Dual pulse single event Raman spectroscopy
View Patent ↗Systems and methods for performing Raman spectrometry wherein a Raman spectroscopy system is mounted on a vehicle for on the move contaminant analysis. The system is configured to interrogate a target with a laser at a predetermined pulse repetition frequency (PRF), wherein during each PRF cycle, defined as 1/PRF, the laser is dual pulsed at a first wavelength and at a second wavelength. Raman spectra are collected and used to identify the target by matching a Raman signature with a given collected Raman spectra.
1. A mobile, stand-off, single-event, dual pulse, on-the-move Raman spectrometry system, comprising:
a laser module that is configured to generate a first wavelength of energy and a second wavelength of energy, wherein the first and second wavelengths of energy are directed, at substantially the same time, along an axis and through free space to a target substance, wherein the first and the second wavelengths of energy are pulsed sequentially with a temporal spacing of ΔT;
a telescope for collecting a spectral energy pattern that returns along the axis and that results from interaction of the target substance with the first and second wavelengths of energy;
a charge coupled device for receiving a collected spectral energy pattern from the telescope; and
an analysis module for analyzing the collected spectral energy pattern and matching the collected spectral energy pattern to a known spectral energy pattern,
wherein ΔT is less than about 10 μS, and
wherein the laser module, telescope and analysis module are mounted on a vehicle and operate while the vehicle is in motion.
2. The system of claim 1 , wherein the first and second wavelengths of energy are controllable.
3. The system of claim 2 , wherein the first and second wavelengths of energy are controllable based on field conditions.
4. The system of claim 1 , wherein the second wavelength of energy is different from the first wavelength of energy.
5. The system of claim 1 , wherein the Raman spectrometry system includes an imaging apparatus and ΔT is set to be consistent with the following equation:
LIB lifetime<ΔT<aperture time of the imaging apparatus
where LIB is laser induced breakdown.
6. The system of claim 5 , wherein the imaging apparatus comprises a charge coupled device (CCD).
7. The system of claim 1 , wherein the wavelengths of the first and the second wavelengths of energy are, respectively, 248 nm and 250 nm.
8. The system of claim 1 , wherein the laser module comprises a single laser configured to provide both the first and the second wavelengths of energy.
9. The system of claim 1 , wherein the first pulse is of sufficient power to photo bleach a background around the target substance.
10. A method for performing Raman spectrometry, comprising:
operating a vehicle having mounted thereon a Raman spectroscopy system, the Raman spectroscopy system comprising a laser, collection optics and an imaging apparatus;
interrogating a target with the laser at a predetermined pulse repetition frequency (PRF), wherein during each PRF cycle, defined as 1/PRF, the laser is dual pulsed at different wavelengths sequentially and spaced apart by a time ΔT that is less than about 10 μs;
collecting Raman spectra, using the collection optics, during each PRF cycle; and
identifying the target by matching a Raman signature with a given collected Raman spectra or series of Raman spectra.
11. The method of claim 10 , wherein the PRF is about 25 Hz.
12. The method of claim 10 , wherein ΔT is set to be consistent with the following equation:
LIB lifetime<ΔT<aperture time of the imaging apparatus
where LIB is laser induced breakdown.
13. The method of claim 10 , further comprising dynamically controlling at least one of the wavelengths.
14. The method of claim 13 , further comprising dynamically controlling the at least one of the wavelengths based on operating or field conditions.
15. The method of claim 10 , further comprising photo bleaching a background around the target substance.
16. A method for performing Raman spectrometry, comprising:
operating a vehicle having mounted thereon a Raman spectroscopy system, the Raman spectroscopy system comprising a laser, collection optics and an imaging apparatus;
interrogating a target with the laser at a predetermined pulse repetition frequency (PRF), wherein during each PRF cycle, defined as 1/PRF, the laser is dual pulsed sequentially at a first wavelength and at a second wavelength, wherein the second wavelength is different from the first wavelength;
collecting Raman spectra, using the collection optics, during each PRF cycle by collecting Raman spectra resulting from irradiation of the target by both the first wavelength and the second wavelength; and
identifying the target by matching a Raman signature with a given collected Raman spectra,
wherein a difference in time, ΔT, between the sequentially dual pulsed first wavelength and the second wavelength is less than about 10 μs.
17. The method of claim 16 , wherein ΔT is set to be consistent with the following equation:
LIB lifetime<ΔT<aperture time of the imaging apparatus
where LIB is laser induced breakdown.
18. The method of claim 16 , further comprising dynamically controlling at least one of the first wavelength and the second wavelength.
19. The method of claim 18 , further comprising dynamically controlling the at least one of the first wavelength and the second wavelength based on operating or field conditions.
20. The method of claim 16 , further comprising photo bleaching a background around the target substance.