Optical vortex generation device, optical analysis device, irradiation device, detection device, spectral measurement device, microscope, optical vortex generation method, and optical analysis method

Abstract

It generates optical vortices on both the left and right sides with high precision. [Solution] The optical vortex generating device (10) includes a modulation unit (12) that generates a first modulated light having spin angular momentum from incident light, and a first spin orbit converter (13) that generates a second modulated light having orbital angular momentum from the first modulated light.

Description

[Technical Field]

[0001] The present invention relates to an optical vortex generation device, an optical analysis device, an irradiation device, a detection device, a spectral measurement device, a microscope, an optical vortex generation method, and an optical analysis method. [Background technology]

[0002] An object is called chiral if its mirror image does not overlap with the object itself. Circular dichroism (CD) and helical dichroism (HD) are known phenomena related to chiral objects.

[0003] Circular dichroism is a phenomenon in which light is absorbed by an object differently depending on whether the light is left-circularly polarized (s=+1) with positive spin angular momentum S=sh / 2π (where h is Planck's constant) or right-circularly polarized (s=-1) with negative spin angular momentum. It is represented by the difference in absorption between left and right circularly polarized light. The signal representing this difference is also called the CD signal.

[0004] This circular dichroism is a property unique to substances with chiral optical activity and is used in the analysis of optically active substances, the measurement of the abundance of optical isomers, and the analysis of the structure and state of biomolecules. However, the CD signal of chiral molecules is generally small, about 0.1% of the absorbance. This is thought to be due to a mismatch in the spatial scale between the wavelength of light (λ) and the size of the object, resulting in a weak chiral interaction between light and the object.

[0005] On the other hand, helical dichroism is the dichroism of an optical vortex (s,l) having spin angular momentum S=sh / 2π and orbital angular momentum L=lh / 2π, and is an extension of the above-mentioned CD (dichroism of circularly polarized light with spin angular momentum). The optical vortex has orbital angular momentum due to the rotation of the wavefront. The above l (L) is sometimes called the topological charge (TC). This l is a quantity determined by the phase gradient per unit azimuthal angle in the cross-section of the beam. TC can take positive or negative values ​​(corresponding to left and right optical vortices), and its magnitude |l| has no upper limit in principle (l=0, ±1, ±2, ...).

[0006] Optical vortices not only possess infinite degrees of freedom compared to circularly polarized light, but in principle, it is also possible to shorten the period of the helical wavefront twist (λ / l), determined by the TC per wavelength λ, to the molecular scale. As the spatial scales of the twist between light and matter and the chirality of matter converge, a strong chiral optical response of matter to optical vortices can be expected. For this reason, the chiral properties of matter that could not be captured by CDs may be captured by HD.

[0007] As an example of the technology for the above HD, Patent Document 1 discloses an orbital angular momentum generation apparatus and method for polarization-modulated orbital angular momentum. In this technology, pulsed light is separated into two and an arbitrary optical vortex is generated by a holographic grating switch. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 7310072 [Overview of the project] [Problems that the invention aims to solve]

[0009] The technology described in Patent Document 1 has the problem that the accuracy of superimposing the optical vortices is low because it separates the pulsed light into two and generates optical vortices in separate optical paths.

[0010] This invention has been made in view of the above-mentioned problems, and its purpose is to provide a technology that can accurately generate or analyze left and right optical vortices. [Means for solving the problem]

[0011] To solve the above problems, an optical vortex generating apparatus according to one aspect of the present invention comprises a modulation unit that generates a first modulated light having spin angular momentum from incident light, and a first spin-orbit converter that generates a second modulated light having orbital angular momentum from the first modulated light.

[0012] To solve the above problems, a method for generating optical vortices according to one aspect of the present invention includes a modulation step of generating a first modulated light having spin angular momentum from incident light, and a spin-orbit conversion step of generating a second modulated light having orbital angular momentum from the first modulated light.

[0013] To solve the above problems, an optical analysis device according to one aspect of the present invention comprises a spin-orbit conversion unit into which target light is incident, a photoelastic modulator into which light that has passed through the spin-orbit conversion unit is incident, and a detection unit for detecting light that has passed through the photoelastic modulator.

[0014] To solve the above problems, an optical analysis method according to one aspect of the present invention includes the steps of: injecting target light into a spin-orbit conversion unit; injecting the light that has passed through the spin-orbit conversion unit into a photoelastic modulator; and detecting the light that has passed through the photoelastic modulator. [Effects of the Invention]

[0015] According to one aspect of the present invention, a technique can be provided that enables the precise generation or analysis of left and right optical vortices on the same optical axis. [Brief explanation of the drawing]

[0016] [Figure 1] This is a block diagram showing the configuration of an optical system including an optical vortex generating device according to Embodiment 1 of the present invention. [Figure 2] This is a diagram illustrating an optical vortex generating device according to Embodiment 1 of the present invention. [Figure 3] This is a flowchart showing the flow of the optical vortex generation method according to Embodiment 1 of the present invention. [Figure 4] This is a block diagram showing the configuration of the optical system according to Embodiment 2 of the present invention. [Figure 5] This figure shows an example of the configuration of the detection unit included in the optical system according to Embodiment 2 of the present invention. [Figure 6] This figure shows an example of detection results using the optical system according to Embodiment 2 of the present invention. [Figure 7] This figure shows an example of detection results using the optical system according to Embodiment 2 of the present invention. [Figure 8] This figure shows an example of detection results using the optical system according to Embodiment 2 of the present invention. [Figure 9] This figure shows an example of detection results using the optical system according to Embodiment 2 of the present invention. [Figure 10] This figure shows an example of detection results using the optical system according to Embodiment 2 of the present invention. [Figure 11] This figure shows an example of detection results using the optical system according to Embodiment 2 of the present invention. [Figure 12] This figure shows an example of detection results using the optical system according to Embodiment 2 of the present invention. [Figure 13] This figure shows an example of detection results using the optical system according to Embodiment 2 of the present invention. [Figure 14] This figure shows an example of detection results using the optical system according to Embodiment 2 of the present invention. [Figure 15] This figure illustrates an embodiment of the present invention. [Figure 16] This figure illustrates an embodiment of the present invention. [Figure 17] This figure illustrates an embodiment of the present invention. [Figure 18] This figure illustrates an embodiment of the present invention. [Figure 19] This figure illustrates an embodiment of the present invention. [Figure 20]This is a block diagram showing the configuration of an optical analysis device according to Embodiment 3 of the present invention. [Figure 21] This is a block diagram showing the configuration of an optical analysis device according to Embodiment 4 of the present invention. [Modes for carrying out the invention]

[0017] [Embodiment 1] The following describes in detail one embodiment of the present invention. Figure 1 is a block diagram showing the configuration of the optical system 1 according to this embodiment. As shown in Figure 1, the optical system 1 includes a light source unit 11, a modulation unit 12, a spin orbit converter 13, and a control unit 20. Here, the modulation unit 12 and the spin orbit converter 13 constitute an optical vortex generation device 10. The optical system 1 may also be referred to as an irradiation system or irradiation device. Hereinafter, the optical vortex generation device 10 may also be referred to as an optical conversion device 10.

[0018] (Optical system 1) (Control unit, light source unit) The control unit 20 controls each part of the optical system 1. Specific examples of control by the control unit 20 will be described later. The light source unit 11 generates incident light IL for the modulation unit 12. Here, the specific configuration of the light source unit 11 is not limited to this embodiment, but as an example, it may be configured to include a light source that generates a white laser and a monochromator located downstream of the light source. The monochromator can extract a specific wavelength from the white laser and use it as incident light IL for the modulation unit 12. Furthermore, the light source unit 11 may further include a spatial filter located downstream of the monochromator, and generate incident light IL with noise reduced by the spatial filter. However, these configurations are not limited to this embodiment.

[0019] (Modulation section) The modulation unit 12 generates a first modulated light ML1 having spin angular momentum from the incident light IL generated by the light source unit 11. The modulation unit 12, as an example, At a certain timing, a left-circularly polarized light with positive spin angular momentum (s=+1) is generated from the incident light IL as the first modulated light ML1. At another time, a right-circularly polarized light with negative spin angular momentum (s=-1) is generated from the incident light IL as the first modulated light ML1.

[0020] The upper part of Figure 2 schematically shows the first modulated light ML1 described above. The first modulated light ML1 (circularly polarized) may also be described as having a helical polarization, as shown in the upper part of Figure 2. The specific configuration of the modulation unit 12 is not limited to this embodiment, but as an example, it can be configured to include at least one of a photoelastic modulator (PEM) and an electro-optic modulator (EOM). Here, the photoelastic modulator (PEM) is an example of an acousto-optic modulator (AOM). Furthermore, the modulation unit 12 may be configured to include a first polarizing element upstream of the PEM, EOM, or AOM. The first polarizing element may also be a linear polarizer. In Figure 2, the barred h represents Planck's constant h divided by 2π (h / 2π). The value h with a bar is also called the reduced Planck's constant or Dirac's constant.

[0021] (Spin-orbit converter) The spin-orbit converter 13 generates a second modulated light ML2 having orbital angular momentum from the first modulated light ML1. Here, the second modulated light ML2 having orbital angular momentum is also called an optical vortex (OV). The spin-orbit converter 13, as an example, The modulation unit 12 generates a second modulated light ML2 having a certain orbital angular momentum from the left circularly polarized light it generates, The modulation unit 12 generates a second modulated light ML2 having a different orbital angular momentum from the right-circularly polarized light it generates.

[0022] The lower part of Figure 2 schematically shows the second modulated light ML2 described above. The second modulated light ML2 (circular vortex) can also be described as having a helical wavefront (equal phase surface), as shown in the upper part of Figure 2. Furthermore, the second modulated light ML2 with a positive value of the topological charge (TC) l is also called a left-handed optical vortex, and the second modulated light ML2 with a negative value of l is also called a right-handed optical vortex.

[0023] The specific configuration of the spin orbit converter 13 is not limited to this embodiment, but as an example, it may be configured with a polarizing element having an anisotropy medium corresponding to the azimuth angle φ with respect to the optical axis. More specifically, the spin orbit converter 13 may be configured with a q-plate. Here, the q-plate is an example of the polarizing element and is configured with a liquid crystal having directionality dependent on the azimuth angle φ. The q-plate is sometimes called a liquid crystal polarizing spiral plate. The second modulated light ML2 generated by the spin orbit converter 13 is irradiated onto a sample (object) SA, for example.

[0024] (Effect of optical system 1) In the optical system 1 configured as described above, • A first modulated light ML1 having spin angular momentum is generated from the incident light IL. • Generate a second modulated light ML2 having orbital angular momentum from the first modulated light ML1. This configuration is employed. Here, in the generation of the first modulated light ML1, at a certain timing, left circularly polarized light with spin angular momentum (s=+1) is generated from the incident light IL, and at another timing, right circularly polarized light with spin angular momentum (s=-1) is generated from the incident light IL.

[0025] In addition, a second modulated light ML2 having a certain orbital angular momentum is generated from the left circularly polarized light at a certain timing, and a second modulated light ML2 having a different orbital angular momentum is generated from the right circularly polarized light at another timing. Here, the second modulated lights ML2 having different orbital angular momentums can be generated on the same optical axis.

[0026] Therefore, with the optical system 1 configured as described above, left and right optical vortices can be generated with high precision. Furthermore, with the optical system 1 configured as described above, left and right optical vortices can be generated using a single optical path and electrical control without mechanical switching such as switching of optical elements. Therefore, with the optical system 1 configured as described above, left and right optical vortices can be generated with high precision at high modulation frequencies.

[0027] (Control example) As an example, the control unit 20 may be configured to switch at a predetermined switching rate whether the modulation unit 12 generates left-circularly polarized light or right-circularly polarized light as the first modulated light ML1. By having the control unit 20 perform such control, it is possible to suppress the superposition of low-frequency noise such as flicker noise and drift on the HD (also called helical dichroism or optical vortex dichroism) signal when measuring the HD signal. In other words, with the above configuration, it is possible to generate optical vortices that enable accurate measurement of HD.

[0028] Furthermore, the control unit 20 may set the switching rate to 1 kHz or higher. This effectively suppresses the superposition of the aforementioned low-frequency noise onto the HD signal when measuring the HD signal. Alternatively, the switching rate may be set to 10 kHz or higher. This more effectively suppresses the superposition of the aforementioned low-frequency noise onto the HD signal when measuring the HD signal.

[0029] (Light conversion method) Next, the optical conversion method according to this embodiment will be described with reference to Figure 3. Figure 3 is a flowchart showing the flow of the optical conversion method S1 according to this embodiment.

[0030] (Step S11) First, in step S11, incident light IL is generated. This step can be performed, for example, by the light source unit 11 described above.

[0031] (Step S12) Next, in step S12, a first modulated light ML1 having spin angular momentum is generated from the incident light IL. This step can be performed, for example, by the modulation unit 12 described above.

[0032] (Step S13) Next, in step S13, a second modulated light ML2 having orbital angular momentum is generated from the first modulated light ML1. This step can be performed, for example, by the spin-orbit converter 13 described above.

[0033] Thus, in the light conversion method S1, • A first modulated light ML1 having spin angular momentum is generated from the incident light IL. • Generate a second modulated light ML2 having orbital angular momentum from the first modulated light ML1. This configuration is employed. The light conversion method S1 produces the same effect as the optical system 1 described above.

[0034] [Embodiment 2] Other embodiments of the present invention are described below. For the sake of clarity, components having the same function as those described in the above embodiments will be denoted by the same reference numerals, and redundant descriptions may be omitted.

[0035] (Optical system 1A) Figure 4 is a block diagram showing the configuration of the optical system 1A according to this embodiment. As shown in Figure 4, the optical system 1A comprises a light source unit 11, a modulation unit 12, a spin-orbit converter 13, a linear polarizing element 14, a control unit 20, and a detection unit 30. The linear polarizing element 14 is also referred to as the second linear polarizing element 14. The optical system 1A may also be referred to as an irradiation system, irradiation device, detection system, detection device, analysis system, analysis device, etc. Furthermore, an optical microscope equipped with the optical system 1A is also included in the invention described herein.

[0036] (Light source part 11) As shown in Figure 4, the light source unit 11 comprises a light source 111, a monochromator 112, and a spatial filter 113. The light source 111 generates a white laser with a wavelength range of 450 nm to 2000 nm, for example. The light source unit 11 also includes a monochromator 112 downstream of the light source 111. The monochromator 112 allows for the extraction of specific wavelengths from the white laser generated by the light source 111. In the example shown in Figure 4, the light source unit 11 further includes a spatial filter 113 downstream of the monochromator 112. The spatial filter 113 removes noise from the light that has passed through the monochromator 112 and adjusts the beam profile. The spatial filter 113 may also have the function of modulating the elliptical polarization of the light that has passed through the monochromator 112 to circular polarization. The light that has passed through the spatial filter 113 becomes, for example, a Gaussian beam (a beam with a spatially Gaussian profile). The light that has passed through the spatial filter 113 is supplied to the modulation unit 12 from the light source unit 11 as incident light IL to the modulation unit 12.

[0037] (Modulation section 12) As shown in Figure 4, the modulation unit 12 includes a first linear polarizing element 121 and a photoelastic modulator (PEM) 122. The photoelastic modulator 122 is also referred to as PEM122. Here, as shown in Figure 4, the first linear polarizing element 121 is positioned upstream of the PEM122 as an example. The first linear polarizing element 121 is also called the first linear polarizer.

[0038] The first linear polarizing element 121 modulates incident light IL, which is, for example, circularly polarized or elliptically polarized, into linearly polarized light. Then, the PEM 122 generates a first modulated light ML1 having spin angular momentum from the linearly polarized light generated by the first linear polarizing element 121. The first modulated light ML1, or the electric field of the first modulated light ML1, is called E. spin It is sometimes written as follows.

[0039] The functions of the first linear polarizing element 121 and PEM 122 can be described in more detail as follows. First, the incident light IL supplied from the light source 11, which has a spatial Gaussian profile, is, for example, a Jones matrix.

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[0040] (Spin-orbit converter 13, second linear polarizer 14) The spin-orbit converter 13 generates a second modulated light ML2 having orbital angular momentum from the first modulated light ML1. Here, the second modulated light ML2 having orbital angular momentum is also called an optical vortex (OV), as in Embodiment 1. The spin-orbit converter 13 is composed of a q-plate as an example. The spin-orbit converter 13 is sometimes referred to as the Q-plate 13. The second linear polarizing element 14 is placed after the Q-plate 13. The second linear polarizing element 14 is also called the second linear polarizer. The functions of the spin-orbit converter 13 and the second linear polarizing element 14 are described in more detail below.

[0041] The first modulated light ML1(E) generated by the modulation unit 12 spin ) is a Jones matrix

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[0042] Then, from the modulated light (second modulated light ML2) generated by the Q plate 13, the Jones matrix is ​​generated as an example.

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[0043] Note that by providing one set of a half-wave plate and a second spin-orbit converter between the Q plate 13 and the second linear polarizer 14, a modulated OV having a TC of ±2 can be generated. Similarly, by providing n sets of a half-wave plate and a second spin-orbit converter between the Q plate 13 and the second linear polarizer 14, a modulated OV beam having a TC of ±(n + 1) can be generated.

[0044] The second modulated light ML2 (E orbit ) that has passed through the second linear polarization element 14 is irradiated onto the sample SA. When the sample SA is a chiral object, the light E orbit from the sample SA irradiated with the second modulated light ML2 (E det ) is

Number

[0045] (Control unit 20, Detection unit 30) The control unit 20 controls each part of the optical system 1A. For example, the control unit 20 sets (changes) the value of the modulation frequency Ω (switching rate) by the PEM 122. The control unit 20 may also be configured to set (change) the frequency extracted by the monochromator 112 from the white laser generated by the light source 111. In other words, the control unit 20 may be configured to set (change) the frequency of the incident light IL. The control unit 20 may also control the PEM 122 and the Q plate 13 so that the PEM 122 and the Q plate 13 can perform modulation that matches the frequency of the incident light IL.

[0046] The detection unit 30 detects light E from the sample into which the second modulated light ML2 is incident. det The detection unit 30 detects the intensity of light I det This is E shown in Equation 12. det It is proportional to the square of the absolute value of . Also, the intensity of light I detected by the detection unit 30 det This is achieved by frequency expansion based on the modulation frequency Ω (switching rate) of PEM122,

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[0047] Furthermore, the detection unit 30, as an example, detects light (E) from the sample SA. detAs a detection method, a lock-in detection method may be implemented that performs lock-in detection according to the switching rate and the wavelength of the incident light IL. Here, lock-in detection refers to a method of detecting only the component of light from the sample SA that has a specific frequency by using a reference signal having a specific frequency. The detection unit 30 or the control unit 20 may be configured to include a lock-in amplifier for performing the lock-in detection. Furthermore, the reference signal can be synchronized with the modulation frequency Ω (switching rate) (it can be set to the same frequency).

[0048] By having the detection unit 30 perform lock-in detection, for example, when measuring an HD (helical dichroism) signal using the second modulated light ML2, it is possible to suppress the superposition of low-frequency noise such as flicker noise and drift onto the HD signal. The control unit 20 may also set the switching rate to 1 kHz or higher. This allows for effective suppression of the superposition of the aforementioned low-frequency noise onto the HD signal when measuring the HD signal. The switching rate may also be set to 10 kHz or higher. More specifically, the switching rate may be set to approximately 50 kHz, and high-speed modulation by PEM122 may be performed. This allows for even more effective suppression of the superposition of the aforementioned low-frequency noise onto the HD signal when measuring the HD signal.

[0049] Furthermore, as will be described in more detail later, the control unit 20 changes the wavelength of the incident light IL, and the detection unit 30 performs lock-in detection according to that wavelength, thereby detecting the light E from the sample SA. det It is also possible to detect the spectrum of the second modulated light ML2. More specifically, as an example, when detecting an HD (helical dichroism) signal using the second modulated light ML2 described above, it is possible to detect how the HD signal changes depending on the wavelength of the incident light IL. For this reason, the optical system 1A is also referred to as a spectral measurement device.

[0050] (Example of the configuration of the detection unit 30, and example of the detection result 1) The following describes a more specific configuration example of the detection unit 30 and an example of detection results using the optical system 1A. Figure 5 is a schematic diagram showing the configuration of the detection unit 30 in this example. In the example shown in Figure 5, the detection unit 30 includes a half mirror 31, a lens 32, a pinhole 33, and a photodetector 34. Here, the pinhole 33 has a diameter of 10 μm (micrometers) as an example. Alternatively, a piezo stage may be used in conjunction with the pinhole 33.

[0051] Furthermore, in the example shown in Figure 5, a spatial light modulator (SLM) is used as the sample SA. This spatial light modulator SLM(SA) is a topological charger. SLM (l SLM It has a helical topological structure characterized by =0,±1,±2,···). Figure 5 shows a more specific example, l SLM This illustrates the helical phase structure in a spatial light modulator (SLM) when the value is -1.

[0052] As shown in Figure 5, the second modulated light ML2(E) passes through the second linear polarizing element 14. orbit ) Topological charge l in This is how it is written. Also, the second modulated light ML2(E orbit The wavelength of (for example, the same as the wavelength of incident light IL) is λ in This is how it is written. As shown in Figure 5, the second modulated light E orbit The light is irradiated onto the spatial light modulator SLM(SA), and light E from the spatial light modulator SLM(SA) det However, it enters the photodetector 34 via the half mirror 31, lens 32, and pinhole 33. Here, as shown in Figure 5, light E from the spatial light modulator SLM(SA) det The topology of the chart out This is how it is written. Also, the light E from the spatial light modulator SLM(SA) det This refers to the emitted light vortex E det It is sometimes called that.

[0053] The upper part of Figure 6 is l SLMFor each of the spatial light modulators SLM(SA) whose values ​​are -2, -1, 0, +1, +2, λ in =800nm, l in The second modulated light ML2(E) = 0 orbit When irradiated with ), E detected by the photodetector 34 det The beam intensity profile is shown. The lower part of Figure 6 shows the narrow-angle interference image detected by the photodetector 34. From Figure 6, it can be seen that the helical phase structure in the spatial light modulator SLM(SA) is properly detected by the photodetector 34.

[0054] Figure 7 shows l SLM For each of the spatial light modulators SLM(SA) whose values ​​are -2, -1, 0, +1, +2, λ in =800nm, l in = +1, 0, -1 Second modulated light ML2(E orbit When each of the ) is irradiated, the E detected by the photodetector 34 det This shows the beam intensity profile. As can be seen from Figure 7, the exit light vortex E det Selection rules regarding the number of turns l out =l SLM +l in This condition holds true. In the example shown in Figure 7, high-speed modulation using PEM122 is not performed. In other words, the switching rate Ω mentioned above is set to a value close to 0.

[0055] Figure 8 shows that while performing high-speed modulation with PEM122, l SLM For each of the spatial light modulators SLM(SA) whose values ​​are -2, -1, 0, +1, +2, l in The second modulated light ML2(E) = ±1 orbit When irradiated with ), E detected by the photodetector 34 detThis shows the beam intensity profile. The upper part of Figure 8 shows the sum of the left and right optical vortex responses by the spatial light modulator SLM(SA), and the lower part of Figure 8 shows the difference (optical vortex dichroism) between the left and right optical vortex responses by the spatial light modulator SLM(SA). Figure 9 also shows the optical vortex dichroism (HD signal) and l based on the detection shown in Figure 8. SLM This graph shows the relationship with the emitted light vortex E. det Selection rules regarding the number of turns l out =l SLM ±1 This is true.

[0056] Figure 10 shows that while performing high-speed modulation with PEM122, l SLM For each of the spatial light modulators SLM(SA) whose values ​​are -2, -1, 0, +1, +2, l in =±2 second modulated light ML2(E orbit When irradiated with ), E detected by the photodetector 34 det This shows the beam intensity profile. The upper part of Figure 10 shows the sum of the left and right optical vortex responses by the spatial light modulator SLM(SA), and the lower part of Figure 10 shows the difference (optical vortex dichroism) between the left and right optical vortex responses by the spatial light modulator SLM(SA). Figure 11 also shows the optical vortex dichroism (HD signal) and l based on the detection shown in Figure 10. SLM This graph shows the relationship with the emitted light vortex E. det Selection rules regarding the number of turns l out =l SLM ±2 This is true.

[0057] (Example of detection result 2) Next, with reference to Figures 12 to 14, we will describe the spectral detection of circular dichroism and optical vortex dichroism when using an object with a spiral nanostructure as the sample SA. The upper part of Figure 12 shows the configuration of the optical system 1A in which the detection was performed. The middle part of Figure 12 shows the spectrum of the detected g-factor. The lower part of Figure 12 shows the spiral nanostructure of the sample SA. A reflective optical microscope equipped with an objective lens with a numerical aperture (NA) of 0.95 was used for this measurement.

[0058] As described above, in the optical system 1A, such a spectrum can be detected by changing the frequency of the incident light IL with the control unit 20 and performing detection with the detection unit 30. Here, the g-factor (also called the g-value) is proportional to the value obtained by dividing the difference in the response of the left and right optical vortices due to the sample SA (for example, Equation 15) by the sum of the responses of the left and right optical vortices due to the sample SA (for example, Equation 14). The g-factor is also an example of a CD signal or HD signal.

[0059] Figure 12 shows the first modulated light ML1(E) that has passed through PEM122 after removing the Q plate 13 and the second linear polarizing element 14 in optical system 1A. spin This is the g-factor spectrum obtained when the sample SA was irradiated with circularly polarized light. As shown in Figure 12, the g-factor differs significantly between left-circularly polarized (LH) and right-circularly polarized (RH) light at wavelengths of 500 nm to 570 nm of the incident light IL, clearly detecting the circular dichroism (CD) of the spiral nanostructure in the sample SA.

[0060] Figure 13 shows the second linear polarizing element 14 removed from the optical system 1A, and the second modulated light ML2(E) that has passed through the Q plate 13. orbit This is the g-factor spectrum obtained when the sample SA was irradiated with the (optical vortex). In the example in Figure 13, the first modulated light ML1(E spin The sign of s in ) and the second modulated light ML2(E orbitThe signs of l in ) are set to be opposite. Similar to Figure 12, dichroism (optical vortex dichroism, HD) can be clearly detected even when using an optical vortex. However, as shown in Figures 12 and 13, an interesting result was obtained in which the spectral shapes of CD and HD are different in the wavelength range of 550-600 nm of the incident light IL.

[0061] Figure 14 shows an optical system 1A comprising a Q plate 13 and a second linear polarizing element 14, where the second modulated light ML2(E) passes through the second linear polarizing element 14. orbit This is the g-factor spectrum obtained when the sample SA was irradiated with the (optical vortex). In the example in Figure 14, the first modulated light ML1(E spin The sign of s in ) and the second modulated light ML2(E orbit The sign of l in ) is set to be the same sign. As is clear from comparing with Figure 13, the first modulated light ML1(E spin The sign of s in ) and the second modulated light ML2(E orbit The spectral profile differs significantly from that in Figure 13, where the sign of l is different from that in Figure 14. Furthermore, in Figure 14, optical vortex dichroism (HD) is also observed in the wavelength range above 600 nm.

[0062] Thus, by using optical system 1A, it was demonstrated that the optical response of chiral materials differs significantly depending on the combination of spin angular momentum and orbital angular momentum. This is a property that was discovered for the first time by spectral detection using optical system 1A.

[0063] (Additional information regarding Embodiment 2) As described above, the light source unit 11 consists of a white laser 111, a monochromator 112, and a spatial filter 113. The white laser 111 contains light with a wide range of wavelengths from visible light to near-infrared light. By incidenting this white light onto the monochromator 112, it is monochromatized and the wavelength of the monochromatized light can be swept. Since the shape of the light beam emitted from the monochromator 112 is elliptical, a circular light beam is obtained by using the spatial filter 113, which consists of a lens and a pinhole.

[0064] A linearly polarized beam is obtained by injecting a circular light beam into a linear polarizer (first linear polarizing element 121) that can be used with a wide range of wavelengths. As described above, by injecting the linearly polarized beam into an acousto-optic element called a photoelastic modulator (PEM 122), the polarization state of the incident light is converted from linear polarization to circular polarization, and the left and right circular polarization states are modulated with a period of approximately 50 kHz. The photoelastic modulator (PEM 122) controls the birefringence that occurs inside the photoelastic element by periodically applying pressure to the photoelastic element using a piezoelectric element such as quartz. Since the pressure to be applied to the photoelastic element changes with the wavelength of the incident light, the pressure applied to the photoelastic element is changed in conjunction with the operation of the monochromator 112 (the voltage applied to the piezoelectric element is changed). This control is performed by the control unit 20.

[0065] By injecting circularly polarized light (s,l)=(±1,0), which has been rapidly modulated by a photoelastic modulator, into the q-plate (Q-plate 13), a rapidly modulated circularly polarized optical vortex (s,l)=(-1,+1)(+1,-1) can be obtained. Here, when left-circularly polarized light is incident on the q-plate, a right-circularly polarized optical vortex that rotates counterclockwise is generated. The q-plate that generates an optical vortex with TC = 1 is a waveplate made of liquid crystal elements, whose optical axis (θ) depends on the azimuth angle (φ) (θ=l*φ / 2), and it gives a phase difference between polarization parallel to the optical axis and polarization perpendicular to the optical axis. This phase difference is determined by the voltage applied to the q-plate. Furthermore, the phase difference required to generate an optical vortex is π, but the applied voltage required to produce this phase difference changes depending on the wavelength of the incident light. Therefore, the voltage applied to the q-plate is changed in conjunction with the operation of the monochromator 112. This control is performed by the control unit 20.

[0066] By injecting the high-speed modulated circularly polarized optical vortex (s,l)=(-1,+1)(+1,-1) emitted from the q-plate into a λ / 4 plate, a high-speed modulated linearly polarized optical vortex (s,l)=(0,±1) can be generated. By injecting it into a λ / 2 plate (half-wave plate) instead of a λ / 4 plate, a high-speed modulated circularly polarized optical vortex (s,l)=(±1,±1) with the same sign for spin and orbit can be generated. In other words, by providing a half-wave plate downstream of the q-plate (first spin-orbit converter), the said circularly polarized optical vortex (s,l)=(±1,±1) can be generated.

[0067] Furthermore, by injecting a high-speed modulated circularly polarized optical vortex (s,l)=(±1,±1) into another q-plate, a high-speed modulated circularly polarized optical vortex (s,l)=(-1,+2)(+1,-2) with a TC of ±2 can be generated. In other words, by providing a half-wave plate downstream of a q-plate (first spin-orbit converter), and further providing another q-plate (second spin-orbit converter) downstream of the half-wave plate, the circularly polarized optical vortex (s,l)=(-1,+2)(+1,-2) can be generated.

[0068] Thus, as with the case where TC is ±1, by introducing an optical element, high-speed modulated circularly polarized light vortices with various spin and orbit combinations can be generated. By injecting the high-speed modulated circularly polarized light vortex into a sample and detecting the transmitted light, reflected light, scattered light, and emitted light with a photodetector that can operate at the modulation frequency, the HD signal for the circularly polarized light vortex can be measured. By focusing the light with a lens and injecting it into the sample, measurement under a microscope is also possible. By using high-speed modulated circularly polarized light vortices with various spin and orbit combinations generated using optical system 1A, it becomes possible to evaluate the contribution of spin and orbit to the HD signal of the sample.

[0069] <Examples> In the following section, a more detailed embodiment of optical system 1A will be described with reference to Figures 15 to 19.

[0070] (overview) As mentioned above, helical dichroism (or optical vortex dichroism, HD) is defined as the difference in optical absorption between pairs of chiral light containing left-handed (LH) and right-handed (RH) optical vortices (OV) with orbital angular momentum (OAM), and is a promising method for characterizing chiral materials. In current major methods of OV generation using spatial light modulators (SLMs), the OAM switching speed is typically slow, around 100 Hz, and is comparable to low-frequency noise, making accurate chiral detection difficult.

[0071] In this embodiment, we theoretically propose and experimentally demonstrate high-speed modulation of LH and RH OV at approximately 50 kHz. This modulation is achieved by combining high-speed modulation of circularly polarized light with spin angular momentum (SAM) and SAM-OAM conversion technology. In this embodiment, we not only established high-speed modulation of OV but also the theory of HD measurement using the modulated OV. We experimentally verify the theory using a helical phase hologram drawn on an SLM as a pseudo-HD active sample. This embodiment provides a new method for accurate HD measurement and opens the way to the development of high-sensitivity chiral optical spectroscopy techniques.

[0072] (1. Introduction) The measurement of optical dichroism quantifies the difference in a material's optical response to a pair of orthogonal light (e.g., horizontal and vertical linear polarization) and is highly dependent on the structural symmetry of the material, such as anisotropy and chirality. Since Pasteur discovered molecular chirality, where molecules cannot be superimposed onto their mirror images, the chirality of materials has been characterized using circular dichroism (CD), defined as the difference in light absorption between chiral pairs of left-handed (LH) and right-handed (RH) circularly polarized light (CPL). CPL exhibits a chiral helical polarization structure due to the rotation of polarization and functions as a chiral probe. CPL has a spin angular momentum (SAM) of sh / 2π (s=±1) (h is Planck's constant) per photon, and positive SAM and negative SAM correspond to LH CPL and RH CPL, respectively.

[0073] However, CPL-based chiral optics techniques have the problem that, in most cases, they are not highly sensitive to structural chirality due to the spatial scale mismatch between the size of molecules and the wavelength λ of CPL. In this embodiment, we propose using optical vortices (OVs) that exhibit a chiral helical phase structure by wavefront rotation as a strategy to increase chiral photo-interactions. OVs have a quantized orbital angular momentum (OAM) of lh / 2π (l=0,±1,±2,...) (where h is Planck's constant), where l represents the topological charge (TC), and positive and negative OAMs correspond to LH and RH OVs, respectively.

[0074] The helical pitch of an OV is represented by |λ / l|. Since |l| can, in principle, be taken to infinity, using an OV with a sufficiently large |l| is expected to significantly reduce the spatial scale mismatch between the molecular size and the helical pitch of the OV, thereby increasing chiral interactions. Thus, helical dichroism (HD) is defined as the difference in light absorption between chiral pairs of LH and RH OV or CPL, or combinations of CPL and OV, and is an extension of the CD concept, with the potential to reveal subtle chiral properties that cannot be captured by conventional CD technology.

[0075] The simplest way to measure the HD signal of a sample is to first measure the absorbance A of the sample using LH chiral light. LH Next, measure the absorbance A of the sample using RH chiral light. RH By measuring and finally subtracting them, the HD signal is obtained (△A HD ≡A LH -A RH This method is applicable to samples where the HD signal is sufficiently large, usually around a few percent of the average absorbance [A ave ≡(A LH +A RH ) / 2]. Here, the HD signal in the nonlinear optical response of a chiral material whose size (r) is much smaller than the wavelength of light (λ) (r≪λ) is A aveIt is known that this is a few percent of the total. Also, the HD signal in the linear optical response of chiral materials whose size (r) is equal to or greater than the wavelength (λ) of the incident light (r≧λ) is A ave It is known to be several tens of percent.

[0076] However, for chiral materials with small r≪λ, i.e., typical chiral molecules, the CD (CPL-based HD) signal of the linear optical response is generally weak, typically less than 0.1% of Aave. Furthermore, OV-based HD has not yet been observed in such materials. When the HD signal is weak, measurements with LH and RH chiral lights can easily be obscured by flicker noise and drift caused by variations in measurement conditions and environment. This drift is more pronounced when measuring samples smaller than the size of the focused beam, especially with OV beams, because the light intensity varies depending on the position.

[0077] Furthermore, when measuring with LH chiral light and RH chiral light, the sample position may differ if the sample is in a different position, as this can lead to differences in beam intensity and thus different excitation rates for the sample. Therefore, false HD signals may be observed even if the sample does not exhibit HD. False signals due to drift cannot be removed by signal averaging. Since the natural frequencies of noise including flicker noise and drift are mainly below 100 Hz, it is thought that rapidly switching between LH chiral light and RH chiral light during measurement can reduce false signals.

[0078] The measurement of small CD signals from chiral molecules has been achieved using LH and RH CPLs modulated at high frequencies of several tens of kHz, employing devices such as acousto-optic modulators (PEMs). On the other hand, OV-based HD measurements have not utilized modulated OVs; instead, the simplest method described above is employed. Holograms drawn on a spatial light modulator (SLM) are commonly used to generate OV beams, with methods including transferring a helical phase structure to the incident beam or diffraction using a fork-shaped diffraction grating structure. In this method, switching between LH and RH OVs is performed by mirror inversion of the hologram. However, the speed of this structural inversion is governed by the refresh rate of the SLM, which is usually slow at 100 Hz and is strongly affected by flicker noise and drift. To achieve high-precision HD measurements comparable to CD measurements, it is essential to develop a method for high-speed modulation of LH and RH OVs at frequencies of at least 1 kHz or higher, as in the configuration of this embodiment.

[0079] In this example, the OV of LH and RH is set to approximately 50 kHz. in We theoretically and experimentally demonstrated high-speed modulation with TCs of ±1 and ±2. The key concept in high-speed OV modulation by OAM is the combination of rapid modulation of CPL by SAM using PEM and optical SAM-OAM conversion using q-plate (see Figure 4 above). In this example, we theoretically describe the evolution of the optical state in the proposed optical system using Jones vectors and matrices, and explicitly show OV modulation using mathematical formulas. Furthermore, we show that by detecting the modulated OV after passing through the sample and demodulating the detected signal using lock-in detection technique, the sum and difference (HD) of the response signals of the HD-active sample for LH and RH OV can be obtained simultaneously. In this example, the TC of the SLM is l SLMWe conducted experiments and model calculations using a system in which a helical phase hologram was treated as a pseudo-HD active sample to verify the theory. We demonstrate that the proposed optical system can rapidly modulate the LH and RH OV and can be used for HD measurements. The method described in this embodiment is expected to form the basis for high-precision HD measurements.

[0080] (2. Overview of the optical system configuration and theory of optical systems) A. High-speed modulation of left-handed and right-handed optical vortices The configuration of the optical system according to this embodiment is shown in Figure 4. The OV modulation portion in this optical system consists of two polarizers (first linear polarizer 121, second linear polarizer 14), one PEM (PEM122), and one q-plate (Q-plate 13).

[0081] The theoretical aspects of the optical system in this embodiment have been described above with reference to Figure 4, etc., so redundant explanations will be omitted. However, equation 10 described above shows the sinusoidal modulation of the amplitudes of LH and RH OV at the modulation frequency Ω. From equation 10 described above, it was shown that rapid OV modulation is possible when the modulation frequency Ω is sufficiently high. Furthermore, it was confirmed that by introducing an OAM modification system consisting of one half-wave plate and one q-plate between the original q-plate and the second polarizer (second linear polarizer 14), a modulated OV beam with a TC of ±2 can be generated.

[0082] In other words, we confirmed that a modulated OV beam with a TC of ±2 can be generated by providing one set of a half-wave plate and a second spin-orbit converter between the Q plate 13 and the second linear polarizer 14. Similarly, we confirmed that a modulated OV beam with a TC of ±(n+1) can be generated by providing n sets of half-wave plates and second spin-orbit converters between the Q plate 13 and the second linear polarizer 14.

[0083] The key point of this method is that by using voltage-driven q-plates, once the optical axis between the center of the q-plates and the beam is adjusted, different TC-modulated OV beams can be generated simply by changing the voltage applied to the q-plates without further adjusting the optical axis. This is useful for measuring the TC dependence of the HD of a sample.

[0084] B. Helical dichroism measurement using modulated optical vortices When the modulated OV interacts with a sample (SA) that exhibits HD, the complex amplitudes of the LH and RH OVs are further modulated by the complex coefficients T + and T - respectively. Finally, a photodetector (detection unit 30) receives the modulated beam. Here, the modulated beam received by the photodetector has the Jones vector E det represented by Equation 12 described above.

[0085] The detected signal is proportional to the square of the magnitude of the complex electric field (i.e., proportional to |E det | 2 ) and contains frequency components of nΩ (where n is an integer) due to the modulation defined by δ = δ0sinΩt described above. By selecting an appropriate phase modulation amount (δ0), the fundamental wave component (the 0th) and the first harmonic component of the detected signal are proportional to the sum (S total ) and the difference (S HD ) of the responses to the LH OV and the RH OV respectively, and they are

Number

Number

[0086] (3. Demonstration) A. Experiment The first measurement of HD in the linear optical response of chiral molecules much smaller than the wavelength of light was attempted in 2005. In such materials, the excitation modes are separated, making the correspondence between elementary excitations and optical responses clear. However, nearly 20 years later, HD signals from chiral small molecules have not been observed, and the mechanism of HD, particularly its relationship to the elementary excitations of materials, remains unclear. This is mainly due to the lack of a system with accuracy comparable to CD. This situation is likely due not only to the absence of a rapid modulation method for OV, but also to the lack of standard samples for HD. The inventor's intuitive understanding is that a helical phase structure with a phase gradient in the azimuthal direction can directly modulate the spatial phase of incident light, inevitably exhibiting different optical responses for LH and RH OV.

[0087] In this example, l drawn on SLM SLM A helical phase hologram with different TCs was used to function as a pseudo-HD active sample. While an SLM can impart different phase modulations to the LH OV and RH OV, it cannot impart different amplitude modulations, making it impossible to measure the HD signal as predicted by Equation 17. However, by propagating the light over a sufficiently long distance or focusing it using a lens, it is possible to convert the phase modulation to amplitude modulation. Therefore, we attempted to measure the HD of a helical phase hologram drawn on an SLM by utilizing the difference in the focusing characteristics of the output beam due to the difference in TCs.

[0088] To measure the HD signal from the helical structure generated by the SLM, an experimental setup was configured to measure the beam intensity profile at the focal plane of the lens. The experimental setup (configuration of the detection unit 30) is shown in Figure 5, but will be described in more detail here. In this embodiment, as shown in Figure 5, in The experiment was conducted using each of the following three types of light as the light incident on the detection unit 30. (a) Linearly polarized Gaussian beam for optical system evaluation (b) Linearly polarized OV beam for deriving the selection rule for the interaction between the incident OV and SLM (c) Rapidly modulated linearly polarized OV beam for HD measurement.

[0089] A continuous-wave titanium-sapphire laser (3900S, Spectra-Physics) with a central wavelength of 800 nm was used as the light source (light source 111). When this light beam was passed through a spatial filter, a Gaussian beam with a radius of approximately 3 mm was obtained. In condition (c), the obtained Gaussian beam was incident on an optical system (optical system 1A) having two polarizers (first linear polarizer 121, second linear polarizer 14) (LPVIS100-MP2, Thorlabs), one PEM122 (II / FS50, HINDS Instruments), and one Q plate 13 (ARCoptix), l in A high-speed modulated OV beam with a TC of ±1 was generated. Due to the polarization characteristics of liquid crystals, the liquid crystal in the LCOS-SLM (X15213-07, Hamamatsu Photonics K.K.) can only undergo phase modulation of horizontal polarization, so a second polarizer (second linear polarizer 14) was used.

[0090] On the other hand, the experimental setup was changed in conditions (a) and (b). In condition (a), the PEM122 and q-plate (Q-plate 13) were removed from the optical system shown in Figure 4. In condition (b), the PEM122 was replaced with a single achromatic quarter-wave plate (ACWP-700-1000-10-4, CVI Melles Griot). Also, in conditions (b) and (c), a set of OAM modification systems consisting of a colorless half-wave plate (AHWP05M-980, Thorlabs) and a q-plate was placed after the original q-plate, l in Overcurrent (OV) was generated with a TC of ±2.

[0091] As shown in Figure 5, the beam passed through the unpolarized half-mirror 31 (CCM1-BS014, Thorlabs) and was successfully incident on the liquid crystal of the silicon (LCOS) SLM (X15213-07, Hamamatsu Photonics K.K.) used as a pseudo-HD active sample SA. To confirm the generation of the OV beam, a Michelson interferometer was fabricated by installing a mirror on the other port of the unpolarized half-mirror, and an interferogram was acquired by placing a camera immediately after the half-mirror's output port (see lower part of Figure 6). The output light was reflected by the same half-mirror and then incident on a plano-convex lens with a focal length of 50 mm (LA1255-B, Thorlabs). The light intensity transmitted through a 10 μm diameter pinhole (P10W, Thorlabs) placed at the focal plane of the lens was detected using a photomultiplier tube (H10723-20, Hamamatsu Photonics K.K.). A closed-loop piezoelectric positioning stage was used to scan the pinhole and obtain a two-dimensional map (i.e., optical image) of the optical signal. total ) and HD signal (S HD The two-dimensional map of ) was used to qualitatively discuss the results obtained from experiments and model calculations described in Chapter 3B.

[0092] B. Model calculation To demonstrate the validity of the experimental results, the behavior of light in the optical system shown in Figure 5 was modeled. The incident light is horizontally linearly polarized, and exp(il) in It has a complex field characterized by φ, and TC is l in That is. SLM Selection rule l based on the interaction between the SLM with TC and incident light out =l in +l SLM However, this was confirmed in this embodiment. According to this selection rule, the complex field of the beam before lens incidence is exp(il out Characterized by φ). The complex field of the beam focused by the lens was calculated using Richards-Wolf vector diffraction theory. In this case, the complex field of the focused beam is,

number

[0093] (4. Results and Discussion) A. Focusing characteristics of beams with different topological charges As a first step toward HD measurement of SLM used as a pseudo-HD active sample SA, TC is l in An incident Gaussian beam with TC = 0 and l SLM The TC that appears after the interaction with the SLM is l out The focusing characteristics of the emitted beam were evaluated.

[0094] Figure 15 shows the topology charge of incident light (TC) in = 0 and spatial light modulator (SLM) l SLM The beam characteristics at lens focal planes of =0, ±1, ±2, and ±3 are shown. More specifically, these are maps of beam intensity profiles obtained by model calculations (a) and experiments (b). The scale bar is 20 μm. Figure 15(c) shows l SLM Figure 15(d)(e) shows the measured (circles) and calculated (solid curve) line profiles of the intensity along the horizontal line passing through the center of the beam at =0, -1, -2, and -3. Figure 15(d)(e) shows the measured (circles) and calculated (solid curve) maximum intensity (d) and diameter (e) of the vortex beam as a function of the absolute value of TC. All intensities are l SLM The beam intensity was normalized to the maximum intensity when = 0.

[0095] In Figure 15, (a) and (b) show that the TC of the SLM is l SLM The calculated and measured values ​​of the intensity distribution of the focused beam emitted from the SLM are shown for the cases of =0, ±1, ±2, and ±3. SLM When l = 0, the output beam contains a bright spot on the axis of the image center that indicates the main Gaussian component of the beam. On the other hand, when the SLM modulates l SLM When ≠0, the output beam showed an annular intensity distribution similar to a donut shape. Model calculations showed the beam's intensity distribution to be centrally symmetric, but in the experiment, distortion was observed, particularly in the donut-shaped beam. Such artifacts (distortion of beam shape) are thought to be due to interference between light modulated by the SLM and unmodulated light reflected from the SLM surface. The spatial phase structure of the output beam was obtained using a Michelson interferometer (exp(il out Upon checking φ)), it was as expected l SLM A fork-shaped fringe pattern was obtained when ≠0. The direction of the fork is l SLM The results were reversed for positive and negative values. out =l SLM This indicates that OV occurs at TC. To quantitatively evaluate the characteristics of the focused beam, a beam profile along a horizontal line passing through the beam center was obtained (Figure 15(c)). As shown in Figures 15(c) to (e), the absolute value of TC (|l out As |) increased, a relative decrease in the maximum beam intensity (Figure 15(d)) and a relative increase in the donut diameter (Figure 15(e)) were observed. The experimental results, although containing artifacts, show good agreement with the model calculation results both qualitatively and quantitatively.

[0096] B. Selection rules for the interaction between helical phase holograms and optical vortices Next, the incident light (l) to the detection unit 30 in ), SLM(l SLM ), light emitted from SLM (l out The selection rules for TC were clarified.

[0097] Figure 16 shows lin =Incident light with topological charge (TC) of +1(a), -1(b), +2(c), -2(d) l SLM This image shows the measured beam intensity map at the focal plane after interaction with a spatial light modulator (SLM) with different TCs. The scale bar is 20 μm. The beam intensity is shown in the image. SLM Normalized by the maximum intensity at -l.

[0098] As mentioned above, Figure 16 shows that TC is l in An OV beam with ≠0 is injected, and the TC of the SLM is l SLM The intensity distribution of the emitted light from the SLM was measured for cases where =0, ±1, ±2, and ±3. SLM =-l in When incident light is incident on an SLM helical phase hologram (sample SA), the annular intensity distribution of the incident light becomes a Gaussian intensity distribution (l) with an intensity peak on the axis. out It is replaced by (=0), and a bright spot appears in the center. As shown in Figures 16(a) and (b), l in = +1, -1 OV beam l SLM When incident on an SLM with values ​​of -1, +1, the Gaussian intensity distribution (l out An image of the exit beam at =0 was obtained. in = +2, -2 OV beam l SLM Similar results were obtained when the SLM was incident on -2 and +2 (Figures 16(c) and (d)). On the other hand, l SLM ≠-l in In the case of l out Since ≠0, a ring-shaped intensity distribution remains, and as can be expected from Figure 16(e), l out The diameter of the donut beam increased or decreased depending on the absolute value of l. As shown in Figures 16(a) and (b), in = ±1 OV beam l SLM When the beam was incident on an SLM with an intensity distribution of ±1, an output beam image with an annular intensity distribution was obtained (l out =±2). in = ±2, l SLM If = ±2, donut beam (l out The diameter of the donut beam (l = ±4) is outThe value was greater than ±2 (Figure 16(c), (d)). From these results, the selection rule l for TC in this optical system can be determined. out =l in +l SLM This was revealed.

[0099] C. Helical dichroism measurement using modulated light vortices Selection rule (l out = in +l SLM By using this method, the spatial distribution of the HD signal observed with this optical system can be qualitatively predicted. The LH and RH OV beams are set to ±|l in When modulated with | and incident on an SLM without helical phase modulation (l SLM (=0), the TC of the output beam will be the same as the TC of the input beam (l out =l in Therefore, the incident LH(+|l in |) and RH(-|l in |) The difference in the intensity distribution of the OV beam is observed as an HD signal, which is ideally zero. On the other hand, l SLM If there is a helical phase hologram of SLM > 0, then the incident LH(+|l in |) For an OV beam, the TC of the output beam is the incident RH (-|l in |) is greater than the TC of the OV beam (l SLM +|l in |>l SLM -|l in |). In this case, a negative HD signal is observed near the beam center, and a positive signal is observed in the peripheral area. This is because the larger the absolute value of TC, the larger the diameter of the donut beam (Figure 15(e)). SLM If an SLM <0 is used, l SLM The distribution trend of the HD signal is reversed when using an SLM with >0. Considering the HD signal at the center of the beam, l SLM =+|l in Under the condition |, there is a negative local maximum, l SLM =-|l in Under the condition |, there is a positive maximum, which is because the HD signal reflects the difference between a Gaussian distribution and a ring distribution.

[0100] Figure 17 shows l SLM On a helical phase hologram drawn on a spatial light modulator (SLM) with TC, l in When a modulated optical vortex with a topological charge (TC) of ±1 is incident, the total signal S total (Figures 17(a) and (b)) and the difference (helical dichroism, HD) signal S HD (Figures 17(c) and (d)) are shown. Figures 17(a) and (c) show the calculated distribution, and (b) and (d) show the measured distribution. The scale bar is 20 μm. All signals are in the image. SLM S at =+1 total Normalized by the maximum value.

[0101] Figure 18 shows l SLM On a helical phase hologram drawn on a spatial light modulator (SLM) with TC, l in When a modulated optical vortex with a topological charge (TC) of ±2 is incident, the total signal S total (Figures 18(a) and (b)) and the difference (helical dichroism, HD) signal S HD (Figures 18(c) and (d)) are shown. Figures 18(a) and (c) show the calculated distribution, and (b) and (d) show the measured distribution. The scale bar is 20 μm. All signals are in the image. SLM S at =+1 total Normalized by the maximum value.

[0102] As shown in Figures 17 and 18, HD signals resulting from asymmetric helical phase modulation of LH and RH OV by SLM were observed. The model calculations and experimental results were consistent with the qualitative predictions described above. In Figure 17, l in When LH and RH OV beams modulated by ±1 are used as the incident beam, SLM = -1 and l SLM Under the condition = +1, prominent positive and negative HD signals were observed near the center of the beam, respectively. In Figure 18, l in =+2,-2, l SLM Similar results were obtained under the conditions of =-2 and +2. SLMWhen = 0, the expected HD signal was not obtained in the model calculation results (Figure 17(c)), but in the experimental results (Figure 17(d)), a small HD signal was obtained due to the difference in beam intensity distribution of the incident LH and RH OV beams. Such HD signal artifacts are l in This was also observed when using a modulated OV beam of ±2 (Figure 18(d)). Artifacts may arise from undesirable surface reflections by the SLM or beam shape distortion due to imperfections in the SAM-OAM conversion by the q-plate.

[0103] To facilitate quantitative discussion of experimental results and model calculations, the total signal (S) at the center of the beam is used. total ) and HD signal (S HD ) to l SLM Figure 19 shows the plot as a function of . More specifically, Figure 19 shows the total signal S at the center of the beam emitted from the spatial light modulator (SLM). total (Figures 19(a) and (c)) and the difference (helical dichroism, HD) signal S HD (Figures 19(b) and (d)) are shown. In Figure 19, each topology charge (TC) of the helical phase hologram drawn on the SLM is shown. SLM The calculated distribution (square) and the measured distribution (circle) for L are shown. in These were obtained using left-handed and right-handed optical vortices modulated with TCs of ±1 ((a) and (b)) and ±2 ((c) and (d)).

[0104] As shown in Figure 19, S total and S HD The value of l SLM It changes depending on S total The value of l SLM With =0 as the base, the sign is not reversed, S HD The value of l SLM The sign is inverted with =0 as the base. The experimental and calculated results are HD signal (S HD ) as well as all signals (S totalThe results also showed good qualitative and quantitative agreement. From these results, it can be seen that the optical system used in this study employs lock-in detection technology as the detection unit 30, and as shown in equations 16 and 17, the total signal (S) and HD signal (S) of the sample are obtained. HD It was found that these two parameters could be measured simultaneously. This means that the rapid modulation of LH and RH OV as shown in Equation 10 is actually realized in the optical system according to this embodiment.

[0105] Helical phase hologram (l SLM The TC of a helical phase hologram is determined by the magnitude of the phase gradient per unit azimuthal angle, and integer and non-integer TCs are possible. It is known that when a Gaussian beam is modulated with a non-integer TC helical phase hologram, an OV beam with a non-integer TC is produced, which is represented by the superposition of multiple OV beams with different integer TCs. This means that the HD signal from a helical structure with a non-integer TC will be an intermediate value between the HD signals from structures with close integer TCs. To verify this, we have a non-integer TC (|l SLM Model calculations were performed for the helical phase hologram of |=0.5). As shown in Figure 19, the OV beam (l) modulated with LH and RH in the incident beam in When using ±1 and ±2, |l SLM The signal with |=0.5 is |l SLM The interpolation between the |=0 and |=1 signals is performed as predicted. This result suggests that, as shown in Figure 19, it is possible to identify unknown samples even when their TC is not an integer by utilizing the correspondence between the TC and HD signals of the helical phase structure.

[0106] (5. Conclusion) In this embodiment, HD measurements were performed on a helical phase hologram drawn on an SLM, and the high-speed modulation technique for OV based on high-speed modulation of CPL by PEM and SAM-OAM conversion by q-plate was theoretically and experimentally demonstrated. High-speed modulation of LH and RH OV is possible not only for ±1 TC but also for ±2 TC by adding an OAM conversion system consisting of a half-wave plate and a q-plate to the proposed optical system (Figure 4). Similarly, by adding a polarizing optical element to this system, it is possible to modulate LH and RH chiral light in various combination states (s,l) of SAM and OAM. For example, by removing the second polarizer (second linear polarizer 14) of this optical system and replacing it with a half-wave plate, optical states (s,l) = (-1,+1)(+1,-1) and (±1,±1) can be realized, respectively. Furthermore, this method can be combined with discrete modulation methods for CPL (such as the use of a pair of polarizing beam displacers or a polarization-modulating dual comb). This flexibility allows for the measurement of HD signals of various chiral lights. Since the wavefunction of a material is often expressed using SAM or OAM, it is advantageous for investigating the relationship between elementary excitations and HD of a material. Due to the local spatial characteristics of CPL, the CD signal of a material originates from the interaction between electric dipoles and magnetic transitions. On the other hand, by utilizing the global characteristics of OV, it is expected that electric quadrupole transitions and higher-order transitions that are strongly dependent on the shape of the material can be induced. Therefore, HD measurement using OV has the potential to become a highly sensitive method for chirality detection. The method shown in this embodiment is expected to establish the foundation for high-precision HD measurement methods.

[0107] [Embodiment 3] Further embodiments of the present invention are described below. For convenience of explanation, components having the same function as those described in the above embodiments may be denoted by the same reference numerals, and redundant descriptions may be omitted.

[0108] (Light analysis device 2) Figure 20 is a block diagram showing the configuration of the optical analysis device 2 according to this embodiment. As shown in Figure 20, the optical analysis device 2 comprises a spin orbit converter 13, a modulation unit 12, a detection unit 50, and a control unit 40. As shown in Figure 20, the optical analysis device 2 is, in general terms, the optical system 1 according to Embodiment 1 with the direction of light propagation reversed. In the optical analysis device 2 according to this embodiment, unknown light (E) is transmitted to the spin orbit converter 13. unknown ) is incident on the spin orbit converter 13 and the modulation unit 12, and the light (E det ) is detected by the detection unit 50.

[0109] As described later, the optical analyzer 2 can detect (analyze) the ratio of left-handed to right-handed circularly polarized light, the ratio of left-handed to right-handed optical vortices, etc., contained in the unknown light. For this reason, the optical analyzer 2 may also be referred to as a circular polarization analyzer or an optical vortex analyzer.

[0110] (Spin-orbit converter 13) The spin-orbit converter 13 has the same configuration as described in Embodiments 1 and 2 and can be constructed using a q-plate. However, in this embodiment, the direction of light incident on the spin-orbit converter 13 is opposite to that in Embodiments 1 and 2, and the way in which the spin-orbit converter 13 is controlled is also different from Embodiments 1 and 2. In this embodiment, when the optical analysis device 2 is used as a circular polarization analysis device, as an example, the spin-orbit converter 13 is controlled so that the light incident on the spin-orbit converter 13 does not cause a spin-orbit conversion. In other words, the spin-orbit converter 13 is controlled so that the light incident on the spin-orbit converter 13 is emitted directly from the spin-orbit converter 13. Such control is achieved, as an example, by adjusting the voltage applied to the spin-orbit converter 13 by the control unit 40.

[0111] On the other hand, when the optical analysis device 2 is used as an optical vortex analysis device, for example, the spin orbit converter 13 is controlled so that the spin orbit converter 13 causes a spin orbit conversion in response to the light incident on the spin orbit converter 13. In other words, the spin orbit converter 13 is controlled so that light with different spin angular momentum and orbital angular momentum than the light incident on the spin orbit converter 13 is emitted from the spin orbit converter 13. Such control can also be achieved, for example, by adjusting the voltage applied to the spin orbit converter 13 by the control unit 40.

[0112] (Modulation section 12) The modulation unit 12 has the same configuration as described in Embodiments 1 and 2. However, in this embodiment, the direction of light incident on the modulation unit 12 is opposite to that in Embodiments 1 and 2. The modulation unit 12 is configured to include a photoelastic modulator (PEM) as an example. Alternatively, the modulation unit 12 may be configured to include a polarizing element downstream of the PEM. The polarizing element may also be a linear polarizer.

[0113] In this embodiment, the modulation unit 12 is controlled so that a component of the light intensity detected by the detection unit 50 (described later) that does not depend on the modulation frequency Ω in the modulation unit 12 satisfies a predetermined condition. More specifically, the magnitude δ0 of the phase modulation by the modulation unit 12 is controlled so that the "component that does not depend on the modulation frequency Ω" satisfies a predetermined condition. This control is also realized by the control unit 40.

[0114] By controlling the modulation unit 12 as described above, the detection unit 50 detects the unknown light (E unknown The sum of the ratios of left-circularly polarized light (or left-handed optical vortex) and right-circularly polarized light (or right-handed optical vortex) contained in the spectrum, and the difference between these ratios, can be suitably detected.

[0115] Thus, the optical analysis device 2 according to this embodiment is • The spin-orbit conversion unit (spin-orbit converter 13) into which the target light (unknown light) is incident, • The photoelastic modulator (modulator 12) into which light that has passed through the spin-orbit conversion unit (spin-orbit converter 13) is incident, A detection unit 50 that detects light that has passed through the photoelastic modulator. The device is equipped with the following features. With this configuration, the detection unit 50 can suitably detect the sum of the ratios of left-circularly polarized light (or left-handed optical vortex) and right-circularly polarized light (or right-handed optical vortex) contained in the unknown light, and the difference between these ratios. Therefore, with this configuration, the polarization component or optical vortex component contained in the unknown light can be suitably analyzed. Furthermore, the optical analysis method according to this embodiment is The steps include: irradiating the target light into the spin-orbit conversion unit, The steps include: igniting the light that has passed through the spin-orbit conversion unit into a photoelastic modulator; A detection step for detecting light that has passed through the photoelastic modulator. It includes the above configuration. According to this configuration, it achieves the same effect as the optical analyzer 2.

[0116] [Embodiment 4] Further embodiments of the present invention are described below. For convenience of explanation, components having the same function as those described in the above embodiments may be denoted by the same reference numerals, and redundant descriptions may be omitted.

[0117] (Light analyzer 2A) Figure 21 is a block diagram showing the configuration of the optical analysis device 2A according to this embodiment. The optical analysis device 2A according to this embodiment corresponds to a more specific configuration of the optical analysis device 2 according to Embodiment 3. As shown in Figure 21, the optical analysis device 2A, like the optical analysis device 2, includes a spin orbit converter 13, a modulation unit 12, a detection unit 50, and a control unit 40. Also, as shown in Figure 21, the modulation unit 12 includes a photoelastic modulator (PEM) 122 and a polarizing element (linear polarizer) arranged downstream of the PEM 122. Furthermore, as will be described later, the optical analysis device 2A may also be configured to include a half-wave plate upstream of the spin orbit converter 13. In such a configuration, the half-wave plate and the spin orbit converter 13 arranged downstream thereof may be collectively referred to as the spin orbit conversion unit.

[0118] (Example of operation of optical analyzer 2A 1) The following describes example 1 of the operation of the optical analyzer 2A. This example corresponds to the operation when the optical analyzer 2A is used as a circular polarization analyzer. However, this is not limited to this embodiment.

[0119] First, the unknown light (E unknown Assume that the light contains left-circularly polarized and right-circularly polarized light in a ratio of A:B. In this case, the state of the unknown light can be expressed as follows:

number

number

number

[0120] The intensity of light detected by the detection unit 50 is E det The square of the absolute value of (|E det | 2 ) is proportional, and the square of the absolute value is,

number

number

number

[0121] (Example of operation of optical analyzer 2A 2) The following describes example 2 of the operation of the optical analyzer 2A. This example corresponds to the operation when the optical analyzer 2A is used as an optical vortex analyzer. However, this is not limited to this embodiment.

[0122] First, the unknown light (E unknown Assume that the light contains right-handed optical vortices (s,l)=(+1,-1) in a left-circularly polarized state and left-handed optical vortices (s,l)=(-1,+1) in a right-circularly polarized state in a ratio of C:D. In this case, the unknown state of light can be expressed as follows.

number

number

[0123] The intensity of light detected by the detection unit 50 is E det The square of the absolute value of (|E det | 2) is proportional to, and the square of the absolute value is

Math

Math

Math

[0124] (Operation Example 3 of the Optical Analysis Device 2A) Hereinafter, Operation Example 3 of the optical analysis device 2A will be described. This operation example corresponds to the operation when the optical analysis device 2A is used as an optical vortex analysis device as an example. However, this does not limit the present embodiment. The optical analysis device 2A that performs the operation of the operation example 3 includes a half-wave plate on the upstream side of the Q plate 13.

[0125] First, it is assumed that the unknown light (E unknown ) contains a left-handed optical vortex (s, l) = (+1, +1) in the left circular polarization state and a right-handed optical vortex (s, l) = (-1, -1) in the right circular polarization state at a ratio of E:F. In this case, the state of the unknown light is expressed as follows.

Math

number

[0126] The intensity of light detected by the detection unit 50 is E det The square of the absolute value of (|E det | 2 ) is proportional, and the square of the absolute value is,

number

number

number

[0127] Thus, according to the optical analysis device 2A, the ratio of the spin angular momentum and the orbital angular momentum included in the unknown light can be analyzed.

[0128] [Example of Realization by Software] The functions of the control units 20 and 40 (hereinafter referred to as "devices") can be realized by a program for causing a computer to function as the device, and can be realized by a program for causing a computer to function as each control block of the device.

[0129] In this case, the above device includes a computer having at least one control device (for example, a processor) and at least one storage device (for example, a memory) as hardware for executing the above program. By executing the above program with this control device and storage device, each function described in each of the above embodiments is realized.

[0130] The above program may be recorded on one or more computer-readable recording media, not temporarily. This recording medium may be provided in the above device or may not be provided. In the latter case, the above program may be supplied to the above device via any wired or wireless transmission medium.

[0131] In addition, part or all of the functions of each of the above control blocks can also be realized by a logic circuit. For example, an integrated circuit in which a logic circuit functioning as each of the above control blocks is formed is also included in the scope of the present invention. In addition to this, for example, it is also possible to realize the functions of each of the above control blocks by a quantum computer.

[0132] (Summary) This specification describes at least the following configurations.

[0133] (Configuration A1) A modulation unit that generates a first modulated light having spin angular momentum from incident light, A first spin-orbit converter that generates a second modulated light having orbital angular momentum from the first modulated light, A light vortex generating device equipped with the following features.

[0134] (Configuration A2) The modulation unit includes a photoelastic modulator. The optical vortex generating device described in configuration A1.

[0135] (Configuration A3) The modulation unit includes a first linear polarizer upstream of the photoelastic modulator. The optical vortex generating device described in configuration A2.

[0136] (Configuration A4) A second linear polarizer is provided downstream of the first spin-orbit converter. The optical vortex generating device described in configuration A3.

[0137] (Configuration A5) The first spin-orbit converter is provided with a half-wave plate downstream. The optical vortex generating device described in configuration A3.

[0138] (Configuration A6) A second spin-orbit converter is provided downstream of the aforementioned half-wave plate. The optical vortex generating device described in configuration A5.

[0139] (Configuration A7) Between the first spin-orbit converter and the second linear polarizer, It comprises one or more sets of a half-wave plate and a second spin-orbit converter. The optical vortex generating device described in configuration A4.

[0140] (Configuration A8) Equipped with a control unit, The control unit switches whether the modulation unit generates left-circularly polarized or right-circularly polarized light as the first modulated light at a predetermined switching rate. A light vortex generating device as described in any one of items A1 to A7.

[0141] (Configuration A9) The light source unit that generates the incident light, A light vortex generating device described in any one of items A1 to A8 and A superior irradiation device.

[0142] (Configuration A10) The irradiation device described in configuration A9, The optical vortex generator generates modulated light which detects light from the sample into which the modulated light is incident. A detection device equipped with the following features.

[0143] (Configuration A11) The detection device described in configuration A10 is provided, The control unit, The wavelength of the incident light generated by the light source is controlled, The modulation unit controls the modulation unit so that it matches the wavelength of the incident light. The detection unit is To detect light from the aforementioned sample, lock-in detection is performed according to the switching rate and the wavelength of the incident light. Spectrum measurement device.

[0144] (Configuration A12) The switching rate is 1 kHz or higher. The spectral measurement device described in configuration A10.

[0145] (Configuration A13) A microscope equipped with the spectral measuring device described in configuration A12.

[0146] (Configuration A14) A modulation step that generates a first modulated light having spin angular momentum from incident light, A spin-orbit conversion step that generates a second modulated light having orbital angular momentum from the first modulated light, A method for generating optical vortices that includes the following:

[0147] (Configuration A15) The spin-orbit conversion unit into which the target light is incident, A photoelastic modulator into which light that has passed through the spin-orbit conversion section is incident, A detection unit for detecting light that has passed through the photoelastic modulator. An optical analyzer equipped with the following features.

[0148] (Configuration A16) A linear polarizer is provided between the photoelastic modulator and the detection unit. The optical analysis device described in configuration A15.

[0149] (Configuration A17) The spin-orbit conversion unit is Half-wave plate and A spin-orbit converter arranged downstream of the half-wave plate and It is equipped with An optical analysis apparatus as described in configuration A15 or A16.

[0150] (Configuration A18) The steps include: irradiating the target light into the spin-orbit conversion unit, The steps include: igniting the light that has passed through the spin-orbit conversion unit into a photoelastic modulator; A detection step for detecting light that has passed through the photoelastic modulator. A light analysis method that includes [a specific component].

[0151] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of Symbols]

[0152] 1,1A...Optical system 2,2A...Optical analysis device 10...Light vortex generator 11...Light source section 12. Modulation section 121 ···First linear polarizing element 122 ···PEM 13. Spin-orbit converter 14. Second linear polarizing element 20 ···Control Unit 30,50 ···Detection unit

Claims

1. A modulation unit that generates a first modulated light having spin angular momentum from incident light, A first spin-orbit converter that generates a second modulated light having orbital angular momentum from the first modulated light, A light vortex generating device equipped with the following features.

2. The modulation unit includes a photoelastic modulator. The optical vortex generating apparatus according to claim 1.

3. The modulation unit includes a first linear polarizer upstream of the photoelastic modulator. The optical vortex generating apparatus according to claim 2.

4. The first spin-orbit converter is provided with a second linear polarizer downstream of it. The optical vortex generating apparatus according to claim 3.

5. A half-wave plate is provided downstream of the first spin-orbit converter. The optical vortex generating apparatus according to claim 3.

6. A second spin-orbit converter is provided downstream of the aforementioned half-wave plate. The optical vortex generating apparatus according to claim 5.

7. Between the first spin-orbit converter and the second linear polarizer, It comprises one or more sets of a half-wave plate and a second spin-orbit converter. The optical vortex generating apparatus according to claim 4.

8. Equipped with a control unit, The control unit switches whether the modulation unit generates left-circularly polarized or right-circularly polarized light as the first modulated light at a predetermined switching rate. The optical vortex generating apparatus according to any one of claims 1 to 7.

9. The light source unit that generates the incident light, The optical vortex generating apparatus according to claim 8 and A superior irradiation device.

10. The irradiation device according to claim 9, The optical vortex generator generates modulated light which detects light from the sample into which the modulated light is incident. A detection device equipped with the following features.

11. The detection device is provided as described in claim 10, The control unit, The wavelength of the incident light generated by the light source is controlled, The modulation unit controls the modulation unit so that it matches the wavelength of the incident light. The detection unit is To detect light from the aforementioned sample, lock-in detection is performed according to the switching rate and the wavelength of the incident light. Spectrum measurement device.

12. The switching rate is 1 kHz or higher. The spectral measuring device according to claim 11.

13. A microscope equipped with the spectral measuring device described in claim 12.

14. A modulation step that generates a first modulated light having spin angular momentum from incident light, A spin-orbit conversion step that generates a second modulated light having orbital angular momentum from the first modulated light, A method for generating optical vortices that includes the following:

15. The spin-orbit conversion unit into which the target light is incident, A photoelastic modulator into which light that has passed through the spin-orbit conversion section is incident, A detection unit for detecting light that has passed through the photoelastic modulator. An optical analyzer equipped with the following features.

16. A linear polarizer is provided between the photoelastic modulator and the detection unit. The optical analysis apparatus according to claim 15.

17. The spin-orbit conversion unit is Half-wave plate and A spin-orbit converter arranged downstream of the half-wave plate and It is equipped with The optical analysis apparatus according to claim 15 or 16.

18. The steps include: irradiating the target light into the spin-orbit conversion unit, The steps include: igniting the light that has passed through the spin-orbit conversion unit into a photoelastic modulator; A detection step for detecting light that has passed through the photoelastic modulator. A light analysis method that includes [a specific component].

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