Methods and devices for standoff differential Raman spectroscopy with increased eye safety and 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-10921187-B2
Publication Date
2021-02-16
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 is a Raman spectroscopy method that projects a first Raman pump beam at a first wavelength onto a sample and detects a first Raman signal representing a first Raman signature and a first background signature. It further projects a second Raman pump beam at a second wavelength different than the first wavelength and detects a second Raman signal representing a second Raman signature and a second background signature. A post-processed signature is generated based on at least one of the first Raman signal or the second Raman signal, where the post-processed signature has a background lower than or equal to the first background signature.
The method constrains the difference between the first and second pump wavelengths to about 0.25 nm to less than 10 nm, and supports standoff operation where the Raman pump beams are projected from a standoff distance of at least 2 centimeters or at least 10 centimeters. It also incorporates illuminating the sample with one or more visible beams and focuses the visible beams and Raman pump beams to the same position, using telescope geometry defined by an optical axis and a marginal ray to form visible illumination spots on the sample.
The invention additionally enables Raman measurement through a barrier by projecting Raman pump beams through the barrier and onto the sample, with the second Raman pump wavelength shifted from the first by about 0.25 nm to less than 10 nm. The barrier is defined as either a window between the sample and a telescope or as a wall of a reaction vessel holding the sample. In this context, the post-processed signature is again generated with a background lower than or equal to the first background signature.
Claims Coverage
The provided independent claims cover multiple Raman spectroscopy methods that generate a post-processed signature with reduced background using two closely spaced Raman pump wavelengths, including standoff operation, visible-beam/telescope alignment geometry, and projection through a barrier. In total, four independent claims are identified (clm-00001, clm-00040, clm-00043, clm-00046).
Generating a post-processed signature with reduced background from two Raman pump wavelengths
Generating a post-processed signature based on at least one of the first Raman signal or the second Raman signal, the post-processed signature having a background lower than or equal to the first background signature.
Two Raman pump beams with wavelength difference constrained to about 0.25 nm to less than 10 nm
Projecting a second Raman pump beam at a second wavelength different than the first wavelength onto the sample from the standoff distance, wherein a difference between the first wavelength and the second wavelength is from about 0.25 nm to less than 10 nm.
Standoff Raman pump projection at least 2 centimeters with first and second Raman signal background signatures
Projecting a first Raman pump beam at a first wavelength onto a sample from a standoff distance of at least 2 centimeters; detecting a first Raman signal emitted by the sample in response to the first Raman pump beam, the first Raman signal representing a first Raman signature and a first background signature; projecting a second Raman pump beam at a second wavelength different than the first wavelength onto the sample from the standoff distance; detecting a second Raman signal emitted by the sample in response to the second Raman pump beam, the second Raman signal representing a second Raman signature and a second background signature.
Visible illumination using telescope optical axis and marginal ray focused to same position
Focusing the at least one visible beam and the first Raman pump beam to the same position, wherein illuminating the sample with at least one visible beam comprises: illuminating the sample with a first visible beam propagating along an optical axis of a telescope of the Raman spectroscopy system to form a first spot on the sample, and illuminating the sample with a second visible beam propagating along a marginal ray of the telescope of the Raman spectroscopy system to form a second spot on the sample.
Standoff Raman pump projection at least 10 centimeters with visible beam geometry
Projecting a first Raman pump beam at a first wavelength onto a sample from a standoff distance of at least 10 centimeters; detecting a first Raman signal emitted by the sample in response to the first Raman pump beam, the first Raman signal representing a first Raman signature and a first background signature; projecting a second Raman pump beam at a second wavelength different than the first wavelength onto the sample from the standoff distance; detecting a second Raman signal emitted by the sample in response to the second Raman pump beam, the second Raman signal representing a second Raman signature and a second background signature; and generating a post-processed signature based on at least one of the first Raman signal or the second Raman signal, the post-processed signature having a background lower than or equal to the first background signature.
Visible illumination rays from the first Raman pump beam defining two visible spots
Illuminating the sample with a first visible beam propagating along a first ray of the first Raman pump beam to form a first visible spot on the sample, and illuminating the sample with a second visible beam propagating along a second ray of the first Raman pump beam to form a second visible spot on the sample.
Projection through a barrier with second Raman pump wavelength shifted about 0.25 nm to less than 10 nm
Projecting a first Raman pump beam at a first wavelength through a barrier and onto the sample; detecting a first Raman signal emitted by the sample in response to the first Raman pump beam, the first Raman signal representing a first Raman signature and a first background signature; projecting a second Raman pump beam at a second wavelength shifted from the first wavelength by about 0.25 nm to less than 10 nm through the barrier and onto the sample; detecting a second Raman signal emitted by the sample in response to the second Raman pump beam, the second Raman signal representing a second Raman signature and a second background signature; and generating a post-processed signature based on at least one of the first Raman signal or the second Raman signal, the post-processed signature having a background lower than or equal to the first background signature.
Across the independent claims, the central claimed capability is producing a post-processed Raman signature with background no greater than the first background signature by detecting Raman signals from two pump wavelengths separated by about 0.25 nm to less than 10 nm. The claim set further differentiates embodiments by standoff distances (at least 2 cm and at least 10 cm), by visible-beam/telescope ray geometry (optical axis and marginal ray or ray-based spots), and by projecting the Raman pump beams through a barrier (window or reaction-vessel wall).
Stated Advantages
A post-processed signature having a background lower than or equal to the first background signature.
Documented Applications
Raman spectroscopy through a barrier, where the barrier is a window between a sample and a telescope used to project Raman pump beams.
Raman spectroscopy of a sample contained in a reaction vessel, where the barrier is a wall of the reaction vessel holding the sample.
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