# US 2019/0317013 A1 · Infra red spectrometer

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- Number: US 2019/0317013 A1
- Document ID: US20190317013A1
- Status: Published application
- Kind: A1
- Application number: 16/344,183
- Filed: 2017-10-27
- Published: 2019-10-17
- Earliest claimed: 2016-10-27
- Assignees: United Kingdom Research and Innovation
- Applicants: United Kingdom Research and Innovation
- Inventors: Damien Weidman
- Web page: https://patentgrep.com/patent/US20190317013A1

## CPC

- G01N 21/3504: for analysing gases, e.g. multi-gas analysis
- G01N 21/39: using tunable lasers
- G01J 3/08: Beam switching arrangements
- G01J 3/42: Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry (beam switching arrangements G01J3/08)
- G01N 21/276: {with alternation of sample and standard in optical path}
- G01J 2003/423: {Spectral arrangements using lasers, e.g. tunable}
- 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)
- 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)

## Abstract

Methods and apparatus are disclosed for detecting one or more species in a sample, wherein laser probe light is frequency swept across at least one infra red absorption spectrum feature of each of the species. A path from the probe light source to a single detector element may be switched between at least one sample absorption cell or volume and one or more reference cells or volumes.

## Claims

### Claim 1

A method of detecting one or more species in a sample, comprising:
generating probe light using one or more laser sources such that the probe light completes one or more frequency sweeps across at least one infra red absorption spectrum feature of each of the one or more species;
providing a plurality of absorption volumes, comprising a sample volume containing said sample, and one or more reference volumes containing known concentrations of said one or more species;
directing said probe light along a path to a single detector element to output a detector signal from the single detector element, wherein the complete path to the single detection element passes through only one of the absorption volumes at any one time;
switching the path to the single detection element to sequentially select each of the absorption volumes a plurality of times during each frequency sweep, so that the detector signal comprises a sample segment when the path comprises the sample volume, and a reference segment when the path comprises a reference volume;
detecting the one or more species from the sample segments including calibration using the reference segments.

### Claim 2 (depends on 1)

The method of claim 1 wherein the one or more species comprise at least first and second species in the sample, and the step of detecting comprises detecting from the sample segments at least a first spectral feature of the first species and at least a second spectral feature of the second species.

### Claim 3 (depends on 2)

The method of claim 2 wherein the step of detecting comprises determining concentrations of both the first and second species calibrated against known concentrations of the at least two species in each of the one or more reference volumes.

### Claim 4 (depends on 3)

The method of claim 3 wherein the first and second species are isotopologues of the same molecule, and the step of determining concentrations of the at least two species comprises determining an isotopic ratio of the two species.

### Claim 5 (depends on 1)

The method of claim 1 wherein the step of detecting one or more species from the sample segments comprises calibrating sample segments from a particular frequency sweep using only reference segments from the same frequency sweep.

### Claim 6 (depends on 1)

The method of claim 1 wherein the step of detecting one or more species from the sample segments comprises calibrating sample segments using only those reference segments which are proximal or adjacent in the detector signal to the sample segment to be calibrated.

### Claim 7 (depends on 1)

The method of claim 1 wherein the at least one reference volume comprises two or more reference volumes, and each reference volume contains a known concentration of at least one of the species, which may be a zero concentration, which is different to the known concentration of that species in each of the other reference volumes.

### Claim 8 (depends on 7)

The method of claim 7 wherein the step of detecting the one or more species comprises calibrating the detector signal from the sample volume using an interpolation between and/or an extrapolation from the detector signal from each of the reference volumes.

### Claim 9 (depends on 1)

The method of claim 1 wherein the path is switched such that the sample volume is selected at a repetition rate of at least 50 Hz.

### Claim 10 (depends on 1)

The method of claim 1 wherein the path is switched to select each reference volume at the same repetition rate as the sample volume.

### Claim 11 (depends on 1)

The method of claim 1 wherein the path is switched using a micro machined electro mechanical optical switch.

### Claim 12 (depends on 1)

The method of claim 1 wherein the plurality of absorption volumes comprise a plurality of sample volumes, each containing a different sample, such that that the sample segments comprise sample segments from each of the different sample volumes, and the step of detecting comprises separately detecting any of the one more species from the sample segments from each of the sample volumes, including calibration using the reference segments.

### Claim 13

A spectrometer for detecting one or more species in a sample, comprising:
one or more laser sources for generating probe light such that the probe light completes one or more frequency sweeps across at least one infra red absorption spectrum feature of each of the one or more species;
a plurality of absorption volumes, comprising a sample volume containing said sample, and one or more reference volumes containing known concentrations of said one or more species;
an optical detector arranged to output a detection signal;
path optics arranged to direct said probe light along an optical path to the optical detector which includes only one of the absorption volumes at any one time, and to switch the optical path to sequentially select each of the absorption volumes a plurality of times during each frequency sweep, so that the detector signal comprise a sample segment when the path comprises the sample volume, and a reference segment when the path comprises each reference volume;
an analyser arranged to calibrate each of a plurality of the sample segments using corresponding one or more reference segments, and to detect said one or more species form the calibrated sample segments.

### Claim 14 (depends on 13)

The spectrometer of claim 13 wherein the one or more species comprise at least first and second species in the sample, the sample segments comprise segments representing at least a first spectral feature of the first species and at least a second spectral feature of the second species, and the analyser detects said first and second species from the sample segments representing said first and second spectral features.

### Claim 15 (depends on 14)

The spectrometer of claim 14 wherein the analyser is arranged to determine concentrations of both the first and second species calibrated against known concentrations of the at least two species in each of the one or more reference volumes.

### Claim 16 (depends on 15)

The spectrometer of claim 15 wherein the first and second species are isotopologues of the same molecule, and the analyser is arranged to determine an isotopic ratio of the two species.

### Claim 17 (depends on 13)

The spectrometer of claim 13 wherein the analyser is arranged to calibrate sample segments from a particular frequency sweep using only reference segments from the same frequency sweep.

### Claim 18 (depends on 13)

The spectrometer of claim 13 wherein the analyser is arranged to calibrate sample segments using only those reference segments which are proximal or adjacent in the detector signal to the sample segment to be calibrated.

### Claim 19 (depends on 13)

The spectrometer of claim 13 wherein the at least one reference volume comprises two or more reference volumes, and each reference volume contains a known concentration of at least one of the species, which may be a zero concentration, which is different to the known concentration of that species in each of the other reference volumes.

### Claim 20 (depends on 19)

The spectrometer of claim 19 wherein the analyser is arranged to calibrate the sample segments by interpolation between and/or extrapolation from the reference segments of each of the two or more reference volumes.

### Claim 21 (depends on 13)

The spectrometer of claim 13 arranged so that the path is switched to select the sample volume at a repetition rate of at least 50 Hz.

### Claim 22 (depends on 13)

The spectrometer of claim 13 arranged such that the path is switched to select each reference volume at the same repetition rate as for the sample volume.

### Claim 23 (depends on 13)

The spectrometer of claim 13 wherein the path optics comprise a micro machined electro mechanical optical switch arranged to switch the path to sequentially select each of the absorption volumes a plurality of times during each frequency sweep.

### Claim 24 (depends on 13)

The spectrometer of claim 13 wherein the optical detector is a single detector element outputting a single detector signal divisible into a sequence of contiguous sample and reference segments.

### Claim 25 (depends on 24)

The spectrometer of claim 24 wherein the single detector element comprises a single semiconductor substrate.

### Claim 26 (depends on 13)

The spectrometer of claim 13 wherein the plurality of absorption volumes comprise a plurality of sample volumes each containing a different sample, such that the sample segments comprise sample segments from each of the different sample volumes, and the analyser is arranged to separately calibrate sample segments from each of the sample volumes, and to detect said one or more species in each of the sample volumes from the calibrated sample segments.