# US 7,612,885 B2 · Spectroscopy method and apparatus for detecting low concentration gases > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,612,885 B2 - Document ID: US7612885B2 - Status: Granted - Kind: B2 - Application number: 11/615,617 - Filed: 2006-12-22 - Published: 2008-06-26 - Granted: 2009-11-03 - Earliest claimed: 2006-12-22 - Assignees: Honeywell International Inc. - Inventors: Barrett E. Cole; James Allen Cox; Yuandong Gu; Rodney H. Thorland - Web page: https://patentgrep.com/patent/US7612885B2 ## CPC - G01J 3/02: Details - G01J 3/021: {using plane or convex mirrors, parallel phase plates, or particular reflectors} - G01J 3/027: {Control of working procedures of a spectrometer; Failure detection; Bandwidth calculation} - G01J 3/0286: {Constructional arrangements for compensating for fluctuations caused by temperature, humidity or pressure, or using cooling or temperature stabilization of parts of the device; Controlling the atmosphere inside a spectrometer, e.g. vacuum} - G01J 3/42: Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry (beam switching arrangements G01J3/08) - G01N 21/15: Preventing contamination of the components of the optical system or obstruction of the light path - G01N 21/39: using tunable lasers - G01N 2021/151: {Gas blown} - G01N 2021/391: {Intracavity sample} - G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N) - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) ## Abstract The invention is a method and apparatus capable of detecting constituents of a gas at extremely low concentrations comprising providing a medium that is absorbent of at least a first particular gas under a first environmental condition and desorbent of the particular gas under a second environmental condition, exposing the medium to a sample gas for a first period of time under the first environmental condition, during a second period of time after the first period of time, exposing the medium to the second environmental condition to cause the medium to desorb gas into an optical cavity of a cavity ring down spectrometer and introducing electromagnetic radiation into the cavity, during a third period of time after the second period of time, ceasing introduction of the electromagnetic radiation into the cavity and detecting the decay of the electromagnetic radiation in the cavity, and analyzing the decay of the light in the cavity to obtain a spectral analysis of the sample gas. ## Claims ### Claim 1 A spectrometer apparatus comprising: a cavity comprising at least two mirrors arranged to provide a continuous light path in said cavity; a source for providing electromagnetic radiation into said optical cavity; a detector for monitoring the amount of radiation in said cavity and generating a first detection signal based thereon; an absorbent medium in fluid communication with said cavity, said medium being absorbent of at least a first particular gas under a first environmental condition and being desorbent of said particular gas under a second environmental condition; a means for controlling the environment of said medium between the first environmental condition and the second environmental condition; a processor adapted to control said apparatus to (a) control an environment of said medium to expose said medium to a sample gas while under the first environmental condition, (b) subsequently switch said environment to said second environmental condition to cause said medium to desorb, (c) cause said source to provide electromagnetic radiation into said cavity during or after said medium desorbs, (d) subsequently turn off said source, and (e) subsequently measure the decay of the electromagnetic radiation in the cavity during the third period of time. ### Claim 2 (depends on 1) The apparatus of claim 1 wherein said processor is adapted to control said apparatus to expose said medium to the sample gas while under the first environmental condition for a first period of time and, at the end of the first period of time, to switch to said second environmental condition to cause said medium to desorb during a second period of time, turn on said source during said second period of time, turn off said source off at the beginning of a third period of time following said second period of time, and measure the decay of the electromagnetic radiation in the cavity during the third period of time. ### Claim 3 (depends on 1) The apparatus of claim 1 wherein said first environmental condition comprises a first temperature and said second environmental condition comprises a second temperature and wherein said means for controlling comprises a heater for heating said material. ### Claim 4 (depends on 3) The apparatus of claim 3 wherein said means for controlling further comprises a cooling unit for cooling said material. ### Claim 5 (depends on 1) The apparatus of claim 1 wherein said first environmental condition comprises a first pressure and said second environmental condition comprises a second pressure and wherein said means for controlling comprises a pump for applying negative or positive pressure around said medium. ### Claim 6 (depends on 1) The apparatus of claim 1 wherein said medium comprises at least one of carbon nano tubes and a zeolyte. ### Claim 7 (depends on 1) The apparatus of claim 1 further comprising a heater coupled to heat said mirrors. ### Claim 8 (depends on 1) The apparatus of claim 1 wherein said source can provide electromagnetic radiation into said cavity at any one of multiple wavelengths and wherein at least one of said mirrors is movable and wherein said processor is further adapted to move said mirror to cause an optical length of said cavity to be equal to an integer multiple of said wavelength of said electromagnetic radiation. ### Claim 9 (depends on 1) The apparatus of claim 1 wherein said processor is further adapted to analyze the length of time for said electromagnetic radiation in said cavity to decay to obtain a spectroscopic analysis of said sample gas. ### Claim 10 (depends on 1) The apparatus of claim 1 wherein said processor is further adapted to analyze the length of time for said electromagnetic radiation in said cavity to decay and determine at least one of the identity of a constituent of said sample gas and a concentration of said constituent in said sample gas. ### Claim 11 (depends on 1) The apparatus of claim 1 wherein said cavity comprises at least one first portion and at least one second portion and a path for permitting said sample gas to flow over said medium wherein said path comprises at least one inlet path for admitting the said sample gas into said cavity and at least one outlet path for evacuating said sample gas from said cavity, said inlet and outlet paths being disposed in said at least one first portion of said cavity, and said mirrors being disposed in said at least one second portion of said cavity, said apparatus further comprising a plurality of baffles disposed in said cavity and positioned to separate said mirrors from said portions of said cavity containing said inlet and outlet paths. ### Claim 12 (depends on 11) The apparatus of claim 11 wherein each of said baffles include an aperture for permitting said electromagnetic radiation to pass through said aperture unobstructed, and a shutter in each said aperture, said shutter being controlled to close said aperture during said first period of time and to open said shutter during said second period of time. ### Claim 13 (depends on 1) The apparatus of claim 1 wherein cavity comprises at least one first portion and at least one second portion, said mirrors being disposed in said at least one second portion of said cavity and said sample gas being disposed in said at least one first portion of said cavity, said apparatus further comprising a plurality of Brewster windows disposed in said cavity and positioned to separate said mirrors from said portions of said cavity containing said inlet and outlet paths. ### Claim 14 (depends on 13) The apparatus of claim 13 wherein said at least one first portion of said cavity is fluidly sealed from said second portion of said cavity and said first portion has said Brewster windows disposed thereon. ### Claim 15 (depends on 14) The apparatus of claim 14 wherein said at least one first portion of said cavity is modular. ### Claim 16 A method of detecting constituents of a gas comprising: a. providing a medium that is absorbent of at least a first particular gas under a first environmental condition and desorbent of said particular gas under a second environmental condition; b. exposing said medium to a sample gas for a first period of time under the first environmental condition; c. during a second period of time after said first period of time, exposing said medium to said second environmental condition to cause said medium to desorb gas into an optical cavity of a cavity ring down spectrometer and providing electromagnetic radiation into said cavity; d. during a third period of time after said second period of time, ceasing provision of said electromagnetic radiation into said cavity and detecting the decay of said electromagnetic radiation in said cavity; and e. analyzing the decay of said light in said cavity to obtain a spectral analysis of said sample gas. ### Claim 17 (depends on 16) The method of claim 16 wherein said first and second environmental conditions are different temperatures. ### Claim 18 (depends on 16) The method of claim 16 wherein steps b, c, and d are repeated for a plurality of different wavelengths of electromagnetic radiation. ### Claim 19 (depends on 18) The method of claim 18 further comprising: adjusting the optical length of said cavity as a function of said wavelength of said electromagnetic radiation so that said cavity length is an integer multiple of a wavelength of said electromagnetic radiation. ### Claim 20 (depends on 18) The method of claim 18 further comprising: analyze the length of time for said electromagnetic radiation in said cavity to decay at said multiple wavelengths to obtain a spectroscopic analysis of said sample gas. ### Claim 21 (depends on 16) The method of claim 16 further comprising: e. during a fourth period of time after said third period of time, exposing said medium to a third environmental condition to cause said medium to further desorb gas into said optical cavity and introducing electromagnetic radiation into said cavity; and f. during a fifth period of time after said forth period of time, ceasing introduction of said electromagnetic radiation into said cavity and detecting the decay of said electromagnetic radiation in said cavity; whereby different constituents of said sample gas may desorb from said medium during said second period of time and said fourth period of time such that the particular environmental condition under which said decay time was measured may provide an additional degree of data as to the identity of constituents of said sample gas based on volatilization environmental condition. ### Claim 22 A method of detecting a constituent of the gas comprising: a. providing a resonant optical cavity having at least one coupler for permitting electromagnetic radiation from a source into said cavity and permitting electromagnetic radiation to escape from said cavity; b. providing an absorbent medium in fluid communication with said cavity, said medium being absorbent of at least a first particular gas under a first environmental condition and being desorbent of said particular gas under a second environmental condition; c. introducing a sample gas into said cavity, sufficient to contact and absorb onto the medium under the first environmental condition; d. exposing said medium to the second environmental condition to cause said medium to desorb at least a portion of the sample gas; e. pumping said cavity with electromagnetic radiation for a first period of time; f. detecting an intensity of said electromagnetic radiation pumped into said cavity; g. simultaneously with step d f, detecting an intensity of electromagnetic radiation escaping said cavity; and h. determining a difference between said intensity of radiation pumped into the cavity and said intensity of electromagnetic radiation escaping from the cavity to derive an absorption characteristic of said sample gas. ### Claim 23 (depends on 22) The method of claim 22 further comprising: i. determining at least one constituent of said sample gas based on said absorption characteristic of said sample gas. ### Claim 24 (depends on 22) The method of claim 22 wherein steps e, f, g, and h are repeated in connection with electromagnetic radiation at a plurality of different wavelengths. ### Claim 25 (depends on 24) The method of claim 24 further comprising: j. determining at least one constituent of said sample gas based on said absorption characteristic. ### Claim 26 A cavity ring-down spectrometer comprising: a resonant cavity comprising at least two mirrors; a source for providing electromagnetic radiation into said optical cavity; a detector for monitoring the amount of radiation in said cavity and generating a first detection signal based thereon; a path for admitting a sample gas to flow over said medium and in said cavity; a processor adapted to control said cavity ring-down spectrometer to expose said medium to the sample gas while under the first environmental condition for a first period of time and, at the end of the first period of time, to switch to said second environmental condition to cause said medium to desorb during a second period of time after said first period of time, turn on said source during said second period of time, turning said source off at the beginning of a third period of time following said second period of time, and measuring the decay of the electromagnetic radiation in the cavity during the third period of time; and a heater coupled to at least one of said mirrors to locally heat at the least a reflecting surface thereof. ### Claim 27 (depends on 26) The cavity ring down spectrometer of claim 26 wherein said heater is adapted to teach said mirror above a volatilization temperature of expected constituents in said sample gas. ### Claim 28 (depends on 26) The cavity ring down spectrometer of claim 26 wherein said heater comprises a Peltier heater. ### Claim 29 (depends on 26) The cavity ring down spectrometer of claim 26 wherein said heater comprises a thermal resistor. ### Claim 30 (depends on 26) The cavity ring down spectrometer of claim 26 wherein said mirror comprises: an optical portion including said reflective surface and an opposing surface; a supporting base; and a thin membrane coupling said optical portion to said supporting base; wherein said heater is disposed on said optical portion. ### Claim 31 (depends on 30) The cavity ring down spectrometer of claim 30 wherein said heater is disposed on said opposing surface of said optical portion. ### Claim 32 (depends on 31) The cavity ring down spectrometer of claim 31 wherein said heater comprises a thermal resistor.