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, when 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.
60 Citations
30 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, when 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. 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 from a laser, shaped by a pulse shaper and then replicated in a time delayed manner by a pulse replicator 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. - View Dependent Claims (17, 18, 19, 20, 21, 22)
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23. A method of using a laser system, the method comprising:
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(a) moving at least one of;
a specimen and a security screening structure, relative to the other;(b) emitting a main laser pulse; (c) shaping the laser pulse which is subsequently used to selectively excite a desired Raman vibration through stimulated Raman scattering, when the associated target is present; (d) creating a delayed replica reference pulse from the main pulse, the main and reference pulses being substantially identical in energy and spectrum; (e) focusing the main and reference pulses; (f) 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 by at least one detector; (g) calculating stimulated Raman loss and/or stimulated Raman gain from the collected reflected laser scatter; (h) using the calculated value associated with the reference pulse to reduce undesired contributions from the calculated value; and (i) automatically determining if a substance trace is present, after at least step (f), including detecting the substance which is less than 100 μ
g of a hazardous substance, over at least 1 cm2 area on a fabric surface of the specimen, in a public transportation facility. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30)
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Specification