# US 11,441,944 B2 · Mode matching method for absorption spectroscopy systems > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,441,944 B2 - Document ID: US11441944B2 - Status: Granted - Kind: B2 - Application number: 16/734,078 - Filed: 2020-01-03 - Published: 2020-05-14 - Granted: 2022-09-13 - Earliest claimed: 2017-05-16 - Assignees: LI-COR, Inc. - Applicants: Li-Cor, Inc. - Inventors: Ahmed Bouzid - Web page: https://patentgrep.com/patent/US11441944B2 ## CPC - G01J 3/0237: {Adjustable, e.g. focussing} - 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 3/10: Arrangements of light sources specially adapted for spectrometry or colorimetry - G01N 21/39: using tunable lasers - G02B 17/004: {Systems comprising a plurality of reflections between two or more surfaces, e.g. cells, resonators (multipass arrangements for optical cuvettes G01N21/031; laser resonators H01S3/05)} - G01N 2021/391: {Intracavity sample} - G01N 2201/06113: Coherent sources; lasers - G01N 2201/0636: Reflectors - H01S 5/0071: {for beam steering, e.g. using a mirror outside the cavity to change the beam direction} - H01S 5/0656: {Seeding, i.e. an additional light input is provided for controlling the laser modes, for example by back-reflecting light from an external optical component (H01S5/14, H01S5/4062 and H01S5/4006 take precedence)} - 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) - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS - H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL ## Abstract Systems and methods for controlling optical feedback in an optical system. A resonant optical cavity includes at least two cavity mirrors, one of which is a cavity coupling mirror, and has a plurality of optical resonance cavity modes. A radiation source emits a beam of continuous wave radiation and is capable of being scanned whereby a mean optical frequency of the continuous wave radiation beam is adjustable over a range of frequencies, wherein the radiation source is responsive to optical feedback radiation emerging from the cavity, and wherein the mode matching optics couples the beam of continuous wave radiation to the cavity via the cavity coupling mirror. The radiation source and the mode matching optics are aligned so that a mode fill ratio is reduced relative to a maximum mode fill ratio, wherein the laser beam is coupled with a fundamental cavity mode. ## Claims ### Claim 1 A method of controlling optical feedback in an optical system having a radiation source optically coupled via mode matching optics with a resonant optical cavity having at least two cavity mirrors, one of which is a cavity coupling mirror, the resonant optical cavity having a plurality of optical resonance cavity spatial modes, wherein the radiation source emits a beam of continuous wave radiation and is capable of being scanned whereby a mean optical frequency of the beam of continuous wave radiation is adjustable over a range of frequencies, wherein the radiation source is responsive to optical feedback radiation emerging from the cavity and impinging on the radiation source, and wherein the mode matching optics couples the beam of continuous wave radiation to the resonant optical cavity via the cavity coupling mirror, the method comprising aligning the radiation source and the mode matching optics to control an amount of the optical feedback radiation emerging from the resonant optical cavity, wherein a mode fill ratio of optical feedback spectral modes is reduced relative to a maximum mode fill ratio, wherein for the maximum mode-fill ratio the beam of continuous wave radiation is coupled with a fundamental cavity spatial mode. ### Claim 2 (depends on 1) The method of claim 1, wherein the aligning the radiation source and the mode matching optics includes: aligning or setting a relative distance between the radiation source and at least one component of the mode matching optics to achieve the maximum mode fill ratio, and thereafter adjusting a shape of the optical feedback spectral modes by altering the relative distance between the radiation source and the at least one component of the mode matching optics to attain the reduced mode fill ratio. ### Claim 3 (depends on 2) The method of claim 2, wherein the adjusting includes reducing the relative distance between the radiation source and the at least one component of the mode matching optics, so that a beam waist size of the continuous wave radiation beam is diverging at the cavity coupling mirror. ### Claim 4 (depends on 2) The method of claim 2, wherein the adjusting includes increasing the relative distance between the radiation source and the at least one component of the mode matching optics, so that a beam waist of the continuous wave radiation beam is converging at the cavity coupling mirror. ### Claim 5 (depends on 2) The method of claim 2, wherein the adjusting includes moving only the radiation source. ### Claim 6 (depends on 2) The method of claim 2, wherein the adjusting includes moving only the at least one component of the mode matching optics or multiple components of the mode matching optics. ### Claim 7 (depends on 2) The method of claim 2, wherein the adjusting includes moving both the radiation source and the at least one component of the mode matching optics, or the radiation source and the multiple components of the mode matching optics. ### Claim 8 (depends on 2) The method of claim 2, wherein the adjusting includes reducing the relative distance between the radiation source and the at least one component of the mode matching optics, so that a beam waist size of the continuous wave radiation beam is smaller or larger than a beam waist size of the radiation circulating in the resonant optical cavity. ### Claim 9 (depends on 1) The method of claim 1, wherein the resonant optical cavity has a configuration selected from the group consisting of a ring cavity having three or more cavity mirrors, a linear cavity having two or more cavity mirrors, and a V-shaped cavity having three cavity mirrors. ### Claim 10 (depends on 1) The method of claim 1, wherein the radiation source comprises a laser. ### Claim 11 (depends on 1) The method of claim 1, wherein for the reduced mode-fill ratio the beam of continuous wave radiation is coupled with the fundamental cavity spatial mode. ### Claim 12 (depends on 1) The method of claim 1, further comprising operating the optical system with the relative distance between the radiation source and the at least one component of the mode matching optics set to attain the reduced mode-fill ratio of the optical feedback spectral modes. ### Claim 13 An optical system, comprising: a resonant optical cavity having at least two cavity mirrors, one of which is a cavity coupling mirror, the resonant optical cavity having a plurality of optical resonance cavity modes; a radiation source that emits a beam of continuous wave radiation, wherein the radiation source is capable of being scanned whereby a mean optical frequency of the beam of continuous wave radiation is adjustable over a range of frequencies, and wherein the radiation source is responsive to optical feedback radiation emerging from the cavity and impinging on the radiation source; mode matching optics configured to couple the beam of continuous wave radiation to the cavity via the cavity coupling mirror, the mode matching optics including at least one component; and an adjustment mechanism coupled with the at least one component of the mode matching optics and/or the radiation source, the adjustment mechanism configured to adjust a relative position of the radiation source relative to the at least one component of the mode matching optics to control an amount of the optical feedback radiation emerging from the resonant optical cavity, wherein a mode fill ratio of optical feedback spectral modes is reduced relative to a maximum mode fill ratio, wherein for the maximum mode-fill ratio the beam of continuous wave radiation is coupled with a fundamental cavity spatial mode. ### Claim 14 (depends on 13) The optical system of claim 13, wherein the adjustment mechanism includes an actuator configured to adjust the relative position of the radiation source and the at least one component of the mode matching optics in response to a control signal. ### Claim 15 (depends on 14) The optical system of claim 14, wherein the control signal is provided by a control system in response to receiving a user input to adjust the relative position of the radiation source and the at least one component of the mode matching optics. ### Claim 16 (depends on 14) The optical system of claim 14, further comprising a detector configured to measure an intensity of an intra-cavity optical power of radiation circulating in the resonant optical cavity, wherein the control signal is provided by a control system in response to receiving a feedback signal from the detector. ### Claim 17 (depends on 14) The optical system of claim 14, wherein the resonant optical cavity has a configuration selected from the group consisting of a ring cavity having three or more cavity mirrors, a linear cavity having two or more cavity mirrors, and a V-shaped cavity having three cavity mirrors. ### Claim 18 (depends on 14) The optical system of claim 14, further including a means for adjusting the mean optical frequency of the radiation source so as to scan the mean optical frequency of the radiation source over a cavity resonance peak. ### Claim 19 (depends on 14) The optical system of claim 14, wherein the resonant optical cavity is capable of being scanned whereby an optical frequency of a cavity resonance mode peak is adjustable over a range of frequencies. ### Claim 20 (depends on 19) The optical system of claim 19, further including a means for controlling a position of one of the cavity mirrors so as to scan the optical frequency of the cavity resonance mode peak. ### Claim 21 (depends on 14) The optical system of claim 14, further including a detector configured to measure an intensity of the intracavity optical power of radiation circulating in the resonant optical cavity and to generate a signal representing the intracavity optical power of radiation circulating in the resonant optical cavity, wherein the resonant optical cavity includes a gaseous medium including one or more analyte species. ### Claim 22 (depends on 14) The optical system of claim 14, wherein the radiation source comprises a laser. ### Claim 23 A gas analyzer, comprising: a resonant optical cavity having at least two cavity mirrors, one of which is a cavity coupling mirror, the resonant optical cavity having a plurality of optical resonance cavity modes, the resonant optical cavity configured to receive a gaseous medium including one or more analyte species; a radiation source that emits continuous wave radiation, wherein the radiation source is capable of being scanned whereby a mean optical frequency of the continuous wave radiation is adjustable over a range of frequencies, and wherein the radiation source is responsive to optical feedback radiation emerging from the cavity and impinging on the radiation source; mode matching optics configured to couple the continuous wave radiation to the resonant optical cavity via the cavity coupling mirror, the mode matching optics including at least one component; an adjustment mechanism coupled with the at least one component of the mode matching optics and/or the radiation source, the adjustment mechanism configured to adjust a relative position of the radiation source relative to the at least one component of the mode matching optics to control an amount of the optical feedback radiation emerging from the resonant optical cavity, wherein a mode fill ratio of the optical feedback spectral modes is reduced relative to a maximum mode fill ratio, wherein for the maximum mode-fill ratio the beam of continuous wave radiation is coupled with a fundamental cavity spatial mode; and a detector configured to measure an intensity of the intracavity optical power of radiation circulating in the resonant optical cavity and to generate a signal representing the intracavity optical power of radiation circulating in the resonant optical cavity. ### Claim 24 (depends on 23) The gas analyzer of claim 23, wherein the radiation source comprises a laser.