CN110780466A - Device for generating surface evanescent wave field with electrically adjustable intensity - Google Patents
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- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/0009—Materials therefor
- G02F1/0045—Liquid crystals characterised by their physical properties
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- G—PHYSICS
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- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
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- G02F1/133528—Polarisers
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- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
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- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
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- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
- G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
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Abstract
The invention belongs to the technical field of guided wave optics, and particularly relates to a surface evanescent wave field device with electrically adjustable intensity. The device of the invention comprises: the device comprises a coupling prism, an electric control birefringence liquid crystal box, an alternating current signal driver and a collimation laser light source; the electric control double refraction liquid crystal box is formed by the involution and encapsulation of an upper substrate and a lower substrate; the surfaces of the upper substrate and the lower substrate are plated with functional films: the transparent ITO conductive film layer and the liquid crystal orientation layer are filled with liquid crystal between the two liquid crystal orientation layers; the coupling prism is attached to the lower substrate of the liquid crystal box; the alternating current signal driver is connected with an upper transparent ITO conductive film layer and a lower transparent ITO conductive film layer in the liquid crystal box; the collimated laser beam emitted by the collimated laser source enters from one bevel edge of the coupling prism, and an electrically adjustable surface evanescent wave field is generated on the outer layer of the upper substrate of the liquid crystal box. The maximum enhancement range of the intensity of the evanescent field can reach many orders of magnitude. The device has important application prospect in the fields of surface microscopic measurement, biology, surface chemistry, microspectroscopy and the like.
Description
Technical Field
The invention belongs to the technical field of guided wave optics, and particularly relates to a device for generating a surface evanescent wave field.
Background
The research of materials, chemistry and life science is an important driving force for the development of various subjects in recent years, new materials determine the application and development of technology, and the research of surface/interface chemical reaction and life science is closely related to the quality of life of people, such as early diagnosis of various diseases, clarification and screening of action mechanisms of various medicines and the like. Among them, the research of single-molecule science or nanoparticles has become a hot point of research because many basic problems such as surface/interface structure and morphology of materials, progress of chemical reaction, and change of biological tissues can be clarified at a microscopic level. Among them, fluorescence spectroscopy and raman spectroscopy have been the main means of research. Molecular fluorescence can study the electronic structure inside the molecule, and raman spectroscopy can resolve the bonding structure of the molecule.
However, Surface Enhanced Raman Scattering (SERS) is generally not available on flat adsorption surfaces and the sample must be deposited on rough metal surfaces or metal nanoparticle surfaces, making SERS largely dependent on sample preparation and the roughness of the substrate surface. The presence of uncertainty in this field enhancement is the greatest weakness of SERS. In addition, the measurement spatial resolution capability of SERS is limited by the diffraction limit of the excitation light and the measurement system. The Tip Enhanced Raman Scattering (TERS) can overcome the defect of space resolution of SERS, can reach the nanoscale, and the signal enhancement factor can reach 10
5-10
6And (4) doubling. However, the tip of TERS is susceptible to damage during the experiment, oxygenChemical contamination and contamination affect the stability of signal measurement.
In recent years, a field enhancement effect based on a Bloch Surface Wave (BSW) has been attracting attention. BSW is electromagnetic wave existing in the periodic multilayer dielectric film stack, and based on the optical waveguide effect, an optical field is limited in the periodic film layer to generate localized enhancement and generate corresponding enhancement effect on an evanescent wave field on the surface of the periodic film layer. At present, the excitation of field enhancement, whether SPR or BSW, is mostly carried out by a prism coupling mode of Kretschmann. The field enhancement performance of the structure is a passive enhancement mechanism, namely once the system structure (1DPC or metal film layer) is prepared, a field Enhancement Factor (EF) is theoretically determined for a determined wavelength and a measured sample, and the specific enhancement quantity, the preparation error of the device structure, the precision of a measuring instrument, the capability of an operator and other factors have great influence.
Therefore, the research of an in-situ adjustable field enhancement mechanism for actively controlling a field enhancement factor, such as continuous adjustment or setting or multiplying power compensation for wavelength change, becomes a problem with important scientific and practical significance, can reduce the uncertainty of experiments and results, is beneficial to quantitative comparison of different measurements, is also beneficial to measurement research of the excitation intensity dependence of fluorescence and Raman signals and the excitation spectrum of characteristic fluorescence signals, and can extract more material structure information.
Disclosure of Invention
The invention aims to provide a surface evanescent wave field generating device with excellent performance and convenient use and with electrically adjustable strength.
The invention provides an intensity-electrically adjustable surface evanescent wave field generating device, which comprises: a coupling prism, an Electrically Controlled Birefringence (ECB) liquid crystal cell, an AC signal driver, and a collimated laser light source; the electric control birefringence liquid crystal box is formed by oppositely assembling and packaging an upper substrate and a lower substrate; wherein, the upper (or lower) surface of the lower substrate is plated with a functional film: a low refractive index coupling layer, a transition layer; the upper surface of the lower substrate is also sequentially plated (coated) with a transparent ITO conductive film layer and a liquid crystal orientation layer; the lower surface of the upper substrate is sequentially plated (coated) with a transparent ITO conductive film layer and a liquid crystal orientation layer; the liquid crystal is filled and encapsulated between the upper liquid crystal orientation layer and the lower liquid crystal orientation layer; the coupling prism is attached to the lower substrate of the liquid crystal box; the alternating current signal driver is connected with the two transparent ITO conductive film layers in the liquid crystal box; the collimating laser beam emitted by the collimating laser source is incident from one bevel edge of the coupling prism, the incident angle is larger than the critical angle of total reflection of the prism to the coupling layer of the liquid crystal box, and an electrically adjustable surface evanescent wave field is generated on the outer layer of the upper substrate of the liquid crystal box. See in particular fig. 1.
In the invention, liquid crystals in the liquid crystal box are arranged in parallel along a plane to form a planar waveguide structure, and the planar waveguide structure works in an Electrically Controlled Birefringence (ECB) mode. Depending on the alignment layer, the liquid crystal can also be operated in other modes such as TN, IPS, VA, etc., and the polarization direction of light waves is controlled by the polarizing plate.
In the invention, the material of the bottom substrate (lower substrate) and the material of the coupling prism of the liquid crystal box both have higher refractive index than that of the low-refractive-index coupling layer. The lower substrate may be selected from glass or other transparent materials.
In the present invention, the low refractive index coupling layer, i.e. the "low refractive index", is a low refractive index coating material such as magnesium fluoride, which is selected from materials such as the coupling prism, the liquid crystal cell substrate and the liquid crystal.
In the invention, the transition layer material can be quartz, fused quartz, magnesium fluoride or the like.
In the invention, the incident angle of the collimated light beam to the normal line of the bottom substrate surface of the liquid crystal box is larger than the total reflection critical angle of the prism to the coupling layer.
In the invention, the collimated light beam emitted by the collimated laser light source is guided into the device by the coupling prism in the polarization direction of transverse magnetic wave (TM). In other modes of operation, the polarization direction of the collimated beam may also be the polarization direction of the transverse electric wave (TE).
In the invention, the transition layer can be made of transparent material such as quartz, and the refractive index of the transition layer is between that of the low-refractive-index coupling layer and the liquid crystal box substrate (such as glass).
In the invention, the liquid crystal in the liquid crystal box can be a positive liquid crystal material or a negative liquid crystal material.
In the present invention, the upper substrate material may be a transparent material having a refractive index higher than that of the low-refractive-index coupling layer, such as glass.
The working principle of the device of the invention is as follows: the collimated light beam emitted by the collimated laser source is guided into the device by the coupling prism in the polarization direction of transverse magnetic wave (TM) to excite a surface evanescent wave field supported by a planar waveguide structure formed by a liquid crystal box; a driving voltage is applied by an alternating current signal driver along the normal direction of the liquid crystal layer, when the driving voltage exceeds the orientation threshold value of the liquid crystal layer, the refractive index of the extraordinary rays of the liquid crystal layer is changed, so that the refractive index distribution of the plane structure of the liquid crystal box is changed, and the intensity of surface evanescent waves is changed. The driving voltage of the liquid crystal layer is continuously adjusted within a certain range, so that the intensity of the surface evanescent wave field can be continuously adjusted.
The device of the invention has the advantages that:
1. and the electric control continuous adjustment of the field intensity of the evanescent wave can be realized. The movement adjustment of any mechanism is not needed in the adjusting process, so that the adjusting stability is good;
2. the field enhancement adjusting range is large and can reach several orders of magnitude under the condition of higher angle adjusting precision;
3. the device of the invention is convenient to use and adjust.
The device of the invention provides a field enhancement adjustable mechanism, which can effectively inhibit some uncertainties of field enhancement, and meanwhile, the electric adjustment mechanism can realize the field enhancement adjustment without additional mechanism movement after the excitation condition is determined, thereby having good stability. In addition, the field enhancement magnification can reach several orders of magnitude according to the coupling of different angles. Therefore, the invention has important application prospect in the fields of surface microscopic measurement, biology, surface chemistry, microspectroscopy and the like.
Drawings
FIG. 1 is a schematic diagram of an intensity-electrically tunable surface evanescent wave field generation apparatus of the present invention.
Fig. 2 shows the spatial distribution of the refractive index along the normal (Z) direction of the cell on both sides of the cell for the designed structure without the application of driving voltage. The angle of incidence of the collimated light at this time is 51.817 deg.. The critical angle of total reflection of the entrance prism to the coupling layer is 46.984 deg..
FIG. 3 is a partial enlargement of the thickness direction of the cell of FIG. 2 to show the spatial subdivision of the refractive index along the normal direction within the cell.
FIG. 4 is a spatial distribution of refractive indices along the cell normal (Z) direction within and outside the cell in FIG. 3 with a drive voltage of 3.6-4.7 volts applied to the cell. The angle of incidence of the collimated light at this time is 51.817 deg.. The critical angle of total reflection of the entrance prism to the coupling layer is 46.984 deg..
Fig. 5 shows the case where the intensity of the surface evanescent field generated at the outer surface of the substrate on the liquid crystal cell with a drive voltage of 4.7 v applied to the liquid crystal cell is varied along the direction of the outer normal (Z) of the liquid crystal cell. The angle of incidence of the collimated light at this time is 51.817 deg.. The critical angle of total reflection of the entrance prism to the coupling layer is 46.984 deg..
Fig. 6 is a graph showing the variation of the intensity of a surface evanescent field generated at the outer surface of a substrate on a liquid crystal cell with a driving voltage of 3.6 to 4.7 volts applied to the liquid crystal cell as a function of the driving voltage. The angle of incidence of the collimated light at this time is 51.817 deg.. The critical angle of total reflection of the entrance prism to the coupling layer is 46.984 deg..
Reference numbers in the figures: the device comprises a collimating incident beam 1, a coupling prism 2, a liquid crystal box lower substrate 3, a low-refractive-index coupling layer 4, a transition layer (which can be multilayer) 5, a transparent conducting film (ITO) layer on the upper substrate and the lower substrate of the liquid crystal box 6, a liquid crystal orientation layer (PI) on the upper substrate and the lower substrate of the liquid crystal box 7, an upper substrate of the liquid crystal box 8, an alternating current signal driver 9, a liquid crystal layer 10 and an evanescent wave area on the surface layer of the upper substrate of the liquid crystal box 11.
Detailed Description
The invention comprises a coupling prism, an Electrically Controlled Birefringence (ECB) liquid crystal cell, an AC signal driver, and a collimated laser source. The structure is shown in figure 1.
The alignment laser source selects a laser working wavelength such as 632.8nm, the coupling prism material such as flint glass and refractive index of 1.778, and the lower substrate of the liquid crystal box is also selected to match with the coupling prism. The upper surface of a lower substrate of the liquid crystal box is plated with a low-refractive-index coupling layer, fused quartz is adopted as a material, the refractive index is 1.457, and the thickness is 500 nm. Then, a transition layer is plated on the quartz, fused quartz, magnesium fluoride, fused quartz and quartz, the refractive indexes are respectively 1.52, 1.457, 1.30, 1.45 and 1.52, and the thicknesses are respectively 500, 500, 100, 200 and 100 nm. Then a transparent conductive film (ITO) layer with the refractive index of 1.9 and the thickness of 100nm is deposited, and then a liquid crystal orientation layer (PI) with the refractive index of 1.54 and the thickness of 100nm is spin-coated. Both losses have a value of 10
-5. The substrate of the liquid crystal box is made of glass, the refractive index is 1.52, and the thickness is 1 mm. The surface of the substrate is sequentially plated with an ITO layer and a liquid crystal orientation layer PI, and the parameters are the same as those of the lower substrate. Taking an antiparallel direction, the liquid crystal alignment layer is rubbed. After the process is finished, the liquid crystal box is formed, and liquid crystal is poured. The liquid crystal material is 5CB, the refractive indexes of the ordinary light and the extraordinary light are 1.532 and 1.692 respectively, and the thickness of the liquid crystal material is 5 mu m. An evanescent field area on the upper surface of the liquid crystal box is a sample area to be detected, an aqueous solution environment is set, and the refractive index is 1.33.
According to the above structural parameters, the critical angle of total reflection of the coupling prism to the low refractive index coupling layer is 46.984 °. The incident angle of the collimated light was taken to be 51.817 °. The TM incident light will couple into the liquid crystal structure in the form of an evanescent wave and propagate in the liquid crystal layer to its upper surface, forming a surface evanescent wave field outside the upper surface.
A normal driving voltage is applied to the liquid crystal layers arranged in parallel, and after the effective value of the voltage is larger than the alignment threshold value of the liquid crystal layers, the positive liquid crystal molecules incline towards the direction of an electric field, and the size of the inclination angle depends on the effective value of the driving voltage. According to the elastic continuum theory of Liquid crystal, (see d.k.yang and s.t.wu, Fundamentals of Liquid crystal devices Wiley 2006) and the elastic parameters of the Liquid crystal material, the tilt angle distribution of the Liquid crystal molecules at different driving voltages can be obtained, and thus the spatial distribution of the refractive index of the Liquid crystal layer in the thickness direction of the Liquid crystal cell can be obtained. On the basis, the spatial distribution of the wave field of the TM light wave in the structure can be calculated by using a calculation method of an optical transmission matrix. Specific methods can be found in our published papers: opt. Express 25(11), 12121-. Here we focus on the intensity of the optical field in the evanescent wave field closest to the glass sheet surface, which is defined as the product of the square of the optical field amplitude and the refractive index. (see M. Born, and E. Wolf, Principles of Optics, 7th ed. (Cambridge Univ. Press,2007) for details).
Under different driving voltages, different orientations of liquid crystal molecules cause the change of the refractive index of the liquid crystal layer, so that the light conduction property of the liquid crystal layer is changed, and the field intensity of a surface evanescent wave is finally influenced. According to the theory, the corresponding relation between the driving voltage and the field intensity of the surface evanescent wave can be calculated. Fig. 2 shows the spatial distribution of refractive indices in the thickness direction of the cell at zero drive voltage, for collimated light at an incident angle of 51.817 °. FIG. 3 is a partial enlargement of the thickness direction of the cell of FIG. 2 to show the spatial subdivision of the refractive index along the normal direction within the cell. Fig. 4 is a graph showing the spatial distribution of refractive indices along the cell normal (Z) direction inside and outside the cell in fig. 3, with a drive voltage of 3.6-4.7 volts applied to the cell at the same incident angle.
The incident angle of collimated light is maintained, and fig. 5 shows the case where the intensity of the surface evanescent field generated at the outer surface of the upper substrate of the liquid crystal cell with a drive voltage of 4.7 v applied to the liquid crystal cell is varied along the direction of the outer normal (Z) of the liquid crystal cell. Fig. 6 is a graph showing the variation of the intensity of a surface evanescent field generated at the outer surface of a substrate on a liquid crystal cell with a driving voltage of 3.6 to 4.7 volts applied to the liquid crystal cell as a function of the driving voltage. This intensity is a ratio with respect to the intensity of the optical field in the coupling layer. And hence also referred to as an enhancement factor of the intensity of the light field. Which continuously changes monotonically with changes in the drive voltage. I.e. a surface evanescent wave field with an electrically adjustable intensity is achieved.
Under the condition that the precision of the coupling angle reaches (1/1000) °, the enhancement of the surface evanescent wave intensity can reach 70 times. This enhancement is relative to the ratio of the intensity of the optical field in the coupling layer. The minimum to maximum range of this ratio is the adjustable range of the intensity of the evanescent wave. Other coupling angles are selected, and the intensity enhancement factor of the evanescent wave may have a greater enhancement rate. In addition, if the control precision of the coupling angle can be further improved, the highest enhancement range of the intensity of the evanescent field can reach multiple orders of magnitude. The device has important application prospect in the fields of surface microscopic measurement, biology, surface chemistry, microspectroscopy and the like.
Claims (6)
1. An intensity-electrically tunable surface evanescent wave field generating apparatus comprising: the device comprises a coupling prism, an electric control birefringence liquid crystal box, an alternating current signal driver and a collimation laser light source; the electric control birefringence liquid crystal box is formed by oppositely assembling and packaging an upper substrate and a lower substrate; wherein, the upper surface or the lower surface of the lower substrate is plated with a functional film: a low refractive index coupling layer, a transition layer; the upper surface of the lower substrate is also sequentially plated (coated) with a transparent ITO conductive film layer and a liquid crystal orientation layer; the lower surface of the upper substrate is sequentially plated (coated) with a transparent ITO conductive film layer and a liquid crystal orientation layer; the liquid crystal is filled and encapsulated between the upper liquid crystal orientation layer and the lower liquid crystal orientation layer; the coupling prism is attached to the lower substrate of the liquid crystal box; the alternating current signal driver is connected with the two transparent ITO conductive film layers in the liquid crystal box; the collimating laser beam emitted by the collimating laser source is incident from one bevel edge of the coupling prism, the incident angle is larger than the critical angle of total reflection of the prism to the coupling layer of the liquid crystal box, and an electrically adjustable surface evanescent wave field is generated on the outer layer of the upper substrate of the liquid crystal box.
2. An intensity-tunable surface evanescent wave field generator as claimed in claim 1, wherein the liquid crystals in said liquid crystal cells are aligned in plane-parallel to form a planar waveguide structure operating in an electrically controlled birefringence mode.
3. An intensity-electrically tunable surface evanescent wave field generating device as claimed in claim 1, wherein the bottom substrate material and the coupling prism material of said liquid crystal cell have a higher refractive index than the low index coupling layer.
4. An intensity-electrically tunable surface evanescent wave field generating device as claimed in claim 1, wherein said collimated light beam has an incident angle to the surface normal of the bottom substrate of the liquid crystal cell larger than the critical angle for total reflection of the coupling layer by the prism.
5. An intensity-electrically tunable surface evanescent wave field generating device as claimed in claim 1, wherein the liquid crystal in said liquid crystal cell is a positive liquid crystal material or a negative liquid crystal material.
6. An intensity-electrically tunable surface evanescent wave field generation apparatus as claimed in any one of claims 1 to 5, characterized by the workflow of: the collimated laser source emits collimated light beams, and the collimated light beams are guided into the device through the coupling prism in the polarization direction of transverse magnetic waves to excite a surface evanescent wave field supported by a planar waveguide structure formed by a liquid crystal box; a driving voltage is applied by an alternating current signal driver along the normal direction of the liquid crystal layer, when the driving voltage exceeds the orientation threshold value of the liquid crystal layer, the refractive index of the extraordinary rays of the liquid crystal layer is changed, so that the refractive index distribution of the plane structure of the liquid crystal box is changed, the intensity of the surface evanescent wave is changed, namely the driving voltage of the liquid crystal layer is continuously adjusted within a certain range, and the continuous adjustment of the intensity of the surface evanescent wave field is realized.
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Cited By (3)
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| CN111913317A (en) * | 2020-08-24 | 2020-11-10 | 张家港奇点光电科技有限公司 | Liquid crystal box and manufacturing method thereof, spatial light modulator and spatial light modulation system |
| CN114112947A (en) * | 2020-08-26 | 2022-03-01 | 横河电机株式会社 | Spectral analysis apparatus, optical system and method |
| CN116520509A (en) * | 2023-05-09 | 2023-08-01 | 中国科学院高能物理研究所 | Evanescent wave modulator and modulation method for changing film growth mode and surface morphology |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111913317A (en) * | 2020-08-24 | 2020-11-10 | 张家港奇点光电科技有限公司 | Liquid crystal box and manufacturing method thereof, spatial light modulator and spatial light modulation system |
| CN111913317B (en) * | 2020-08-24 | 2024-08-09 | 张家港奇点光电科技有限公司 | Liquid crystal box, manufacturing method, spatial light modulator and spatial light modulation system |
| CN114112947A (en) * | 2020-08-26 | 2022-03-01 | 横河电机株式会社 | Spectral analysis apparatus, optical system and method |
| CN116520509A (en) * | 2023-05-09 | 2023-08-01 | 中国科学院高能物理研究所 | Evanescent wave modulator and modulation method for changing film growth mode and surface morphology |
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