Hyperspectral imaging with a spatial heterodyne spectrometer
Inventors
Angel, Stanley Michael • Carter, Jerry Chance
Assignees
University of South Carolina • Lawrence Livermore National Security LLC
Publication Number
US-12072290-B2
Publication Date
2024-08-27
Expiration Date
2040-09-11
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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−1) and for LIBS as well.
Core Innovation
The invention provides an optical apparatus and method for hyperspectral imaging using a spatial heterodyne spectrometer (SHS), coupled with an array detector, an excitation source, and an optical collection element. The apparatus allows the simultaneous acquisition of spatially isolated Fizeau fringe patterns, each containing an encoded light product that can be decoded to yield a spectral fingerprint of an interrogated object. This configuration enables capture of both spatial and spectral information in parallel without the need for moving parts in the spectrometer.
Key features include use of a microlens array (MLA) to collect light from different regions of a sample surface and direct it into the SHS, leading to the formation of multiple, distinct Fizeau fringe patterns on the detector array. Each pattern corresponds to a specific region of the object under study, and spectral data is retrieved by decoding these patterns using Fourier transform methods. The system is compatible with Raman spectroscopy and laser-induced breakdown spectroscopy (LIBS), and the optical design may be realized with monolithic or free space configurations and further optimized with elements such as field-widening prisms, additional diffraction gratings, or refractive corrective optics.
The apparatus addresses longstanding limitations of hyperspectral techniques, particularly the tradeoff between time resolution and spectral or spatial data density, by providing simultaneous acquisition of complete hyperspectral datasets. This simultaneous acquisition enables rapid imaging and spectral measurement at multiple sample locations, significantly reducing acquisition times from hours to seconds or minutes, and also decreases degradation of the sample due to reduced exposure to excitation radiation.
Claims Coverage
The independent claim describes an optical apparatus comprising several key inventive features for simultaneous hyperspectral imaging via spatially isolated Fizeau fringe patterns.
Simultaneous acquisition of spatially isolated Fizeau fringe patterns
The apparatus is capable of producing and simultaneously acquiring at least two spatially isolated Fizeau fringe patterns, each representing an encoded light product resulting from the light received from at least one object. This enables the decoding and production of spectral fingerprints for multiple spatial locations at the same time.
Spatial heterodyne spectrometer with beam splitter and diffraction gratings
Includes at least one spatial heterodyne spectrometer constructed to receive at least two light input beams and produce, from each, two corresponding light output beams forming the spatially isolated Fizeau fringe patterns. The spectrometer comprises a beam splitter for directing and recombining light, and one or more diffraction gratings configured to adjust the wavelength of the light product.
Optical collection element for generating multiple input beams
Employs an optical element to receive the light product from the object and produce at least two light input beams directed into the spatial heterodyne spectrometer. This may include microlens arrays, lens arrays, or similar collection optics that spatially resolve signals from different sample regions.
Means for directing excitation source to produce the light product
Incorporates a means for directing at least one excitation source to interact with the object and produce the light product, enabling spectroscopic interrogation such as Raman or LIBS.
Detector array for imaging spatially isolated fringe patterns
Provides at least one detector array and an optical imaging element for simultaneously recording the spatially isolated Fizeau fringe patterns. This arrangement supports the simultaneous acquisition of hyperspectral data from multiple spatial points.
Taken together, these features define a hyperspectral imaging apparatus that enables parallel acquisition of spatially and spectrally resolved data using spatial heterodyne interferometry, an array detector, targeted excitation, and advanced optical collection elements.
Stated Advantages
Enables simultaneous acquisition of spectral and spatial information, overcoming the prior need to trade time resolution for data density.
Reduces image and spectrum acquisition times from hours to seconds or minutes by capturing multiple locations in a single acquisition.
Minimizes sample degradation by reducing repeated or prolonged exposure to excitation sources.
Allows high throughput owing to large entrance aperture and acceptance angle, which increases sensitivity, particularly for low-signal or imaging applications.
Provides robust and stable operation, especially in monolithic configurations, with no moving parts and resistance to vibration.
Achieves approximate doubling of spectral range by using rotated (in contrast to tilted) diffraction grating design, simplifying manufacture and alignment.
Documented Applications
Industrial process analysis, including pharmaceutical manufacturing, materials production, and chemical process feedback and control.
Real-time, off-line, in-situ, on-line, or in-line measurement of chemical constituents in heterogeneous samples.
Spectroscopic imaging using Raman and laser-induced breakdown spectroscopy (LIBS) for mapping identity, concentration, and spatial or temporal changes in samples.
Applications in biology, medicine, materials science, forensics, and chemistry where rapid, robust, and spatially resolved spectral analysis is needed.
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