Method for optimizing detection of inelastically scattered light from a distant target by measuring the target distance using inelastically scattered light
Inventors
Pohl, Kenneth R. • Neglia, Christopher
Assignees
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Publication Number
US-10352863-B1
Publication Date
2019-07-16
Expiration Date
Abstract
The present invention comprises a novel approach for optimizing detection performance of a standoff optical detection system using the inelastic scattering of light from the target and/or inelastic scattering of light from molecules between the light emitting source and the target. This is a useful approach primarily for systems which already employ a pulsed light source, a detector, and a timing mechanism but whose primary function is not the detection of range. Using this methodology removes the need to deploy a secondary device to find range or augments the ability of any included range finder to widen the overall system operating envelope, reliability, and performance.
Core Innovation
The invention relates to standoff inelastic scattering optical spectroscopy chemical analysis systems that optimize detection by using time-dependence of an inelastic scattered light signal from a target and/or surrounding medium. Time-dependent behavior of inelastic scattering is used to select a range of times at which to collect scattered light, to focus optical elements, and/or to adjust mechanical or electrical settings to optimize detection performance at a target distance away from the analysis system.
An analysis system is configured with a Raman spectroscopy system that includes at least a pulsed laser source, an optical transmitter subsystem to direct light toward the target, and an optical receiver subsystem to collect scattered light. Wavelength-dispersive components separate received light based on wavelength, while a time-selective subsystem passes received light to a detector only during selected periods of time, using an intensifier tube with controllable time delay and time width, together with a detector comprising a CCD or CMOS array.
Operation is further optimized by a control subsystem and signal processing system that vary timing over a multiplicity of delay times and store and analyze measured spectra for each delay time to determine an optimal delay time. The optimal delay time is determined based on detecting changes in intensity trends of spectral features, including oxygen Raman features and/or nitrogen Raman features, and also spectral features not attributable to components of air, as the delay time increases from distances closer than the target to distances farther than the target.
Claims Coverage
The partial content provides five independent claims, all directed to optimizing operation of a standoff inelastic scattering (Raman) optical spectroscopy chemical analysis system by exploiting time-dependence to select time windows and determine an optimal delay time. Across the independent claims, the main inventive features include the time-dependent selection of collection times and optimization actions, the specified Raman system architecture, and the use of signal processing over multiple delay times to maximize detected Raman signal at a target distance.
Time-dependence driven optimization of collection times, focus, and settings at target distance
Utilizing time-dependence of an inelastic scattered light signal from the target and/or surrounding medium to select a range of times at which to collect scattered light and/or focus optical elements and/or adjust mechanical or electrical settings to optimize detection performance at the target distance.
Raman system architecture with pulsed laser, wavelength dispersive separation, and time-selective gating
Providing a Raman spectroscopy system incorporating at least a pulsed laser source, an optical transmitter subsystem, an optical receiver subsystem, a wavelength-dispersive component, and a time-selective subsystem that passes received light to a detector only during selected periods of time, wherein the time-selective subsystem comprises an intensifier tube with controllable time delay and time width and the detector comprises a CCD or CMOS array.
Optimal delay determination by storing and analyzing spectra over multiplicity of delay times
Storing and analyzing measured spectra for each of the multiplicity of delay times to determine an optimal delay time to maximize detected Raman signal from the target.
Timing accuracy/precision-controlled delay based on laser emission detection
In which the control subsystem comprises an optical detector which detects the emission of the laser pulse and a programmable delay generator, each with a timing accuracy and precision of 10 nanoseconds or less.
Detecting oxygen or nitrogen spectral-feature intensity decrease to determine optimal delay time
Determining the optimal delay time based on detecting a decrease in the intensity of the spectral features of oxygen at a Raman shift in the range 1503-1603 cm−1 or nitrogen at a Raman shift in the range 2280-2380 cm−1 as the delay time is increased from a delay time corresponding to distances closer than the target to a delay time corresponding to distances farther than the target.
Increase-then-decrease trend in spectral features not attributable to air as delay time increases
Determining the optimal delay time based on detecting an increase and then a decrease in the intensity of spectral features not attributable to components of air as the delay time is increased from a delay time corresponding to distances closer than the target to a delay time corresponding to distances farther than the target.
Combined oxygen/nitrogen decrease and non-air increase-then-decrease to determine optimal delay time
Determining the optimal delay time based on a combination of factors including detecting a decrease in the intensity of spectral features attributable to oxygen and/or nitrogen and/or an increase and then a decrease in the intensity of spectral features not attributable to components of air as the delay time is increased from a delay time corresponding to distances closer than the target to a delay time corresponding to distances farther than the target.
Across the independent claims, the coverage centers on optimizing a standoff inelastic scattering (Raman) optical spectroscopy system by using time-dependence to select collection times and adjust focus and/or settings, by using a Raman architecture with pulsed laser illumination, wavelength-dispersive separation, and time-selective gating of received light to a multielement detector, and by using signal processing over multiple delay times to determine an optimal delay time from specified spectral-intensity trends including oxygen and/or nitrogen features and spectral features not attributable to components of air.
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