US-12618714-B2 - Raman spectroscopy system with standoff detection

US12618714B2US 12618714 B2US12618714 B2US 12618714B2US-12618714-B2

Abstract

In one embodiment, a system includes a pump light source configured to produce a pump beam of light at a pump frequency and a Stokes light source configured to produce a Stokes beam of light at a Stokes frequency. The pump and Stokes frequencies are offset by a frequency offset Ω, and the pump and Stokes beams are directed to an object. The system further includes one or more optical elements configured to collect a Raman signal produced by coherent Raman scattering of the pump and Stokes beams of light at the object. The system also includes an optical receiver configured to detect the Raman signal. The optical receiver includes a probe light source configured to produce a probe beam of light at a probe frequency and an optical detector configured to coherently mix the Raman signal with the probe beam of light to produce a corresponding photocurrent signal.

Inventors

Joseph G. LaChapelle
Roger S. Cannon

Assignees

Haemanthus, Inc.

Dates

Publication Date: 20260505
Application Date: 20240830

Claims (20)

1 . A system comprising: a pump light source configured to produce a pump beam of light at a pump frequency; a Stokes light source configured to produce a Stokes beam of light at a Stokes frequency, wherein the pump and Stokes frequencies are offset by a frequency offset Ω, and wherein the pump and Stokes beams are directed to an object; one or more optical elements configured to collect a Raman signal produced by coherent Raman scattering of the pump and Stokes beams of light at the object; an optical receiver configured to detect the Raman signal, the optical receiver comprising: a probe light source configured to produce a probe beam of light at a probe frequency; an optical detector configured to coherently mix the Raman signal with the probe beam of light to produce a corresponding photocurrent signal; and an electronic circuit configured to produce a digital output signal corresponding to the photocurrent signal; and a processor configured to determine a characteristic of the photocurrent signal based on the digital output signal.
2 . The system of claim 1 , wherein the object is located external to the system.
3 . The system of claim 2 , wherein the object is located between 1 meter and 10 kilometers from the system.
4 . The system of claim 2 , wherein the optical elements comprise an optical scanner configured to direct the pump and Stokes beams of light to the object.
5 . The system of claim 2 , wherein the pump and Stokes beams of light are directed to the object by an operator of the system.
6 . The system of claim 2 , wherein the processor is further configured to select a pulse energy or an optical power of the pump beam of light or the Stokes beam of light based on a distance from the system to the object, wherein the selected pulse energy or optical power is higher for larger values of distance.
7 . The system of claim 1 , further comprising a lidar system, wherein: the object is located external to the system; the lidar system is configured to scan a region around the system and determine a location of the object.
8 . The system of claim 7 , wherein: prior to the system producing the pump and Stokes beam of light, the lidar system is configured to scan the region around the system and determine the location of the object; and after the location of the object has been determined, the optical elements are further configured to direct the pump and Stokes beams of light to the object based on the determined location of the object.
9 . The system of claim 7 , wherein: the lidar system is further configured to classify one or more objects in the region around the system, the one or more objects comprising the object, wherein the object is classified as an object of interest; and the optical elements are further configured to direct the pump and Stokes beams of light to the object in response to the object being classified as an object of interest.
10 . The system of claim 1 , wherein: the object is located external to the system; prior to producing the pump and Stokes beams of light, the pump light source or the Stokes light source is configured to produce a lidar output beam comprising a plurality of output pulses of light; the optical elements comprise an optical scanner configured to scan the lidar output beam across a region around the system; the optical receiver is further configured to detect a lidar input beam comprising input pulses of light, each input pulse of light including scattered light from one of the output pulses of light, wherein: the optical detector is further configured to produce a pulse of photocurrent corresponding to an input pulse of light, the input pulse of light including light from a corresponding output pulse of light scattered from the object; and the electronic circuit is further configured to produce a digital output signal that corresponds to the pulse of photocurrent; and the processor is further configured to determine a location of the object based on the digital output signal that corresponds to the pulse of photocurrent, wherein determining the location of the object comprises determining a distance to the object based on a time of arrival of the input pulse of light.
11 . The system of claim 10 , wherein: the processor is further configured to classify one or more objects in the region around the system based on one or more scans of the lidar output beam across the region, wherein the one or more objects comprise the object, and the object is classified as an object of interest; and the pump and Stokes beams of light are directed to the object in response to the object being classified as an object of interest.
12 . The system of claim 10 , wherein, after the location of the object has been determined, the optical scanner is further configured to direct the pump and Stokes beams of light to the object based on the determined location of the object.
13 . The system of claim 10 , wherein determining the distance to the object comprises determining a difference between the time of arrival of the input pulse of light and a time of emission of the corresponding output pulse of light.
14 . The system of claim 10 , wherein each of the output pulses of light has a duration between 0.1 nanosecond and 10 nanoseconds and a pulse energy between 1 microjoule and 1 millijoule.
15 . The system of claim 10 , wherein: the probe light source is further configured to produce a local-oscillator (LO) beam of light; and the optical detector is further configured to coherently mix the LO beam of light and the input pulse of light to produce the pulse of photocurrent.
16 . The system of claim 15 , wherein the processor is further configured to determine, based on the digital output signal that corresponds to the pulse of photocurrent, that the input pulse of light includes light from the corresponding output pulse of light.
17 . The system of claim 1 , wherein: the object is located external to the system; the pump light source or the Stokes light source is further configured to produce an output pulse of light that is directed to the object; the optical receiver is further configured to detect an input pulse of light that includes light from the output pulse of light scattered from the object, wherein: the optical detector is further configured to produce a pulse of photocurrent corresponding to the input pulse of light; and the electronic circuit is further configured to produce a digital output signal that corresponds to the pulse of photocurrent; and the processor is further configured to determine a distance to the object based on the digital output signal that corresponds to the pulse of photocurrent, wherein determining the distance to the object comprises determining a time of arrival of the input pulse of light.
18 . The system of claim 17 , wherein: the probe light source is further configured to produce a local-oscillator (LO) beam of light; and the optical detector is further configured to coherently mix the LO beam of light and the input pulse of light to produce the pulse of photocurrent.
19 . The system of claim 1 , wherein: the object is located external to the system; the Stokes beam of light comprises a Stokes pulse of light, wherein the Raman signal is produced by coherent Raman scattering of the pump beam of light and the Stokes pulse of light; the optical receiver is further configured to detect an input pulse of light, the input pulse of light including light from the Stokes pulse of light scattered from the object, wherein: the photocurrent signal produced by the optical detector comprises a pulse of photocurrent corresponding to the input pulse of light; and at least a portion of the digital output signal produced by the electronic circuit corresponds to the pulse of photocurrent; and the processor is further configured to determine a distance to the object based on the portion of the digital output signal that corresponds to the pulse of photocurrent.
20 . The system of claim 1 , wherein: the object is located external to the system; the pump beam of light comprises a pump pulse of light, wherein the Raman signal is produced by coherent Raman scattering of the pump pulse of light and the Stokes beam of light; the system further comprises: an optical beamsplitter configured to direct an input pulse of light to a pump detector, the input pulse of light including light from the pump pulse of light scattered from the object; and the pump detector, wherein the pump detector is configured to produce a pulse of photocurrent corresponding to the input pulse of light; and the processor is further configured to determine a distance to the object based on a time of arrival of the input pulse of light.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of U.S. patent application Ser. No. 18/762,412, filed 2 Jul. 2024, issued as U.S. Pat. No. 12,203,862, which claims the benefit, under 35 U.S.C. § 119(e), of U.S. Provisional Patent Application No. 63/560,521, filed 1 Mar. 2024, the entireties of which are incorporated by reference herein. TECHNICAL FIELD This disclosure generally relates to Raman spectroscopy systems and methods that use Raman scattering. BACKGROUND Raman spectroscopy is an optical measurement technique that can be applied to the study of molecular dynamics (e.g., to investigate vibrational and rotational states of molecules). Molecules typically exhibit molecular vibrations with frequencies ranging from less than 10 terahertz (THz) to approximately 100 THz, which corresponds to wavenumbers of approximately 300 cm−1 to 3000 cm−1 and wavelengths of approximately 30 to 3 micrometers (μm). Raman spectroscopy is based on the inelastic scattering of photons (referred to as Raman scattering) that occurs when light interacts with molecular vibrations or phonons in a sample. Raman scattering causes the energy (or equivalently, the frequency) of scattered light to be shifted, and this shift in energy can provide information about the vibrational modes of molecules in the sample. Raman spectroscopy can be used in various chemical sensing applications to identify molecular components in a sample. Since many molecules exhibit a unique Raman scattering spectrum, the spectrum of Raman-scattered light produced when light interacts with a sample can serve as a fingerprint to sense or identify various molecular species within the sample. A sample illuminated with light may produce Raman scattered light at different wavelengths from the illumination light, and measurement of the spectrum of the Raman scattered light is typically performed in the optical domain. For example, the spectrum of Raman scattered light can be measured using an optical spectrometer which separates the Raman scattered light into its optical frequency components using a diffractive element, such as a diffraction grating. BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1-2 each illustrates an example Raman spectroscopy system. FIGS. 3-4 each illustrates an example Raman signal produced by coherent Raman scattering. FIG. 5 illustrates the example Raman signal of FIG. 4 along with a probe beam. FIG. 6 illustrates an expanded view of a portion of the Raman signal of FIG. 5. FIG. 7 illustrates an expanded view of a portion of the Raman signal of FIG. 6. FIGS. 8-10 illustrate time-domain and frequency-domain plots of an example electronic signal resulting from coherent mixing of the Raman signal and probe beam of FIG. 7. FIG. 11 illustrates an example Raman signal that is measured at multiple probe frequencies. FIG. 12 illustrates an example Raman spectrum corresponding to the Raman signal of FIG. 11. FIG. 13 illustrates another example Raman signal that is measured at multiple probe frequencies. FIGS. 14-15 each illustrates a second example Raman signal obtained by changing the frequency offset between a pump beam and a Stokes beam. FIG. 16 illustrates an example Raman signal along with two probe beams of light. FIG. 17 illustrates an example optical receiver for measuring the Raman signal and pump beam of light from FIG. 16. FIG. 18 illustrates an example Raman spectroscopy system for measuring a Raman signal produced by spontaneous Raman scattering. FIG. 19 illustrates an example Raman signal produced by the Raman spectroscopy system of FIG. 18. FIG. 20 illustrates an example laser diode that produces a free-space beam of light. FIG. 21 illustrates an example laser diode that produces seed light that is amplified by a semiconductor optical amplifier (SOA). FIG. 22 illustrates an example laser diode that produces seed light that is amplified by a fiber-optic amplifier. FIG. 23 illustrates an example sampled-grating distributed Bragg reflector (SG-DBR) laser. FIG. 24 illustrates an example light source with multiple laser diodes and an optical multiplexer that combines light produced by the laser diodes into a single output beam of light. FIG. 25 illustrates an example pump laser and Stokes laser with a fiber-optic combiner that produces a combined pump-Stokes beam coupled into an optical fiber. FIG. 26 illustrates an example laser diode coupled to a waveguide of a photonic integrated circuit (PIC). FIG. 27 illustrates an example pump laser and Stokes laser with a photonic integrated circuit (PIC) that produces a combined pump-Stokes beam coupled into an optical waveguide of the PIC. FIG. 28 illustrates an example fiber-optic combiner that combines a Raman signal with a probe beam. FIG. 29 illustrates an example photonic integrated circuit (PIC) with a waveguide combiner that combines a Raman signal with a probe beam. FIGS. 30-35 each illustrates example frequency ranges of a pump beam and a Stokes beam. FIG. 36 ill