Hyperspectral imaging with a spatial heterodyne spectrometer

Abstract

A hyperspectral imaging apparatus based on a monolithic or free space optical spatial heterodyne spectrometer (SHS) design, array detector, electromagnetic radiation source, and optical collection element is described. The apparatus enables the simultaneous acquisition of spatially isolated Fizeau fringe patterns, each having an encoded light product that is decoded to produce a spectral fingerprint of the interrogated object. Features specific to the SHS, such as a large entrance aperture, large acceptance angle, and no moving parts, enable a variety of optical collection schemes including lens arrays, solid-core and hollow core waveguides, and others. In one example, a microlens array (MLA) is configured with the hyperspectral imaging apparatus to simultaneously image many hundred spatially isolated Fizeau fringe patterns while interrogating an object using an electromagnetic radiation source. Each Fizeau fringe pattern recorded by the array detector is decoded to produce a full Raman or laser-induced breakdown spectroscopy (LIBS) spectrum. Compared to prior art, the hyperspectral imaging apparatus overcomes the primary limitations of needing to trade time resolution for both spectral and spatial data density because the imaging apparatus simultaneously acquires both spectral and special information. Based on the selection and configuration of diffraction gratings, the grating aperture size, Littrow wavelength (i.e., heterodyne wavelength), and optical collection configuration, the apparatus can be tailored to produced low or high spectral resolution with a spectral bandpass that covers a portion or the entire Raman spectral range (up to 4200 cm) and for LIBS as well.