Space-based spectrometers are the primary means of identifying the chemical composition,
temperature, and motion of stars, galaxies, and exoplanetary atmospheres. By dispersing light into its component wavelengths and reading the spectral fingerprint, spectroscopy is how we know that, for instance, 91.2% of atoms in the Sun are hydrogen, and that water vapor exists in the atmosphere of an exoplanet 700 light-years away. Yet the accuracy of that measurement depends entirely on the optical system’s ability to separate wavelengths precisely and consistently, and transmissive diffraction gratings are the dispersive optical element at the heart of that design.
Operating in some of the harshest photonic environments, spectrometers must resolve extremely faint signals. The difference between detecting a chemical signature and missing it can come down to spectral resolution: any drift in a diffraction grating’s behavior shifts where wavelengths land on the detector, corrupting spectral data.
Chromatic effects compound this challenge by causing wavelengths to focus at different points on the detector. Stray light then further raises the noise floor, contaminating spectral channels. The solution is precise, stable spectral separation that controls which wavelengths reach the focal plane.
Diffraction gratings are the fundamental means of achieving spectral dispersion in compact optical
systems: separating incident light by wavelength, with each wavelength diffracted at a different angle. Compared to reflective gratings, transmissive designs deliver lower alignment sensitivity – critical in conditions where temperature-induced shifts risk optical element movement – alongside greater throughput, and reduced polarization dependence throughout the full spectral range.
Three characteristics are essential when specifying transmissive diffraction gratings for space spectrometer applications:
● Groove density and uniformity: determine wavefront quality; non-uniform grooves can introduce wavefront errors that distort where wavelengths are mapped on the detector
● Fused silica substrates: have a very low coefficient of thermal expansion (CTE), meaning groove spacing stays stable across the extreme swings of orbit (typically -120º to +120º per orbit cycle).
At Torrent Photonics, our transmissive diffraction gratings use a fused silica substrate, cover a spectral range spanning the visible through near-infrared (NIR), and are engineered for high diffraction efficiency, environmental stability, and repeatable performance.
Long operational durations, for instance, 10-15 years for geostationary Earth orbit and multi-year for low-Earth orbit missions, mean optical components must maintain spectral calibration across thousands of thermal cycles.
Radiation exposure such as charged particles, UV, and vacuum ultraviolet deteriorates material integrity over time, while fused silica offers greater radiation protection than other glass types. Left uncorrected, any drift in grating groove spacing directly translates to spectral calibration drift throughout the mission lifetime.
To discuss transmissive diffraction gratings for your aerospace or scientific instrumentation application, contact our engineering team today.