Tunable Quantum Cascade Lasers and Photoacoustic Detection of Trace Gases, TNT, TATP and Precursors Acetone and Hydrogen Peroxide
First Claim
1. A laser illumination system for providing laser light over a multiwavelength spectrum, comprising:
- a two-segment QCL chip laser light source emitting light, said chip having an approximately flat saturation region and being powered by a current;
said source powered by a current selected according to the equation
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Abstract
Methods and apparatus for broad tuning of single wavelength quantum cascade lasers and the use of light output from such lasers for highly sensitive detection of trace gases such as nitrogen dioxide, acetylene, and vapors of explosives such as trinitrotoluene (TNT) and triacetone triperoxide (TATP) and TATP'"'"'s precursors including acetone and hydrogen peroxide. These methods and apparatus are also suitable for high sensitivity, high selectivity detection of other chemical compounds including chemical warfare agents and toxic industrial chemicals. A quantum cascade laser (QCL) system that better achieves single mode, continuous, mode-hop free tuning for use in L-PAS (laser photoacoustic spectroscopy) by independently coordinating gain chip current, diffraction grating angle and external cavity length is described. An all mechanical method that achieves similar performance is also described. Additionally, methods for improving the sensor performance by critical selection of wavelengths are presented.
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Citations
18 Claims
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1. A laser illumination system for providing laser light over a multiwavelength spectrum, comprising:
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a two-segment QCL chip laser light source emitting light, said chip having an approximately flat saturation region and being powered by a current; said source powered by a current selected according to the equation
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2. A method for leveling power for a tunable EGC-QCL system, the steps comprising:
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determining a current saturation peak for a first QCL gain chip system; determining a first current periodicity value that shifts a Fabry-Perot comb mode of said first QCL gain chip system one free spectral range; setting a first injection current to a current value near said saturation peak plus or minus approximately 1 to 2 first current periodicity values; and
shifting said first injection current by said first current periodicity value to maintain said first injection current within approximately 1 to 2 first current periodicity values of said current saturation peak;
wherebysuch that said first injection current can be adjusted to selectably shift said Fabry-Perot comb mode with diminished effect upon laser power output of said first QCL gain chip system;
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3. A method for leveling power for a tunable EGC-QCL system, the steps comprising:
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determining a current saturation peak for a QCL gain chip system having first and second segments optically linked to one another; determining a first current periodicity value that shifts a Fabry-Perot comb mode of said QCL gain chip system one free spectral range; operating said first segment with said first injection current on one side of said current saturation peak; and operating said second segment with a second injection current on a second side of said current saturation peak; and maintaining a current difference between said first and second injection currents, said current difference selected from the group consisting of; a) a constant current difference of said first current periodicity value between said first and second injection currents such that a total power output is maintained relatively constant while enabling changes in said first and second injection currents to selectably shifting a refractive index of said QCL gain chip system; and b) a varying current difference between said first and second injection currents such that selected power output for several wavelengths of the tunable EGC-QCL system are leveled with wavelengths having stronger outputs being diminished while wavelengths having weaker outputs being augmented; and c) combinations thereof;
wherebysaid first and second injection currents may be selectably adjusted to shift a Fabry-Perot comb mode of said QCL gain chip system.
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4. A laser illumination system for providing laser light over a multiwavelength spectrum, comprising:
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a multiwavelength laser light source emitting light; a wavelength-selective reflector in optical communication with said source; a translator coupled to said reflector, said translator displacing said reflector according to a first signal and controlling a distance between said reflector and said source; and a rotation stage coupled to said translator, said rotation stage rotating said reflector according to a second signal and controlling an angle between said reflector and said source;
wherebysingle mode, continuous, mode-hop free tuning is provided by the laser illumination system. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12)
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13. A method for leveling power for a tunable EGC-QCL system, the steps comprising:
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determining a current saturation peak for a first QCL gain chip system; determining a first current periodicity value that shifts a Fabry-Perot comb mode of said first QCL gain chip system one free spectral range; and setting a first injection current to a current value near said saturation peak plus or minus approximately 1 to 2 first current periodicity values;
whereby said first injection current can be adjusted to selectably shift said Fabry-Perot comb mode with diminished effect upon laser power output of said first QCL gain chip system. - View Dependent Claims (14, 15, 16, 17, 18)
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Specification