First results from an all-reflection spatial heterodyne spectrometer with broad spectral coverage

Area of Science:

• Optics and Photonics
• Spectroscopy
• Instrumental Science

Background:

• Spatial heterodyne spectroscopy (SHS) offers high resolution but is often limited to narrowband applications.
• Previous SHS designs utilized stable interferometers but faced challenges in broadband operation and spectral ambiguity.
• The development of advanced optical components is crucial for expanding the capabilities of spectroscopic instruments.

Purpose of the Study:

• To report the successful operation of a novel all-reflection, broadband spatial heterodyne spectrometer (SHS).
• To demonstrate the utility of a custom-designed diffraction grating in an SHS instrument.
• To showcase methods for eliminating spectral ambiguity and achieving wide wavelength coverage.

Main Methods:

• Construction of a Mark 2 SHS utilizing a custom 18 grooves/mm diffraction grating with a symmetric blaze.
• Integration of the grating with a plane mirror and a roof mirror to form a stable ring interferometer.
• Implementation of a small mirror tilt to resolve spectral ambiguities and separate diffraction orders.

Main Results:

• The custom grating functions simultaneously as a dispersing element and a beam splitter/combiner.
• Unexpected constructive interference was observed between primary fringes and fringes from extra grating orders.
• Ambiguity between wavelengths above and below blaze was eliminated, and order separation was achieved.
• A factor of four in wavelength coverage was demonstrated within a single CCD frame.

Conclusions:

• The all-reflection, broadband SHS design is a viable and effective spectroscopic tool.
• The custom grating design significantly enhances the performance and versatility of SHS instruments.
• This SHS configuration enables efficient, wide-range spectral measurements in a single acquisition.