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 pulse with a single-mode laser in response to an electrical pulse;
illuminating the sample with the chirped signal pulse so as to cause the chirped signal pulse to interact with the sample;
detecting a heterodyne modulation caused by interference of the chirped signal pulse and a chirped reference pulse generated with the single-mode laser, 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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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.
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Citations
24 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 pulse with a single-mode laser in response to an electrical pulse; illuminating the sample with the chirped signal pulse so as to cause the chirped signal pulse to interact with the sample; detecting a heterodyne modulation caused by interference of the chirped signal pulse and a chirped reference pulse generated with the single-mode laser, 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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A system for making a spectroscopic measurement of a sample, the system comprising:
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a single-mode laser, in optical communication with the sample, to generate a chirped signal pulse in response to an electrical pulse, the chirped signal pulse interacting with the sample; and a photodetector, in optical communication with the sample, to detect a heterodyne modulation caused by interference of the chirped signal pulse and a chirped reference pulse generated with the single-mode laser, the heterodyne modulation being related to a dispersion and/or an absorption of the sample. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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Specification