LASER SYSTEM FOR STANDOFF DETECTION
First Claim
1. A method of using a laser system, the method comprising:
- (a) emitting a main laser pulse;
(b) shaping the laser pulse which is subsequently used to selectively excite a desired Raman vibration through stimulated Raman scattering, if the associated target is present;
(c) creating a delayed replica reference pulse from the main pulse, the main and reference pulses being substantially identical in energy and spectrum;
(d) focusing the main and reference pulses;
(e) collecting diffuse laser scatter such that relative intensities of at least one spectral half of the scatter generated by each of the main and reference pulses are received and identified by at least one photodetector;
(f) calculating stimulated Raman loss and/or stimulated Raman gain from the collected reflected laser scatter;
(g) using the calculated value associated with the reference pulse to reduce undesired contributions from the calculated value associated with specimen absorptivity and texture; and
(h) automatically determining if a substance trace is present, after at least step (e).
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Abstract
A laser system and method employing stimulated Raman scattering using a main laser pulse and a delayed replica reference pulse are provided. A further aspect calculates stimulated Raman loss and stimulated Raman gain from a reflected laser light scatter collected from a fabric or paper specimen. In another aspect, a laser system receives a low energy portion of a spectrum of main and reference laser pulses with a first photodetector, receives a higher energy portion of the spectrum of the main and reference pulses with a second photodetector, and uses a controller to determine a Raman active phonon transfer of energy manifested as an increase in the reflected laser scatter in a lower energy portion of the spectrum and a decrease in a higher energy portion of the spectrum. In yet another aspect, the controller automatically determines if a hazardous particle or substance such as an explosive, is present on a specimen.
6 Citations
37 Claims
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1. A method of using a laser system, the method comprising:
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(a) emitting a main laser pulse; (b) shaping the laser pulse which is subsequently used to selectively excite a desired Raman vibration through stimulated Raman scattering, if the associated target is present; (c) creating a delayed replica reference pulse from the main pulse, the main and reference pulses being substantially identical in energy and spectrum; (d) focusing the main and reference pulses; (e) collecting diffuse laser scatter such that relative intensities of at least one spectral half of the scatter generated by each of the main and reference pulses are received and identified by at least one photodetector; (f) calculating stimulated Raman loss and/or stimulated Raman gain from the collected reflected laser scatter; (g) using the calculated value associated with the reference pulse to reduce undesired contributions from the calculated value associated with specimen absorptivity and texture; and (h) automatically determining if a substance trace is present, after at least step (e). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method of using a laser system, the method comprising, for each laser pulse emitted from a laser toward a specimen:
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(a) replicating a delayed laser pulse from the emitted pulse which is an original laser pulse, the replica and original pulses being substantially identical in energy and spectrum; (b) detecting a transfer of energy occurring when a Raman active mode couples multiple laser frequencies from the original pulse but not the replica pulse, through stimulated Raman scattering at the specimen using only the pulses having a broad bandwidth and without sharp spectral features; (c) receiving a lower energy portion of the spectrum of the original and replica pulses with at least one photodetector; and (d) using a programmable controller to determine a Raman active phonon transfer of energy manifested as an increase in the reflected laser scatter in a lower energy portion of the spectrum and a decrease in a higher energy portion of the spectrum. - View Dependent Claims (17, 18, 19, 20)
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21. A method of using a laser system, the method comprising:
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(a) emitting an initial laser pulse and tuning its phase to enable it to coherently excite a target Raman characteristic, the initial laser pulse being converted into a train of pulses with a specific time delay that substantially matches the Raman characteristic; (b) creating a detuned reference pulse, the initial and reference pulses being substantially identical in energy and spectrum, the detuning assisting in causing the reference pulse to break into a train of pulses with a specific time delay that does not match the desired Raman characteristic; (c) focusing the initial and reference pulses; (d) moving at least one of;
(i) clothing or luggage specimens, having a light scattering surface, and (ii) a security screening structure, relative to the other;(e) selectively exciting the targeted desired Raman characteristic of a particle, if present, on the specimen, through stimulated Raman scattering; (f) diffusely scattering the initial and reference pulses, from the clothing or luggage specimen; (g) using at least one photodetector coupled to the structure to collect the laser light scattered from the clothing or luggage specimen, the photodetector detecting spectral changes in the reflected laser light; (h) using a programmable controller to automatically calculate at least one of stimulated Raman loss or stimulated Raman gain from the collected laser light; and (i) using the programmable controller to automatically determine if a trace, being less than 100 μ
g of a harmful substance, is present over at least 1 cm2 area on the specimen in a public transportation facility using 0.5 Watt or less of laser power. - View Dependent Claims (22, 23)
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24. Software stored in non-transient computer memory, the software comprising:
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a first set of instructions adapted to cause a laser pulse to be emitted, shaped and then replicated in a time delayed manner such that a primary and a secondary laser pulse, having substantially identical energies and spectra, are targeted onto a specimen at least 0.5 m away; a second set of instructions adapted to receive signals associated with at least one spectral half of light diffusely scattered from the specimen, associated with each of the primary and secondary pulses, which are detected by at least one photodetector; a third set of instructions adapted to calculate at least one of stimulated Raman loss or stimulated Raman gain from the detected scattered light; a fourth set of instructions adapted to minimize at least one of;
distortions and background noise, in the detected reflected light by comparing values associated with the primary and secondary pulses, which have a different spectral phase; anda fifth set of instructions adapted to determine if a harmful substance trace is present on the specimen within three seconds of operation of the first set of instructions.
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25-33. -33. (canceled)
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34. A laser system comprising:
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a laser emitting a main laser pulse with an energy greater than 30 nJ; a replicator creating a duplicate reference pulse from the main pulse, delayed in time, but otherwise the energies and spectra are substantially identical; an optic introducing dispersion to the main and reference pulses; a modulator adding additional dispersion to every other pulse in order to create a main train of subpulses and a reference train of subpulses; a lens focusing the main and reference trains of subpulses; at least one photodetector which senses spectral changes in scatter originating from the main and the reference trains of subpulses; and a security scanning structure upon which the laser and photodetectors are mounted; and a programmable controller receiving signals from the photodetector for use in determining a Raman active phonon transfer of energy manifested as a spectral change in the scattered light.
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- 35. (canceled)
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37-48. -48. (canceled)
Specification