Standoff Raman system (PRIED)
Inventors
Babnick, Robert Dean • VUNCK, Darius • WATERBURY, Robert Douglas • Molner, Timothy • Dottery, Ed
Assignees
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Publication Number
US-10663404-B1
Publication Date
2020-05-26
Expiration Date
Abstract
The present invention relates to a highly portable, highly flexible standard of distance chemical detector such as can be used, for example, for standoff detection of explosives. Aspects of the invention include techniques for portability compactness and ways to diminish influence of fluorescence on Raman spectroscopy. Additional features can include a compact imaging spectrometer, a wirelessly connected smart device for user interface, and an auto-focus/range finder.
Core Innovation
The invention provides a highly portable standoff distance sensing apparatus for chemicals or chemical compounds, using a portable housing that contains an imaging spectrometer, an electrical power source, and a portable light source and receiver. The light source is a collimated illumination source adapted to direct light energy of a predetermined interrogation transmission wavelength along an optical axis to a target surface at standoff distances, while the receiver has a field of view adapted to collect light energy, including reflectance from the illuminated target surface, along the optical axis. The collected reflectance is transported from the optical receiver to the imaging spectrometer through an optical connection comprising a bundle of individual optical fibers with input ends and output ends, where the input ends are generally circularly arranged and the output ends are arranged in a linear array for imaging spectrometer input.
The imaging spectrometer is configured with a fiber optic input to receive transmitted light from the linear array, a collimator, a holographic grating, and a focusing lens that focuses the diffracted light to a 2D detection plane comprising an array of pixels of a digital imager. The configuration is configured to achieve an imaging performance comprising a spot size at the image plane on the order of 100 μm in diameter while providing the components in a centimeter scale housing instead of tens of centimeter scale. This compact imaging spectrometer configuration is used to conduct Raman spectroscopy on light from each fiber at the image plane, enabling detection based on spectral analysis from spatially correlated fiber outputs.
The invention further addresses interpretation of Raman results by comparing spectra from at least two fibers of the linear array from different spatial correlations, and signaling presence of a chemical species of interest when an offset between compared spectra indicates the chemical species of interest at that spatial location. In the same sensing workflow, the offset indicates that other spectra comprises noise or fluorescence, and the apparatus signals presence to a portable user interface via a communication connection to the imaging spectrometer and a display adapted to present or generate information relevant to sensing presence.
In additional apparatus embodiments, a telescope with primary and secondary mirrors along a telescope optical axis is used to focus collected light based on distance between the primary and secondary mirrors, and an optical splitter directs collected light into two paths: one path to the fiber optic bundle for use at the imaging spectrometer and another path to a photo-detector sensitive to the transmission wavelength of the interrogation beam. An actuator adjusts the primary to secondary mirror distance based on measured intensity of the transmission wavelength to automatically focus the telescope, and a position resolver estimates distance to the target surface from sensed distance between the primary and secondary mirrors. The sensing output is therefore generated with telescope focusing control and, in relevant embodiments, a user interface signaling presence of the chemical species of interest.
Claims Coverage
The document includes three independent claims: an apparatus claim using a compact fiber-fed imaging spectrometer with a holographic grating and a portable user interface, a related apparatus claim adding telescope focusing with a wavelength-sensitive photodetector and an actuator via an optical splitter, and a method claim for highly portable standoff Raman sensing that performs Raman spectroscopy per fiber, compares spectra across spatial correlations, and signals a chemical species of interest to a user interface based on spectral offsets and noise/fluorescence discrimination. Across these independent claims, the inventive features are centered on compact imaging spectrometer architecture with fiber-optic bundle mapping to a 2D pixel plane, standoff Raman spectroscopy per fiber at an image plane, and spectrum-offset signaling of a chemical species of interest, with optional telescope focusing and range/distance-related estimation based on measured transmission wavelength intensity and sensed mirror spacing.
Fiber-optic bundle mapping to linear array for spectrometer input
An optical connection between the optical receiver and the imaging spectrometer comprising a bundle of a plurality of individual optical fibers having input ends and output ends, wherein the input ends are generally circularly arranged in a plane transverse to the optical axis and the collected light energy of the optical receiver, each optical fiber roughly carrying a portion of the collected reflectance that is spatially related to the field of view of the optical receiver, and wherein the output ends are arranged in a linear array such that each output end transmits its portion of the field of view of the optical receiver to the imaging spectrometer.
Compact holographic-grating imaging spectrometer with 2D pixel plane
An imaging spectrometer comprising a fiber optic input to receive transmitted light from the linear array at the output ends of the fiber optic bundle, a collimator, a holographic grating which diffracts the light from the collimator, and a focusing lens to focus the diffracted light to a 2D detection plane comprising an array of pixels of a digital imager, configured to achieve an imaging performance comprising a spot size at the image plane on the order of 100 μm in diameter and in a centimeter scale housing instead of tens of centimeter scale.
Portable user interface connected to sensing information from imaging spectrometer
A portable user interface comprising a communication connection to the imaging spectrometer and a display adapted to present or generate information relevant to sensing presence of chemicals or chemical compounds by the imaging spectrometer.
Telescope focusing with optical splitter and transmission-wavelength photodetector
An illumination source and optical receiver further comprising a primary mirror and a secondary mirror comprising a telescope along a telescope optical axis to focus collected light based on distance between the primary and secondary mirror, the collected light including an image of reflectance from the target surface of the interrogation beam at its transmission wavelength, an optical splitter along the optical axis after the primary and secondary mirrors to split received collected light into two paths including one path directed to the input ends of the fiber optic bundle and the other path directed to a photo-detector sensitive to the transmission wavelength of the interrogation beam collected from the target surface.
Automatic adjustment of primary-to-secondary mirror distance based on measured transmission intensity
An actuator in operative connection to at least one of the primary and secondary mirrors operatively connected to the photodetector to automatically adjust primary to secondary mirror distance based on measured intensity of the transmission wavelength of the interrogation beam to automatically focus the telescope.
Raman spectroscopy per fiber and spectral comparison across different spatial correlations
Configuring a compact imaging spectrometer by providing light comprising target surface reflectance through a linear array of a plurality of fiber optics and collimating, diffracting, and imaging the light in an image plane of a digital imager where each fiber optic of the linear array is correlated spatially to a portion of the target surface, and conducting Raman spectroscopy on light from each said fiber optic of the linear array at the image plane, and comparing spectra from at least two said fiber optics of the linear array of the fiber optics from different spatial correlations.
Signaling chemical species of interest using spectral offset indicating noise or fluorescence
Assuming that an offset between the compared spectra indicates a chemical species of interest at that spatial location and that the other spectra comprises noise or fluorescence, and signaling presence of the chemical species of interest to a user interface.
Across the independent claims, the document centers on a portable standoff chemical sensing system that uses an optical receiver coupled through a fiber-optic bundle with circularly arranged inputs and linearly arranged outputs to feed a compact imaging spectrometer with a holographic grating and a 2D pixel array, configured for an imaging spot size on the order of 100 μm in a centimeter scale housing. The method and related apparatus embodiments conduct Raman spectroscopy at the image plane per fiber, compare spectra across different spatial correlations, and signal the presence of a chemical species of interest based on spectral offsets that distinguish it from noise or fluorescence, with optional telescope focusing using an optical splitter, a transmission-wavelength photodetector, and an actuator for automatic focus.
Stated Advantages
An imaging performance comprising a spot size at the image plane on the order of 100 μm in diameter.
The imaging spectrometer is implemented in a centimeter scale housing instead of tens of centimeter scale.
Enables signaling presence of a chemical species of interest by assuming an offset between compared spectra indicates chemical species of interest while other spectra comprises noise or fluorescence.
Automatically focuses the telescope based on measured intensity of the transmission wavelength of the interrogation beam.
Documented Applications
Detecting the presence of chemicals or chemical compounds from a standoff distance.
Explosives detection as the chemical species of interest.
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