Systems and Methods Using Multi-Wavelength Single-Pulse Raman Spectroscopy

• US 20180136043A1
• Filed: 10/02/2017
• Published: 05/17/2018
• Est. Priority Date: 09/30/2016
• Status: Active Grant

• Current Assignee: University of Maryland Baltimore County (University of Maryland)
• Original Assignee: University of Maryland Baltimore County (University of Maryland)
• Inventors: ARNOLD, BRADLEY, COOPER, CHRISTOPHER, CATALDI, JOHN
• Granted Patent: US 10,078,013 B2
• Time in Patent Office: Days
• CPC Class Codes: G01J 3/0221 the fibers defining an entry slit
• CPC Class Codes: G01J 3/06 Scanning arrangements arrangements for order-selection
• CPC Class Codes: G01J 3/18 using diffraction elements, e.g. grating gratings per se G02B
• CPC Class Codes: G01J 3/2803 using photoelectric array detector
• CPC Class Codes: G01J 3/36 Investigating two or more bands of a spectrum by separate detectors
• CPC Class Codes: G01J 3/44 Raman spectrometry; Scattering spectrometry ; Fluorescence spectrometry
• CPC Class Codes: G02B 5/1814 structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings G02B5/189 takes precedence
• CPC Class Codes: G02B 5/1861 Reflection gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence
• CPC Class Codes: G02B 6/29311 Diffractive element operating in transmission
• CPC Class Codes: G02B 6/32 having lens focusing means positioned between opposed fibre ends with lens being an integral part of the single fibre end G02B6/262
• CPC Class Codes: G02B 6/4215 the intermediate optical elements being wavelength selective optical elements, e.g. variable wavelength optical modules or wavelength lockers G02B6/4246 takes precedence

Abstract

The invention provides methods and apparatus comprising a multi-wavelength laser source that uses a single unfocused pulse of a low intensity but high power laser over a large sample area to collect Raman scattered collimated light, which is then Rayleigh filtered and focused using a singlet lens into a stacked fiber bundle connected to a customized spectrograph, which separates the individual spectra from the scattered wavelengths using a hybrid diffraction grating for collection onto spectra-specific sections of an array photodetector to measure spectral intensity and thereby identify one or more compounds in the sample.

Claims

1. An apparatus for Raman spectra measurement, comprising:

a Nd YAG laser configured to simultaneously output a single pulse of an unfocused beam of photons in two or more excitation wavelengths selected from 213 nm, 266 nm, 532 nm and 1064 nm onto an sample, said laser output ranging from 1-100 mJ per pulse at 10 Hz;

a dichroic Rayleigh filter stack in optical communication with scattered light from the single pulse of unfocused beam of photons incident on the sample;

a singlet lens in optical communication with the dichroic Rayleigh filter stack to focus the scattered light from the sample and couple the scattered light into a proximal end of a stacked fiberoptic bundle;

a spectrograph equipped with a hybrid diffraction grating attached to a distal end of the stacked fiberoptic bundle, said hybrid diffraction grating comprised of a stack of at least two diffraction surfaces, each diffraction surface configured for blaze density and wavelength for one of the two or more excitation wavelengths, each diffraction surface individually angle-tuned and target-adjusted to disperse the scattered light, wherein the spectrograph is configured to to illuminate all of the at least two diffraction surfaces simultaneously;

an array detector system in optical communication with the spectrograph and configured to receive the dispersed scattered light from each diffraction surface onto a specific target section of an array detector, and output a spectral intensity measurement.

2. The apparatus of claim 1, wherein the hybrid diffraction grating is a surface relief reflection grating wherein depth of a surface relief pattern on the grating modulates the phase of the scattered light.

3. The apparatus of claim 1, wherein the hybrid diffraction grating is a volume phase grating wherein the scattered light phase is modulated as it passes through a volume of a periodic phase structure.

4. The apparatus of claim 1, wherein the hybrid diffraction grating comprised of a stack of four diffraction surfaces.

5. The apparatus of claim 1, wherein the hybrid diffraction grating comprised of a stack of eight diffraction surfaces.

6. The apparatus of claim 1, wherein the laser output is 3-9 mJ per pulse at 10 Hz.

7. The apparatus of claim 1, wherein the array detector is selected from a charge-coupled device (CCD), an intensified charge-coupled device (ICCD), an InGaAs photodetector, and a CMOS photodetector.

8. The apparatus of claim 1, wherein the array detector system comprises two or more arrays selected from the group consisting of a CCD, an ICCD, an InGaAs photodetector, and a CMOS photodetector.

9. The apparatus of claim 1, wherein the apparatus is mounted on a vehicle, an unmanned vehicle, a piloted aircraft, a drone aircraft, or a satellite.

10. The apparatus of claim 1, wherein the dichroic Rayleigh filter stack and the singlet lens are mounted within a remote probe housing.

11. The apparatus of claim 1, wherein the laser, the dichroic Rayleigh filter stack, the singlet lens, the spectrograph, and the array detector system are mounted within a single housing.

12. The apparatus of claim 11, wherein the housing is 8-16 cm in height, 50-90 cm in length, and 30-90 cm in width.

13. A method for comparing the Raman spectral intensity measurement of an unknown sample against a library of spectral intensity measurements, comprising the steps:

providing an apparatus according to claim 1;

subjecting the unknown sample to a single unfocused pulse from the Nd YAG laser, wherein said sample has a standoff distance from the laser ranging from 0.30 meters to 20,000 meters;

obtaining a Raman spectral intensity measurement of the unknown sample; and

comparing the Raman spectral intensity measurement of the sample against a library of spectral intensity measurements of known samples.

14. The method of claim 13, wherein the standoff distance from the laser ranges from 0.30 meters to 200 meters.

15. The method of claim 13, wherein the sample is selected from the group consisting of a particle, a powder, a flake, a solid, a liquid, a gas, a plasma, a gel, a foam, and combinations thereof.

16. The method of claim 13, further comprising the step of identifying a match for the spectral intensity measurement of the unknown sample from the spectral intensity measurement of the known samples.

17. The method of claim 16, further comprising the step wherein the identified match is used in a system selected from the group consisting of:

real-time detection of a roadbed explosive;

assessment of diamond quality;

real-time identification of chemical species within a plasma reactor environment;

real-time identification of drilling fluids;

real-time identification of hydrocarbon oil mixtures;

real-time identification of constituents of a process stream at an inlet of a reaction vessel;

real-time characterization of fuel at a fuel dispenser;

real-time monitoring of reacting chemicals in semi-conductor manufacturing;

real-time monitoring of reacting chemicals in pharmaceutical manufacturing;

identification of a horticultural chemical;

identification of a biochemical compound;

identification of a polymer;

authentication of a product;

identification of a pathogen;

identification of a toxin;

real-time detection of a target compound on baggage in an airport;

real-time detection of a target compound on shipping containers and boxes;

real-time detection of a target compound in a water treatment facility;

real-time detection of a target compound in smokestack emissions;

real-time detection of a target compound in waste water;

real-time detection of a target compound in a hazardous spill;

real-time detection of a target compound on a law enforcement forensic sample.