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-10488260-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 spectrometer that illuminates a sample at a distance from the spectroscopy system and uses Raman pump beam(s) whose scanning behavior is designed to improve eye safety. A beam steering element scans a spot formed by the laser beam across a surface of a sample, with the disclosed purpose of reducing effective radiance at the sample during operation. This approach supports laser-safety classification handling by addressing maximum permissible exposure limits and accessible emission limits under the IEC 60825-1 framework, including downgrading from a first laser safety class to a second laser safety class.
The disclosed system includes a monitoring system operably coupled to the beam steering element and/or to the laser to detect a malfunction of the beam steering system that would cause the laser beam to exceed a maximum permissible exposure for a second laser safety class. In response to detection, the system is configured to at least one of attenuate, redirect, block, or turn off the laser beam. The disclosed monitoring concepts also extend to temperature monitoring, including using infrared thermal emission and threshold-based shutdown, and to Raman-based temperature measurement via Stokes/anti-Stokes and an optional Raman temperature marker.
The invention further addresses robustness and measurement reliability under standoff operation by incorporating scanning strategies and background suppression for ambient-light conditions. The system uses difference Raman operation with two closely spaced Raman pump wavelengths to cancel fluorescence, and ambient-light suppression via interleaved background frames. The invention also includes fail-safe beam-position or malfunction detection concepts, and architecture elements suitable for handheld and robot-mounted operation, with camera-based aiming/image stabilization and synchronized timing for drift robustness.
Claims Coverage
The partial record includes two independent claims (clm-00001 and clm-00013). Both independent claims center on the combination of standoff laser/Raman illumination, scanning using a beam steering element, and a monitoring system that detects beam-steering malfunction that would otherwise cause the beam to exceed a maximum permissible exposure for a specified (lower) laser safety class, followed by attenuation, redirect, block, or turn off actions. Inventive features include standoff illumination geometry, scanning beam-spot across the sample, and malfunction detection tied to maximum permissible exposure compliance with the specified laser safety class.
Standoff laser illumination with a first laser safety class
A spectroscopy system comprising a laser to illuminate a sample at a distance of at least 2 centimeters from the spectroscopy system with a laser beam having first laser safety class.
Beam-spot scanning using a beam steering element
A beam steering element, in optical communication with the laser, to scan a spot formed by the laser beam across a surface of a sample.
Monitoring for beam-steering malfunction exceeding MPE for a second safety class
A monitoring system, operably coupled to the beam steering element and/or to the laser, to detect a malfunction of the beam steering system that would cause the laser beam to exceed a maximum permissible exposure for a second laser safety class.
Safety response to malfunction by attenuating, redirecting, blocking, or turning off
In response to detection of the malfunction, at least one of attenuate, redirect, block, or turn off the laser beam.
Standoff Raman illumination with Raman pump beam wavelength range and power
A spectroscopy system configured to illuminate a sample at a distance of at least 10 centimeters from the spectroscopy system with a Raman pump beam at a wavelength of about 700 nanometers to about 1050 nanometers and with a power of at least 10 mW.
Raman pump spot scanning using a beam-steering element
A beam-steering element to scan a spot formed by the Raman pump beam across a surface of a sample.
Monitoring for beam-steering malfunction exceeding MPE for Class 3R
A monitoring system, operably coupled to the beam steering element and/or to the laser, to detect a malfunction of the beam steering system that would cause the laser beam to exceed a maximum permissible exposure for a Class 3R laser.
Safety response to malfunction for Raman system by attenuating, redirecting, blocking, or turning off
In response to detection of the malfunction, at least one of attenuate, redirect, block, or turn off the laser beam.
Across both independent claims, the claim coverage requires standoff illumination of a sample, scanning of a beam spot across the sample surface using a beam steering element, and a monitoring system that detects beam-steering malfunctions that would cause the laser beam to exceed a maximum permissible exposure for a specified second laser safety class, including Class 3R. Upon detection, the system performs at least one of attenuate, redirect, block, or turn off the laser beam.
Stated Advantages
Improves eye safety by reducing exposure and supporting compliance with maximum permissible exposure and accessible emission limits during standoff operation with scanning.
Mitigates explosion or ignition risk by controlling effective radiance at the sample through scanning of the Raman pump beam(s).
Documented Applications
Handheld standoff spectrometer architecture for illuminating a sample at a distance and performing Raman/difference Raman operation.
Robot-mounted and microscope/macroscope embodiments for standoff differential Raman spectroscopy.
Ambient-light suppression during Raman/difference Raman operation using interleaved background frames.
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