Methods and devices for standoff differential Raman spectroscopy decreased risk of explosion
Inventors
Vakhshoori, Daryoosh • Blanchard, Romain • Chen, Peili • Azimi, Masud • Mansuripur, Tobias • Krishnamurthy, Kalyani • Bibby, Arran M. • Huettig, III, Fred R. • Ulu, Gokhan • Rhodes, Greg Vander
Assignees
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Publication Number
US-10488252-B1
Publication Date
2019-11-26
Expiration Date
Abstract
A compact, portable Raman spectrometer makes fast, sensitive standoff measurements at little to no risk of eye injury or igniting the materials being probed. This spectrometer uses differential Raman spectroscopy and ambient light measurements to measure point-and-shoot Raman signatures of dark or highly fluorescent materials at distances of 1 cm to 10 m or more. It scans the Raman pump beam(s) across the sample to reduce the risk of unduly heating or igniting the sample. Beam scanning also transforms the spectrometer into an instrument with a lower effective safety classification, reducing the risk of eye injury. The spectrometer's long standoff range automatic focusing make it easier to identify chemicals through clear and translucent obstacles, such as flow tubes, windows, and containers. And the spectrometer's components are light and small enough to be packaged in a handheld housing or housing suitable for a small robot to carry.
Core Innovation
The invention provides a portable standoff differential Raman spectroscopy system that uses a housing containing visible ranging laser beams and Raman pump lasers operating at first and second wavelengths. The system projects first and second visible ranging beams to respective spots on a sample to provide an indication of range, while focusing the Raman pump beams on or near a surface of the sample. A beam scanner scans the Raman pump beams across a portion of the sample in first and second periods, and a detector detects Raman signals during the Raman periods and ambient illumination transmitted or scattered by the sample during a later period.
The Raman pump lasers emit a first Raman pump beam during a first period based on a flicker period of ambient illumination, and emit a second Raman pump beam at a second wavelength different than the first wavelength during a second period equal to and after the first period. The processor produces a post-processed signature based on the first Raman signal, the second Raman signal, and the ambient illumination signal. The post-processed signature has a lower fluorescent background than the first Raman signal and the second Raman signal.
The disclosure additionally addresses standoff implementation aspects, including integrating a telescope and a beam scanner within the housing, enabling modular hand-held or robot-mounted embodiments, and incorporating monitoring and shutdown based on beam-scanner position monitoring and temperature-based shutdown. It also uses optical and sensing sub-systems such as visible imaging and infrared optical sub-systems for dual-wavelength Raman pump focusing, with a camera acquiring an image of the sample and a spectrometer detecting Raman light scattered by the sample in response to the Raman pump beams.
Claims Coverage
The provided independent claims are directed to dual-wavelength Raman pump operation and processor-determined post-processed Raman signatures with lower fluorescent background, with additional independent claims covering ranging-guided scanning, imaging and Raman detection via optical subsystems, and numerical aperture constraints. Across the independent claims, the main inventive features are dual-wavelength Raman pumping, staged detection, ambient illumination input, and imaging-based system architectures.
Dual-wavelength Raman pumping with ambient illumination post-processing signature
A housing that contains at least one Raman pump laser to emit a first Raman pump beam at a first wavelength and a power level during a first period based on a flicker period of ambient illumination, and to emit a second Raman pump beam at a second wavelength different than the first wavelength during a second period equal to and after the first period; a beam scanner to scan the first Raman pump beam across a portion of the sample during the first period and to scan the second Raman pump beam across the portion of the sample during the second period; a detector to detect a first Raman signal during the first period, a second Raman signal during the second period, and ambient illumination transmitted or scattered by the sample during a third period equal to and after the second period; and a processor to produce a post-processed signature based on the first Raman signal, the second Raman signal, and the ambient illumination signal, wherein the post-processed signature has a lower fluorescent background than the first Raman signal and the second Raman signal.
Ranging-guided scanning Raman system with visible spots
A housing with at least one ranging laser to emit a first visible ranging beam and a second visible ranging beam; a telescope in optical communication with the ranging laser to project the first visible ranging beam to a first spot on a sample and to project the second visible ranging beam to a second spot on the sample, the first spot and the second spot providing an indication of a range to the sample; and a beam scanner to scan the first Raman pump beam and scan the second Raman pump beam across a portion of the sample during their respective periods while the telescope focuses the Raman pump beams on or near a surface of the sample.
Post-processed Raman signature from dual-wavelength Raman pump focusing with NA contrast
A spectroscopy system comprising a housing and an optical assembly, a camera disposed within the housing in optical communication with the optical assembly to acquire an image of a sample with a first numerical aperture; an infrared optical subsystem in optical communication with the optical assembly; at least one Raman pump laser disposed in the housing in optical communication via the infrared optical subsystem to emit a first Raman pump beam at a first wavelength and a second Raman pump beam at a second wavelength different than the first wavelength, wherein the optical assembly and the infrared optical subsystem focus the first Raman pump beam and the second Raman pump beam at a second numerical aperture greater than the first numerical aperture; a spectrometer to detect a first Raman signal and a second Raman signal scattered by the sample in response to the respective Raman pump beams; and a processor to determine a post-processed Raman signature of the sample based on the first Raman signal and the second Raman signal, wherein the post-processed Raman signature has a lower fluorescent background than the first Raman signal and the second Raman signal.
Wide field and higher object-space NA Raman collection with camera imaging
A spectroscopy system comprising a housing and an optical assembly; a camera to acquire an image of a sample via the optical assembly; a laser to emit a first Raman pump beam at a first wavelength and a second Raman pump beam at a second wavelength different than the first wavelength; an actuator to move the optical assembly relative to the sample and/or the sample relative to the optical assembly; and a spectrometer to detect Raman light scattered by the sample in response to the first Raman pump beam and the second Raman pump beam, wherein the camera is configured to image the sample over a field of view greater than 5 mm with an object-space numerical aperture of less than 0.2, and wherein the optical assembly is configured to focus the first Raman pump beam and the second Raman pump beam and collect the Raman light with an object-space numerical aperture of at least 0.3.
The coverage is centered on dual-wavelength Raman pump operation and processor-determined post-processed Raman signatures with lower fluorescent background. The independent claims further define ranging-guided scanning, camera imaging, spectrometer detection, and numerical aperture relationships within the Raman spectroscopy system.
Stated Advantages
Post-processed Raman signature has a lower fluorescent background than the first Raman signal and the second Raman signal.
Documented Applications
Not explicitly described in patent.
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