Apparatus and a method for carrying out spectroscopy
An apparatus obtains a first spectrum beam from an interaction between a first portion of a laser beam and a sample and a second spectrum beam from an interaction between a second portion of the laser beam and a reference sample. A diffraction element splits the first spectrum beam into a first spectrum associated with the sample and splits the second spectrum beam into a second spectrum associated with the reference sample. A detector with pixels for detecting the first and second spectrum. A data acquisition device carries out a measurement, wherein first data indicative of the first spectrum is detected and second data indicative of the second spectrum is detected, wherein the first data is collected in different pixels than the second data. The data acquisition device: a) determines a point spread function PSF using a convolution function; and b) determines a real spectrum of the sample using the PSF.
1 . An apparatus for carrying out spectroscopy, in particular Raman spectroscopy, on a sample,
the apparatus being configured to obtain a first spectrum beam from an interaction between a first portion of a laser beam and a sample and a second spectrum beam from an interaction between a second portion of the laser beam and a reference sample,
the apparatus comprises an optical system which is configured to guide the first spectrum beam and the second spectrum beam to a diffraction element,
the diffraction element being configured to split the first spectrum beam into a first spectrum of spatially separated wavelength components associated with the sample and to split the second spectrum beam into a second spectrum of spatially separated wavelength components associated with the reference sample;
the apparatus comprising a detector with an array of pixels for detecting the first and second spectrum;
the apparatus comprising a data acquisition device which is configured:
to carry out at least one measurement using the detector, wherein, simultaneously, first data which is indicative of the first spectrum of spatially separated wavelength components is detected over time by the array of pixels and second data which is indicative of the second spectrum of spatially separated wavelength components is detected over time by the array of pixels, wherein the first data is collected in different pixels than the second data;
the data acquisition device being further configured to carry out the following processes:
a) determining a point spread function PSF from the second data related to a measured spectrum of the reference sample and a predetermined spectrum of the reference sample, wherein the PSF is determined using a convolution function that provides a predetermined relationship between the PSF, a measured spectrum in the second data and an ideal spectrum of the reference sample;
b) determining a real spectrum of the sample using the determined PSF and the first data related to the measured spectrum of the sample.
2 . The apparatus of claim 1 ,
wherein the determining of the real spectrum of the sample includes using the determined PSF and the first data related to the measured spectrum of the sample in a deconvolution function, which is the inverse of the convolution function.
3 . The apparatus of claim 1 ,
wherein the data acquisition device is configured to detect a predefined event, when the event occurs during the measurement, wherein the data acquisition device is configured to carry out steps a) and b) in response to the detection of the predefined event.
4 . The apparatus of claim 3 ,
wherein the predefined event is causing a movement or a change in position of the first spectrum or the second spectrum on the array of pixels during a measurement.
5 . The apparatus of claim 3 ,
wherein the predefined event is a mode hop of a laser used to provide the laser beam.
6 . The apparatus of claim 1 ,
wherein predefined boundary conditions of the optical system are included in at least one of the following: the convolution function and the deconvolution function.
7 . The apparatus of claim 1 ,
wherein, in the data acquisition device a second PSF obtained from a second reference sample, such as diamond or calcite, is provided, and wherein the data acquisition device is configured to determine a deblurred real spectrum of the sample using the second PSF.
8 . The apparatus of claim 1 ,
wherein the data acquisition device is configured to carry out a wavelength calibration over time on the first data using the second data that has been simultaneously detected.
9 . The apparatus of claim 8 ,
wherein the data acquisition device is configured to identify in the second data at least one peak of the reference spectrum and to employ the identified at least one peak for wavelength calibration of the first data.
10 . The apparatus of claim 1 ,
wherein the data acquisition device is configured to measure an intensity over time of at least one of the following:
the first portion of a laser beam, the second portion of the laser beam, a common laser beam from which the first and second portions of the laser beam are generated, an intensity of the first spectrum, an intensity of the second spectrum; and
wherein the data acquisition device is configured to employ the measured intensity for normalizing simultaneously measured intensity values which are included in the first data.
11 . The apparatus of claim 1 ,
wherein the data acquisition device is configured to calculate an intensity over time of the second spectrum from the second data and to employ the calculated intensity for normalizing simultaneously measured intensity values which are included in the first data.
12 . The apparatus of claim 1 ,
wherein the apparatus comprises at least one laser for generating the first and second portions of the laser beam, wherein the laser is split into the first and second portions of the laser beam by use of a beam splitter.
13 . The apparatus of claim 12 ,
wherein the laser is at least one of the following: a non-wavelength stabilized laser, a non-temperature stabilized laser, a tunable laser, a diode laser.
14 . The apparatus of claim 1 ,
wherein the apparatus comprises an optical system which comprises a slit or a pinhole through which the first and second spectrum beams are guide before they pass through the diffraction element, wherein a width of the slit or a diameter of the pinhole is larger than an optimal value for the width of diameter, wherein the optimal value is associated with the pixel limited spectral resolution of the array of pixels.
15 . The apparatus of claim 14 ,
wherein the width of the slit or the diameter of the pinhole corresponds to or is larger than 1.2 or 1.3 or 1.4, or 1.5 time the optimal value.
16 . The apparatus of claim 14 ,
wherein the reference sample is arranged on one side of an element that forms the slit or pinhole.
17 . The apparatus of claim 14 ,
wherein each of the first and second spectrum beam is focused to a focal point when passing through the slit or pinhole, wherein the focal point of the first spectrum beam is shifted from the focal point of the second spectrum beam.
18 . The apparatus of claim 1 ,
wherein the apparatus comprises an optical system configured to compress a width of the first spectrum and a width of the second spectrum at the location of the detector to a value which is in the range of the size of a pixel and optionally lower than the pixel size, wherein the width is measured in a plane of the pixel surface and in a direction which is orthogonal to a spectral direction of the spectra.
19 . A computer implemented method for carrying out spectroscopy, in particular Raman spectroscopy, on a sample, wherein the method uses an apparatus which is configured to obtain a first spectrum beam from an interaction between a first portion of a laser beam and a sample and to obtain a second spectrum beam from an interaction between a second portion of the laser beam and a reference sample,
wherein the apparatus comprises an optical system which is configured to guide the first spectrum beam and the second spectrum beam to a diffraction element, and the diffraction element is configured to split the first spectrum beam into a first spectrum of spatially separated wavelength components associated with the sample and to split the second spectrum beam into a second spectrum of spatially separated wavelength components associated with the reference sample, wherein the apparatus further comprises a detector with an array of pixels for detecting the first and second spectrum, and wherein the method comprises:
detecting, simultaneously and as a function of time, first data which is indicative of the first spectrum of spatially separated wavelength components on the array of pixels and second data which is indicative of the second spectrum of spatially separated wavelength components on the array of pixels, wherein the first data is collected in different pixels than the second data,
determining a point spread function PSF from the second data related to a measured spectrum of the reference sample and a predetermined spectrum of the reference sample, wherein the PSF function is determined using a convolution function that provides a predetermined relationship between the PSF, a measured spectrum and a spectrum in the second data and an ideal spectrum of the reference sample;
determining a real spectrum of the sample using the determined PSF and the first data related to the measured spectrum of the sample.
20 . The computer implemented method of claim 19 ,
wherein determining the real spectrum of the sample comprises using the determined PSF and the first data related to the measured spectrum of the sample in a deconvolution function, which is the inverse of the convolution function.