Space agencies like NASA use a variety of novel instruments to study materials beyond Earth’s atmosphere, often requiring more compact and lightweight designs to accommodate the unique environment onboard spacecraft and satellites. NASA researchers currently use hyperspectral imaging in space to analyze a variety of solids and liquids, which requires high spatial resolution and low spectral resolution, but in order to better use imaging spectroscopy to study Earth’s atmosphere from space – or the atmospheres of other planets – there is a need for smaller spectrometers with higher spectral resolution.
Researchers from NASA’s Jet Propulsion Laboratory have now designed new high-dispersion imaging spectrometers with the necessary spectral resolution for such missions, that are just a fraction of the size of conventional hyperspectral imaging instruments. The novel spectrometers include near-infrared (NIR) and long-wave infrared (LWIR) designs with a number of features to both reduce their size and increase their spectral resolution. This includes an immersed grating that reduces the grating size by as much as the refractive index, a Littrow optical configuration that utilizes the same optics before and after the grating, and the use of a grating on a spherical surface, which simplifies the correction of Petzval field curvature.
The NIR instrument has a spectral range of 2302 to 2370 nm, and has 2,048 spectral pixels and 512 spatial pixels at an aperture of f/1.9. The LWIR spectrometer has a spectral range covering 8 to 12 μm, with 1536 spectral pixels and 256 spatial pixels at f/1.7. Light, compact, and relatively inexpensive to produce, the instruments are well-suited for use both in space, and potentially in other hyperspectral imaging applications. With lower spatial resolution but high spatial resolution, the designs could aid in the analysis of atmospheric gases, both from satellites orbiting Earth and potentially onboard crafts sent throughout the galaxy. This research will be presented by James P. McGuire, Jr., deputy manager of the Optics Section at NASA’s Jet Propulsion Laboratory, at the Optica Design and Fabrication Conference, which takes place in Quebec City, Canada from June 4 to 8, 2023.
“This spectrometer provides the same measurement capabilities as conventional designs, but at one tenth the size and mass and at lower cost,” said McGuire. “Smaller, lighter, and cheaper open the door to new applications and markets.”