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 • Vander Rhodes, Greg
Assignees
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Publication Number
US-11300448-B2
Publication Date
2022-04-12
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 compact portable standoff differential Raman spectroscopy in which a Raman pump beam is scanned over a sample while maintaining standoff operation to improve eye safety and reduce explosion/ignition risk. It improves laser safety performance by reducing retinal radiance and thermal hot spots through effective scan area expansion, and supports laser safety classification downgrading. The approach also enables long standoff ranges with focusing based on measured range to the sample.
The invention generates a post-processed Raman signature using differential Raman concepts with two closely spaced excitation wavelengths and interleaved ambient light or background frames. By estimating and combining Raman signatures from the two pump wavelengths, and optionally incorporating ambient light, the method reduces fluorescence and ambient artifacts in the resulting signature. The Raman pump beam and ranging or telescope optics are integrated so that range measurement informs focusing before Raman signal measurement.
The invention further includes fail-safe monitoring and sample thermal monitoring associated with scanning. It monitors the Raman pump beam scanning position using tip-tilt mirror monitoring and can shut off the system if a scan malfunction is detected, and it monitors sample temperature using infrared thermometry and Raman Stokes/anti-Stokes temperature markers. System embodiments described include handheld, robot-mounted, and macroscope configurations, supported by camera stabilization and timing synchronization with the scan period and ambient light flicker.
Claims Coverage
The document provides two independent methods with distinct inventive coverage: range measurement with automatic focusing for two Raman pump wavelengths followed by generation of a post-processed signature with a fluorescent-background change, and telescope-based distance detection using two ranging spots on the optical axis and a marginal ray with telescope focus adjustment prior to Raman signal measurement.
Automatic focusing of a Raman pump beam based on range
Measuring a range from a Raman spectroscopy system to the sample; automatically focusing a Raman pump beam emitted by the Raman spectroscopy system based on the range to the sample; detecting a Raman signal from the sample in response to the Raman pump beam; estimating a Raman signature of the sample based on the Raman signal.
Post-processed signature using two Raman pump beams and reduced fluorescent background
Automatically focusing another Raman pump beam emitted by the Raman spectroscopy system at a wavelength different than a wavelength of the Raman pump beam to the spot on or below the surface of the sample based on the range; detecting another Raman signal from the sample in response to the other Raman pump beam; estimating another Raman signature of the sample based on the other Raman signal; generating a post-processed signature based on the Raman signature and the other Raman signature, the post-processed signature having a fluorescent background change.
Two-spot distance measurement using telescope optical axis and marginal ray spots
Illuminating the sample, via a telescope, with a first ranging beam propagating along an optical axis of the telescope to form a first spot on the sample; illuminating the sample, via the telescope, with a second ranging beam propagating along a marginal ray of the telescope to form a second spot on the sample; detecting a distance between the first spot and the second spot.
Telescope focus adjustment based on detected inter-spot distance before Raman signal measurement
Adjusting a focus of the telescope based on the distance between the first spot and the second spot; illuminating the sample, via the telescope, with a Raman pump beam propagating along the optical axis of the telescope; and measuring a Raman signal scattered by the sample in response to the Raman pump beam.
Overall, the claim coverage centers on range-informed automatic focusing combined with estimating Raman signatures from multiple pump wavelengths and generating a post-processed signature with a changed fluorescent background, and telescope-based two-spot ranging using optical-axis and marginal-ray beams followed by telescope focus adjustment and Raman signal measurement.
Stated Advantages
Improves eye safety by reducing retinal radiance and thermal hot spots through scanning Raman pump beams over a sample to effectively increase scan area and enabling laser safety classification downgrading.
Reduces explosion/ignition risk.
Reduces fluorescent background and ambient artifacts in the post-processed Raman signature.
Supports long standoff range operation with focusing based on range measurement.
Provides fail-safe monitoring including scan position monitoring and automatic shutoff if scan malfunction is detected.
Enables sample temperature monitoring using infrared thermometric detector and Raman Stokes/anti-Stokes temperature measurement markers to support temperature-threshold-based laser attenuation/shutdown.
Documented Applications
Compact portable standoff differential Raman spectroscopy for eye-safe operation and reduced explosion/ignition risk at standoff range.
Handheld Raman system configurations, robot-mounted Raman system configurations, and macroscope embodiments for performing standoff Raman spectroscopy.
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