Optical Activity Measurement by Frequency Modulation

Abstract

The system 1 for measuring the optical activity of a sample 2 comprises at least one frequency modulation device 3, at least one synchronization device 4, and at least one detection device 5. The frequency modulation device 3 is configured to modulate the frequency of incident electromagnetic radiation emitted from and / or irradiated onto the sample 2 using at least one frequency modulation signal Sf. The synchronization device 4 is configured to receive the at least one frequency modulation signal Sf and to emit at least one detection modulation signal Sd synchronized with the at least one frequency modulation signal Sf. The system 1 is configured such that the detection device 5 detects the incident electromagnetic radiation EMs synchronized with the detection modulation signal Sd.

Description

Technical Field

[0001] The present invention relates to a system for measuring the optical activity of a sample according to claim 1, a method for measuring the optical activity of a sample according to claim 14, and a method for manufacturing a system for measuring the optical activity of a sample according to claim 15.

Background Art

[0002] The majority of pharmaceutical compounds are chiral, and the effects of drugs depend on their chirality. In fact, the enantiomers of chiral drugs have different interactions with enzymes, proteins, receptors, etc., and the differences in these interactions ultimately lead to differences in biological activities such as the pharmacological properties, pharmacokinetics, metabolic effects, toxicity, and immune responses of the two enantiomers. Therefore, the enantioselective synthesis or chiral separation of racemic drugs and subsequent inspections are necessary tasks in the pharmaceutical industry and in clinical treatments.

[0003] Optical activity refers to the property of a chiral compound that changes the polarization of electromagnetic radiation. For this reason, spectroscopy is a common means for examining chiral compounds. For example, Patent Document 1 discloses the application of spectroscopy to the measurement of circular polarization, and the selective mutual conversion of the polarization states of coherent light and incoherent light is used to realize the time-averaged offset-free measurement of optical activity scattering or circular dichroism. For this purpose, an optical element is inserted into the optical path of the excitation light, or the optical path of the transmitted light or scattered light.

[0004] This system, like other current systems, measures by spatially separating left-circularly polarized light and right-circularly polarized light onto a CCD detector before reading. These systems are slow, difficult to manufacture and maintain, and troubled by high noise. Although the equipment of the current state of the art is commercialized, it is far from being widely used to the extent it should be.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] U.S. Patent Application Publication No. 2004 / 0169923 [Summary of the Invention]

[0006] An object of the present invention is to provide a system for measuring the optical activity of a sample that overcomes the drawbacks of this current state of the art. In particular, an object of the present invention is to provide a system for measuring the optical activity of a sample that has a high optical throughput and is at the same time highly sensitive and stable.

[0007] This object is achieved by the system according to claim 1. In particular, a system for measuring the optical activity of a sample is provided. The system comprises at least one frequency modulation device, at least one synchronization device, and at least one detection device. The at least one frequency modulation device is configured to modulate the frequency of the incident electromagnetic radiation emitted from and / or irradiated onto the sample using at least one frequency modulation signal. The at least one synchronization device is configured to receive at least one frequency modulation signal. The at least one synchronization device is further configured to emit at least one detection modulation signal that is synchronized with the at least one frequency modulation signal. The system is configured such that the at least one detection device detects the incident electromagnetic radiation in synchronization with the at least one detection modulation signal.

[0008] Therefore, it is conceivable to irradiate the sample with electromagnetic radiation to excite the sample, and then modulate the frequency of the electromagnetic radiation emitted from the excited sample during relaxation. In this case, the frequency modulation device is arranged behind the sample with respect to the optical path extending from the excitation source towards the detection device. The excitation of the sample in this case preferably occurs by electromagnetic radiation that is not frequency modulated. However, it is equally conceivable to modulate the frequency of the electromagnetic radiation irradiated onto the sample in order to excite the sample. In this case, the frequency modulation device is arranged in front of the sample with respect to the optical path. Thus, in the latter case, the excitation of the sample occurs by frequency-modulated electromagnetic radiation.

[0009] In any case, electromagnetic radiation emitted from the excited sample is detected. Therefore, the present system is based on frequency modulation in the measurement of the photoluminescence optical activity.

[0010] Frequency modulation is preferably achieved by applying at least one electrical signal to a frequency modulation device, where this same electrical signal is preferably also transmitted to a synchronization device. In other words, it is preferable that the frequency modulation signal corresponds to the signal transmitted to the synchronization device.

[0011] Since the detection modulation signal emitted from the synchronization device is synchronized with the frequency modulation signal, the present system enables the detection of electromagnetic radiation emitted from the sample, which is modulated in synchronization with the frequency modulation signal.

[0012] Thus, the present system enables the measurement of optical activity by using frequency modulation to separate optical signals. In this way, the present system enables an efficient measurement of the optical activity of a sample starting from a few minutes. A further advantage lies in the stability of the components of the system, which requires little maintenance, is easy to manufacture, and can be used more easily by non-expert users. Furthermore, frequency modulation reduces noise and thereby improves the measurement accuracy. Therefore, the present system makes it possible to change slow and niche measurements, as performed in known systems, into routine measurements carried out in various industrial and academic research institutes.

[0013] The frequency modulation device is preferably configured to separate components of the incident electromagnetic radiation having two or more polarization states into components of electromagnetic radiation having one or more frequencies.

[0014] There are three basic types of polarization (types of degenerate polarization), which may also be referred to as Stokes parameters. These basic types are circular polarization, linear polarization, and 45-degree polarization. Any electromagnetic radiation that is a mixture of these three types is called elliptical polarization. Using a frequency modulation device, it is possible to separate these polarization states or types into different frequencies, thereby enabling a distinction between left-circularly polarized electromagnetic radiation and right-circularly polarized electromagnetic radiation, or between +45-degree polarized electromagnetic radiation and -45-degree polarized electromagnetic radiation. In particular, the frequency modulation device used in this system enables modulation to be observed at one of these frequencies and synchronized with a detection device. In this way, a time separation with respect to intensity is obtained.

[0015] The electromagnetic radiation incident on the frequency modulation device preferably includes elliptical polarized electromagnetic radiation that can be represented as a degenerate polarization state such as a horizontally linearly polarized state, a vertically linearly polarized state, a left-circularly polarized state, or a right-circularly polarized state. However, other polarization states are also possible.

[0016] The frequency modulation device is configured to separate electromagnetic radiation having these various polarization states into components of electromagnetic radiation having one or more frequencies. For example, if the electromagnetic radiation incident on the frequency modulation device includes a circular polarization state and a linear polarization state, the frequency modulation device will associate or assign a first frequency to the circular polarization state of the electromagnetic radiation and a second frequency different from the first frequency to the linear polarization state.

[0017] Left-circularly polarized electromagnetic radiation and right-circularly polarized electromagnetic radiation can be detected separately from each other by a detection device by modulating circularly polarized electromagnetic radiation including both left-circularly polarized and right-circularly polarized states at a predetermined frequency and, in synchronization with a detection modulation signal emitted by a synchronization device, preferably with the help of a masking device. See further below.

[0018] Therefore, the frequency modulation device can be regarded as a polarization state converter. In particular, the frequency modulation device preferably has a variable frequency retardance. For example, when the frequency modulation device is set to "quarter-wave retardance", it preferably oscillates sinusoidally between a plus quarter-wave (+QW) retardance and a minus quarter-wave (-QW) retardance, which means that the circular polarization component of the electromagnetic radiation is converted into a +1 / -1 linearly polarized state and oscillates between them. At an exemplary time t = 1 of the oscillation, the retardation is +QW, and the left-handed circularly polarized electromagnetic radiation (LHCPL) is "converted" into +1 linearly polarized light, and the right-handed circularly polarized electromagnetic radiation (RHCPL) is "converted" into a +1 linearly polarized state. When a linear polarizer is used, see also the following, the polarizer converts this into an intensity signal. At an exemplary time t = 2, the process reverses to a -QW retardation, which means that the LHCPL becomes a -1 linearly polarized state and the RHCPL becomes a +1 linearly polarized state.

[0019] Therefore, when the modulation is set to QW, a signal whose intensity varies slightly over time based on the amounts of LHCPL and RHCPL is obtained at a predetermined frequency (determined by the modulation). The detection device and the masking device (see also the following) then acquire this signal at one frequency and synchronize the masking performed by the masking device with the frequency of the modulation to separate the RHCPL from the LHCPL, so that the detection device reads the "time = 1" of the oscillation in one of its regions, such as in one column of the detection device which is a CCD sensor, and reads the "time = 2" in another region of the detection device, such as in another column of the CCD sensor.

[0020] It should be noted that the retardance of the frequency modulation device is preferably a setting that can be changed. In fact, when it is desired to generate circularly polarized electromagnetic radiation, the setting of the frequency modulation device should be set to QW retardance, and when it is desired to generate linearly polarized electromagnetic radiation, the setting of the frequency modulation device should be set to the so-called half-wave (HW) retardance.

[0021] Therefore, the system preferably utilizes frequency modulation to separate different polarization states from each other. In other words, the system enables frequency polarization modulation measurements for recording optical activity.

[0022] The frequency modulation signal is preferably configured to separate two or more polarization states of electromagnetic radiation that is incident on the sample or emitted from the sample from each other. As will be described in more detail below, the frequency modulation signal is preferably sinusoidal and / or square-shaped and is preferably provided by a frequency modulation device such as is known and commercially available in the art.

[0023] The system can be configured such that components of electromagnetic radiation having one or more frequencies are detected by the detection device simultaneously with respect to each other or with a temporal delay.

[0024] That is, if the frequency-modulated electromagnetic radiation includes two or more frequency components, these two or more frequency components may be detected simultaneously or with a temporal delay.

[0025] When detection is understood to be the reading of an electrical signal from the detection device, simultaneous detection can be achieved by the use of selective masking where a masking device (see further below) is moved to different one or more regions of the detection device in synchronization with the modulation of the detection device and then after a while all polarization states are read out, i.e., detected simultaneously.

[0026] Time-delayed detection is achieved using a high-speed detection device that can be detected directly in synchronization with the modulation, and different polarization states are read directly from the detection device at different times. Thus, whether to detect one frequency or more frequencies depends on how the modulation looks and how it is coupled to the detection device and / or the masking device. For example, as described now, two frequencies can be detected "simultaneously" in the sense that they are measured in the same measurement, but are temporally shifted relative to each other in the same way that left-circularly polarized electromagnetic radiation and right-circularly polarized electromagnetic radiation are separated at different time steps.

[0027] The system preferably further comprises at least one intensity modulation device, which is configured such that the intensity of the incident electromagnetic radiation is modulated, thereby generating intensity-modulated electromagnetic radiation.

[0028] The intensity modulation device is preferably a polarizer, and particularly preferably a linear polarizer.

[0029] The intensity modulation device is preferably configured to modulate the intensity of the incident electromagnetic radiation such that the intensity of electromagnetic radiation in an unwanted polarization state is removed or at least reduced. An unwanted polarization state refers to the polarization state of electromagnetic radiation that should not be detected by the detection device at a particular point in time. In this way, the intensity modulation device enables additional polarization modulation of the electromagnetic radiation.

[0030] The intensity modulation device is preferably arranged later in the optical path than the frequency modulation device.

[0031] When the intensity modulation device is present in the system, the intensity-modulated electromagnetic radiation is preferably detected by the detection device. In other words, in this case, the system is preferably configured such that the detection device detects the intensity-modulated electromagnetic radiation.

[0032] The system preferably further comprises at least one masking device, which is configured to mask one or more regions of the detection device, thereby preventing the detection device from detecting incident electromagnetic radiation, preferably incident intensity-modulated electromagnetic radiation, in these one or more masked regions.

[0033] When a masking device is present, the synchronization device is preferably connected to the masking device, and the synchronization device is configured to transmit a detection modulation signal to the masking device, and the masking device is configured to mask one or more regions of the detection device in synchronization with the detection modulation signal.

[0034] The detection device is preferably an image sensor, the region is at least 2 pixels, preferably at least 2 pixel columns, particularly preferably at least 4 pixel columns or exactly 4 pixel columns, and the masking device is configured to mask 1 pixel at a time, preferably one or more pixel columns, particularly preferably at least 3 pixel columns or exactly 3 pixel columns.

[0035] The synchronization device is preferably configured such that a specific polarization state is detected by one specific pixel at a time, preferably by one specific pixel column.

[0036] That is, the detection device is preferably an image sensor such as a CCD sensor. For example, in the case of a CCD sensor, the masking device is configured to circulate the photoelectric charges between the pixel columns of the CCD sensor. Since the masking device circulates the photoelectric charges in synchronization with the detection modulation signal, a specific pixel or a specific pixel column detects a specific polarization state of the modulated incident sample or, if available, intensity-modulated electromagnetic radiation. The masking device is preferably configured to spatially separate different polarization states from each other. Preferably, the masking device corresponds to one or more focusing elements such as microlenses within a lens array, and these are configured to focus the electromagnetic radiation onto a specific area of the detection device such as a specific pixel of the CCD sensor. In other words, the masking device is configured to focus the electromagnetic radiation onto the "open" or "unmasked" pixels of the CCD sensor.

[0037] For example, when electromagnetic radiation including a circular polarization component and a linear polarization component is irradiated onto a frequency modulation device set to QW retardation at an exemplary frequency of f = 1f, the circular polarization component of the electromagnetic radiation is modulated at 1f, and the linear polarization component of the electromagnetic radiation is modulated at an exemplary frequency of f = 2f, so that both the circular polarization component and the linear polarization component can be detected by a detection device which is a 4-column CCD sensor.

[0038] It is particularly preferred that the detection device, the masking device and the synchronization device correspond to a system known as "Zurich Imaging Polarimeter" (ZIMPOL). In other words, it is preferred that the system comprises a frequency modulation device and a ZIMPOL imaging system. In this case, the frequency modulation device is used to separate the polarization states of the incident electromagnetic radiation into different frequencies as described above, which is preferably electronically communicated to the synchronization device of the ZIMPOL system, and this synchronization device synchronizes these frequencies with the selective masking of the image sensor to generate a final image with separate measurements of different polarization states.

[0039] In the absence of a masking device, synchronization is preferably connected to the detection device, the synchronization device is configured to transmit a detection modulation signal to the detection device, and the detection device is configured to detect incident electromagnetic radiation, preferably incident intensity-modulated electromagnetic radiation, in synchronization with the detection modulation signal.

[0040] For this purpose, the detection of individual polarization states can be realized in various ways. For example, if the electromagnetic radiation incident on the detection device is still frequency-modulated or intensity-frequency-modulated, it is conceivable that the detection device collects light from a specific pixel (or group of pixels) at a predetermined frequency. Such a setting can replace the masking device. However, it is also possible to provide a detection device that is sensitive to various polarization states. In this case, a linear polarizer that modulates the intensity is not necessary, and instead, the polarization state can be directly measured.

[0041] In any case, by using an image sensor, the system utilizes frequency polarization modulation combined with spatially resolved imaging.

[0042] The system preferably further comprises at least one separation device, which is configured to spatially separate one or more wavelengths constituting the incident electromagnetic radiation, preferably one or more wavelengths constituting the incident intensity-modulated electromagnetic radiation, to the detection device.

[0043] Accordingly, the separation device is configured to decompose the electromagnetic radiation incident on the separation device into its components according to the wavelength of the incident electromagnetic radiation. Then, different components of the decomposed electromagnetic radiation are incident on different regions of the detection device. The separation device is preferably a spectrometer. For this purpose, any type of spectrometer known in the art can be considered. The spectrometer typically uses a lens or a diffraction grating or a dispersive element configured to focus the electromagnetic radiation onto the detection device. However, it should be noted that a spectrometer is not necessary at all. For example, if one essentially wants to measure Rayleigh scattering, the spectrometer can be omitted.

[0044] The spectrometer thus enables detection as a function of, or dependent on, the wavelength of the spatially resolved electromagnetic radiation emitted from the sample.

[0045] The system preferably further comprises an excitation source, preferably a radiation source such as a laser, which is configured to excite the sample.

[0046] The excitation source is preferably configured to excite the sample into one or more excited states. Upon relaxation, the sample will emit the electromagnetic radiation described above. The sample is preferably a chiral sample, such as a solution containing chiral molecules, a solid sample containing one or more chiral molecules or consisting of chiral molecules, or a film provided on a slide glass or the like and containing chiral molecules or consisting of chiral molecules. Due to its chirality, the sample will change the polarization of the electromagnetic radiation. With this system, various chiral optical phenomena can be measured. For example, the system can be used to measure the optical activity of a sample by detecting an absorption spectrum, a fluorescence spectrum, or a scattering spectrum. In fact, when an absorption spectrum is recorded, the differential extinction coefficient for left-circularly polarized electromagnetic radiation and right-circularly polarized electromagnetic radiation can be determined. These phenomena are called circular dichroism (CD) or vibrational circular dichroism (VCD) in this technical field. When a fluorescence spectrum is recorded, the polarization or intensity of the emitted photons having different incident polarizations can be determined. These phenomena are called circularly polarized luminescence (CPL) or fluorescence detection circular dichroism in this technical field. When a scattering spectrum is recorded, the diffractive scattering from left-circularly polarized or right-circularly polarized electromagnetic radiation in the scattered beam, i.e., the electromagnetic radiation scattered from the sample, or the different amounts of left-circularly polarized and right-circularly polarized electromagnetic radiation can be determined. These phenomena are called Rayleigh optical activity or Raman optical activity in this technical field. For this purpose, the system can be used in a forward scattering, backward scattering, or angular scattering configuration, as is known in the art.

[0047] In particular, when backscattering measurements are performed, the electromagnetic radiation used to excite the sample is irradiated onto the sample from the direction in which the electromagnetic radiation scattered from the sample is detected by the detection device. In forward scattering measurements, the electromagnetic radiation used to excite the sample is irradiated onto the sample from a direction opposite to the direction in which the electromagnetic radiation scattered from the sample is detected by the detection device. In angular scattering measurements, the electromagnetic radiation is irradiated onto the sample from a direction arranged at an angle with respect to the direction in which the electromagnetic radiation scattered from the sample is detected by the detection device.

[0048] The system preferably further comprises one or more polarization adjustment elements, the polarization adjustment elements being configured to change the polarization state of the electromagnetic radiation incident on the polarization adjustment elements and preferably arranged so as to be able to irradiate the sample with non-polarized electromagnetic radiation and / or so as to reduce noise.

[0049] The polarization adjustment element preferably corresponds to one or more linear rotators and / or one or more circular rotators. The linear rotator is configured to rotate the polarization plane of incident linearly polarized electromagnetic radiation and reverse the direction of circular polarization. The circular rotator is configured to reverse the direction of incident circularly polarized electromagnetic radiation. Both the linear rotator and the circular rotator are preferably half-wave plates. Further, the half-wave plate used as the linear rotator preferably rotates within the optical path extending from the excitation source towards the sample, i.e., within the excitation path, and / or within the optical path extending from the sample, i.e., within the collection path. It is particularly preferred to use two linear rotators within the excitation path and one linear rotator within the collection path. The linear rotator is preferably arranged and configured such that the polarization of the incident electromagnetic radiation is disrupted. In other words, the linear rotator is configured to generate unpolarized electromagnetic radiation that irradiates the sample and remove the linearly polarized state from the electromagnetic radiation emitted from the sample. The half-wave plate used as the circular rotator is preferably moved into and out of the excitation path. These circular rotators are preferably configured and arranged such that two or more spectral images are generated and subtracted from each other to remove noise. This procedure is also known in this technical field as virtual enantiomers.

[0050] In this regard, it should be noted that the system enables the measurement of the optical activity of the sample when unpolarized or polarized electromagnetic radiation irradiates the chiral sample. In fact, unpolarized electromagnetic radiation may irradiate the sample. In this case, left-circularly polarized electromagnetic radiation, right-circularly polarized electromagnetic radiation, and linearly polarized electromagnetic radiation can be detected.

[0051] Similarly, it is also conceivable to irradiate the sample with circularly polarized electromagnetic radiation. In this case, left-circularly polarized electromagnetic radiation, right-circularly polarized electromagnetic radiation, and linearly polarized electromagnetic radiation can be detected. However, it is also conceivable to irradiate the sample with linearly polarized electromagnetic radiation. In this case, left-circularly polarized electromagnetic radiation, right-circularly polarized electromagnetic radiation, and linearly polarized light can be detected. That is, in order to excite the sample, unpolarized or randomly polarized electromagnetic radiation may be used, and polarized electromagnetic radiation may also be used. However, it has been found that it is preferable to use unpolarized or randomly polarized electromagnetic radiation to excite the sample. In fact, when polarized electromagnetic radiation is used to excite the sample, the polarization state of the radiation should be maintained during the measurement, which is quite difficult.

[0052] The system preferably further comprises at least one filter element, preferably a Rayleigh filter, which is configured to filter one or more wavelengths of electromagnetic radiation, preferably intensity-modulated electromagnetic radiation incident on the filter element.

[0053] The filter element preferably filters electromagnetic radiation emitted by an excitation source, typically laser radiation. In other words, the filter element can be used to remove any contribution from the excitation source. Various arrangements of the filter element are conceivable. For example, the filter element can be arranged in front of or behind the sample, in front of or behind the frequency modulation device, in front of or behind the intensity modulation device, etc. with respect to the optical path.

[0054] The frequency modulation device is preferably a high-frequency modulation device and is preferably at least one of a photoelastic modulator, a liquid crystal retarder, and a Pockels cell. In addition to or as an alternative to this, the frequency modulation device is preferably configured to modulate at a frequency higher than 500 Hz, preferably higher than 1 kHz.

[0055] As already described above, the frequency modulation device preferably corresponds to a commercially available device well known in the art. The generated frequency modulation signal depends on the frequency modulation device used. For example, when a liquid crystal retarder is used as the frequency modulation device, a frequency modulation signal having a rectangular shape is generated. However, a photoelastic modulator, also called a PEM, is based on the strain-birefringence response of a substance and generates a frequency modulation signal having a sine wave shape.

[0056] In a further aspect, preferably using a system as described above, a method for measuring the optical activity of a sample is provided, the method comprising: i) irradiating the sample with electromagnetic radiation so as to excite the sample and modulating the frequency of the electromagnetic radiation emitted from the excited sample using at least one frequency modulation signal of at least one frequency modulation device, and / or ii) modulating the frequency of the electromagnetic radiation incident on the sample using at least one frequency modulation signal of at least one frequency modulation device so as to excite the sample with the frequency-modulated electromagnetic radiation, and iii) synchronizing at least one detection modulation signal with at least one frequency modulation signal using at least one synchronization device, and iv) detecting the electromagnetic radiation in synchronization with at least one detection modulation signal using at least one detection device.

[0057] That is, as already outlined at the beginning, it is conceivable to irradiate the sample with electromagnetic radiation so as to excite the sample and then perform frequency modulation using the electromagnetic radiation emitted during relaxation from the excited sample. In addition to or as an alternative to this, it is also conceivable to perform frequency modulation using electromagnetic radiation and then irradiate the sample with the electromagnetic radiation so as to excite the sample.

[0058] Method steps i) to iv) are preferably carried out in the order from i) to iv).

[0059] Any description and explanation provided for the system is equally applicable to the method for measuring the optical activity of a sample, and vice versa.

[0060] In a further aspect, there is provided a method of manufacturing a system for measuring the optical activity of a sample, in particular a method of manufacturing a system as described above, the method comprising: i) providing at least one frequency modulation device; ii) providing at least one synchronization device; and iii) providing at least one detection device. The at least one frequency modulation device is configured to modulate the frequency of incident electromagnetic radiation emitted from and / or irradiated onto the sample using at least one frequency modulation signal. The at least one synchronization device is configured to receive at least one frequency modulation signal. The at least one synchronization device is further configured to emit at least one detection modulation signal synchronized with the at least one frequency modulation signal. The system is configured such that at least one detection device detects the incident electromagnetic radiation synchronized with the at least one detection modulation signal.

[0061] That is, as already outlined at the beginning, it is conceivable to irradiate the sample with electromagnetic radiation so as to excite the sample, and then to perform frequency modulation using the electromagnetic radiation emitted during relaxation from the excited sample. In addition or alternatively, it is also conceivable to perform frequency modulation using electromagnetic radiation and then to irradiate the sample with the electromagnetic radiation so as to excite the sample.

[0062] Method steps i) to iv) may be performed in the order from i) to iv), but may equally well be performed in any other order.

[0063] Any description and explanation provided with respect to a system or method for measuring the optical activity of a sample is equally applicable to a method of manufacturing a system for measuring the optical activity of a sample, and vice versa.

[0064] Preferred embodiments of the present invention are described below with reference to the drawings, which are provided to illustrate preferred embodiments of the present invention and are not intended to limit the present invention.

Brief Description of the Drawings

[0065]

Figure 1

Figure 2

Figure 3

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Figure 8

Figure 9

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Figure 11

[0066] Figures 1 to 9 show various embodiments of a system 1 for measuring the optical activity of a sample 2. In each case, the system 1 according to these figures comprises a frequency modulation device 3, a synchronization device 4, and a detection device 5. Although not shown in the figures, the system 1 further comprises an excitation source configured to excite the sample 2. The excitation source preferably corresponds to a radiation source such as a laser, and the radiation source is configured to emit electromagnetic radiation EM. The electromagnetic radiation EM is indicated by a solid line and defines an optical path P extending from the excitation source to the detection device 5. When the electromagnetic radiation EM hits the sample 2, the electromagnetic radiation EM puts the sample 2 into one or more excited states. Upon relaxation of the excited sample, electromagnetic radiation EMs is emitted from the sample 2. The electromagnetic radiation EMs emitted from the sample generally constitutes a quantity to be finally detected by the detection device after further spectroscopic or optical procedures. In this specification, the electromagnetic radiation emitted during relaxation of the sample is shown as EMs and is indicated by a dashed line.

[0067] Depending on the characteristics of the sample 2 and / or the characteristics of the electromagnetic radiation EM irradiated on the sample 2, various phenomena such as absorption, fluorescence, or scattering occur, which can be measured by this system 1. The system 1 shown in the figure comprises a detection device 5 arranged on the side opposite to the direction in which the electromagnetic radiation EM irradiates the sample 2. When this system 1 is used for scattering measurement, the measurement performed by this setting is called forward scattering measurement. However, it should be noted that any other type of scattering measurement, such as backscattering measurement or angular scattering measurement, can be similarly performed by arranging the detection device 5 and / or the excitation source correspondingly with respect to the sample 2.

[0068] The frequency modulation device 3 is configured to modulate the frequency of the incident electromagnetic radiation EM, EMs. As can be readily apparent from a comparison of FIGS. 1 to 8 and FIG. 9, at least two different arrangements of the frequency modulation device 3 with respect to the sample 2 are conceivable. That is, in the former case shown in FIGS. 1 to 8, the frequency modulation device 3 is arranged behind the sample 2 with respect to the optical path P. In this case, the electromagnetic radiation EMs emitted during the relaxation of the excited sample are incident on the frequency modulation device 3. That is, a plurality of electromagnetic radiations EM emitted from the sample 2 are frequency-modulated by the frequency modulation device 3. In the latter case shown in FIG. 9, the frequency modulation device 3 is arranged in front of the sample 2 with respect to the optical path P, which is different from the system 1 according to FIGS. 1 to 8. As a result, the sample 2 is excited by the frequency-modulated electromagnetic radiation EM.

[0069] Therefore, it can be said that the frequency modulation device 3 is configured to modulate the frequency of the incident electromagnetic radiation EMs emitted from the sample 2 using at least one frequency modulation signal Sf and to modulate the frequency of the electromagnetic radiation EM irradiating the sample 2 using at least one frequency modulation signal Sf.

[0070] The synchronization device 4 communicates with the frequency modulation device 3 and is configured to receive the frequency modulation signal Sf emitted from the frequency modulation device 3. The synchronization device 4 is further configured to emit at least one detection modulation signal Sd synchronized with at least one frequency modulation signal Sf, and the system 1 is configured such that the detection device 5 detects the incident electromagnetic radiation EMs in synchronization with the detection modulation signal Sd. The frequency modulation is achieved by applying an electrical signal to the frequency modulation device 3, and this same electrical signal is also transmitted to the synchronization device 4.

[0071] Here too, various methods are conceivable. That is, on the one hand, the synchronization device 4 can communicate with the detection device 5 (see FIGS. 1, 2, 5, and 6 to 9). In this case, the synchronization device 4 transmits the detection modulation signal Sd to the detection device 5, and the detection device 5 detects the incident electromagnetic radiation EMs in synchronization with the detection modulation signal Sd. In practice, the detection of the two polarization states P1 and P2 is detected by the detection device 5 according to FIG. 1, and the detection of the four polarization states P1, P2, P3, and P4 is detected by the detection device 5 according to FIG. 2. The detection device 5 according to these figures preferably corresponds to a detection device such as a camera system capable of detecting various polarization states themselves. However, on the other hand, it is equally conceivable that the synchronization device 4 communicates with the masking device 7 (see FIGS. 3 and 4). The purpose and function of the masking device 7 will be described in more detail below.

[0072] The sample 2 is preferably a chiral sample such as a solution containing chiral molecules, for example, a solid sample containing one or more chiral molecules or consisting of such molecules, or a film provided on a slide glass or the like and containing chiral molecules or consisting of such molecules. Due to its chirality, the sample 2 will change the polarization of the incident electromagnetic radiation EM.

[0073] The frequency modulation device 3 is configured to separate components of incident electromagnetic radiation EM, EMs having two or more polarization states into components of electromagnetic radiation EM, EMs having one or more frequencies. Thus, in the system 1 according to FIGS. 1 to 8, the electromagnetic radiation EMs emitted from the sample 2 hits the frequency modulation device 3, and the frequency modulation device 3 separates different polarization states of the emitted electromagnetic radiation EMs into components of different frequencies. In the system 1 according to FIG. 9, different polarization states of the incident electromagnetic radiation EM are similarly separated into different frequencies, and then the sample 2 is excited by the thus frequency-modulated electromagnetic radiation EM. Thus, in the former case, different polarization states of the electromagnetic radiation EMs emitted from the sample 2 are separated into different frequency components, and in the latter case, the sample 2 is excited using the electromagnetic radiation EM whose different polarization states have been previously separated into different frequency components. In the latter case, it is preferable to detect the total intensity of the electromagnetic radiation EMs emitted during the relaxation of the excited sample 2. For this purpose, at least one polarization adjustment element 9 is preferably arranged with respect to the optical path P, behind the sample 2 and in front of the detection device 5 (see FIG. 9). In particular, a polarization adjustment element 9 in the form of a so-called depolarizer such as a Lyot depolarizer may be arranged behind the sample 2 with respect to the optical path P so that the electromagnetic radiation EMs emitted from the sample 2 during its relaxation can hit the depolarizer 9. The depolarizer 9 scrambles the polarization of the electromagnetic radiation EMs, thereby generating electromagnetic radiation EMs with random polarization. The thus generated electromagnetic radiation EMs with random polarization can then be detected directly or indirectly by the detection device 5. Indirect detection is shown in FIG. 9. That is, the spectroscope 8 may be arranged with respect to the optical path P, behind the depolarizer 9 and in front of the detection device 5. The spectroscope 8 serves as a separation device configured to decompose the incident electromagnetic radiation EMs into its components according to the wavelength of the incident electromagnetic radiation EMs. The different components of the decomposed electromagnetic radiation EMs then enter different regions a1, a2,... of the detection device 5. However, in the former case, it is preferable that the system 1 further comprises at least one intensity modulation device 6.The intensity modulation device 6 is configured such that the intensity of the incident electromagnetic radiation EMs is modulated, thereby generating intensity-modulated electromagnetic radiation EMsi. Here, the electromagnetic radiation emitted from the sample and further intensity-modulated is denoted as EMsi.

[0074] It should be noted that the intensity-modulated electromagnetic radiation EMsi still includes the frequency-modulated electromagnetic radiation EMs emitted from the sample 2, with the difference that the electromagnetic radiation further includes intensity modulation. Therefore, the description made regarding the electromagnetic radiation or frequency-modulated electromagnetic radiation EMs emitted from the sample also applies to the intensity-modulated electromagnetic radiation EMsi, and vice versa. As can be easily seen from FIGS. 1 to 8, the intensity modulation device 6 is arranged behind the frequency modulation device 3 with respect to the optical path P. The intensity modulation device 6 is a polarizer, preferably a linear polarizer, and is capable of selecting one or more specific frequency components of the frequency-modulated electromagnetic radiation EMs. The selected one or more frequency components of the electromagnetic radiation EMsi are stronger than the one or more unselected frequency components of the electromagnetic radiation EMsi. When the system 1 includes the intensity modulation device 6, it can be said that the intensity-modulated electromagnetic radiation EMsi is incident on the detection device 5. In particular, when the system 1 includes both the intensity modulation device 6 and the frequency modulation device 3, the frequency-intensity-modulated electromagnetic radiation EMsi can be detected by the detection device 5. Further, as can be seen from FIGS. 5 to 8, in this former case, it is conceivable that the system 1 includes a spectrometer 8. In particular, the spectrometer 8 is preferably arranged behind the linear polarizer 6 and in front of the detection device 5 with respect to the optical path P. As in the latter case described above, the spectrometer 8 serves as a separation device configured to decompose the incident electromagnetic radiation EMs into its components according to the wavelength of the incident electromagnetic radiation EMs. The different components of the decomposed electromagnetic radiation EM are then incident on different regions a1, a2,... of the detection device 5.

[0075] The detection device 5 preferably corresponds to a CCD sensor that includes one or more pixels, in particular one or more pixel columns each including one or more pixels in any case. Each of these pixels is understood as regions a1, a2,... of the detection device 5.

[0076] As described above and as can be seen from FIGS. 3 and 4, the system 1 may additionally include at least one masking device 7. The masking device 7 is configured to mask one or more regions a1, a2, a3, a4 of the detection device 5, whereby in these one or more masked regions a1m, a2m, a3m, a4m, the incident electromagnetic radiation EMs, preferably the incident intensity-modulated electromagnetic radiation EMsi when the intensity modulation device 6 is used, is prevented from being detected by the detection device 5. Also, as can be seen from these figures, the synchronization device 4 is connected to the masking device 7 so as to transmit the detection modulation signal Sd to the masking device 7. As a result, the masking device 7 masks one or more regions a1, a2, a3, a4 of the detection device 5 in synchronization with the detection modulation signal Sd.

[0077] The masking device 7 is configured to spatially separate different polarization states of the incident electromagnetic radiation EMs from each other. Here, the masking device 7 corresponds to one or more focusing elements 10a, 10b,... such as microlenses in a lens array, and these are configured to focus the incident electromagnetic radiation EMs, EMsi onto specific regions a1, a2,... of the detection device, for example onto specific pixels of the CCD sensor 5.

[0078] The masking device 7 in FIG. 3 includes two focusing elements. One of the two focusing elements 10a is configured to focus the incident electromagnetic radiation EMsi in the first polarization state P1 onto one region a1 of the detection device 5, and the other focusing element 10b is configured to focus the incident electromagnetic radiation EMsi in the second polarization state P2 onto another region a2 of the detection device 5. This selective focusing is made possible by the fact that the electromagnetic radiation EMsi is modulated by the frequency modulation device 3 using a frequency modulation signal Sf corresponding to the detection modulation signal Sd. The second focusing element 10b is shown in black, indicating that the second focusing element 10b is inactive at this particular point in time. Instead, only the first focusing element 10a, shown in white, is active and is configured to focus the incident electromagnetic radiation EMsi onto the first region a1 of the detection device. As a result, the second region a2 of the detection device 5 is the masked region a2m and does not receive any electromagnetic radiation EMsi.

[0079] This relationship is further illustrated in FIG. 4, where a masking device 7 is used that includes four focusing elements 10a, 10b, 10c, 10d configured to focus the incident electromagnetic radiation EMsi onto four regions a1, a2, a3, a4 of the detection device 5. In this exemplary embodiment, the frequency modulation device 3 modulates the incident electromagnetic radiation EMs with a sinusoidal frequency modulation signal Sf such that four frequency-modulated polarization states P1, P2, P3, and P4 are generated in the electromagnetic radiation EMs. Since the detection modulation signal Sd is synchronized with this frequency modulation signal Sf, the microlens arrays 10a, 10b,... of the masking device 7 are induced by the detection modulation signal Sd such that electromagnetic radiation EMsi of a specific frequency-modulated polarization state P1, P2, P3, or P4 is directed towards a specific region a1, a2, a3, a4 of the detection device 5. In the exemplary embodiment of FIG. 4, the microlens arrays 10a, 10b,... are induced such that the second polarization state P2 is focused onto the second column a2 of the detection device 5. This second column a2 can be considered an unmasked column. For example, if the first frequency-modulated polarization state P1 corresponds to left circular polarization, the second frequency-modulated polarization state P2 corresponds to vertical linear polarization, the third frequency-modulated polarization state P3 corresponds to right circular polarization, and the fourth frequency-modulated polarization state P4 corresponds to horizontal linear polarization, the system 1 can, for example, detect left circular polarization in the highest pixel column a1 of the detection device 5, detect vertical linear polarization in the second-highest pixel column a2 of the detection device 5, detect right circular polarization in the second-lowest pixel column a3 of the detection device 5, and detect horizontal linear polarization in the lowest pixel column a4 of the detection device 5. In other words, the masking device 7 is configured to circulate the frequency-modulated polarization states P1, P2, P3, P4 among the pixel columns a1, a2, a3, a4 of the CCD sensor 5. Since the masking device 7 circulates the photocharges in synchronization with the detection modulation signal Sd, a specific pixel column a1, a2, a3, or a4 detects a specific polarization state P1, P2, P3, or P4 of the incident electromagnetic radiation EMsi.

[0080] Furthermore, when a spectroscope 8 that decomposes incident electromagnetic radiation EMs, EMsi according to its wavelength is used, the detection device 5 further detects specific polarization states P1, P2, P3, P4 of the incident electromagnetic radiation EMs, EMsi according to its wavelength. For example, when each pixel column a1, a2,... includes three pixels (not shown), the lowest wavelength or wavelength range is detected by the first pixel of a specific pixel column, the intermediate wavelength or wavelength range is detected by the second pixel of the specific pixel column, and the highest frequency or frequency range may be detected by the third pixel of the specific pixel column.

[0081] The system 1 shown in FIGS. 5 to 8 further includes one or more polarization adjustment elements 9. The polarization adjustment element 9 is configured to change the polarization state of the electromagnetic radiation EMs, EMsi incident on the polarization adjustment element 9.

[0082] The polarization adjustment element 9 corresponds to one or more linear rotators and / or one or more circular rotators. The linear rotator 9 is configured to rotate the polarization plane of the incident linearly polarized electromagnetic radiation EM, EMs, EMsi and reverse the direction of the incident circularly polarized electromagnetic radiation EM, EMs, EMsi. The circular rotator 9 is configured to reverse the direction of the incident circularly polarized electromagnetic radiation EM, EMs, EMsi. Both the linear and circular rotators 9 are preferably half-wave plates. Further, the half-wave plate used as the linear rotator 9 preferably rotates within the optical path P extending from the excitation source toward the sample 2, i.e., within the excitation path, and / or within the optical path P extending from the sample 2 toward the detection device 5, i.e., within the collection path. The half-wave plate used as the circular rotator 9 is preferably repeatedly moved into and out of the optical path P.

[0083] Depending on the number and specific arrangement of one or more polarization adjustment elements 9, different effects can be achieved. In practice, the system 1 according to FIG. 5 includes a single polarization adjustment element 9 that is a linear rotator arranged in front of the sample 2 in the optical path P, that is, the linear rotator 9 is arranged in the excitation path. The linear rotator serves the purpose of scrambling the polarization of the incident electromagnetic radiation. The system 1 according to FIG. 6 includes two polarization adjustment elements 9, both of which are linear rotators. One linear rotator 9 is arranged in front of the sample 2 with respect to the optical path P, that is, in the excitation path, and the other linear rotator 9 is arranged behind the sample 2 with respect to the optical path P, that is, in the collection path. As indicated by the arrows facing along the same direction of rotation, both linear rotators 9 are rotated along the same direction of rotation. When two or more linear rotators 9 are used, faster scrambling of polarization is achieved. The system 1 according to FIG. 7 includes three polarization adjustment elements 9, all of which are linear rotators. For this purpose, two linear rotators 9 are arranged in front of the sample 2 with respect to the optical path P, that is, in the excitation path, and one linear rotator 9 is arranged behind the sample 2 with respect to the optical path P, that is, in the collection path. The two linear rotators 9 in the excitation path rotate along opposite directions of rotation as indicated by the arrows facing along different directions of rotation. These linear rotators 9 are arranged and rotated such that the polarization of the incident electromagnetic radiation EM, EMs is disrupted. In other words, the linear rotator 9 is configured to generate non-polarized electromagnetic radiation EM that irradiates the sample 2 and remove the linearly polarized state from the electromagnetic radiation EMs emitted from the sample 2. The system 1 according to FIG. 8 includes three polarization adjustment elements 9 as in the case of the system 1 according to FIG. 7, and additionally includes two circular rotators 9. The first circular rotator 9 is arranged in the excitation path, that is, behind the two linear rotators 9 but in front of the sample 2 with respect to the optical path P. The second circular rotator 9 is arranged in the collection path, that is, behind the sample 2 and behind the third linear rotator 9 with respect to the optical path P. As indicated by the double arrows, the circular rotator 9 is moved into and out of the optical path P.These circular rotors 9 are preferably configured and arranged such that noise is removed when two or more spectral images are recorded and subtracted from each other. This procedure is also known in this technical field as virtual enantiomers.

[0084] Figures 10 and 11 show two spectra recorded using the system 1 according to FIG. 8, that is, in particular, a frequency modulation device 3 arranged behind the sample 2 with respect to the optical path P, an intensity modulation device 6 in the form of a linear polarizer, a spectroscope 8, three linear rotors 9, and two circular rotors 9. The spectra were measured in a forward scattering configuration, and a laser beam with an output of 1.5 watts at 532 nanometers was used to excite the sample 2. The sample 2 corresponds to a neat solution of β-pinene. FIG. 10 shows the measured Raman signals for the enantiomers of (+)β-pinene (solid line, upper part) and (-)β-pinene (dashed line, lower part). Each signal corresponds to the sum of left-circularly polarized electromagnetic radiation (I L ) and right-circularly polarized electromagnetic radiation (I R ), and S = I L + I R . The peaks in these signals correspond to the vibrational modes of β-pinene. As can be seen from a comparison of the signal recorded for the enantiomer of (+)β-pinene and the signal recorded for the enantiomer of (-)β-pinene, the peaks are the same for both enantiomers. FIG. 11 shows the Raman optical activity (ROA) spectra of the two enantiomers of β-pinene, that is, the difference between right-circularly polarized and left-circularly polarized electromagnetic radiation for Raman scattering from the two enantiomers, and S = I L - I R . The spectrum of the enantiomer of (+)β-pinene is shown as a solid line, and the spectrum of the enantiomer of (-)β-pinene is shown as a dashed line. As can be seen from FIG. 11, the spectra of these two enantiomers are almost perfect mirror images of each other.

Explanation of symbols

[0085] 1 System 2 Sample 3 Frequency Modulation Device 4 Synchronization Device 5 Detection Device 6 Intensity Modulation Device 7 Masking Device 8 Separation Device 9 Polarization Adjustment Element 10a, 10b,... Focusing Elements Sf Frequency Modulation Signal Sd Detection Modulation Signal EM Electromagnetic Radiation Ems Electromagnetic Radiation EMsi Electromagnetic Radiation P Optical Path a1,... Regions a1m,... Masked Regions

Claims

1. A system (1) for measuring the optical activity of a sample (2), comprising: at least one frequency modulation device (3); at least one synchronization device (4); at least one detection device (5); wherein at least one of the frequency modulation devices (3) is configured to modulate the frequency of incident electromagnetic radiation emitted from and / or irradiated onto the sample (2) using at least one frequency modulation signal (Sf); at least one of the synchronization devices (4) is configured to receive at least one of the frequency modulation signals (Sf); at least one of the synchronization devices (4) is further configured to emit at least one detection modulation signal (Sd) synchronized with at least one of the frequency modulation signals (Sf); the system (1) is configured such that at least one of the detection devices (5) detects incident electromagnetic radiation (EMs) synchronized with at least one of the detection modulation signals (Sd).

2. The system (1) according to claim 1, wherein the frequency modulation device (3) is configured to separate components of incident electromagnetic radiation having two or more polarization states into components of electromagnetic radiation (EMs) having one or more frequencies.

3. The system (1) according to claim 2, wherein the system (1) is configured such that components of electromagnetic radiation (EMs) having one or more of the frequencies are detected by the detection device (5) while being simultaneously or temporarily delayed relative to each other.

4. The system (1) according to any one of claims 1 to 3, further comprising at least one intensity modulation device (6), wherein the intensity modulation device (6) is configured such that the intensity of incident electromagnetic radiation (EMs) is modulated, thereby generating intensity-modulated electromagnetic radiation (EMsi).

5. The system (1) according to any one of claims 1 to 4, further comprising at least one masking device (7), wherein the masking device (7) is configured to mask one or more regions (a1, a2, a3, a4) of the detection device (5), thereby preventing the detection device (5) from detecting incident electromagnetic radiation (EMs) in these one or more masked regions (a1m, a2m, a3m, a4m).

6. The system (1) according to claim 5, wherein the synchronization device (4) is connected to the masking device (7), the synchronization device (4) is configured to transmit the detected modulation signal to the masking device (7), and the masking device (7) is configured to mask one or more regions (a1, a2, a3, a4) of the detection device (5) in synchronization with the detected modulation signal (Sd).

7. The system (1) according to claim 5 or 6, wherein the detection device (5) is an image sensor, the regions (a1, a2, a3, a4) are at least two pixels, and the masking device (7) is configured to mask one pixel at a time.

8. The system (1) according to claim 7, wherein the synchronization device (4) is configured such that a specific polarization state is detected by one specific pixel.

9. The system (1) according to any one of claims 1 to 4, wherein the synchronization device (4) is connected to the detection device (5), the synchronization device (4) is configured to transmit the detected modulation signal (Sd) to the detection device (5), and the detection device (5) is configured to detect incident electromagnetic radiation (EMs) in synchronization with the detected modulation signal (Sd).

10. The system (1) according to any one of claims 1 to 9, further comprising at least one separation device (8), the separation device (8) being configured to spatially separate one or more wavelengths constituting the incident electromagnetic radiation (EMs) to the detection device (5).

11. The system (1) according to any one of claims 1 to 10, further comprising an excitation source, the excitation source being configured to excite the sample (2).

12. The system (1) according to any one of claims 1 to 11, further comprising one or more polarization adjustment elements (9), the polarization adjustment elements (9) being configured to change the polarization state of the electromagnetic radiation incident on the polarization adjustment elements (9), and and / or further comprising at least one filter element, the filter element being configured to filter one or more wavelengths of the electromagnetic radiation (EMs).

13. The system (1) according to any one of claims 1 to 12, wherein the frequency modulation device (3) is a high-frequency modulation device, and / or the frequency modulation device (3) is configured to modulate at a frequency higher than 500 Hz, said system. **Claim 14** A method for measuring the optical activity of a sample (2), said method comprising: irradiating the sample (2) with electromagnetic radiation so as to excite the sample (2), and modulating the frequency of the electromagnetic radiation emitted from the excited sample (2) using at least one frequency modulation signal (Sf) of at least one frequency modulation device (3), and / or modulating the frequency of the electromagnetic radiation irradiating the sample (2) using at least one frequency modulation signal (Sf) of at least one frequency modulation device (3) so as to excite the sample (2) with the frequency-modulated electromagnetic radiation; using at least one synchronization device (4) to synchronize at least one detection modulation signal (Sd) with at least one of said frequency modulation signals (Sf); using at least one detection device (5) to detect electromagnetic radiation (EMs) in synchronization with at least one of said detection modulation signals (Sd); said method comprising. **Claim 15** A method for manufacturing a system (1) for measuring the optical activity of a sample (2), said method comprising: providing at least one frequency modulation device (3); providing at least one synchronization device (4); providing at least one detection device (5); comprising, wherein at least one of said frequency modulation devices (3) is configured to modulate the frequency of incident electromagnetic radiation emitted from and / or irradiating the sample (2) using at least one frequency modulation signal (Sf); at least one of said synchronization devices (4) is configured to receive at least one of said frequency modulation signals (Sf); at least one of said synchronization devices (4) is further configured to emit at least one detection modulation signal (Sd) that is synchronized with at least one of said frequency modulation signals (Sf); said method, wherein said system (1) is configured such that at least one of said detection devices (5) detects incident electromagnetic radiation (EMs) in synchronization with at least one of said detection modulation signals (Sd).

16. The system (1) according to claim 4, wherein the intensity modulation device (6) is a polarizer and / or a linear polarizer.

17. The system (1) according to claim 5, wherein the masking device (7) is configured to mask one or more regions (a1, a2, a3, a4) of the detection device (5), whereby the detection device (5) is configured to prevent detection of incident intensity-modulated electromagnetic radiation (EMsi) in these one or more masked regions (a1m, a2m, a3m, a4m).

18. The system (1) according to claim 7, wherein the regions (a1, a2, a3, a4) are at least two pixel columns, or at least four pixel columns or exactly four pixel columns, and the masking device (7) is configured to mask one or more pixel columns at a time, or at least three pixel columns or exactly three pixel columns.

19. The system (1) according to claim 18, wherein the synchronization device (4) is configured such that a specific polarization state is detected by exactly one specific pixel column at a time.

20. The system (1) according to claim 9, wherein the detection device (5) is configured to detect incident intensity-modulated electromagnetic radiation (EMsi) in synchronization with the detection modulation signal (Sd).

21. The system (1) according to claim 10, further comprising at least one separation device (8), the separation device (8) being configured to spatially separate one or more wavelengths constituting the incident intensity-modulated electromagnetic radiation (EMsi) to the detection device (5).

22. The system (1) according to claim 11, wherein the excitation source is a laser.

23. The system (1) according to claim 12, The polarization adjustment element (9) is arranged such that unpolarized electromagnetic radiation can irradiate the sample (2) and / or such that noise is reduced, and / or The filter element is a Rayleigh filter and / or is configured to filter one or more wavelengths of the intensity-modulated electromagnetic radiation (EMsi) incident on the filter element. Claim 24. The system (1) according to claim 13, wherein the frequency modulation device (3) is at least one of a photoelastic modulator, a liquid crystal retarder, and a Pockels cell.

Images