Combined spectroscopy system including Raman and ATR-FTIR
View Patent ↗System for simultaneous measurement Raman and mid-infrared absorption signals from a sample, the system comprising an ATR crystal adapted for holding a sample thereon, at least one Raman excitation light source for Raman excitation, at least one FTIR excitation light source for FTIR excitation, at least one photodetector configured for collecting signals with a wavelength comprised at least in one of the IR spectrum or the Raman spectrum, a wavelength-dispersive device, such as a spectrometer, for collecting Raman signals, an excitation lens, and collection optics comprising a first collection lens.
1. System for simultaneous measurement of Raman and infrared absorption signals from a sample, the system comprising:
an ATR crystal adapted for holding the sample thereon,
at least one Raman excitation light source for Raman excitation,
at least one FTIR excitation light source for FTIR excitation,
at least one photodetector configured for collecting signals with a wavelength comprised at least in one of an IR spectrum and/or a Raman spectrum,
a wavelength-dispersive device for collected Raman signals,
an excitation lens, and
collection optics comprising a first collection lens,
wherein the ATR crystal is configured to receive a light beam from the at least one FTIR excitation light source, to redirect the light beam to the sample, to receive modified reflected radiation due to interaction of an evanescent field with the sample and to redirect it so that it can be received by the at least one photodetector,
wherein the excitation lens and the ATR crystal are positioned so that a first optical path is defined, such that the excitation lens is configured to focus into the sample a light beam emitted from the at least one Raman excitation light source,
wherein the ATR crystal and the collection optics are positioned so that a second optical path is defined, such that the collection optics is configured to collect Raman scattered light emitted by the sample and to redirect said Raman scattered light to the at least one photodetector through the wavelength-dispersive device,
wherein a Raman subsystem is an off-axis system,
wherein the collection lens is configured to be movable along a direction parallel to the second optical path, and
wherein the excitation lens is configured to be movable along a direction parallel to the first optical path and/or in a direction transverse to the first optical path.
2. The system according to claim 1 , wherein the wavelength-dispersive device is a spectrometer.
3. The system according to claim 1 , wherein the collection lens has a high numerical aperture value.
4. The system according to claim 3 wherein the excitation lens has a high numerical aperture value.
5. The system according to claim 3 , wherein the collection lens has a numerical aperture value greater than 0.4.
6. The system according to claim 4 , wherein the excitation lens has a numerical aperture value greater than 0.4.
7. The system according to claim 1 , wherein the excitation lens and/or the collection lens has a low numerical aperture value.
8. The system according to claim 7 , wherein the excitation lens and/or the collection lens has a numerical aperture value lower than 0.2.
9. The system according to claim 1 , further comprising:
a first prism configured to receive a light beam from the at least one FTIR excitation light source and to redirect said light beam to the ATR crystal; and/or
a second prism configured to receive the modified reflected radiation from the ATR crystal, and to redirect said modified reflected radiation.
10. The system according to claim 1 , further comprising a fixed mirror, a beam splitter and a movable mirror, wherein the beam splitter is configured to split the light beam emitted by the FTIR excitation light source into two split beams, wherein the fixed mirror is arranged to receive one split beam and to reflect it back to the beam splitter, wherein the movable mirror is arranged to receive the other split beam and to reflect it back to the beam splitter and wherein the first mirror is arranged to receive the beam resulting from an interference of the two split beams and to redirect it.
11. The system according to claim 1 , wherein the at least one photodetector comprises a first photodetector configured for collecting signals with a wavelength comprised in the IR spectrum and a second photodetector configured for collecting signals with a wavelength comprised in the Raman spectrum together with the wavelength-dispersive device, wherein the ATR crystal is configured to redirect the modified reflected radiation so that it can be received by the first photodetector, and wherein the collection optics is configured to redirect Raman scattered light to the second photodetector through the wavelength-dispersive device.
12. The system according to claim 1 , further comprising a processing unit in data communication with the at least one photodetector and the wavelength-dispersive device, the processing unit comprising a spectral data library for identifying signals measured by the at least one photodetector.
13. The system according to claim 1 , further comprising a band pass filter for filtering the light beam from the at least one Raman excitation light source, wherein the band pass filter is located on the first optical path between the at least one Raman excitation light source and the excitation lens.
14. The system according to claim 1 , further comprising a controller configured to control a position of the excitation lens and/or of the collection optics.
15. The system according to claim 1 , wherein light beams in both Raman subsystem and FTIR subsystem are transmitted through free space without using optical fibers.
16. The system according to claim 1 , further comprising:
a first mirror configured to receive a light beam from the at least one FTIR excitation light source, and to redirect said light beam; and/or
a second mirror configured to redirect the modified reflected radiation to the at least one photodetector.
17. The system according to claim 16 , wherein the first mirror and/or the second mirror is a paraboloidal mirror.
18. The system according to claim 1 , wherein the at least one photodetector comprises a single photodetector configured for collecting signals with a wavelength comprised both in the IR spectrum and in the Raman spectrum, wherein the ATR crystal is configured to redirect the modified reflected radiation due to interaction of the evanescent field with the sample so that it can be received by said single photodetector, and wherein the collection optics is configured to redirect Raman scattered light to said single photodetector through the wavelength-dispersive device.
19. The system according to claim 18 , wherein:
the collection optics further comprises a long pass filter and a second collection lens, wherein the first collection lens, the long pass filter and the second collection lens are located on the second optical path such that:
the first collection lens is configured to collect and collimate Raman scattered light from the sample,
the long pass filter is configured for filtering the Raman scattered light collected by the first collection lens, and
the second collection lens is configured for collecting the filtered Raman scattered light from the long pass filter and to redirect said filtered Raman scattered light to the single photodetector through the wavelength-dispersive device.
20. The system according to claim 1 , wherein the collection optics further comprises a long pass filter and a second collection lens, wherein the first collection lens, the long pass filter and the second collection lens are located on the second optical path such that:
the first collection lens is configured to collect and collimate Raman scattered light from the sample,
the long pass filter is configured for filtering the Raman scattered light collected by the first collection lens, and
the second collection lens is configured for collecting the filtered Raman scattered light from the long pass filter and to redirect said filtered Raman scattered light to the at least one photodetector through the wavelength-dispersive device.
21. The system according to claim 20 , wherein the first collection lens, the long pass filter, the second collection lens comprised in the collection optics, the wavelength dispersive device and the second photodetector are assembled so as to be movable in a direction transverse to the second optical path.
22. A method for adding a new record to a spectral data library, wherein the method comprises the steps of:
i) providing a system according to claim 12 ;
ii) placing a new sample on the ATR crystal to be held thereon;
iii) activate both the at least one Raman excitation light source for Raman excitation and the at least one FTIR excitation light source for FTIR excitation;
iv) collecting both signals by the at least one photodetector;
v) associating a measured signal to such new sample thus forming the new record; and
vi) adding such new record to the spectral data library stored in the processing unit of the system.