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Method of performing wavelength modulated differential laser photothermal radiometry with high sensitivity

  • US 8,649,835 B2
  • Filed: 11/17/2010
  • Issued: 02/11/2014
  • Est. Priority Date: 11/17/2009
  • Status: Active Grant
First Claim
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1. A method of operating a wavelength modulated differential photothermal radiometry system for detecting the presence of an analyte within a substance, said method comprising the steps of:

  • providing a first optical beam and a second optical beam, wherein said first optical beam is characterized by a first wavelength and said second optical beam is characterized by a second wavelength, and wherein said first wavelength is selected so that analyte concentrations within a concentration range of interest will cause sufficient absorption of said first optical beam to produce detectable thermal-wave emission, and wherein an absorption coefficient of said analyte at said first wavelength exceeds that at said second wavelength;

    producing a first modulated beam and a second modulated beam by modulating an intensity of said first optical beam and an intensity of said second optical beam, respectively;

    wherein said first modulated beam and said second modulated beam are modulated at a substantially equal modulation frequency, and wherein a phase difference between said first modulated beam and said second modulated beam is approximately 180 degrees;

    providing a reference sample substantially free of analyte;

    directing and substantially overlapping said first modulated beam and said second modulated beams onto said reference sample;

    measuring a first photothermal signal produced by said first modulated beam;

    measuring a second photothermal signal produced by said second modulated beam;

    obtaining a relative photothermal phase between said first photothermal signal and said second photothermal signal;

    controlling a relative intensity of said first modulated beam and said second modulated beam such that a ratio of said first photothermal signal amplitude and said second photothermal signal amplitude is approximately unity; and

    controlling a relative phase of said first modulated beam and said second modulated beam so that said relative photothermal phase is approximately 180 degrees.

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