65 μm. Other spectral regions sense important constituent molecules that will be accessible by re-tuning PICTURE. We will also explore a future instrument concept that exploits the broad wavelength potential of the PICS design to provide spectroscopy spanning the full MIR and longwave IR (LWIR) bands for wide applicability in planetary science, for example to probe CO₂, H₂O, and CH₄, the strongest transitions from which are difficult (CH₄) or impossible (CO₂, H₂O) to detect using Earth-based telescopes. The fully developed PICTURE instrument will provide a cost-effective high-resolution spectrometer for CubeSat and SmallSat, as well as larger satellites.