Spatial heterodyne spectrometer

A spatial heterodyne spectrometer (SHS) comprising:

• an input for launching an input beam of light;
• a beam splitter for separating the input beam of light into first and second sub-beams, and directing the first and second sub-beams along first and second paths, respectively;
• a first field-widening prism in the first path for deflecting the first sub-beam;
• a second field-widening prism in the second path for deflecting the second sub-beam;
• a first diffraction grating in the first path for diffracting the first sub-beam into constituent wavelengths, each travelling back to the beam splitter at a different angle;
• a second diffraction grating in the second path for diffracting the second sub-beam into the constituent wavelengths, each travelling back to the beam splitter at a different angle;
• a camera for recording a fringe pattern created by interference of the first and second diffracted sub-beams;
• and
• a controller for determining a spectrum of the input beam from the fringe pattern;
• wherein the first and second diffraction gratings include a same Littrow wavelength providing a heterodyne wavelength creating a zero-path element within the fringe pattern;
• wherein a first average optical path length of the first path is longer than a second average optical path length of the second path;
• wherein the first field-widening prism includes a wider thickness than the second prism providing the longer first average optical path length of the first path;
• and
• wherein the optical path lengths to the first grating and to the second grating, which correspond to a zero path difference, includes a same ratio of air to glass, and a same total thickness.

A spatial heterodyne spectrometer (SHS) comprising:

• an input for launching an input beam of light;
• a beam splitter for separating the input beam of light into first and second sub-beams, and directing the first and second sub-beams along first and second paths, respectively;
• a first field-widening prism in the first path for deflecting the first sub-beam;
• a second field-widening prism in the second path for deflecting the second sub-beam;
• a first diffraction grating in the first path for diffracting the first sub-beam into constituent wavelengths, each travelling back to the beam splitter at a different angle;
• a second diffraction grating in the second path for diffracting the second sub-beam into the constituent wavelengths, each travelling back to the beam splitter at a different angle;
• a camera for recording a fringe pattern created by interference of the first and second diffracted sub-beams;
• and
• a controller for determining a spectrum of the input beam from the fringe pattern;
• wherein the first and second diffraction gratings include a same Littrow wavelength providing a heterodyne wavelength creating a zero-path element within the fringe pattern;
• wherein the first diffraction grating includes a first groove depth at least 10× greater than a second groove depth of the second diffraction grating.