Device, method and apparatus for performing near field raman light spectroscopy, computer program and computer readable medium

Abstract

The invention discloses a device 20 for performing near field Raman spectroscopy comprising a light beam confinement unit 21 for forming a focal field of a transmitted incident light 23, and a sample stage 30 for providing a test sample 32, which is analysable with the incident light 22 passing through said light beam confinement unit 21, wherein said sample stage 30 is designed to move in at least two spatial directions. A spherical near field source device 25 is arranged between said light beam confinement unit 21 and said sample stage 30, wherein said spherical near field source device 25 is arranged in a focal field of said light beam confinement unit 21 for providing a near field into the test sample 32. Furthermore, the invention discloses a method for investigating a test sample with near field Raman light, a computer program, a computer-readable medium and an apparatus for performing Raman spectroscopy.

Description

[0001] P400159WO_20250922 Seite 1 | 26 v1.3

[0002] Device, method and apparatus for performing near field Raman light spectroscopy, computer program and computer readable medium

[0003] The present invention relates to a device for performing near field Raman light spectroscopy according to claim 1, a method for investigating a test sample with near field Raman light according to claim 13, a computer program according to claim 19, a computer-readable medium according to claim 20, a device holder stage according to claim 21 and an apparatus for performing Raman light spectroscopy according to claim 24.

[0004] Technical field of the Invention

[0005] The system design of modern Raman light spectroscopy systems has usually a strong emphasis on high spatial resolution and high signal-to-noise ratios. Fulfilling these features, it is possible to detect small structures or weak signal strength. But one fundamental aspect of such spectroscopic measurement techniques has been left mostly unattended, i.e., full polarization control in excitation and detection of Raman scattering from nanoscopic structures.

[0006] Background of the Invention

[0007] Typically, near-field Raman imaging is an exceptional microscopy technique which links Raman information (chemical, stress or strain information) to high-resolution Scanning Near-field Optical Microscopy (SNOM). Thus near-field Raman allows for the acquisition of complete high-resolution confocal Raman images. Typically, lateral resolutions of below 100 nm can be achieved. The excitation laser light is focused through a SNOM-tip resulting in a “near-field” (evanescent field). While the sample is moved on a scan stage, the transmitted light is spectroscopically detected point-by- point and line-by-line in order to generate a hyperspectral Raman image. Using a beam deflection setup, it is ensured that the probe can be in contact with the sample. In addition, the topography can be recorded simultaneously to the measurement.

[0008] A publication from Young Chai Cho & Sung II Ahn (Scientific Reports Volume 10, Article number: 11692 (2020), “Fabricating a Raman spectrometer using an optical P400159WO_20250922 Seite 2 | 26 v1.3 pickup unit and pulsed power”), discloses an optical pickup unit (OPU)-based Raman spectrometer, which is fabricated with 3D printer-made components, a Raman edge filter and a laser diode with a wavelength of 520 nm as light source. A function generator was used as a pulsed power source to analyse the characteristics of the OPU Raman spectrometer according to various frequencies and duty ratios. When using a pulsed DC power supply, the laser wavelength tended to move to a longer wavelength with increases in duty ratios.

[0009] The disadvantage of those devices is, that there is no polarisation control in the near field region.

[0010] WO 2002068919 A1 discloses a tip enhanced Raman measurement apparatus. A laser beam is focused to a small spot size onto a sample. A silver coated metal probe has its tip positioned within the beam, either close to or directly with the sample. A reflected Raman signal is detected. The metal probe enhances the Raman signal and provides high resolution. It may be cantilevered, and scanned across the surface of the sample, with its position monitored via optical means.

[0011] The disadvantage of this apparatus is, that the apparatus must comprise a metal probe, and a laser beam is necessary for alignment of the metal probe to perform the Raman measurement.

[0012] JP2010078584A discloses a method for evaluating plasmon including the steps of: irradiating, with first irradiating light the surface of a sample obtained by forming on a metal structure, a light-generating film that either emits light or generates Raman scattering light when irradiated with excitation light, to excite plasmon on the surface of the metal structure, irradiating the light-generating film with second irradiating light to cause the light-generating film to either emit light or generate the Raman scattering light, and scanning the surface of the sample with a probe having metal particles provided on the tip thereof; receiving the light emitted from the light-generating film, while scanning with the probe; and obtaining an image of the light thus received.

[0013] US 2010245816 A1 discloses near-field Raman imaging, performed by holding a dielectric microsphere (e.g. of polystyrene) on or just above the surface of a sample in a Raman microscope. An illuminating laser beam is focused by the microsphere so as to produce a near-field interaction with the sample. Raman scattered light at shifted P400159WO_20250922 Seite 3 | 26 v1.3 wavelengths is collected and analysed. The microsphere may be mounted on a cantilever of an atomic force microscope or other scanning probe microscope, which provides feedback to hold it in position relative to the sample surface. Alternatively, the microsphere may be held on the sample surface by an optical tweezer effect of the illuminating laser beam.

[0014] The disadvantage on these imaging methods and apparatus is, that a micro-particle is placed on a probe of a scanning probe microscope or on a cantilever, which introduces disturbances in the signal that have to be considered in the analysis.

[0015] US6002471 A discloses a method of obtaining high-resolution spectroscopic information from a scanning microscope. An optical beam is directed at a sample and light emitted from the sample (e.g., from Raman scattering or fluorescence) is collected. Resolution is improved by supporting a tiny conductive element (e.g., a silver particle) from a probe located within the optical beam area. The conductive element enhances the light emitted from molecules in the vicinity of the probe. The invention provides the high spatial resolution of microscopes such as the AFM with the high chemical detection sensitivity of surface enhanced Raman spectroscopy. This combination allows the isolation and differentiation of single molecules on surfaces of nanostructures.

[0016] The disadvantage on this imaging method and apparatus is, that a bottom illuminated AFM with probe on top is provided. Such a probe setup causes distortions in the measurement.

[0017] Summary of the Invention

[0018] An object of the present invention is to overcome at least one disadvantage of the prior art. It is further an object of the present invention to provide an enhanced device for performing spectroscopy for providing a near field into the test sample, which preferably allows full polarization control in excitation and detection of Raman light scattering from nanoscopic structures.

[0019] At least one of these objects has been solved by the features of the independent patent claims. Other preferred embodiments are indicated in the dependent claims. P400159WO_20250922 Seite 4 | 26 v1.3

[0020] According to a first aspect of the present invention, a device for performing near field Raman light spectroscopy is provided, which comprises a light beam confinement unit for forming a focal field of a transmitted incident light and a sample stage for providing a test sample, which is analysable with the incident light passing through said light beam confinement unit, wherein said sample stage is designed to move in at least two spatial directions. A spherical near field source device Is arranged between said light beam confinement unit and said sample stage, wherein said spherical near field source device is arranged in a focal field of said light beam confinement unit for providing a near field into the test sample. Using this device, it is possible to detect even smaller structures or weaker signal strength, even down to the single molecule level. The device allows full polarization control in excitation and detection of Raman light scattering from nanoscopic structures. Thus, a fundamental aspect of such spectroscopic measurement techniques can be controlled by the device disclosed herein. Its main advantage is the improvement of the information content and data quality on a technical as well as commercial level.

[0021] Said light beam confinement unit could be embodied as a commercially available microscope objective with high numerical aperture between 0.6 and 0.95, preferably 0.9. The magnification of said microscope objective may vary between 40 and 400. The light beam confinement unit will be able to form certain focal fields that are applied towards said spherical near field source device, like nanoparticles.

[0022] As said spherical near field source device can be placed in the centre of the focal field, or the desired position of the focal field, the test sample itself can be brought closer to said spherical near field source device by the sample stage. As said spherical near field source device can be placed with intent in the central axis, modes inside said spherical near field source device can be generated, that could be used for measurement purposes on the test sample.

[0023] Due to the structure of the transmitted incident light beam that does form a certain focal field, the spherical near field source device will be oscillating. Depending on the several parameters like, size, material of the spherical near field source device or the wavelength and focal field, different dipole or multipole oscillations can appear inside said spherical near field source device generating strong and confined near fields in the test sample. P400159WO_20250922 Seite 5 | 26 v1.3

[0024] Said spherical near field source device allows symmetric near field enhancement on a test sample. Said near field source device can be embodied by a symmetric particle. Thus, a high control of polarization can be assumed using full intensity of the transmitted incident light beam. As there is no AFM-like tip, no light intensity is lost at the cantilever structure which is present in certain AFM configurations known from the state of the art. Said spherical near field source device can be arranged between said structured focal field of light beam confinement and said sample stage.

[0025] The tailored focal-field towards said near field source device will result in an even more confined and enhanced near-field that will enhance Raman light scattering within the test sample. The enhanced Raman light then can be collected via said near field source device and be converted back into the far-field. The enhanced Raman light is then collected by an optical collection system, preferably embodied in said beam confinement unit, which then will be processed by an analysing unit.

[0026] Said spherical near field source device is arranged on a transparent device holder. Thus, the handling of said near field source device in the focal field of said light beam confinement unit is improved and a more accurate positioning of said spherical near field source device is possible. Said light transparent device holder can be symmetric towards the focal field, homogeneous and isotropic in refractive index. It is very important to know that the spherical near field source device alone generates the near field, that should be symmetrical, and no artefacts, or disturbances in the focal field, are generated by a holder of the spherical near field source device. Therefore, the holder of the spherical near field source device must be transparent. This near-field with the selected polarization field is used to generate Raman-spectra from the sample.

[0027] As said spherical near field source device can be placed with intent slightly off the central axis also additional modes inside said spherical near field source device can be generated that could be used for measurement purposes on the test sample. Said test sample will interact with said additional modes and may send a signal back to said spherical near field source device. This signal is detected and analysed. Thus, anisotropic Raman light measurements are possible in both transverse and longitudinal modes.

[0028] Said transparent device holder may comprise glass or is preferably a glass sheet, which is a low refractive index material, ensuring that most light energy is propagated P400159WO_20250922 Seite 6 | 26 v1.3 towards said spherical near field source device. Furthermore, said transparent device holder may comprise a transparent polymer, like plexiglass (PMMA), or Indium Tin Oxide (ITO), or quartz like materials. Those materials are easy to process and said spherical near field source device can be placed in an accurate way on those materials.

[0029] Said transparent device holder is arranged on a moveable device holder stage which is designed to move at least in two spatial directions for shifting said spherical near field source device within the focal field. Thus, the positioning of said spherical near field source device is reproduceable. Said positioning of said spherical near field source device slightly off the central axis is performed more accurately. Said transparent device holder may be moved in x-, y, and z-direction relative to said light beam confinement unit. Another advantage of this invention is, that the near-field can be defined by positioning the spherical near field source device in the focal field. The sample would have to be readjusted if the spherical near field source device is moved in the focal field, so that the same sample position gets measured with different near field properties. Furthermore, said spherical near field source device can be positioned in the focal field so that the different polarisations are generated and consequently out of the different polarisations different Raman spectra can be obtained. Meaning that the focal field can be scanned with the spherical near field source device. If a defined sample position should be measured with different near field polarisations, the sample would have to be moved according to the position of said spherical near field source device, while the spherical near field source device is scanned through the focal field.

[0030] In a preferred embodiment said spherical near field source device is a resonant structure with a high refractive index. Thus, a high control of polarization can be assumed allowing for different near-fields that can be controlled transversely as well as longitudinally. In particular, said spherical near field source device is a plasmonic structure. Said spherical near field source device could be embodied by a metallic or dielectric nanoparticle like gold, silver, silicon or other resonant materials with a high refractive index. Said spherical near field source device could be embodied by a more complex structure, where properties of said spherical near field source device influence the resonance behaviour. These properties would be defined by, for example, Mie coefficients, geometrical diameter, symmetry of the particle, surface layers, refractive index of environment, etc. As possible embodiment, a spherical gold or silicon nanoparticle with a diameter of 50nm to 400nm could be used, using an incident light P400159WO_20250922 Seite 7 | 26 v1.3 source with a wavelength of 532nm, for example a laser light source. Preferably said laser light source emits a narrow band beam. Another wavelength of said incident light source could be 633nm. Thus, a wavelength comparable with a scattering resonance of said spherical near field source device would be advantageable. As said spherical near field source device can be embodied by a symmetric particle, a high control of polarization can be assumed allowing for different near-fields that can be controlled transversely as well as longitudinally.

[0031] In a preferred embodiment an optical feedback arrangement is provided, comprising at least one sensor for arranging said spherical near field source device in the focal field. For example, said sensor may detect the signal intensity generated by said spherical near field source device and said spherical near field source device Is moved relative to said beam confinement unit to maximize the signal intensity. Said sensor may be an optical sensor, for example a camera or a photodiode, for enhanced control of the position of said spherical near field source device.

[0032] As the device comprises said sensor, focusing and positioning of said spherical near field source device into the focal spot can be performed purely optically, requiring no expensive feedback mechanism of the device holder stage. Hence, it does not require any absolute position accuracy. This fact offers the remarkable opportunity to simplify the device holder stage in terms of cost and size.

[0033] In a preferred embodiment an evaluation unit is provided for analysing Raman light emitted from said test sample. Thus, enhanced Raman light measurements may be performed reproducibly. As the evaluation unit can also analyse signals from Raman light scattering, the near field focusing of said spherical near field source device towards the test sample can be performed by reflection or by Raman light scattering, even at a different wavelength. As embodiment several measurement methods are possible including measurement of beam diameter using the optical feedback arrangement, measurement of beam intensity over z-direction, by moving z of the sample stage, or Raman light intensity scan over z-direction of the sample stage.

[0034] In a preferred embodiment a processing unit is provided, at least for controlling an incident light into said light beam confinement unit. The regulation of the position of said spherical near field source device inside the focal field can be performed by a signal of the sensor provided to the processing unit or to the evaluation unit. A P400159WO_20250922 Seite 8 | 26 v1.3 positioning-control loop can be performed in regular reflection, using incident light beam. The processing unit is preferably responsible for scanning the test sample close to of said spherical near field source device, while protecting it from crashing into the test sample. The processing unit may be furthermore responsible for switching different modes of the polarization influencing elements.

[0035] It is most likely that fluorescence effects or photoluminescence effects or such experiments with said device using said spherical near field source device can also be investigated. As this device allows for precise control of the excitation polarization and corresponding measurement in elastically or inelastically scattered light measured in reflection, it establishes the possibility to measure the Raman light anisotropy of the test sample on a small length-scales. This Is possible as said spherical near field source device is symmetric and therefore the dipole (or even multipoles) of said spherical near field source device can be switched between longitudinal and transversal orientation depending on the focal field orientation.

[0036] According to a further aspect of the present invention, a method for investigating a test sample with near field Raman light using a device described herein, comprising:

[0037] - emitting an incident light into a light beam confinement unit,

[0038] - arranging a spherical near field source device in the focal field of said light beam confinement unit,

[0039] - arranging a sample stage with a test sample in direction to said spherical near field source device for providing a near field into the test sample,

[0040] - measuring at least a Raman light, emitted from said near field of said test sample.

[0041] Using this method, it is possible to detect even smaller structures or weaker signal strength, even down to the single molecule level. The method allows full polarization control in excitation and detection of Raman light scattering from nanoscopic structures. Thus, a fundamental aspect of such spectroscopic measurement techniques can be controlled by the device disclosed herein. Its main is the improvement of the information content and data quality on a technical as well as P400159WO_20250922 Seite 9 | 26 v1.3 commercial level. Said spherical near field source device performs like a sensor to enhance inelastic Raman light scattering and allows full polarization control to measure materials and material properties on a nanoscopic level. Said method can be performed as a computer implemented method on a computer.

[0042] In a preferred embodiment said spherical near field source device Is moved in said focal field of said light beam confinement unit for exiting at least one Raman mode in said test sample. As said spherical near field source device can be placed with intent slightly off the central axis also additional Raman modes inside said spherical near field source device can be generated that could be used for measurement purposes on the test. Thus, a to further increase of the range of polarization measurement capabilities is possible.

[0043] In a preferred embodiment said spherical near field source device (25) is positioned relative to the centre of the focal field in at least a first direction. In a preferred embodiment said spherical near field source device (25) is positioned relative to the centre of the focal field in at least a second direction. Said method differs fundamentally from common Raman spectroscopy, if one uses a polarization-resolved Raman spectroscopy. This is only possible if one moves the spherical near field source device and the test sample through the focal field. Thus at least three measurements may be performed, A first measurement moving the spherical near field source device to the centre of the focal field and placing the spherical near field source device on top of the centre of the test sample using the transparent device holder. A further measurement (x-polarized near field) is performed after shifting the spherical near field source device and the test sample in a first direction (x-direction) relative to the centre of the focal field using the transparent device holder. Another further measurement (y- polarized near field) is performed after shifting the spherical near field source device and the test sample in a second direction (y-direction) relative to the centre of the focal field using the transparent device holder. A total of three Raman measurements are thus performed at the same position on the biological cell, but with three orthogonal polarization orientations, enabling more information to be obtained from the Raman tensor and, depending on the tensor, even allowing the Raman tensor to be reconstructed. The measured Raman spectra can be used as intermediate results, but one may easily get the Raman tensor, as it contains more information than the Raman spectrum itself. P400159WO_20250922 Seite 10 | 26 v1.3

[0044] As this method allows for precise control of the excitation polarization and corresponding measurement in elastically or inelastically scattered light measured in reflection, it establishes the possibility to measure the Raman light anisotropy of the test sample on a small length-scales. This is possible as said spherical near field source device is symmetric and therefore the dipole (or even multipoles) of said spherical near field source device can be switched between longitudinal and transvers orientation depending on the focal field orientation.

[0045] In a preferred embodiment said movement of said spherical near field source device is monitored by at least one optical feedback system. Said at least one optical feedback system may detect the signal intensity generated by said spherical near field source device and said spherical near field source device is moved relative to said beam confinement unit to maximize the signal intensity.

[0046] In a preferred embodiment said test sample is moved in at least two spatial directions for measuring Raman light on different regions of the test sample. Thus, a large test sample with several structures may be scanned. Changing the test sample is not necessary. Said sample stage comprising the test sample may be moved in x-, y, and z-direction relative to said light beam confinement unit.

[0047] According to a further aspect of the present invention, a computer program comprising instructions which, when the program is executed by a computer, cause the the device disclosed herein, to carry out the method disclosed herein. Said computer may be part of said device or may be a stand-alone computer. Said instructions are used to control at least the performance or movement of said incident light and the light beam confinement unit and the sample stage and the device holder. Thus, the complex measurement scenario is performed automatically. Even for large test samples, investigation of a specific area in the test sample can be performed several times automatically. Finding specific areas on a large test sample is a challenge, without such a computer program. A computer could be also an Arduino, or Minicomputer.

[0048] According to a further aspect of the present invention, a computer-readable medium comprising instructions which, when executed by a computer, cause the device described herein, to carry out the method disclosed herein. Said computer-readable medium may comprise the computer program as well as important calibration data for P400159WO_20250922 Seite 11 | 26 v1.3 calibrating the device disclosed herein. Comprising all the information on a computer- readable medium supports the user of said device.

[0049] According to a further aspect of the present invention, a device holder stage is disclosed, which is designed to move at least in two spatial directions for shifting a spherical near field source device arranged on a transparent device holder within the focal field of a light beam confinement unit. Said device holder stage may be part of a set with a beam confinement unit or may be purchased separately. Said device holder stage may comprise at least one fixation unit for reproducibly positioning the device holder stage to a beam confirmation unit.

[0050] Preferably said device holder stage may comprise a pure levitation system using integrated coils. Thus, no springs, or no mechanical connections to the spherical near field source device, are necessary. The movement of said spherical near field source device is performed continuously, without interruptions. Thus, a resonant frequence of the stage is easily changeable.

[0051] According to a further aspect of the present invention, an apparatus for performing Raman light spectroscopy is disclosed, which comprises a light generation unit for emitting a light, preferable a laser beam, at least one optical component for manipulating said light and forming an incident light, a light beam confinement unit for transmitting said incident light, a sample stage for providing a test sample, which is analysable with the incident light from the light beam confinement unit, wherein said sample stage is designed to move in at least two spatial directions, a spherical near field source device is arranged between said light beam confinement unit and said sample stage, wherein said spherical near field source device is arranged in a focal field of said light beam confinement unit for providing a near field into the test sample and an analysing unit for analysing said Raman light emitted from said test sample.

[0052] As this apparatus allows for precise control of the excitation polarization and corresponding measurement in elastically or inelastically scattered light measured in reflection, it establishes the possibility to measure the Raman light anisotropy of the test sample on a small length-scales. This is possible as said spherical near field source device is symmetric and therefore the dipole (or even multipoles) of said spherical near field source device can be switched between longitudinal and transvers P400159WO_20250922 Seite 12 | 26 v1.3 orientation depending on the focal field orientation, especially by changing the ratio of longitudinal and transvers orientation.

[0053] In a preferred embodiment a processing unit is provided, wherein said processing unit is designed to control at least said sample stage. Its purpose is to control, regulate or set the different disclosed units into different states. These controls are necessary to switch to a certain mode, adjust the position of said spherical near field source device or to move the test sample. The processing unit could be embodied by a personal computer, or any other type of controlling unit.

[0054] The analysing unit may be responsible for analysis of the received signal from said spherical near field source device. This unit can contain several polarization influencing components, embodied for example by linear polarizers or, wave plates, which could be rotatable, or also using liquid crystal polarizing elements. After the incident light has been manipulated with respect to its polarization, it can be measured by different elements, which could be embodied by photodiode, camera and spectrometer with a sensitive detector. With this configuration of detection elements, combined with polarization influencing components, a full Stokes measurement is possible in reflection (Rayleigh light scattering) and or even in Raman light scattering. Preferably said processing unit is designed to control at least said analysing unit. The control is necessary to analyse a certain mode.

[0055] The light generation unit may be responsible to generate a specific spatial and, alternatively or supplementary, polarization-tailored incident light mode, for example a laser light mode. Preferably, this unit comprises a monochromatic and coherent light source. This light source could be embodied as a laser emitting a laser beam. Following by an optional filter that could be embodied by a laser line filter. The laser beam then could be directed by several mirrors to towards several polarization influencing elements. The polarization influencing elements can be controlled in certain embodiments either electrically, via magnetic fields or mechanically, by rotation or via mechanical pressure to generate different types of beam polarizations. To name a few, this could be radially polarized beam (RPB), azimuthal polarized beam (APB), Gaussian beam with controllable polarization (Gauss), counter rotating radially polarized beam (CRPB) or counter rotating azimuthal polarized beam (CAPB). The elements for influencing the polarization can be embodied by linear polarizers, liquid crystal variable retarders, liquid crystal beam shapers (e.g., q- or s-plates) or wave P400159WO_20250922 Seite 13 | 26 v1.3 plates with different rotation angles. Behind the polarization influencing elements, an optional element could be placed to optimize the modal quality and purity, which could be embodied by a pinhole filter or Fourier filter. After this optional element, another optional element could be placed to direct the backscattered light from the objective to the analysing unit. One possible embodiment could be a beam splitter or spectrally selective mirror system. Preferably said processing unit Is designed to control at least said light generation unit. The control is necessary to generate a certain mode.

[0056] Alternative or supplementary said processing unit is designed to control at least said device holder stage comprising said spherical near field source device is provided. Thus, the handling of said near field source device in the focal field of said light beam confinement unit is improved and a more accurate positioning of said spherical near field source device is possible.

[0057] By means of the following figures, the invention is explained in more detail by means of examples of embodiments. The list of references is part of the disclosure.

[0058] Positional indications, such as "above", "below", "right" or "left" are in each case related to the corresponding embodiments and are not to be understood as restrictive.

[0059] Indications, such as "first", "second", or "further" are in each case related to the corresponding device and are not to be understood as restrictive or enumeration.

[0060] Brief Description of the Drawings

[0061] In order to facilitate better understanding of the present invention, reference is made below to the drawings. These show only exemplary embodiments of the subject matter of the invention. These embodiments, offered not to limit but only to exemplify and teach the invention, are shown and described in sufficient detail to enable those skilled in the art to implement or practice the invention. Thus, where appropriate to avoid obscuring the invention, the description may omit certain information known to those of skill in the art.

[0062] In the figures and the associated description, identical or functionally analogous parts are provided with the same reference numerals. P400159WO_20250922 Seite 14 | 26 v1.3

[0063] The invention also encompasses individual features shown in the figures, even if they are shown there in connection with other features and / or are not mentioned above. Further, the term "comprising" and derivatives thereof do not exclude other elements or steps. Likewise, the indefinite article "a" or "one" and derivatives thereof do not exclude a plurality. The functions of multiple features recited in the claims may be performed by a single unit. The terms "substantially", "approximately", "about" and the like in connection with a characteristic or a value define, in particular, also exactly the characteristic or exactly the value. All reference signs in the claims are not to be understood as limiting the scope of the claims.

[0064] Fig. 1 : shows the inventive device for performing near field Raman light spectroscopy in a schematic view,

[0065] Fig. 2: shows a movement of a spherical near field source device within the focal field of a radially polarized beam within a device according to Fig.1 ,

[0066] Fig. 3: shows the x-direction of the electric field orientations of a radially polarized beam according to Fig. 2,

[0067] Fig. 4: shows the y-direction of the electric field orientations of the radially polarized beam according to Fig. 2,

[0068] Fig. 5: shows the z-direction of the electric field orientations of the radially polarized beam according to Fig. 2,

[0069] Fig. 6: shows a near-field simulation of a spherical near field source device within a focal field in x- direction, placed on the optical axis of a tightly focused x-polarized Gaussian beam,

[0070] Fig. 7: shows a near-field simulation of a spherical near field source device within a focal field in z- direction, placed on the optical axis of a tightly focused x-polarized Gaussian beam,

[0071] Fig. 8: shows an inventive device holder stage of the device according to Fig. 1 in a schematic view, P400159WO_20250922 Seite 15 | 26 v1.3

[0072] Fig. 9: shows an inventive apparatus comprising the device according to Fig. 1 in a schematic view, and

[0073] Fig. 10: shows a logic diagram of the processing unit, the device according to Fig. 1, the analysing unit, the light generation unit according to Fig. 9.

[0074] Detailed Description

[0075] Figure 1 shows a device 20 for performing near field Raman light spectroscopy, which comprises a light beam confinement unit 21 for forming a focal field of a transmitted incident light 23 and a sample stage 30 for providing a test sample 32. Said test sample 32 is analysable with the incident light 22 passing through said light beam confinement unit 21 , and said sample stage 30 is designed to move the test sample 32 in three spatial directions. Said light beam confinement unit 21 comprises a microscope objective 24 with high numerical aperture.

[0076] A spherical near field source device 25 is arranged on a glass holder 26 between said light beam confinement unit 21 and said sample stage 30. Said spherical near field source device 25 is arranged in the focal field of said light beam confinement unit 21 for providing a near field into the test sample 32. The glass holder 26 is arranged on a moveable device holder stage 27, which is designed to move in three spatial directions for shifting said spherical near field source device 25 within the focal field.

[0077] Said near field source device 25 is a symmetric particle. Due to the structure of the transmitted incident light beam 23, that does form a certain focal field, the spherical near field source device 25 will be oscillating. Depending on the several parameters like, size, material of the spherical near field source device 25 or the wavelength and focal field of the incident light 22, different dipole or multipole oscillations can appear inside said spherical near field source device 25 generating strong and confined near fields.

[0078] Said device 20 comprises an optical feedback arrangement 33, comprising a camera 34 for arranging said spherical near field source device 25 in the focal field. The camera 34 detects the signal intensity generated by said spherical near field source device 25 and said spherical near field source device 25 Is moved relative to said beam confinement unit 21 to maximize the signal intensity. P400159WO_20250922 Seite 16 | 26 v1.3

[0079] Furthermore, an evaluation unit 39 is provided for analysing Raman light emitted from said test sample 32. Said evaluation unit 39 is connected to said camera 34, to said beam confinement unit 21 and to said moveable device holder stage 27. Said evaluation unit 39 comprises a control unit and a computer to control the said camera 34, said beam confinement unit 21 and said moveable device holder stage 27 as well as said sample stage 30.

[0080] As possible embodiment, a spherical gold nanoparticle with a diameter of 80nm is used as said spherical near field source device 25, using an incident light 22 with a wavelength of 532nm, for example a laser light source. Figure 2 to Figure 5 show a possible measurement scenario for the device according to Figure 1, which illustrates numerically calculated focal fields of a radially polarized beam. As simulation parameters, an objective 24 with magnification of 100 and a numerical aperture (NA) of 0.9 was chosen. Depending on the spatial position of the spherical gold nanoparticle inside the focal field, different electric field orientations dominate. When moving the spherical gold nanoparticle through this field also the plasmonic dipole orientation will align with the dominating electric field. As example, the spherical gold nanoparticle could be placed in the centre of the focal field to excite a longitudinal z-oriented plasmonic oscillation, where its nearfield can be used to excite Raman modes within a specimen to be measured. When moving the spherical gold nanoparticle half a wavelength in the x-direction, a transverse x-oriented plasmonic oscillation will manifest, with its x-polarized nearfield to be used to measure the specimen - see shifted circle in the Figure 2 to Figure 5. Alternatively, a spherical silicon nanoparticle with a diameter of 220nm could be used.

[0081] To demonstrate how to the spherical gold nanoparticle can be employed as nearfield sensor we show numerically calculated near-fields in in Figure 6 and Figure 7Simulations were performed using an 80nm gold particle that was excited with an x- polarized Gaussian beam. As seen in the x-component of the electric field, there is a strong near-field in the x-direction outside of the gold nanoparticle. This strong nearfield can be used to excite Raman modes within a specimen placed in close vicinity. For simplification purposes, the refractive index of the specimen was neglected here.

[0082] Figure 8 shows said device holder stage 27, which is designed to move in three spatial directions for shifting said spherical near field source device 25 arranged on the transparent device holder 26 within the focal field of a light beam confinement unit 21 , P400159WO_20250922 Seite 17 | 26 v1.3 as shown in Figure 2 to Figure 5. Said device holder stage 27 comprises a fixation unit 28 for reproducibly positioning the device holder stage 27 to a beam confirmation unit 21 . Said device holder stage 27 comprises a pure levitation system using integrated coils 29. Thus, no springs or mechanical connection are necessary.

[0083] Figure 9 shows an inventive apparatus 40 for performing Raman light spectroscopy comprising said device 20 according to Figure 1. Furthermore, the apparatus 40 comprises a light generation unit 45 for emitting a light, preferable a laser beam, several optical components for manipulating said light and forming an incident light 22, and an analysing unit 55 for analysing said Raman light emitted from said test sample 32.

[0084] In addition, a processing unit 60 is provided, wherein said processing unit 60 is designed to control said sample stage 30. Its purpose is to control, regulate or set the different disclosed units into different states as shown in Figure 10. The processing unit 60 comprises a personal computer 61 . The personal computer 61 is hosting a computer program 62, comprising instructions which, when the program is executed by the personal computer 62, cause the personal computer 62 to carry out the method disclosed herein. Furthermore at least one computer-readable medium 63 is provided comprising instructions which, when executed by said personal computer 62, cause the personal computer 62 to carry out the method disclosed herein.

[0085] The analysing unit 55 is responsible for analysing the received signals from said spherical near field source device 25. This unit can contain several polarization influencing components, embodied for example by linear polarizers 56 and wave plates 57, which could be rotatable, or also using liquid crystal polarizing elements. After the incident light has been manipulated with respect to its polarization, it can be manipulated by a monochromator 58 and it is measured by different elements 59, which could be embodied by photodiode, camera and spectrometer with a sensitive detector. With this configuration of detection elements 59, combined with polarization influencing components, a full Stokes measurement is possible in reflection (Rayleigh light scattering) and or even in Raman light scattering. Said processing unit 60 is designed to control at least said analysing unit 55.

[0086] The light generation unit 45 is responsible to generate a specific spatial and, alternatively or supplementary, polarization-tailored incident light mode, for example a P400159WO_20250922 Seite 18 | 26 v1.3 laser light mode. The light generation unit 45 comprises a monochromatic and coherent light source 46. This light source 46 is a laser emitting a laser beam 22. Following by a laser line filter 47. The laser beam then is directed by several mirrors to towards several polarization influencing elements 48. The polarization influencing elements 48 are controlled electrically. The elements 48 for influencing the polarization can be embodied by linear polarizers, liquid crystal variable retarders, liquid crystal beam shapers (e.g., q- or s-plates) or wave plates with different rotation angles. Behind the polarization influencing elements 48, a Fourier filter 49 is placed to optimize the modal quality and purity. After the Fourier filter 49 a beam splitter 50 is placed to direct the backscattered light from the test sample 32 to the analysing unit 55.

[0087] Said processing unit 60 controls the incident light 22 into said light beam confinement unit 21 . The regulation of the position of said spherical near field source device 25 inside the focal field can be performed by the camera 34 and the analysing unit 55 or the evaluation unit 39. A positioning-control loop can be performed in regular reflection, using incident light beam 22. The processing unit 60 is responsible for scanning the test sample 32 close to of said spherical near field source device 25.

[0088] A method for investigating a test sample 32 with near field Raman light comprising at least the following steps:

[0089] - emitting an incident light 22 into a light beam confinement unit 21 ,

[0090] - arranging a spherical near field source device 25 in the focal field of said light beam confinement unit 21,

[0091] - arranging a sample stage 30 with a test sample 32 in direction to said spherical near field source device 25 for providing a near field into the test sample 32,

[0092] - measuring at least a Raman light, emitted from said near field of said test sample 32.

[0093] One example of the method describes an investigation of a biological cell as the test sample 32 performed with a laser wavelength of 532 nm and a radially polarized beam. A biological cell could have a diameter of about 15 pm, and the spherical near field P400159WO_20250922 Seite 19 | 26 v1.3 source device 25, for example a gold sphere, has a diameter of 200 nm. In a common Raman test equipment without the gold sphere, the biological cell is almost invisible through Raman emission. By moving the gold sphere to the centre of the focal field and placing the gold sphere on top of the centre of the biological cell using the transparent device holder 26 and using a radially polarized incident light beam 22, a Raman measurement with z-polarization is performed. Afterwards lifting the gold sphere and move the gold sphere and biological cell in x-direction (to x=340 nm and y=0 nm) relative to the centre of the focal field using the transparent device holder 26 and placing the gold sphere back on the biological cell. Here, a Raman measurement would now be performed where the amplified field of the gold sphere mainly emits x-polarized near field into the biological cell. Afterwards lifting the gold sphere again and moving the hold sphere and biological cell to the position in y- direction (x=0 nm and y=340 nm) and perform another Raman measurement, where the amplified field of the gold sphere mainly emits y-polarized near field into the biological cell.

[0094] v1.3

[0095] Reference List

[0096] 20 device

[0097] 21 light beam confinement unit

[0098] 22 incident light

[0099] 23 transmitted incident light

[0100] 24 microscope objective

[0101] 25 spherical near field source device

[0102] 26 transparent device holder

[0103] 27 device holder stage

[0104] 28 fixation unit

[0105] 29 coils

[0106] 30 sample stage

[0107] 32 test sample

[0108] 33 optical feedback arrangement

[0109] 34 camera

[0110] 39 evaluation unit

[0111] 40 apparatus

[0112] 45 light generation unit

[0113] 46 light source

[0114] 47 laser line filter

[0115] 48 polarization influencing elements

[0116] 49 Fourier filter

[0117] 50 beam splitter

[0118] 55 analysing unit

[0119] 56 linear polarizers

[0120] 57 wave plate

[0121] 58 monochromator

[0122] 59 detector

[0123] 60 processing unit

[0124] 61 personal computer

[0125] 62 computer program

[0126] 63 computer-readable medium

Claims

P400159WO_20250922 Seite 21 | 26 v1.3Claims1.A device (20) for performing near field Raman spectroscopy comprising a light beam confinement unit (21 ) for forming a focal field of a transmitted incident light (23) and a sample stage (30) for providing a test sample (32), which is analysable with the incident light (22) passing through said light beam confinement unit (21), wherein said sample stage (30) is designed to move in at least two spatial directions, characterized in that a spherical near field source device (25) is arranged between said light beam confinement unit (21) and said sample stage (30), wherein said spherical near field source device (25) is arranged in a focal field of said light beam confinement unit (21) for providing a near field into the test sample (32), and said spherical near field source device (25) is arranged on a transparent device holder (26), while said transparent device holder (26) is arranged on a moveable device holder stage (27) which is designed to move at least in two spatial directions for shifting said spherical near field source device (25) within the focal field.

2. The device according to claim 1 , characterized in that, said spherical near field source device (25) is a resonant structure.

3. The device according to claim 1 or 2, characterized in that, an optical feedback arrangement (33) is provided, comprising at least one sensor for arranging said spherical near field source device (25) in the focal field.

4. The device according to any of the previous claims, characterized in that, an evaluation unit (39) is provided for analysing Raman light emitted from said test sample (32).

5. The device according to any of the previous claims, characterized in that, a processing unit (60) is provided, at least for controlling an incident light (22) into said light beam confinement unit (21).

6. The device according to any of the previous claims, characterized in that, said light beam confinement unit could be embodied as a microscope objective with high numerical aperture between 0.6 and 0.95, preferably 0.9 and the magnification of said microscope objective preferably vary between 40 and 400.P400159WO_20250922 Seite 22 | 26 v1.

37. The device according to any of the previous claims, characterized in that, said transparent device holder (26) comprises glass, or is preferably a glass sheet, which is a low refractive index material, and / or comprise a transparent polymer, like plexiglass (PMMA), or Indium Tin Oxide (ITO), or quartz like materials.

8. The device according to any of the previous claims, characterized in that, an optical feedback arrangement (33) is provided, comprising at least one sensor for arranging said spherical near field source device (25) in the focal field.

9. The device according to any of the previous claims, characterized in that, an evaluation unit (39) is provided for analysing Raman light emitted from said test sample (32).

10. The device according to any of the previous claims, characterized in that, a processing unit is provided at least for controlling an incident light into said light beam confinement unit (60).11 . The device according to any of the previous claims, characterized in that, said device holder stage (27) comprises a fixation unit (28) for reproducibly positioning the device holder stage (27) to a beam confirmation unit (21).

12. The device according to any of the previous claims, characterized in that, said device holder stage (27) comprises a pure levitation system using integrated coils (29).

13. A method for investigating a test sample (32) with near field Raman light, preferably using a device (20) according to at least one of the claims 1 to 12, comprising:- emitting an incident light (22) into a light beam confinement unit (21),- arranging a spherical near field source device (25) in the focal field of said light beam confinement unit (21), arranging a sample stage (30) with a test sample (32) in direction to said spherical near field source device (25) for providing a near field into the test sample (32),P400159WO_20250922 Seite 23 | 26 v1.3- measuring at least a Raman light, emitted from said near field of said test sample (32).

14. The method according to claim 13, characterized in that, said spherical near field source device (25) is moved in said focal field of said light beam confinement unit (21) for exiting at least one Raman mode in said test sample (32).

15. The method according to claim 13 or 14, characterized in that, said spherical near field source device (25) is positioned relative to the centre of the focal field in at least a first direction.

16. The method according to claim 15, characterized in that, said spherical near field source device (25) is positioned relative to the centre of the focal field in at least a second direction.

17. The method according to any of the claims 13 to 16, characterized in that, said movement of said spherical near field source device (25) is monitored by at least one optical feedback system (33).

18. The method according to any of the claims 13 to 17, characterized in that, said test sample (32) is moved in at least two spatial directions for measuring Raman light on different regions of the test sample (32).

19. A computer program (62) comprising instructions which, when the program is executed by a computer (61 ), cause a device (20) according to one of the claims 1 to 12 to carry out the method of one of the claims 13 to 18.

20. A computer-readable medium (63) comprising instructions which, when executed by a computer (61), cause a device (20) according to one of the claims 1 to 12 to carry out the method of one of the claims 13 to 18.21 . A device holder stage (27) for a device (20) according to any of the claims 1 to 12, which is designed to move at least in two spatial directions for shifting a spherical near field source device (25) arranged on a transparent device holder (26) within the focal field of a light beam confinement unit (21).P400159WO_20250922 Seite 24 | 26 v1.

322. The device holder stage according to claim 21 , characterized in that, a fixation unit (28) is provided for reproducibly positioning the device holder stage (27) to a beam confirmation unit (21).

23. The device holder stage according to claim 21 or 22, characterized in that, said device holder stage (27) comprises a pure levitation system using integrated coils (29).

24. An apparatus (40) for performing Raman spectroscopy comprising:- a light generation unit (45) for emitting a light, preferable a laser beam- at least one optical component for manipulating said light and forming an incident light (22),- a light beam confinement unit (21 ) for transmitting said incident light (22),- a sample stage (30) for providing a test sample (30), which is analysable with the incident light (22) from the light beam confinement unit (21), wherein said sample stage (30) is designed to move in at least two spatial directions,- a spherical near field source device (25) is arranged between said light beam confinement unit (21) and said sample stage (30), wherein said spherical near field source device (25) is arranged In a focal field of said light beam confinement unit (21) for providing a near field into the test sample (32), and and said spherical near field source device (25) is arranged on a transparent device holder (26), while said transparent device holder (26) is arranged on a moveable device holder stage (27) which is designed to move at least in two spatial directions for shifting said spherical near field source device (25) within the focal field- an analysing unit (55) for analysing said Raman light emitted from said test sample (32).

25. The apparatus according to claim 24, characterized in that, a processing unit (60) is provided, wherein said processing unit (60) is designed to control at least said sample stage (30).P400159WO_20250922 Seite 25 | 26 v1.

326. The apparatus according to claim 25, characterized in that, said processing unit (60) is designed to control at least said analysing unit (55).

27. The apparatus according to claim 25 or 26, characterized in that, said processing unit (60) is designed to control at least said light generation unit (45).

28. The apparatus according to any of the claims 25 to 27, characterized in that, said processing unit (60) is designed to control at least at least device holder stage (27) comprising said spherical near field source device (25).

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