WO2025202604A1

WO2025202604A1 - Spectroscopy

Info

Publication number: WO2025202604A1
Application number: PCT/GB2025/050540
Authority: WO
Inventors: Brian John Edward Smith
Original assignee: Renishaw PLC
Current assignee: Renishaw PLC
Priority date: 2024-03-28
Filing date: 2025-03-17
Publication date: 2025-10-02
Anticipated expiration: 2026-09-28
Also published as: GB202404528D0

Abstract

A spectroscopy method to be carried out with a detector (130) comprising a plurality of pixels (P1, P2, P3, P4, P5… Pn), each pixel (P1, P2, P3, P4, P5… Pn) comprising at least two single photon detector elements (133), wherein the detector (130) records 5 a distribution of single photon detections by each pixel (P1, P2, P3, P4, P5… Pn) with time from a most-recent pulse of an excitation beam on a sample (124). The method comprises:- receiving spectral light produced by exciting the sample (124) with pulses of the excitation beam; and dispersing the spectral light onto a spectrum. During a first time period, directing a first portion (150) of the spectrum onto a first 10 pixel (P1) of the plurality of pixels (P1, P2, P3, P4, P5… Pn) and a second portion (151) of the spectrum onto a second pixel (P2) of the plurality of pixels (P1, P2, P3, P4, P5… Pn), and reading out from the detector (130) a first distribution of single photon detections made by the first pixel (P1) and a second distribution of single photon detections made by the second pixel (P2). During a second time period, 15 directing the first portion (150) of the spectrum onto the second pixel (P2) and the second portion of the spectrum onto a third pixel (P3) of the plurality of pixels (P1, P2, P3, P4, P5… Pn), and reading out from the detector (130) a third distribution of single photon detections made by the second pixel (P2) and a fourth distribution of single photon detections made by the third pixel (P3). Spectral data is generated by 20 associating the first and third distributions with the first portion (150) of the spectrum and the second and fourth distributions with the second portion (151) of the spectrum.

Description

SPECTROSCOPY

Field of Invention

This invention concerns spectroscopy and, in particular, spectroscopes, spectrometers, spectroscopy apparatus and methods for generating spectral data for carrying time correlated single photon counting (TCSPC).

Background

The Raman Effect is a phenomenon in which a sample scatters excitation light of a given frequency into a frequency spectrum, which has characteristic peaks caused by interaction of the excitation light with the molecules making up the sample. Different molecular species have different characteristic Raman peaks, and so the effect can be used to analyse the molecular species present.

For some samples, the excitation radiation gives rise to fluorescent radiation together with the Raman radiation. Since the Raman signals are emitted from the sample in a shorter time frame (less than a picosecond) compared to the fluorescence signals (a few thousand picoseconds or even tens of nanoseconds), a fast-time resolved detector can be used to distinguish spectra from the two processes. It is known to use time correlated single photon counting (TCSPC) to separate out the Raman and fluorescence signals.

US2012/0194815 Al discloses apparatus comprising a single-photon detector, which may be a single photon avalanche diode (SP D) array, that functions in a “Geiger-mode”, wherein a single photon impacting on the photodetector causes an output pulse to be generated (likened to a “click” of a Geiger counter). Detecting Raman radiation in a pulsed mode effectively filters the background noise and fluorescence out, since outside the detecting or registration period no optical nor electric pulses are taken into account. US2013/0342835 Al discloses a time-resolved Raman spectroscopy apparatus that uses a SP D with optical or electrical triggering.

EP2956748 Al discloses apparatus for measuring Raman radiation from an object comprising a detector having a plurality of single-photon avalanche diode (SPAD) elements.

US5442438 discloses spectroscopic apparatus comprising a diffraction grating mounted on a precision rotary table or stage to be rotatable about an axis. The light dispersed by the diffraction grating is focussed onto a charge-coupled device (CCD). The dispersion across the CCD is a function of an angle the incident beam makes with the normal to the diffraction grating. Using the precision rotary table, the grating can be stepped to a variety of different angles so as to cover a range of Raman spectra to be investigated. One method is to expose one part of the spectrum onto the CCD for a sufficient time, and then to read all of the data relating to that part of the spectrum from the CCD into a computer. Next the turntable is indexed so that the next part of the spectrum is received by the CCD, sufficient exposure time is allowed, and all the data from that part of the spectrum is read out into the computer. Another method is to scan the spectrum along a column or row of pixels synchronously with the shifting of the charge from one pixel to the next and reading out the data from the end pixel into the computer.

Summary of Invention

According to a first aspect there is provided a spectroscopy method to be carried out with a detector comprising a plurality of pixels, each pixel comprising at least two single photon detector elements, wherein the detector records a distribution of single photon detections by each pixel with time from a most-recent pulse of an excitation beam on a sample, the method comprising:- receiving spectral light produced by exciting the sample with pulses of the excitation beam; dispersing the spectral light onto a spectrum; during a first time period, directing a first portion of the spectrum onto a first pixel of the plurality of pixels and a second portion of the spectrum onto a second pixel of the plurality of pixels, and reading out from the detector a first distribution of single photon detections made by the first pixel and a second distribution of single photon detections made by the second pixel; and during a second time period, directing the first portion of the spectrum onto the second pixel and the second portion of the spectrum onto a third pixel of the plurality of pixels, and reading out from the detector a third distribution of single photon detections made by the second pixel and a fourth distribution of single photon detections made by the third pixel; and generating spectral data by associating the first and third distributions with the first portion of the spectrum and the second and fourth distributions with the second portion of the spectrum.

For a detector comprising single photon detector elements, the single photon detector elements can have very different performances and, often, certain ones of the single photon detector elements are not useable at all. This difference in performance and, in some cases, arbitrary pattern of non-working single photon detector elements within a pixel introduces a pattern noise into the detections made by each pixel dependent on the illumination and the pattern of single photon detector elements used. In conventional collection techniques, this can make the pattern noise sample dependent and so not amenable to characterisation and correction. By recording distributions for different (the first and second) portions of the spectrum with at least one common pixel (at least the second pixel), pattern noise introduced by the at least one common pixel is present in the distributions for each of these different portions of the spectrum. Accordingly, detections for different portions of the spectrum made by the same pixel can be compared as the same pattern noise will be present in these detections and differences in the detections for the same portions of the spectrum made by different pixels can be compared to account for pattern noise. The spectroscopy method may comprise generating combined spectral data by summing the first and third distributions on a per time basis and summing the second and fourth distributions on a per time basis. As single photon detections for each different (the first and second) portions of the spectrum are carried out across multiple pixels, pattern noise introduced into a summed distribution for that portion of the spectrum is an average of the noise pattern for each pixel used to generate the distribution. If the summed distribution for each portion of the spectrum is determined from detections made by the same set of pixels, then the pattern noise for each distribution will be the same. A common background level of noise, such as dark current, between different portions of the spectrum, facilitates analysis of the spectrum. Furthermore, it may allow more single photon detector elements in each pixel to be used, thereby increasing the sensitivity of the detector.

The method may comprise successively directing the first portion of the spectrum onto each one of a set of the plurality of pixels, and successively directing the second portion of the spectrum onto each one of the set of the plurality of pixels, reading out from the detector first corresponding distributions of single photon detections made by pixels of the set for the first portion of the spectrum and second corresponding distributions of single photon detections made by the pixels of the set for the second portion of the spectrum, and generating spectral data by summing the first corresponding distributions on a per time basis and summing the second corresponding distributions on a per time basis. The method may comprise locating the spectrum on the detector such that the first portion of the spectrum is directed to one pixel (such as the first or second pixel) of the set whilst, at the same time, the second portion of the spectrum is directed to another pixel (such as the second or third pixel, respectively) of the set. The method may comprise locating the spectrum at multiple positions on the detector where such conditions are met.

The set of the plurality of pixels may comprise all pixels in one row of the detector.

The row of the detector may be in a direction in which the spectrum is shifted to move the first and second portions between pixels of the detector. The row of the detector may be in a dimension (referred to herein as the “spectral dimension”) in which the spectrum is dispersed, for example by a dispersive optic. In this way, spectral data for both the first and second portions is collected across the same set of pixels.

Alternatively, the set of the plurality of pixels may comprise a subset of the pixels in one row of the detector. For example, it may be deemed sufficient for the averaging out of the pattern noise to collect data for both portions of the spectrum across only the subset of pixels in a row rather than all the pixels. Spectral data for each of the first and second portions of the spectrum may be collected across different pixels in addition to the common pixels of the set. In one embodiment, the spectrum may be dithered such that each of the first and second portions of the spectrum are directed to two or more but not all pixels of the row of pixels.

The term “single photon detector element” is used herein to mean a photodetector element arranged to generate an output signal when a single photon is detected by the photodetector such that detection of each photon can be distinguished. For example, the single photon detector element may generate a signal pulse for each photon that is detected by the photodetector. The single photon detector element may be arranged to generate an output signal when a single photon is detected by the photodetector and, for a “off’ period after detection of the single photon, the single-photon detector is unable to detect further photons that impact the photodetector. The “off’ period may be at least ten nanoseconds. The single photon detector element may comprise a single photon avalanche diode (SP D).

For the array, detection of photons by the single photon detector elements are recorded on a per-pixel basis, i.e. there is no separate counting of photons detected by different ones of the single photon detector elements that make up the pixel.

Each pixel may comprise a set of single photon detector elements, each single photon detector element of the set for detecting light in the same wavelength range.

The detector may comprise a one-dimensional array of pixels.

Each pixel may comprise a plurality of single photon detector elements in a spectral dimension (in which the spectrum is dispersed) and/or in spatial a dimension orthogonal to the spectral dimension.

The array of single photon detector elements may be a line sensor (a onedimensional array of pixels). The line sensor may be oriented to only have a single pixel width in the spatial dimension and a plurality of pixels in the spectral dimension. For example, the line sensor may be as described in “A CMOS SP D Line Sensor With Per-Pixel Histogramming TDC for Time-Resolved Multispectral Imaging”, IEEE Journal of Solid State Circuits, Volume: 54, Issue: 6, June 2019, incorporated herein in its entirety by reference.

The method may comprise outputting the spectral data or combined spectral data, for example in the form of a representation on a display or as a digital output from a spectrometer and/or computer.

The method may comprise analysing the spectral data or combined spectral data, such as a Raman signal in the spectral data or combined spectral data, to identify a property of the sample and controlling a process and/or carrying out further processing on the sample based upon the identified property. For example, the process may be a manufacturing process. The sample may be a sample of one or more manufactured products and the identified property may be used to determine if the manufactured products meet a required specification. Failure to meet the required specification may require an adjustment of the process such that products are manufactured to the required specification. The sample may be a tissue sample and the process may be treatment of a patient providing the tissue sample. The method may be used as part of a checking procedure, for example a security procedure or a quality control procedure), comprising generating an alarm based upon the analysis of the spectral data.

The method may comprise identifying a number of Raman detections from the spectral data or combined spectral data for each of a plurality of wavenumbers. For example, a number of Raman detections for the first portion (wavenumber) of the spectrum may be determined from the summing of the first and third distributions and a number of Raman detections for the second portion (wavenumber) of the spectrum may be determined from the summing the second and fourth distributions.

A number of Raman detections may be determined using the method disclosed in EP2956748 Al, UK patent application No. 2404511.4, which are incorporated herein in their entirety by reference.

The association of the first and third distributions with the first portion of the spectrum and the second and fourth distributions with the second portion of the spectrum may be based on the timing of movement of the dispersive optic that disperses the spectral light into a spectrum and/or the detector, for example a rotation of a dispersive optic to alter an incident angle of the spectral light on the dispersive optic. The dispersive optic may be stepped from a first position, in which the first portion of the spectrum is directed onto the first pixel and the second portion of the spectrum is directed onto the second pixel to a second, different position, in which the first portion of the spectrum is directed onto the second pixel and the second portion of the spectrum is directed onto the third pixel. The first and second distributions may be read out from the detector before the dispersive optic is located in the second position.

According to a second aspect of the invention there is provided a spectrometer comprising an optical input for receiving spectral light produced by exciting a sample with pulses of an excitation beam, a detector comprising a plurality of pixels, each pixel comprising at least two single photon detector elements, wherein the detector is configured to record a distribution of single photon detections by each pixel with time from a most-recent pulse of the excitation beam on the sample, and a dispersive optic for dispersing the spectral light into a spectrum across the plurality of pixels of the detector, wherein the dispersive optic and/or detector is/are adjustable to, in one configuration, direct a first portion of the spectrum to a first pixel of a plurality of the pixels and a second portion of the spectrum to a second pixel of the plurality of pixels and, in a second configuration, direct the first portion of the spectrum to the second pixel and the second portion of the spectrum to a third pixel of the plurality of pixels.

In this way, the spectrometer may be used in the method of the first aspect of the invention.

The spectrometer may comprise a controller arranged to:- during a first time period, control the dispersive optic and/or the detector to direct a first portion of the spectrum onto the first pixel and the second portion onto the second pixel; during a second time period, control the dispersive optic and/or the detector to direct the first portion of the spectrum onto the second pixel and the second portion of the spectrum onto the third pixel.

The dispersive optic may be mounted for rotation to alter an incident angle of the spectral light on the dispersive optic. The spectrometer may comprise a motor for driving rotation of the dispersive optic. The controller may control the movement of the motor.

The spectrometer may comprise a processor arranged to, during the first time period, read out from the detector a first distribution of single photon detections made by the first pixel and a second distribution of single photon detections made by the second pixel; and, during the second time period, read out from the detector a third distribution of single photon detections made by the second pixel and fourth distribution of single photon detections made by the third pixel. The processor may be part of or separate from the controller.

The processor or a further processor may be arranged to generate combined spectral data by summing the first and third distributions on a per time basis and summing the second and fourth distributions on a per time basis. The combined spectral data may comprise a histogram for each portion (wavenumber) of the spectrum, a histogram for the first portion of the spectrum formed from the summing of the first and third distributions and a histogram for the second portion formed from summing the second and fourth distributions.

The processor may be arranged to output the spectral data, for example on a display or in digital form on a data carrier.

According to a third aspect of the invention there is provided a controller for a spectrometer according to the second aspect of the invention, the controller arranged to:- during a first time period, control the dispersive optic and/or the detector to direct a first portion of the spectrum onto the first pixel and the second portion onto the second pixel; during a second time period, control the dispersive optic and/or the detector to direct the first portion of the spectrum onto the second pixel and the second portion of the spectrum onto the third pixel.

According to a fourth aspect of the invention there is provided a data carrier which the when executed on a controller of a spectrometer according to the second aspect of the invention, causes the controller to:- during a first time period, control the dispersive optic and/or the detector to direct a first portion of the spectrum onto the first pixel and the second portion onto the second pixel; during a second time period, control the dispersive optic and/or the detector to direct the first portion of the spectrum onto the second pixel and the second portion of the spectrum onto the third pixel.

According to a fifth aspect of the invention there is provided a computer- implemented time correlated single photon counting (TCSPC) method comprising:- receiving first, second, third and fourth distributions generated using the method of the first aspect of the invention; and generating combined spectral data by summing the first and third distributions on a per time basis and summing the second and fourth distributions on a per time basis.

The combined spectral data may comprise a histogram for each portion (wavenumber) of the spectrum, a histogram for the first portion of the spectrum formed from the summing of the first and third distributions and a histogram for the second portion formed from summing the second and fourth distributions. The summing of the first and third distributions and the second and fourth distributions may be on a per time basis.

The method may comprise outputting the combined spectral data, for example on a display or in digital form on a data carrier.

According to a sixth aspect of the invention there is provided a processor configured to carry out the method of the fifth aspect of the invention.

According to a seventh aspect of the invention there is provided a data carrier which the when executed on a processor, causes the processor to carry out the method of the fifth aspect of the invention.

The data carrier of the above aspects of the invention may be a non-transient data carrier, such as volatile memory, e.g. RAM, non-volatile memory, e.g. ROM, flash memory and data storage devices, such as hard discs, optical discs, or a transient data carrier, such as an electronic or optical signal.

Description of Drawings

FIGURE 1 is a schematic representation of a spectroscopy apparatus according to an embodiment of the invention;

FIGURES 2 is a schematic representation of a spectral analyser and detector of a spectrometer;

FIGURES 3a and 3b are illustrate the detector and the method of making detection using the detector; and

FIGURE 4 schematically illustrates combining the sets of histograms corresponding to different positions of the spectrum on the detector.

Description of Embodiments

Referring to Figure 1, spectroscopy apparatus comprises a spectrometer 117, a source 110 of an excitation beam, in this embodiment a laser beam, and a microscope 118 for delivering the laser beam to a sample 124 and spectral light, such as Raman-shifted light, to a spectral analyser 128 of the spectrometer 117. The spectral analyser 128 spatially disperses the received spectral light by wavelength into a spectrum and delivers the spectrum to a detector 130. Detector 130 comprises an array of single-photon detector elements 133, for example a two-dimensional array of single photon avalanche diodes (SPADs). The spectrometer 117 is controlled by controller 170.

In this embodiment the light source 110 is a pulsed laser configured to generate laser pulses along laser optical input path 113 to an optical device. The optical device comprises a mirror 114 and a Rayleigh filter 116. In this embodiment, the Rayleigh filter 116 is a notch or edge filter, which acts as a dichroic beam splitter. The mirror 114 and Rayleigh filter 116 reflect the laser beam directed along the optical input path 113 to a sample 124. The laser beam directed to the sample 124 enters into the microscope 118, wherein the laser beam is deflected by an optic 120 through an objective lens 122 and focused on to a sample 124. Raman scattering takes place at the sample, producing Raman-shifted light at different wavenumbers from the incident laser line.

The sample is mounted on a stage 123 that can be moved in two dimensions (x,y) perpendicular to the laser beam. Movement of the stage 123 allows the laser beam to be positioned at different locations on the sample 124 enabling spectroscopy data to be gathered at each of these locations.

The Raman-shifted light is collected by the objective lens 122 and passed back along a spectroscopy optical path 115 via the optic 120 to the Rayleigh filter 116. Whereas the Rayleigh filter 116 reflects light of the laser wavelength, it transmits the Raman-shifted wavenumbers. While doing so, it rejects the much more intense laser line. The Raman-shifted light then passes through a Raman analyser 128 and to the detector 130.

Referring to Figure 2, the spectral analyser 128 comprises a housing 136 having an optical input port 137 and an optical output port 141. The housing 136 contains a collimating lens 142, a prism 135, a spectral dispersive optic, in this embodiment a diffraction grating 143 and a focussing optic 144. The array 130 of single photon avalanche diodes 133 is mounted to the spectral analyser 128 to receive spectral light from optical output port 141. The diffraction grating 143 is mounted on a rotary table 146 such that rotation of the table 146 rotates the dispersive grating 143 to alter an incident angle of the spectral light on the diffraction grating 143. A motor (not shown) for driving the rotary table is controlled by controller 170.

Altering the incident angle of the spectral light on the diffraction grating 143 alters a location of the spectrum on the detector 130. In particular, rotation of the diffraction grating 143 moves the spectrum across the detector 130 in a spectral dimension X (see Figure 3a) in which the spectrum is dispersed.

Referring to Figure 3a, the detector 130 comprises single photon detector elements 133 in a two-dimensional array. The single photon detector elements 133 are grouped into pixels Pi to Pn. Each pixel comprises a plurality of single photon detector elements 133, including a plurality of single photon detector elements 133 in a spatial dimension, S orthogonal to the spectral dimension, X. (The dotted box encloses the single photon detector elements 133 that make up pixel Pi. Each other pixel Pi to Pn comprises a corresponding set of single photon detector elements 133.) In this embodiment, each pixel comprises single photon detector elements 133 in the spatial dimension and two single photon detector elements 133 in the spectral dimension. |Detection of photons by the single photon detector elements 133 are recorded on a per-pixel basis, i.e. there is no separate counting of photons detected by different ones of the single photon detector elements 133 that make up the pixel Pi to Pn.

For a typical array of single photon detectors 133, a number of the single photon detectors 133’ may operate in a manner that is not suitable for detecting Raman signals. For example, some of the single photon detectors 133’ may produce a dark signal that swamps any Raman signal that may be detected. The apparatus may be operated to only use the single photon detectors 133 of each pixel Pi to Pn deemed to have a satisfactory operation, e.g. a small enough dark current. The apparatus may be operated to only use a set number, such as four, of the single photon detectors 133 of each pixel Pi to Pn deemed to have the smallest dark current. The pattern of the single photon detectors 133 that are used is likely to be different between the pixels Pi to Pn.

Detector 130 is linked to the laser 110 via a trigger line 132 used to synchronise operation of the detector 130 with the pulses of the laser 110. Further details of the operation and timing of the detector 130 can be found in “A CMOS SP D Line Sensor With Per-Pixel Histogramming TDC for Time-Resolved Multispectral Imaging”, IEEE Journal of Solid State Circuits, Volume: 54, Issue: 6, June 2019. In particular, after detecting a photon, each single photon detector element is unable to detect a further photon at least until the next laser pulse.

The detector 130 stores a distribution, in this embodiment a histogram, of the photon detections on a per pixel basis detected over a number of pulses (exposures) of the sample to the laser beam. The detector 130 allocates detections by each pixel to appropriate bins of a corresponding histogram based on the measured time of arrival of the photon from the most-recent laser pulse. Hence, the resultant histogram for each pixel plots time of arrival versus number of detections (counts). Different portions (indicted by the different dotted lines 150, 151, 153 in Figure 3b) of the spectrum having corresponding different wavenumbers are incident on different pixels Pi to Pn. The pixel on which a portion of the spectrum is directed is dependent on the position of the diffraction grating 143 to the incident spectral light.

Figures 3a and 3b show a first portion 150 of the spectrum directed towards a first pixel Pi, a second portion 151 of the spectrum directed towards a second pixel P2 and a third portion 152 of the spectrum directed towards a third pixel P3. In use, detections are recorded by the detector 130 for a first period and then, at the end of the first period, the recorded distributions read out from the detector 130. A position of the diffraction grating 143 is then altered to shift the spectrum in direction d in the spectral dimension such that the first portion 150 of the spectrum is directed towards second pixel P2, the second portion 151 of the spectrum is directed towards third pixel P3 and the third portion of the spectrum is directed towards fourth pixel P4. Detections are made by the second pixel P2for the first portion 150, by the third pixel P3 for the second portion and by the fourth pixel P4 for the third portion 152 and histograms are read out from the pixels for a second time period. This process is continued until each portion 150, 151, 152 of the spectrum that is of interest is detected by each pixel Pi to Pn of the detector 130. (Before the position shown in Figures 3a and 3b, the diffraction grating 143 is positioned such that the second portion 151 and third portion 152 of the spectrum are directed towards pixel Pi and shifts in the spectrum in the direction d on the detector 130 progress the spectrum to the position that is shown in the Figures and described above). In this embodiment, all the detection time periods are the same.

This process results in sets of histograms for each time period. An example of a histogram produced is shown in Figure 5, (only one histogram is shown but it will be understood that a histogram per pixel is produced as illustrated by the pixel axis). For different time periods, different pixels detect photons for a particular portion 150, 151, 152 of the spectrum. As the pixels may have different sensitivity and produce a different number of dark counts, the resultant histograms may differ for the same portion of the spectrum between different pixels Pi to Pn. The set of histograms may be sent by controller 170 to a further computer for combining the histograms into combined spectral data or the combining of the histograms may be carried out on controller 170.

Referring to Figure 5, the histograms for each portion of the spectrum are combined by adding together the counts in corresponding time bins of the histogram. For example, for the first portion 150 of the spectrum, the counts made by the first pixel Pi during the first time period are added to the counts made by the second pixel P2 during the second time period and so on up to the counts made by the nth pixel Pn during the nth time period. Corresponding summations of the counts are made for the other portions of the spectrum (i.e. for the second portion 151 of the spectrum, the counts made by the first pixel Pi during an earlier (zeroth) time period are added to the counts made by the second pixel P2 during the first time period and so on up to the counts made by the nth pixel Pn during the (n-l)th time period). This results in combined spectral data in the form of a histogram for each wavenumber (corresponding to each portion of the spectrum).

For a sample that emits both Raman light and fluoresces, the histogram will contain counts due to the Raman effect (peak 160) and the fluorescence (peak 161). However, due to the effects occurring in different overlapping time frames from the excitation pulse, the time separation of the Raman and fluorescence can be used to determine the Raman and/or fluoresce spectra in a known manner.

In a further embodiment, rather than stepping the spectrum across the detector 130 such that each portion of the spectrum that is of interest is directed to every pixel within a row of the detector, each portion is directed to multiple but not all of the pixels within the row. Detections of different portions 150, 151, 152 of the spectrum are made simultaneously and thus, different sets of pixels within the row are used for detections of different portions 150, 151, 152 of the spectrum (e.g. the detections of the first portion 150 of the spectrum may be made by pixels Pi to P3, whereas detections of the second portion 151 of the spectrum may be made by pixels P2 to P4). In particular, the spectrum may be dithered (e.g. moved back and forth) over a distance that is less than an entire width of the row of pixels. In this way, detections for a particular portion 150, 151, 152 of the spectrum would only see the pattern noise for some but not all of the pixels and therefore, different noise patterns may be present in the detections for different portions of the spectrum. However, such a process would take less time than moving the spectrum across the entire width of a row of the detector 130.

Modifications and alterations may be provided to the above-described embodiments without departing from the invention as defined herein.

Claims

1. A spectroscopy method to be carried out with a detector comprising a plurality of pixels, each pixel comprising at least two single photon detector elements, wherein the detector records a distribution of single photon detections by each pixel with time from a most-recent pulse of an excitation beam on a sample, the method comprising:- receiving spectral light produced by exciting the sample with pulses of the excitation beam; dispersing the spectral light onto a spectrum; during a first time period, directing a first portion of the spectrum onto a first pixel of the plurality of pixels and a second portion of the spectrum onto a second pixel of the plurality of pixels, and reading out from the detector a first distribution of single photon detections made by the first pixel and a second distribution of single photon detections made by the second pixel; and during a second time period, directing the first portion of the spectrum onto the second pixel and the second portion of the spectrum onto a third pixel of the plurality of pixels, and reading out from the detector a third distribution of single photon detections made by the second pixel and a fourth distribution of single photon detections made by the third pixel; and generating spectral data by associating the first and third distributions with the first portion of the spectrum and the second and fourth distributions with the second portion of the spectrum.

2. A spectroscopy method according to claim 1, comprising generating combined spectral data by summing the first and third distributions on a per time basis and summing the second and fourth distributions on a per time basis.

3. A spectroscopy method according to claim 1 or claim 2, comprising successively directing the first portion of the spectrum onto each one of a set of the plurality of pixels, and successively directing the second portion of the spectrum onto each one each of the set of the plurality of pixels, reading out from the detector first corresponding distributions of single photon detections made by pixels of the set for the first portion of the spectrum and second corresponding distributions of single photon detections made by the pixels of the set for the second portion of the spectrum, and generating spectral data by summing the first corresponding distributions on a per time basis and summing the second corresponding distributions on a per time basis.

4. A spectroscopy method according to claim 3, comprising locating the spectrum on the detector such that the first portion of the spectrum is directed to one pixel of the set whilst, at the same time, the second portion of the spectrum is directed to another pixel of the set.

5. A spectroscopy method according to claim 3 or claim 4, wherein the set of the plurality of pixels comprises all pixels in one row of the detector.

6. A spectroscopy method according to claim 3 or claim 4, wherein the set of the plurality of pixels comprises a subset of the pixels in one row of the detector.

7. A spectroscopy method according to claim 6, wherein the spectrum is dithered such that each of the first and second portions of the spectrum are directed to two or more but not all pixels of the row of pixels.

8. A spectroscopy method according to any one of claims 5 to 7, wherein the row of the detector is in a direction in which the spectrum is shifted to move the first and second portions between pixels of the detector.

9. A spectroscopy method according to any one of claims 5 to 8, wherein the row of the detector is in a dimension in which the spectrum is dispersed.

10. A spectroscopy method according to any one of the preceding claims comprising outputting the spectral data or combined spectral data from a spectrometer and/or computer.

11. A spectroscopy method according to any one of the preceding claims comprising analysing the spectral data or combined spectral data to identify a property of the sample and controlling a process and/or carrying out further processing on the sample based upon the identified property.

12. A spectrometer comprising an optical input for receiving spectral light produced by exciting a sample with pulses of an excitation beam, a detector comprising a plurality of pixels, each pixel comprising at least two single photon detector elements, wherein the detector is configured to record a distribution of single photon detections by each pixel with time from a most-recent pulse of the excitation beam on the sample, and a dispersive optic for dispersing the spectral light into a spectrum across the plurality of pixels of the detector, wherein the dispersive optic and/or detector is/are adjustable to, in one configuration, direct a first portion of the spectrum to a first pixel of a plurality of the pixels and a second portion of the spectrum to a second pixel of the plurality of pixels and, in a second configuration, direct the first portion of the spectrum to the second pixel and the second portion of the spectrum to a third pixel of the plurality of pixels.

13. A spectrometer according to claim 12, comprising a controller arranged to:- during a first time period, control the dispersive optic and/or the detector to direct a first portion of the spectrum onto the first pixel and the second portion onto the second pixel; during a second time period, control the dispersive optic and/or the detector to direct the first portion of the spectrum onto the second pixel and the second portion of the spectrum onto the third pixel.

14. A spectrometer according to claim 12 or claim 13, comprising a processor arranged to, during the first time period, read out from the detector a first distribution of single photon detections made by the first pixel and a second distribution of single photon detections made by the second pixel; and, during the second time period, read out from the detector a third distribution of single photon detections made by the second pixel and fourth distribution of single photon detections made by the third pixel.

15. A spectrometer according to any one of claims 12 to 14, wherein the processor or a further processor is arranged to generate combined spectral data by summing the first and third distributions on a per time basis and summing the second and fourth distributions on a per time basis.

16. A spectrometer according to claim 15, wherein the processor is arranged to output the spectral data on a display or in digital form on a data carrier.

17. A controller for spectroscopy apparatus according to any one of claims 12 to 16, the controller arranged to:- during a first time period, control the dispersive optic and/or the detector to direct a first portion of the spectrum onto the first pixel and the second portion onto the second pixel; during a second time period, control the dispersive optic and/or the detector to direct the first portion of the spectrum onto the second pixel and the second portion of the spectrum onto the third pixel.

18. A data carrier which the when executed on a controller of a spectrometer according to any one of claims 12 to 16, causes the controller to:- during a first time period, control the dispersive optic and/or the detector to direct a first portion of the spectrum onto the first pixel and the second portion onto the second pixel; during a second time period, control the dispersive optic and/or the detector to direct the first portion of the spectrum onto the second pixel and the second portion of the spectrum onto the third pixel.

19. A computer-implemented time correlated single photon counting method comprising:- receiving first, second, third and fourth distributions generated using the method of any one of claims 1 to 11; and generating combined spectral data by summing the first and third distributions on a per time basis and summing the second and fourth distributions on a per time basis.

20. A computer-implemented time correlated single photon counting method according to claim 19, wherein the combined spectral data comprises a histogram for each portion of the spectrum, a histogram for the first portion of the spectrum formed from the summing of the first and third distributions and a histogram for the second portion formed from summing the second and fourth distributions.

21. A computer-implemented time correlated single photon counting method according to claim 19 or claim 20, comprising outputting the combined spectral data on a display or in the form of a data carrier.

22. A processor configured to carry out the method of any one of claims 19 to 21.

23. A data carrier which the when executed on a processor, causes the processor to carry out the method of any one of claims 19 to 21.