Molecular gas analysis by Raman scattering in intracavity laser configuration

Abstract

The concentration of multiple polyatomic gases are determined almost simultaneously by Raman scattering. The gas sample is placed in a sampling cell located in the resonance cavity of a laser and a polarized laser beam having sufficient intensity to produce detectable signals of Raman scattered light is passed through the cell. The scattered light is captured and redirected by means of a reflection mirror located parallel to the axis of the laser beam adjacent to and outside of the cell. Signals of both inelastic Raman scattered light and elastic laser scattered light are collected by a collection lens means opposite the reflection mirror and outside the gas cell. The collection lens is also parallel to the axis of the laser beam. The collected scattered signals are directed onto a laser line rejection filter where the scattered elastic laser signals are filtered out and the inelastic Raman scattered signals are transmitted to come in contact with a rotating filter wheel containing a series of interference filters with each filter being specific to the transmission of one Raman line. The Raman lines passing through the rotating filters are sensed sequentially by a single detector means and amplified and converted into digital electrical pulses which are processed and converted into visual readouts indicative of the concentration of each of the polyatomic molecules in the gas being determined.

.Iadd.I claim:.Iaddend. 
     
       1. A system for the near simultaneous analysis and quantitation of selected multiple polyatomic gases in a gas sample by Raman light scattering comprising in combination; (a) laser means capable of producing a .[.polarized laser.]. .Iadd.light .Iaddend.beam of a selected wavelength .[.containing a laser cavity said laser cavity containing a plasma tube and wherein one end of said laser cavity contains a high reflectivity output coupler mirror.].;   (b) a gas sampling cell .[.located.]. .Iadd.having a chamber for containing said gas sample.Iaddend.within said .[.laser cavity between said plasma tube and said output coupler mirror.]. .Iadd.light beam.Iaddend., said cell having .[.opposing parallel end windows.]. .Iadd.an entrance window to allow said light beam to enter said chamber, .Iaddend..[.interconnected by a continuous sidewall, said end windows and sidewall defining a longitudinal gas chamber oriented such that, when said laser beam is activated, the laser beam is coincident with and traverses the axis of said longitudinal gas chamber, said end windows being positioned to be substantially normal to the axis of the longitudinal gas cell chamber,.]. said cell also having opposing, aligned side windows .[.in said sidewall parallel to and on either side of the axis of said longitudinal gas chamber.]. .Iadd.to allow Raman scattered light to exit said chamber.Iaddend., said gas cell further containing inlet and outlet means communicating with said chamber to pass a sample gas through said cell;   (c) a reflection mirror positioned adjacent to and outside of said gas cell .[.parallel to and .]. in alignment with said side windows on one side thereof to capture and redirect a proportion of scattered elastic laser light and inelastic Raman light through said side windows,   (d) collection .[.lens.]. means .[.positioned parallel to and in alignment with said side windows outside said gas cell and on the side opposite from said reflection mirror.]. to collect elastic .[.laser.]. scattered light and inelastic Raman light passing through said side windows, .[.(e) laser line rejection filter means positioned to receive the scattered light passing through said collection lens means, said filter being selected to reject elastic laser scattered light passing through said collection lens means while allowing the transmission of inelastic Raman scattered light,.].   (f) a .[.rotatable.]. filter .[.wheel.]. .Iadd.support .Iaddend.containing a .[.series.]. .Iadd.plurality .Iaddend.of .[.interference.]. filters wherein each .[.interference.]. filter .Iadd.has a predetermined bandwidth which .Iaddend.is selected to transmit .[.only a single.]. .Iadd.at least one .Iaddend.Raman .[.spectra.]. .Iadd.spectral .Iaddend.line of a predetermined wavelength, said filter .[.wheel.]. .Iadd.support .Iaddend.being positioned such that.[., as it rotates,.]. each .[.interference.]. .Iadd.said .Iaddend.filter will sequentially receive Raman scattered light .[.passing through said laser line rejection filter means.].,   (g) detection .[.and amplification.]. means for sequentially receiving Raman line signals passing through each of said .[.interference.]. filters and converting said signals to .[.digital.]. electrical .[.pulses.]. .Iadd.signals.Iaddend.;   (h) processing means for interpreting said .[.digital.]. electrical .[.pulses.]. .Iadd.signals .Iaddend.and converting them to .[.visual .]. readouts indicative of the concentration of each of said selected polyatomic molecular gases in said sample; and   (i) power means to operate said laser means, .[.rotating filter wheel,.]. detection .[.and amplification.]. means and processing means. .[.   
     
     
       2.  A system according to claim 1 wherein said end windows are coated with an antireflection coating specific to the selected wavelength of the laser beam..]. 
     
     
       3. A system according to claim 1 wherein said reflection mirror .[.and output coupler mirror are.]. .Iadd.is .Iaddend.of high reflectivity. 
     
     
       4. A system according to claim 3 wherein said reflection mirror has a radius of curvature and is located relative to the .[.laser.]. .Iadd.light .Iaddend.beam at a distance from said beam equal to the radius of curvature of said mirror. 
     
     
       5. A system according to claim 4 wherein said reflection mirror is a spherical mirror. 
     
     
       6. A system according to claim 4 wherein said reflection mirror is a cylindrical mirror. 
     
     
       7. A system according to claim 1 wherein said side windows in said gas cell are coated with a broad band antireflection coating adapted to pass desired wavelengths of inelastic Raman scattered light. 
     
     
       8. A system according to claim 1 wherein said filter .[.wheel.]. .Iadd.support .Iaddend.and processing means are signally connected such that, as single Raman line signals pass through each .[.interference.]. filter, the processing means determines which polyatomic gaseous molecule is being analyzed. 
     
     
       9. A system according to claim 8 wherein said filter .[.wheel.]. .Iadd.support .Iaddend.contains a series of alternating .[.interference.]. filters and blanks and wherein one of said .[.interference.]. filters is a reference filter. 
     
     
       10. A system according to claim 1 wherein .[.said output coupler mirror allows passage of an extracavity laser beam when said laser beam is activated and wherein.]. means are located to receive .Iadd.a portion of .Iaddend.said .[.extracavity laser.]. .Iadd.light .Iaddend.beam signals and convert said signals to current which is directed to one channel of a two channel current amplifier-filter for simultaneous correlation with photocurrent signal in a second channel of said amplifier-filter to correct Raman signal intensity for random fluctuation in laser optical power. 
     
     
       11. A method for the near simultaneous and instantaneous determination of the concentration of multiple polyatomic gas molecules in a gas sample comprising; (a) introducing said gas sample into a gas sampling cell .[.located within the resonance cavity of a laser.].;   (b) subjecting said gas sample in said .[.laser cavity.]. .Iadd.gas cell .Iaddend.to a .[.polarized.]. laser beam of selected wavelength and having sufficient intensity to produce detectable signals of inelastic Raman scattered light,   (c) capturing and redirecting signals of both inelastic Raman scattered light and elastic laser scattered light .[.in a plane normal to the axis of said laser beam.]. by means of a reflection mirror located adjacent to and outside of said gas cell .[.said reflection mirror being parallel to the axis of said laser beam.].,   (d) collecting signals of both inelastic Raman scattered light and elastic laser scattered light by collection .[.lens.]. means located opposite said reflection mirror .[.said collection lens means also being parallel to the axis of said laser beam and in alignment with said reflection mirror.]. ,   (e) directing said signals of both inelastic Raman scattered light and elastic scattered light onto a .[.laser line rejection.]. filter wherein scattered elastic laser light signals are rejected and signals of inelastic Raman scattered light .Iadd.corresponding to a specific gas species .Iaddend.are transmitted;   (f) subjecting said simple signals of Raman scattered light to a .[.rotating.]. filter .[.wheel.]. .Iadd.support .Iaddend.containing a .[.series.]. .Iadd.plurality .Iaddend.of .[.interference.]. filters wherein each .[.interference.]. filter is specific for the transmission of a .[.single.]. .Iadd.particular predetermined .Iaddend.Raman line,   (g) sequentially sensing .[.single.]. .Iadd.particular .Iaddend.Raman line signals passing through the .[.interference.]. filters of said filter .[.wheel.]. .Iadd.support .Iaddend.by detection .[.and amplification.]. means and converting said signals into .[.digital.]. electrical .[.pulses.]. .Iadd.signals; and .Iaddend.   (h) .[.sequentially.]. processing said .[.digital.]. electrical .[.pulses.]. .Iadd.signals .Iaddend.in processing means and converting them to .[.visual.]. readouts indicative of the concentration of each of said polyatomic molecules in said gas sample being determined.   
     
     
       12. A method according to claim 11 wherein said polyatomic gases are members selected from the group consisting of respiratory and anesthetic gases. 
     
     
       13. A method according to claim 12 wherein said polyatomic gases are members selected from the group consisting of nitrogen, oxygen, carbon dioxide.Iadd., nitrous oxide .Iaddend.and halogenated anesthesia gases. 
     
     
       14. A method according to claim 13 wherein said gases are sampled by means connected to the airway of a patient. 
     
     
       15. A method according to claim 11 wherein the gas sample is contained in a gas cell having .[.opposing parallel end windows interconnected by a continuous sidewall, said end windows and sidewall defining a longitudinal gas chamber oriented such that, when gas sample is subjected to said laser beam, the laser beam is coincident with and traverses the axis of said longitudinal gas chamber, said end windows being positioned to be substantially normal to the axis of the longitudinal gas cell chamber, said cell also having.]. .Iadd.a chamber for containing said gas sample, an entrance window to allow said light beam to enter said chamber, and .Iaddend.opposing, aligned side windows .[.in said side wall parallel to and on either side of the axis of said longitudinal gas chamber,.]. .Iadd.to allow Raman scattered light to exit said chamber, .Iaddend.said gas cell further containing inlet and outlet means communicating with said chamber to pass a sample gas through said cell. 
     
     
       16. A method according to claim 15 wherein said inelastic Raman scattered light and elastic laser scattered light are captured and redirected by said reflection mirror wherein said reflection mirror has a radius of curvature and is located relative to the .[.laser.]. .Iadd.light .Iaddend.beam at a distance from said beam equal to the radius of curvature of said mirror. 
     
     
       17. A method according to claim 16 wherein said mirror is a spherical mirror. 
     
     
       18. A method according to claim 16 wherein said mirror is a cylindrical mirror. 
     
     
       19. A method according to claim 16 wherein the said .[.end windows.]. .Iadd.entrance window .Iaddend.in said gas sampling cell .[.are.]. .Iadd.is .Iaddend.coated with an antireflection coating specific to the wavelength of the .[.laser.]. .Iadd.light .Iaddend.beam. 
     
     
       20. A method according to claim 16 wherein sample gas is continuously passed through said inlet and outlet means in said gas cell by pump means located in a gas supply line on the inlet side of said gas cell. .Iadd. 
     
     
       21.  A method according to claim 16, wherein sample gas is continuously passed through said inlet and outlet means in said gas cell by pump means located in a gas supply line on the outlet side of said gas cell..Iaddend. .Iadd.22. A method for analyzing a sample, comprising: (a) introducing said sample into a sampling cell;   (b) subjecting said sample in said sampling cell to a light beam of a selected wavelength having sufficient intensity to produce detectable signals of inelastic Raman scattered light;   (c) collecting signals of said inelastic Raman scattered light with a collection means;   (d) positioning a filter support comprising a plurality of filters such that said collected signals of inelastic Raman scattered light are incident on each filter sequentially, wherein each filter selectively transmits light within a narrow bandwidth, said narrow bandwidth encompassing a predetermined Raman spectral line;   (e) detecting the light which is transmitted through each of said plurality of filters and generating a corresponding electrical signal for light passing through each individual filter; and   
     
     
       (f) processing said electrical signals..Iaddend. .Iadd.23.  A method for analyzing a sample as defined in claim 22 further comprising calculating the concentration of each said specific components in said sample..Iaddend. .Iadd.24. A method for the breath-by-breath analysis of multiple respiratory gases of a patient's breath by Raman light scattering, comprising the steps of: (a) collecting a sample of said respiratory gases;   (b) introducing said sample into a sampling cell, wherein said cell has an inlet and an outlet to facilitate time dependent sampling and analysis of said respiratory gases;   (c) subjecting said sample in said sampling cell to a light beam of a selected wavelength having sufficient intensity to produce detectable signals of inelastic Raman scattered light;   (d) collecting signals of said inelastic Raman scattered light with a collection means;   (e) directing said collected signals of inelastic Raman scattered light to a filter support comprising a plurality of filters such that said light is sequentially directed to individual filters wherein each filter selectively transmits light within a narrow bandwidth, said narrow bandwidth encompassing a predetermined Raman spectral line;   (f) detecting the light which is transmitted through each of said plurality of filters and generating a corresponding electrical signal for light passing through each individual filter; and   
     
     
       (g) processing said electrical signals..Iaddend. .Iadd.25.  A method as defined in claim 24 further comprising the step of selecting the volume of said sampling cell to be in the range of from about 0.1 to about 1.0 cubic centimeters..Iaddend. .Iadd.26. A method as defined in claim 24 further comprising the step of repeating steps (a) through (g) several times every second..Iaddend. .Iadd.27. A method, utilizing Raman light scattering, for monitoring anesthetic agents in a patient's respiratory system to determine the identity of specific anesthetic agents in the patient's system and to determine the quantity of the agents present, said method comprising the steps of: (a) collecting a sample of the patient's respiratory gases;   (b) introducing said sample into a sampling cell, wherein said cell has an inlet and an outlet to facilitate time dependent sampling and analysis of said respiratory gases;   (c) subjecting said sample in said sampling cell to a light beam of a selected wavelength having 24 sufficient intensity to produce detectable signals of inelastic Raman scattered light;   (d) collecting signals of said inelastic Raman scattered light with a collection means;   (e) directing said collected signals of inelastic Raman scattered light to a filter support comprising a plurality of filters such that said light is directed to individual filters sequentially, wherein each filter selectively transmits light within a narrow bandwidth, said narrow bandwidth encompassing a predetermined Raman spectral line which is indicative of specific anesthetic agents;   (f) detecting the light which is transmitted through each of said plurality of filters and generating a corresponding electrical signal for light passing through each individual filter; and   (g) processing said electrical signals to identify the specific anesthetic agents present in the patient's breath and to determine the concentration   
     
     
        of each of the agents found to be present..Iaddend. .Iadd.28.  A system for the near simultaneous analysis and quantitation of a sample by Raman light scattering, comprising in combination: (a) a light source for producing a light beam of a selected wavelength;   (b) a sample cell having a chamber for containing a sample within said light beam;   (c) collection optics to collect Raman scattered light from said sample;   (d) a filter support containing a plurality of filters wherein each filter has a predetermined bandwidth and is selected to transmit at least one Raman spectral line of a predetermined wavelength, said filter support being capable of positioning each said filter to individually receive said Raman scattered light;   (e) a detector for receiving said Raman scattered light which has passed through one of said filters, said detector generating a signal in response to receiving said Raman scattered light;   (f) processing means for interpreting said detector signal and converting it to an output signal which is indicative of the concentration of one of said selected polyatomic molecular gases in said sample; and   (g) power means to operate said light source, detector and processing means..Iaddend. .Iadd.29. A system according to claim 28 wherein said light further comprises a laser..Iaddend. .Iadd.30. A system according to claim 29 wherein said laser further comprises a semi-conductor laser..Iaddend. .Iadd.31. A system according to claim 29 wherein said laser further comprises a gas laser..Iaddend. .Iadd.32. A system according to claim 29 wherein said laser further comprises a solid state laser..Iaddend. .Iadd.33. A system according to claim 28 wherein said gas cell has an inlet means and an outlet means communicating with said chamber to pass said sample gas through said cell..Iaddend. .Iadd.34. A system according to claim 28 wherein said collection optics further comprises refractive optic elements..Iaddend. .Iadd.35. A system according to claim 28 wherein said collection optics further comprises reflective optic elements..Iaddend. .Iadd.36. A system according to claim 28 wherein said filters are interference filters..Iaddend. .Iadd.37. A system according to claim 28 wherein said detector is a photmultiplier tube..Iaddend. .Iadd.38. A system according to claim 28 wherein said   
     
     
        detector is a solid state photon detector. .Iadd.39.  A system for analyzing a sample comprising: (a) a light source incident upon said sample such that Raman scattering from said sample creates Raman scattered light along an axis;   b) a filter section positioned with respect to said axis so as to receive said Raman scattered light, wherein said filter section comprises a plurality of filters and each filter has a predetermined bandwidth which is selected to transmit at least one Raman spectral line of a predetermined wavelength, each of said plurality of filters being positionable with respect to said axis such that each of said filters can independently receive said Raman scattered light;   (c) detection means for receiving said Raman scattered light after transmission through any one of said filters and converting said scattered light to an electrical signal; and   (d) processing means for interpreting said electrical signal..Iaddend. .Iadd.40. A system for the near simultaneous analysis of a sample by Raman light scattering comprising in combination:   (a) a laser capable for producing a light beam;   (b) a sampling cell having a chamber for containing a sample within said light beam, said cell having an entrance window to allow said light beam to enter said chamber and an exit window to allow Raman scattered light to exit said chamber along a first direction;   (c) collection optics to collect said Raman scattered light propagating along said first direction;   (d) a filter support containing a plurality of filters wherein each filter defines a predetermined bandwidth which is selected to transmit a Raman spectral line of a predetermined wavelength, said filter support being positioned such that each said filter is capable of sequentially receiving said Raman scattered light propagating along said first direction;   (e) a detector for receiving said Raman scattered light and converting said light to electrical signals; and   (f) a processor for interpreting said electrical signals and converting them to readouts indicative of characteristics of said sample..Iaddend.   
     
     
        .Iadd.41.  A method for analyzing a sample as defined in claim 22 wherein said processing step further comprises the step of identifying specific 
     
     
        components in said sample..Iaddend. .Iadd.42.  A method for analyzing a sample, comprising: (a) introducing said sample into a sampling cell;   (b) subjecting said sample in said sampling cell to a light beam having sufficient intensity to produce detectable signals of inelastic Raman scattered light;   (c) directing said inelastic Raman scattered light to a wavelength discrimination filter device adapted to receive said Raman scattered light and to sequentially transmit Raman light of predetermined wavelengths;   (d) detecting light which is provided by said filter device and generating a corresponding electrical signal for said light which passes through said filter device; and   
     
     
       (e) processing said electrical signal..Iaddend. .Iadd.43.  A method for the breath-by-breath analysis of multiple respiratory gases of a patient's breath by Raman light scattering, comprising the steps of: (a) collecting a sample of said respiratory gases;   (b) introducing said sample into a sampling cell, wherein said cell has an inlet and an outlet to facilitate time dependent sampling and analysis of said respiratory gases;   (c) subjecting said sample in said sampling cell to a light beam having sufficient intensity to produce detectable signals of inelastic Raman scattered light;   (d) directing said inelastic Raman scattered light to a wavelength discrimination filter device adapted to receive said Raman scattered light and to sequentially transmit Raman scattered light of predetermined wavelengths;   (e) detecting the light which is sequentially transmitted through said filter device and generating a corresponding electrical signal for light passing through said filter device; and   
     
     
       (f) processing said electrical signals..Iaddend. .Iadd.44.  A method, utilizing Raman light scattering, for monitoring anesthetic agents in a patient's respiratory system to determine the identity of specific anesthetic agents in the patient's system and to determine the quantity of the agents present, said method comprising the steps of: (a) collecting a sample of the patient's respiratory gases;   (b) introducing said sample onto a sampling cell, wherein said cell has an inlet and an outlet to facilitate time dependent sampling and analysis of said respiratory gases;   (c) subjecting said sample in said sampling cell to a light beam having sufficient intensity to produce detectable signals of inelastic Raman scattered light;   (d) directing said inelastic Raman scattered light to a wavelength discrimination filter device adapted to receive said Raman scattered light and to sequentially transmit Raman scattered light of predetermined wavelengths;   (e) detecting the light which is transmitted through said filter device and generating an electrical signal for light passing through said filter device; and   (f) processing said electrical signals to identify the specific anesthetic agents present in the patient's breath and to determine the concentration   
     
     
        of each of the agents found to be present..Iaddend. .Iadd.45.  A system for the near simultaneous analysis and quantitation of a sample by Raman light scattering, comprising in combination: (a) a light source for producing a light beam;   (b) a sample cell having a chamber for containing a sample within said light beam;   (c) a light filtering element having a plurality of configurations wherein each configuration has a specific transmission characteristic for Raman scattered light and said element sequentially assumes said plurality of configurations;   (d) a detector for receiving Raman scattered light which has passed through said filtering element, said detector generating a signal in response to receiving said light;   (e) processing means for interpreting said detector signal and converting it to an output signal; and   (g) power means to operate said light source, detector and processing means..Iaddend. .Iadd.46. A system for analyzing a sample comprising:   (a) a light source incident upon said sample such that Raman scattering from said sample creates Raman scattered light;   (b) a filter section for receiving said Raman scattered light, wherein said filter section comprises a plurality of filter configurations and at least one configuration has a predetermined characteristic which is selected to transmit at least one Raman spectral line of a predetermined wavelength, each of said plurality of configurations being capable of independently receiving said Raman scattered light;   (c) a detector for receiving said Raman scattered light after transmission through any one of said filter section configurations and converting said scattered light to an electrical signal; and   (d) a processor for interpreting said electrical signal..Iaddend. .Iadd.47. A system for the near simultaneous analysis of a sample by Raman light scattering comprising in combination:   (a) a laser capable of producing a light beam;   (b) a sampling cell having a chamber for containing a sample within said light beam, said cell having an entrance window to allow said light beam to enter said chamber and an exit window to allow Raman scattered light to exit said chamber;   (c) collection optics to collect said Raman scattered light;   (d) a filter section for receiving said Raman scattered light, wherein said filter section comprises a plurality of filter configurations and at least one configuration has a predetermined characteristic which is selected to transmit at least one Raman spectral line of a predetermined wavelength, each of said plurality of configurations being capable of independently receiving said Raman scattered light;   (e) a detector for receiving said Raman scattered light and converting said light to electrical signals; and   (f) a processor for interpreting said electrical signals and converting them to readouts indicative of characteristics of said sample..Iaddend. .Iadd.48. A system for the near simultaneous monitoring of multiple gases by Raman light scattering comprising a single detector which receives Raman line spectra from a filter section which comprises a plurality of filter configurations wherein each configuration is specific to a particular gas species being monitored..Iaddend.