Active remote sensing using a spectral lock-in technique
First Claim
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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Abstract
A system for sensing a characteristic of a sample may include a tunable source configured to emit optical radiation that varies over a wavelength range at a first frequency and a reference source configured to emit optical radiation that varies in amplitude at a second frequency. A science detector may be configured to detect the optical radiation from the tunable source and the reference source after interaction with the sample and generate a science signal. A number of lock-in amplifiers may be respectively configured to generate components of the science signal that are present at the first and second frequencies. A processor may be configured to determine a characteristic of the sample based on the components of the science signal that are present at the first and second frequencies.
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Citations
23 Claims
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1. A system for sensing a sample, comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method of remotely sensing a sample, comprising:
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transmitting a beam of optical radiation toward the sample, the beam including a first tunable source that is swept over a range or wavelengths periodically varying at a first frequency and a second fixed source at a predetermined fixed wavelength that is amplitude modulated at an amplitude varying at a second frequency, the first tunable source and the second fixed source transmitted simultaneously;
detecting the beam of optical radiation after scattering/reflection from the sample to produce a detection signal;
determining a portion of the detection signal that is present at the first frequency;
determining another portion of the detection signal that is present at the second frequency; and
obtaining information about the sample based on the portion of the detection signal and the another portion of the detection signal, wherein the first and second frequencies are not harmonically related to each other and are preselected to reduce inter-modulation between each other. - View Dependent Claims (8, 9, 10, 11)
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12. A system for sensing a characteristic of a sample, comprising:
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a tunable source configured to emit optical radiation that varies over a wavelength range at a first frequency;
a reference source configured to emit optical radiation at a predetermined fixed wavelength that varies in amplitude at a second frequency, the tunable source and the reference source emitted simultaneously;
a science detector configured to detect the optical radiation from the tunable source and the reference source after scattering/reflection from the sample and generate a science signal;
a plurality of lock-in amplifiers respectively configured to generate components of the science signal that are present at the first and second frequencies; and
a processor configured to determine a characteristic of the sample based on the components of the science signal that are present at the first and second frequencies, wherein the first and second frequencies are not harmonically related to each other and are preselected to reduce inter-modulation between each other. - View Dependent Claims (13, 14, 15, 16, 17)
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18. A method of remotely sensing a target, comprising:
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generating a first beam of optical radiation that is wavelength modulated at a first frequency;
generating a second beam of optical radiation that is amplitude modulated at a second frequency, wherein the first and second frequencies are not harmonically related to each other and are preselected to reduce inter-modulation between each other;
combining the first and second beams of optical radiation for transmission to the target;
generating first and second reference signals at the first and second frequencies; and
detecting first radiation and second radiation scattered/reflected from the target using a phase sensitive technique and the first and second reference signals. - View Dependent Claims (19, 20, 21, 22, 23)
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Specification