Search

US-20260126391-A1 - GAS ANALYSIS BASED ON RAMAN SPECTROSCOPY

US20260126391A1US 20260126391 A1US20260126391 A1US 20260126391A1US-20260126391-A1

Abstract

A method for detecting a presence of at least one constituent of an analyte gas is based on Raman scattering. The method comprises: mixing a buffer gas with the analyte gas; exciting the mixture with a laser excitation beam; detecting scattered photons resulting from interaction between photons of the laser excitation beam and molecules of the analyte gas to thereby determine a spectral content of the scattered photons; and analyzing the spectral content to determine the presence of the at least one constituent.

Inventors

  • Maryam SHIRMOHAMMAD
  • Michael Anthony Short
  • Haishan Zeng

Assignees

  • PROVINCIAL HEALTH SERVICES AUTHORITY

Dates

Publication Date
20260507
Application Date
20251222

Claims (20)

  1. 1 . A method for detecting a presence of at least one constituent of an analyte gas based on Raman scattering, the method comprising: mixing a buffer gas with the analyte gas; exciting the mixture with a laser excitation beam; detecting scattered photons resulting from interaction between photons of the laser excitation beam and molecules of the analyte gas to thereby determine a spectral content of the scattered photons; and analyzing the spectral content to determine the presence of the at least one constituent.
  2. 2 . The method of claim 1 wherein an interaction pathlength between the photons of the excitation beam and the molecules of the analyte gas in the mixture is greater than an interaction pathlength between the photons of the excitation beam and the molecules of the analyte gas in an absence of the buffer gas.
  3. 3 . The method of claim 1 wherein determining the presence of the at least one constituent is based on identifying at least one peak in the spectral content corresponding to the at least one constituent.
  4. 4 . The method of claim 3 wherein the magnitude of the at least one peak is greater than a magnitude of the at least one peak in the absence of the buffer gas.
  5. 5 . The method of claim 1 comprising increasing the temperature of the mixture relative to a temperature of the ambient environment.
  6. 6 . The method of claim 5 wherein increasing the temperature of the mixture relative to the temperature of the ambient environment increases the average speed of molecules of the mixture compared to an average speed of the molecules of the mixture at the temperature of the ambient environment.
  7. 7 . The method of claim 1 wherein the buffer gas has a buffer gas partial pressure and the analyte gas has an analyte gas partial pressure wherein the buffer gas partial pressure is different from (preferably greater than) the analyte gas partial pressure.
  8. 8 . The method of claim 7 wherein a ratio of the buffer gas partial pressure to the analyte gas partial pressure is in a range of about 0.01 to about 1000.
  9. 9 . The method of claim 7 comprising holding the analyte gas partial pressure constant and increasing the buffer gas partial pressure relative to the analyte gas partial pressure.
  10. 10 . The method of claim 1 comprising mixing the buffer gas and the analyte gas in a gas cell.
  11. 11 . The method of claim 10 wherein exciting the mixture with the laser excitation beam comprises directing the laser excitation beam into the gas cell.
  12. 12 . The method of claim 10 wherein the gas cell comprises a hollow-core fiber, the hollow-core fiber comprising a hollow core which permits permeation of fluid in the hollow core, and mixing the buffer gas with the analyte gas in the gas cell comprises introducing the buffer gas and the analyte gas into the hollow core of the hollow-core fiber.
  13. 13 . The method of claim 12 wherein a diameter of the hollow core is in a range of about 2 μm to about 50 μm.
  14. 14 . The method of claim 12 wherein the hollow-core fiber has a longitudinal length in a range of about 0.5 m to about 20 m.
  15. 15 . The method of claim 12 wherein the hollow-core fiber comprises a band-gap transmission hollow-core fiber.
  16. 16 . The method of claim 12 wherein the hollow-core fiber comprises a hollow-core photonic crystal fiber.
  17. 17 . The method of claim 12 wherein the hollow-core fiber comprises an anti-resonant hollow-core fiber.
  18. 18 . The method of claim 12 comprising directing the laser excitation beam into the hollow core of the hollow-core fiber.
  19. 19 . The method of claim 18 wherein the laser excitation beam is confined by the hollow-core fiber to the hollow core.
  20. 20 . The method of claim 1 comprising mixing the buffer gas and the analyte gas at an analyte source.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation of Patent Cooperation Treaty (PCT) application No. PCT/CA2024/050885 having an international filing date of 28 Jun. 2024, which in turn claims priority from, and for the purposes of the United States of America the benefit under 35 U.S.C. § 119 in relation to U.S. application No. 63/523,728 filed 28 Jun. 2023. All of the applications in this paragraph are hereby incorporated herein by reference. FIELD This invention relates to systems and methods for gas analysis based on Raman scattering. Aspects of the invention provide systems and methods for detecting a presence of at least one constituent of an analyte gas based on Raman scattering. Aspects of the invention relate to enhancing Raman scattering for gas analysis. BACKGROUND Raman spectroscopy is a versatile chemical analytical technique having a wide range of applications. Raman spectroscopy is based on the phenomenon of Raman scattering, which refers to the interaction (i.e. inelastic scattering of photons) of light with a material (e.g. vibrational or rotational modes of a molecule of the material). Molecules vibrate with different modes known as normal modes or natural frequencies. Each of these vibrational modes has a unique fundamental frequency. Rotational modes of a molecule refer to the quantized rotational motion of the molecule around its center of mass and are characterized by discrete energy levels determined by the molecule's moment of inertia and rotational constants. These vibrational and rotational modes are specific to the chemical bonds present in the particular molecules. As a result, Raman scattering may yield detailed information about the chemical structure of the molecules, thereby enabling a “fingerprint” type of analysis to identify molecules in a sample. One application of Raman spectroscopy is gas analysis, where Raman spectroscopy is applied to determine compositions (i.e. one or more constituents) of a gas mixture. Raman gas analyzers based on spontaneous Raman scattering have been used in petrochemical industries, environmental studies, analysis of exhaled breath, etc. There is a general desire to analyze exhaled breath. Raman spectroscopy for analyzing exhaled breath has the advantages of lower cost, more compact size and faster turnaround time compared to other common techniques of breath analysis, such as mass spectrometers. However, Raman gas analysis of exhaled breath is also challenging due to the low-molecular-number densities of the analyte gas and the intrinsically inefficient spontaneous Raman scattering due to low inelastic Raman scattering cross-sections. For example, approximately only one in a million interactions between photons of an excitation light and molecules of an analyte gas results in spontaneous Raman scattering. Consequently, there is a desire to provide Raman enhancement techniques to improve the practical utility of Raman scattering based gas analysis and, for example, Raman scattering based analysis of exhaled breath. Various Raman enhancement techniques have been developed and proposed to improve Raman signal intensity. Some Raman enhancement techniques strive to increase the Raman interaction pathlength, which refers to the distance over which the incident excitation light interacts with the sample. An increase in interaction pathlength allows more photons of the excitation light to interact with molecules of the sample, leading to a higher probability of inelastic scattering event to thereby enhance Raman scattering. One enhancement technique that strives to increase the interaction pathlength is cavity-enhanced Raman spectroscopy. In cavity-enhanced Raman spectroscopy, the effective pathlength for Raman interaction is increased through multiple-beam passing by using specialized reflection mirrors in a gas cell. However, the specialized reflection mirrors are costly to manufacture due to the requirement of precision manufacturing. Moreover, achieving and maintaining proper alignment of the lasers and the optical components (e.g. the specialized reflection mirrors) is tedious and complicated. Another example enhancement technique that strives to increase the interaction pathlength is fiber-enhanced Raman spectroscopy (FERS). FERS utilizes specialized hollow-core optical fibers to significantly lower attenuation loss thereby enabling longer fiber length for light gas interaction. Example hollow-core optical fibers include bandgap transmission hollow-core fibers and anti-resonant hollow-core fibers. One type of bandgap transmission hollow-core fibers is the hollow-core photonic-crystal fiber (HCPCF). The use of these hollow-core fibers increases the light-gas interaction pathlength without significant attenuation of the Raman signal. Nonlinear enhancement techniques such as coherent anti-Stokes Raman scattering (CARS) and double-beam stimulated Raman scattering (SRS) have also been proposed. These enhancement techniques ut