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Active remote sensing using a spectral lock-in technique

  • US 6,949,734 B2
  • Filed: 04/22/2003
  • Issued: 09/27/2005
  • Est. Priority Date: 04/22/2003
  • Status: Expired due to Term
First Claim
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1. A system for sensing a sample, comprising:

  • a first tunable source configured to emit first optical radiation over a range of wavelengths that is swept at a first frequency;

    a second fixed source configured to emit second optical radiation at a predetermined fixed wavelength that is amplitude modulated at a second frequency, the first tunable source and the second fixed source emitted simultaneously;

    a first detector configured to detect the first and second optical radiation scattered/reflected from the sample and generate a first detection signal;

    a first lock-in amplifier configured to process the first detection signal based on the first frequency to produce a first output signal; and

    a second lock-in amplifier configured to process the first detection signal based on the second frequency to produce a second output signal, wherein the first and second frequencies are not harmonically related to each other and are preselected to reduce inter-modulation between each other.

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