Description: The US Naval Research Laboratory has demonstrated a passive, broadband (8.4 to 11.2 µm), LWIR spectrometer with a resolving power of ~500 that has no moving parts, is immune to scene changes and has high throughput. It uses a compression assembly spatial heterodyne spectrsocopy (SHS) interferometer (C-SHS) which employs precision spacers that result in a robust, self-aligning, economical assembly, and enables easy replacement of optical components. The basic principle of spatial heterodyne spectroscopy is similar to a Fourier-transform spectrometer (FTS) in that it also features a beamsplitter which divides the incoming signal into two interferometer arms. However, in SHS, the latter terminate at fixed, tilted gratings that impose a wavelength-dependent tilt onto the diffracted wavefronts. After recombination at the beamsplitter and imaging onto a detector array, a complete interferogram can be recorded without using any moving parts.

Advantages/Features Include:

  • Rugged - no moving parts coupled with a self-aligning, nestled design.
  • High throughput - performance comparable to field-widened FTS but much easier to design and implement field-widening concepts.
  • Excellent on moving platforms and rapidly changing scenes - ideal in applications where jitter is a concern, such as airplanes or ground vehicles and for imaging fast events such as combustion processes or explosions.
  • Reduced manufacturing cost - broadened optical tolerances coupled with simple, flexible design allows C-SHS to enjoy reduced costs and assembly time compared to traditional monolithic SHS.

Applications Include:

  • Satellite remote sensing of the Earth's atmosphere
  • Planetary astronomy
  • Laboratory spectroscopy

References:

  • "Spatial Heterodyne Spectroscopy for Long-Wave Infrared: First Measurements of Broadband Spectra" Optical Engineering 48(10) (2009) 105602.

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