Devices and methods for coherent detection using chirped laser pulses
First Claim
1. A method of making a spectroscopic measurement of a sample, the method comprising:
- generating a chirped signal with at least one single-mode laser;
illuminating the sample with the chirped signal so as to cause the chirped signal to interact with the sample;
detecting a heterodyne modulation caused by interference of the chirped signal and a chirped reference, the heterodyne modulation depending on a dispersion and/or an absorption of the sample; and
determining the dispersion and/or the absorption of the sample from the detected heterodyne modulation, wherein illuminating the sample with the chirped signal pulse comprises;
transmitting the chirped signal through a lens along a first path;
focusing the chirped signal onto a surface;
reflecting the chirped signal back through the lens from the surface; and
directing the chirped signal from the lens along a second path parallel to the first path.
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Abstract
We present here systems and methods for generating a heterodyne signal using the naturally occurring chirp of a pulsed single-mode laser. The electrical square-wave pulse used to drive the laser heats the laser cavity, causing the laser frequency to change or chirp during the emission of the optical pulse. This chirped optical pulse can be split into a chirped signal pulse that interacts with a sample and a chirped reference pulse that interferes with the chirped signal pulse on a detector to produce a heterodyne modulation whose instantaneous phase and amplitude depend on the sample'"'"'s dispersion and absorption, respectively. The chirp is reproducible, so the heterodyne modulation, instantaneous phase, and/or instantaneous amplitude can be average over many measurements, either with multiple pulses from the same laser or multiple pulses from different lasers, each emitting at a different wavelength.
7 Citations
21 Claims
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1. A method of making a spectroscopic measurement of a sample, the method comprising:
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generating a chirped signal with at least one single-mode laser; illuminating the sample with the chirped signal so as to cause the chirped signal to interact with the sample; detecting a heterodyne modulation caused by interference of the chirped signal and a chirped reference, the heterodyne modulation depending on a dispersion and/or an absorption of the sample; and determining the dispersion and/or the absorption of the sample from the detected heterodyne modulation, wherein illuminating the sample with the chirped signal pulse comprises; transmitting the chirped signal through a lens along a first path; focusing the chirped signal onto a surface; reflecting the chirped signal back through the lens from the surface; and directing the chirped signal from the lens along a second path parallel to the first path. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A system for making a spectroscopic measurement of a sample, the system comprising:
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at least one single-mode laser, in optical communication with the sample, to emit a chirped signal along a first path through the sample; a photodetector, in optical communication with the sample, to detect a heterodyne modulation caused by interference of the chirped signal and a chirped reference, the heterodyne modulation depending on a dispersion and/or an absorption of the sample; and a lens, in optical communication with the sample, to focus the chirped signal to a surface, disposed in a focal plane of the lens, that reflects the chirped signal back through the lens along a second path through the sample. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
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19. A method of making a spectroscopic measurement of a sample, the method comprising:
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driving a single-mode laser with a first electrical signal; illuminating the sample with a first chirped signal from the single-mode laser in response to the first electrical pulse; detecting interference of the first chirped signal and a first chirped reference, the interference depending on a dispersion and/or an absorption of the sample and the first chirped signal jittering in phase with respect to the first chirped reference. - View Dependent Claims (20)
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21. A method of making a spectroscopic measurement of a sample, the method comprising:
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emitting a first chirped pulse from a single-mode laser; after emitting the first chirped pulse from the single-mode laser, emitting a second chirped pulse from the single-mode laser; illuminating the sample with the first chirped pulse so as to cause the first chirped pulse to interact with the sample; detecting a heterodyne modulation caused by interference of the first chirped pulse and the second chirped pulse, the heterodyne modulation depending on a dispersion and/or an absorption of the sample; and determining the dispersion and/or the absorption of the sample from the detected heterodyne modulation.
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Specification