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Tunable quantum cascade lasers and photoacoustic detection of trace gases, TNT, TATP and precursors acetone and hydrogen peroxide

  • US 20080159341A1
  • Filed: 06/22/2007
  • Published: 07/03/2008
  • Est. Priority Date: 06/23/2006
  • Status: Active Grant
First Claim
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1. A method for obtaining power-maximized single-frequency continuous tuning for a coupled cavity laser system, the steps comprising:

  • a) powering a QCL gain chip to provide a source of multiwavelength laser light at a first power level;

    b) selectively reflecting said multiwavelength laser light with a diffraction grating in a cavity back to said QCL gain chip to select a first laser wavelength;

    c) adjusting a position of said diffraction grating with a piezoelectric translator (PZT) to adjust a distance of said cavity to obtain a maximum output distance for said first laser wavelength and said first power level, said maximum output distance maximizing output of the laser system at said first laser wavelength, said position of said diffraction grating selectively altered on the order of a few wavelengths of said first laser frequency to find said maximum output distance;

    d) making a fine angular displacement step with said diffraction grating to select a new laser wavelength and repeating steps b and c in an ongoing fashion for each new laser wavelength to obtain sufficient data to determine Fabry-Perot mode comb peaks for said QCL gain chip at said first power level over a desired wavelength range;

    e) determining a maximizing power level for said first wavelength by determining a mode comb power level of the QCL gain chip that causes a mode comb wavelength spike of said QCL gain chip to coincide with said first laser wavelength, said maximizing power level achieved by determining a first power level change to shift one of said laser output peaks a first known fractional FP mode distance to determine Δ

    IFSR, selecting a wavelength at which the laser will operate, determining a second fractional FP mode distance said selected wavelength is from a first output peak, and powering said QCL gain chip by a current equal to

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