CN110780466A - A device for generating a surface evanescent wave field with an electrically adjustable intensity - Google Patents
A device for generating a surface evanescent wave field with an electrically adjustable intensity Download PDFInfo
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Abstract
本发明属于导波光学技术领域,具体为一种强度可电调节的表面倏逝波场装置。本发明装置包括:耦合棱镜,电控双折射液晶盒,交流电信号驱动器,以及准直激光光源;电控双折射液晶盒由上、下两块基板对合封装组成;上、下基板的表面镀制有功能薄膜:透明ITO导电膜层、液晶定向层,液晶灌注于两液晶定向层之间;耦合棱镜与液晶盒的下基板处贴合;交流电信号驱动器与液晶盒中的上下两透明ITO导电膜层连接;所述准直激光光源发出的准直激光束从耦合棱镜的一个斜边入射,在液晶盒的上基板外层产生可电调节的表面倏逝波场。倏逝场的强度最高增强范围可达到多个数量级。本装置在表面显微测量,生物学,表面化学,显微光谱等领域有重要应用前景。
The invention belongs to the technical field of guided wave optics, in particular to a surface evanescent wave field device whose intensity can be adjusted electrically. The device of the invention comprises: a coupling prism, an electronically controlled birefringent liquid crystal cell, an AC signal driver, and a collimated laser light source; the electronically controlled birefringent liquid crystal cell is composed of two upper and lower substrates that are assembled and packaged; the surfaces of the upper and lower substrates Coated with functional films: transparent ITO conductive film layer, liquid crystal alignment layer, liquid crystal is poured between the two liquid crystal alignment layers; the coupling prism is attached to the lower substrate of the liquid crystal cell; the AC signal driver is transparent to the upper and lower sides of the liquid crystal cell The ITO conductive film layers are connected; the collimated laser beam emitted by the collimated laser light source is incident from a hypotenuse 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 cell. The intensity of the evanescent field can be up to several orders of magnitude enhanced. The device has important application prospects in the fields of surface microscopic measurement, biology, surface chemistry, and microscopic spectroscopy.
Description
技术领域technical field
本发明属于导波光学技术领域,具体涉及表面倏逝波场的产生装置。The invention belongs to the technical field of guided wave optics, and in particular relates to a device for generating a surface evanescent wave field.
背景技术Background technique
材料,化学,和生命科学的研究是近年来牵引各学科发展的重要动力,新材料决定着技术的应用与发展,表/界面化学反应以及生命科学的研究则与人们的生活品质息息相关,如各种疾病的早期诊断,各种药物的作用机理的澄清与筛选等。而这其中,单分子科学或纳米颗粒的研究,由于可以在微观层面阐明材料的表/界面结构和形态,化学反应的进程及生物组织的变化等许多基本问题,成为人们研究的热点。而这其中荧光光谱和拉曼光谱技术成为研究的主要手段。分子荧光可以研究分子内部的电子结构,而拉曼光谱可以分辨分子的成键结构。Research on materials, chemistry, and life sciences has been an important driving force for the development of various disciplines in recent years. New materials determine the application and development of technologies. Research on surface/interface chemical reactions and life sciences is closely related to people's quality of life. Early diagnosis of various diseases, clarification and screening of the mechanism of action of various drugs, etc. Among them, single-molecule science or nanoparticle research has become a research hotspot because it can elucidate the surface/interface structure and morphology of materials at the microscopic level, the process of chemical reactions and the changes of biological tissues. Among them, fluorescence spectroscopy and Raman spectroscopy have become the main means of research. Molecular fluorescence can study the electronic structure inside the molecule, while Raman spectroscopy can distinguish the bonding structure of the molecule.
然而,表面增强的拉曼散射(SERS)一般不能在平整的吸附表面获得,样品必须沉积在粗糙的金属表面或金属纳米颗粒表面,使得SERS在很大程度上取决于样品制备和基底表面的粗糙度。这种场增强存在不确定性是SERS的最大弱点。另外,SERS 的测量空间分辨能力受到激发光的和测量系统的衍射极限的限制。针尖增强的拉曼散射(Tip enhancedRaman Scattering, TERS)能克服SERS的这一空间分辨的缺点,可以达到纳米尺度,且其信号增强因子可达105-106倍。但TERS的针尖在实验中容易受损,氧化,及沾染而影响信号测量的稳定性。However, surface-enhanced Raman scattering (SERS) generally cannot be obtained on flat adsorption surfaces, and samples must be deposited on rough metal surfaces or metal nanoparticle surfaces, making SERS largely dependent on sample preparation and substrate surface roughness Spend. The uncertainty of this field enhancement is the biggest weakness of SERS. In addition, the spatial resolution of SERS measurements is limited by the diffraction limit of the excitation light and the measurement system. Tip enhanced Raman Scattering (TERS) can overcome this shortcoming of spatial resolution of SERS, and can reach the nanoscale, and its signal enhancement factor can reach 10 5 -10 6 times. However, the tip of TERS is easily damaged, oxidized, and contaminated during the experiment, which affects the stability of signal measurement.
近年来, 基于Bloch 表面波(Bloch Surface Wave, BSW)的场增强作用受到人们关注。BSW 是存在于周期性多层介质膜堆中的电磁波,基于光波导效应,光场被限制在周期性的膜层中产生局域化增强,并对其表面的倏逝波场也产生相应增强作用。目前无论是SPR还是BSW,场增强的激发,大多是都是通过Kretschmann 的棱镜耦合方式进行。这样的结构,其场增强性能是一种被动增强机制,即一旦系统结构(1DPC 或金属膜层) 制备完成,对确定的波长和被测样品,理论上场增强因子(EF)就确定了,具体的增强量,受器件结构制备误差,测量仪器的精度,以及操作者的能力等因素影响较大。In recent years, field enhancement based on Bloch Surface Wave (BSW) has attracted much attention. BSW is an electromagnetic wave existing in a periodic multilayer dielectric film stack. Based on the optical waveguide effect, the optical field is confined in the periodic film layer to generate localized enhancement, and the evanescent wave field on its surface is also enhanced accordingly. effect. At present, whether it is SPR or BSW, the excitation of field enhancement is mostly carried out by Kretschmann's prism coupling method. For such a structure, its field enhancement performance is a passive enhancement mechanism, that is, once the system structure (1DPC or metal film layer) is prepared, the theoretical field enhancement factor (EF) is determined for a certain wavelength and the sample to be tested. The amount of enhancement is greatly affected by factors such as the fabrication error of the device structure, the accuracy of the measuring instrument, and the operator's ability.
因此, 研究一种原位的可调的场增强机制,对场增强因子进行主动控制,如连续的调节或设定,或对波长的改变进行倍率补偿,成为一个具有重要科学和实际意义的问题,它可以减少实验和结果的不确定性,有利于对不同的测量进行量化对比,同时还有利于进行荧光及拉曼信号的激发强度依赖性及特征荧光信号的激发谱的测量研究,可提取更多的材料结构信息。Therefore, researching an in-situ tunable field enhancement mechanism to actively control the field enhancement factor, such as continuous adjustment or setting, or magnification compensation for wavelength changes, has become a problem of important scientific and practical significance. , which can reduce the uncertainty of experiments and results, facilitate the quantitative comparison of different measurements, and also facilitate the measurement of the excitation intensity dependence of fluorescence and Raman signals and the excitation spectrum of characteristic fluorescence signals. More material structure information.
发明内容SUMMARY OF THE INVENTION
本发明的目的是提供一种性能优异、使用方便的强度可电调节的表面倏逝波场产生装置。The object of the present invention is to provide a surface evanescent wave field generating device with excellent performance and convenient use with an electrically adjustable intensity.
本发明提供的强度可电调节的表面倏逝波场产生装置,包括:一个耦合棱镜,一个电控双折射(ECB)液晶盒,一个交流电信号驱动器,以及一个准直激光光源;其中,所述电控双折射液晶盒,由上、下两块基板对合封装组成;其中,下基板的上(或下)表面镀制有功能薄膜:低折射率耦合层,过渡层;下基板的上表面还依次镀(涂)有透明ITO导电膜层、液晶定向层;上基板的下表面依次镀(涂)有透明ITO导电膜层、液晶定向层;液晶灌注封装于上、下两液晶定向层之间;所述耦合棱镜与液晶盒的下基板处贴合;所述交流电信号驱动器与液晶盒中的两透明ITO导电膜层连接;所述准直激光光源发出的准直激光束从耦合棱镜的一个斜边入射,入射角大于棱镜对液晶盒耦合层的全反射临界角,在液晶盒的上基板外层产生可电调节的表面倏逝波场。具体参见图1所示。The device for generating a surface evanescent wave field with an electrically adjustable intensity provided by the present invention comprises: a coupling prism, an electronically controlled birefringence (ECB) liquid crystal cell, an AC signal driver, and a collimated laser light source; The electronically controlled birefringent liquid crystal cell is composed of an upper and a lower substrate butt-packed; wherein, the upper (or lower) surface of the lower substrate is coated with a functional film: a low-refractive-index coupling layer, a transition layer; The surface is also plated (coated) with a transparent ITO conductive film layer and a liquid crystal alignment layer in turn; the lower surface of the upper substrate is sequentially plated (coated) with a transparent ITO conductive film layer and a liquid crystal alignment layer; between the coupling prism and the lower substrate of the liquid crystal cell; the AC signal driver is connected with two transparent ITO conductive film layers in the liquid crystal cell; the collimated laser beam emitted by the collimated laser light source is coupled from the One oblique side of the prism is incident, and the incident angle is greater than the critical angle of total reflection of the prism to the coupling layer of the liquid crystal cell, and an electrically adjustable surface evanescent wave field is generated on the outer layer of the upper substrate of the liquid crystal cell. See Figure 1 for details.
本发明中,所述的液晶盒中液晶沿面平行排列,构成平面波导结构,工作于电控双折射(ECB)模式。根据定向层的不同,液晶也可工作于其它模式,如TN,IPS,VA 等,并用偏振片控制光波的偏振方向。In the present invention, the liquid crystals in the liquid crystal cell are arranged in parallel along the plane to form a planar waveguide structure, and work in an electronically controlled birefringence (ECB) mode. Depending on the alignment layer, the liquid crystal can also work in other modes, such as TN, IPS, VA, etc., and use polarizers to control the polarization direction of light waves.
本发明中,所述液晶盒的底部基板(下基板)材料与耦合棱镜的材料,两者都具有较高的折射率,高于低折射率耦合层的折射率。下基板可选择玻璃或其他透明材料。In the present invention, the material of the bottom substrate (lower substrate) of the liquid crystal cell and the material of the coupling prism both have a higher refractive index, which is higher than the refractive index of the low-refractive index coupling layer. The lower substrate can be selected from glass or other transparent materials.
本发明中,低折射率耦合层,所谓“低折射率”是相对于耦合棱镜和液晶盒基板及液晶等材料的较高折射率而言,其材料可选用如氟化镁等低折射率镀膜材料。In the present invention, the low refractive index coupling layer, the so-called "low refractive index" is relative to the higher refractive index of the coupling prism, the liquid crystal cell substrate and the liquid crystal, and its material can be selected from a low refractive index coating such as magnesium fluoride. Material.
本发明中,所述过渡层材料可以选用石英、熔石英或氟化镁等。In the present invention, the material of the transition layer can be selected from quartz, fused silica or magnesium fluoride.
本发明中,所述准直光束对液晶盒底部衬底表面法线的入射角大于棱镜对耦合层的全反射临界角。In the present invention, the incident angle of the collimated light beam to the surface normal of the bottom substrate of the liquid crystal cell is greater than the total reflection critical angle of the prism to the coupling layer.
本发明中,所述准直激光光源发出的准直光束以横磁波(TM)的偏振方向由耦合棱镜导入装置。在其它工作模式下,准直光束的偏振方向也可以是横电波(TE)的偏振方向。In the present invention, the collimated beam emitted by the collimated laser light source is guided into the device by the coupling prism in the polarization direction of the transverse magnetic wave (TM). In other working modes, the polarization direction of the collimated beam can also be the polarization direction of the transverse electric wave (TE).
本发明中,所述过渡层可采用石英等透明材料,其折射率介于低折射率耦合层与液晶盒基板(如玻璃)的折射率。In the present invention, the transition layer can be made of a transparent material such as quartz, and its refractive index is between that of the low-refractive index coupling layer and the liquid crystal cell substrate (eg glass).
本发明中,所述的液晶盒中液晶可以是正性液晶材料,也可以是负性液晶材料。In the present invention, the liquid crystal in the liquid crystal cell can be either a positive liquid crystal material or a negative liquid crystal material.
本发明中,上基板材料可采用具有高于低折射率耦合层的折射率的透明材料,如玻璃等。In the present invention, the material of the upper substrate can be a transparent material having a higher refractive index than the low-refractive index coupling layer, such as glass.
本发明装置的工作原理:准直激光光源发出的准直光束以横磁波(TM)的偏振方向由耦合棱镜导入装置,激发由液晶盒构成的平面波导结构所支持的表面倏逝波场;由交流电信号驱动器沿液晶层法线方向施加一个驱动电压,当驱动电压大小超过液晶层取向阈值时,液晶层的非寻常光折射率发生变化,使液晶盒平面结构的折射率分布发生改变,从而改变表面倏逝波的强度。在一定范围内连续调节液晶层的驱动电压,可以实现对表面倏逝波场强度的连续调节。The working principle of the device of the present invention: the collimated beam emitted by the collimated laser light source is introduced into the device by the coupling prism in the polarization direction of the transverse magnetic wave (TM) to excite the surface evanescent wave field supported by the planar waveguide structure composed of the liquid crystal cell; The AC signal driver applies a driving voltage along the normal direction of the liquid crystal layer. When the driving voltage exceeds the orientation threshold of the liquid crystal layer, the refractive index of the extraordinary light of the liquid crystal layer changes, which changes the refractive index distribution of the planar structure of the liquid crystal cell. Changes the intensity of the surface evanescent waves. Continuously adjusting the driving voltage of the liquid crystal layer within a certain range can realize the continuous adjustment of the surface evanescent wave field intensity.
本发明装置的优点:The advantages of the device of the present invention:
1、可以实现倏逝波场强的电控连续调节。在调节过程中无需任何机构的运动调整,因此具有很好的调节稳定性;1. It can realize the electric control continuous adjustment of evanescent wave field strength. There is no need for any movement adjustment of the mechanism during the adjustment process, so it has good adjustment stability;
2、场增强的调节范围大,在角度调节精度较高的条件下,场增强的调节范围可达到几个数量级;2. The adjustment range of field enhancement is large. Under the condition of high angle adjustment accuracy, the adjustment range of field enhancement can reach several orders of magnitude;
3、本发明的装置使用和调整方便。3. The device of the present invention is convenient to use and adjust.
本发明装置提出一种场增强的可调机机制,使得场增强的一些不确定性得到有效抑制,同时,电调节机制,可以在激发条件确定后,不再需要额外的机构运动以实现场增强的调节,因而具有很好的稳定性。另外,根据不同的角度的耦合,场增强倍率可达到几个数量级。因此,本发明可以在表面显微测量,生物学,表面化学,显微光谱等领域有重要应用前景。The device of the present invention proposes an adjustable mechanism of field enhancement, so that some uncertainties of field enhancement can be effectively suppressed, and at the same time, the electric adjustment mechanism can eliminate the need for additional mechanism movement to realize field enhancement after the excitation conditions are determined. adjustment, so it has good stability. In addition, depending on the coupling at different angles, the field enhancement magnification can reach several orders of magnitude. Therefore, the present invention can have important application prospects in the fields of surface microscopic measurement, biology, surface chemistry, microscopic spectroscopy and the like.
附图说明Description of drawings
图1为本发明的强度可电调节的表面倏逝波场产生装置示意图。FIG. 1 is a schematic diagram of a surface evanescent wave field generating device with an electrically adjustable intensity according to the present invention.
图2为未加驱动电压情况下所设计的结构在液晶盒两侧沿液晶盒法线(Z)方向的折射率的空间分布。 此时准直光的入射 角为51.817°。入射棱镜对耦合层的全反射临界角为46.984°。FIG. 2 shows the spatial distribution of the refractive index along the normal (Z) direction of the liquid crystal cell on both sides of the liquid crystal cell for the designed structure without applying a driving voltage. At this time, the incident angle of the collimated light is 51.817°. The critical angle of total reflection of the incident prism to the coupling layer is 46.984°.
图3 为图2 的液晶盒厚度方向的局部放大,以显示液晶盒内部沿法线方向的折射率空间分部。FIG. 3 is a partial enlargement of the thickness direction of the liquid crystal cell of FIG. 2 to show the spatial division of the refractive index inside the liquid crystal cell along the normal direction.
图4 为对液晶盒施加3.6-4.7伏的驱动电压情况下在图3中的液晶盒内及外侧沿液晶盒法线(Z)方向的折射率的空间分布。此时准直光的入射 角为51.817°。入射棱镜对耦合层的全反射临界角为46.984°。Fig. 4 shows the spatial distribution of the refractive index along the normal (Z) direction of the liquid crystal cell inside and outside the liquid crystal cell in Fig. 3 when a driving voltage of 3.6-4.7 volts is applied to the liquid crystal cell. At this time, the incident angle of the collimated light is 51.817°. The critical angle of total reflection of the incident prism to the coupling layer is 46.984°.
图5为对液晶盒施加4.7伏的驱动电压情况下在液晶盒上基板的外表面处产生的表面倏逝场的强度沿液晶盒外法线(Z)方向变化的情况。此时准直光的入射 角为51.817°。入射棱镜对耦合层的全反射临界角为46.984°。Figure 5 shows the intensity of the surface evanescent field generated at the outer surface of the upper substrate of the liquid crystal cell when a driving voltage of 4.7 volts is applied to the liquid crystal cell varies along the outer normal (Z) direction of the liquid crystal cell. At this time, the incident angle of the collimated light is 51.817°. The critical angle of total reflection of the incident prism to the coupling layer is 46.984°.
图6 为对液晶盒施加3.6-4.7伏的驱动电压情况下在液晶盒上基板的外表面处产生的表面倏逝场的强度随驱动电压变化的情况。此时准直光的入射 角为51.817°。入射棱镜对耦合层的全反射临界角为46.984°。FIG. 6 shows the intensity of the surface evanescent field generated at the outer surface of the upper substrate of the liquid crystal cell as a function of the driving voltage when a driving voltage of 3.6-4.7 volts is applied to the liquid crystal cell. At this time, the incident angle of the collimated light is 51.817°. The critical angle of total reflection of the incident prism to the coupling layer is 46.984°.
图中标号:1为准直入射光束,2为耦合棱镜,3为液晶盒下基板,4为低折射率耦合层,5为过渡层(可为多层),6为液晶盒上、下基板上的透明导电膜 (ITO) 层,7为液晶盒上、下基板上的液晶定向层(PI),8为液晶盒上基板,9为交流电信号驱动器,10为液晶层,11为液晶盒上基板表层的倏逝波区域。Labels in the figure: 1 is the collimated incident beam, 2 is the coupling prism, 3 is the lower substrate of the liquid crystal cell, 4 is the low-refractive index coupling layer, 5 is the transition layer (can be multi-layered), and 6 is the upper and lower substrates of the liquid crystal cell The transparent conductive film (ITO) layer on the top, 7 is the liquid crystal alignment layer (PI) on the upper and lower substrates of the liquid crystal cell, 8 is the upper substrate of the liquid crystal cell, 9 is the AC signal driver, 10 is the liquid crystal layer, and 11 is the liquid crystal cell. The evanescent wave region of the upper substrate surface.
具体实施方式Detailed ways
本发明包括: 一个耦合棱镜,一个电控双折射(ECB)液晶盒,一个交流电信号驱动器,以及一个准直激光光源。结构如图1所示。The invention includes: a coupling prism, an electronically controlled birefringence (ECB) liquid crystal cell, an alternating current signal driver, and a collimated laser light source. The structure is shown in Figure 1.
对准直激光光源选定一个激光工作波长如: 632.8nm, 选定耦合棱镜材料如火石玻璃, 折射率1.778,液晶盒的下基板也选这种材料,使之与耦合棱镜相匹配。液晶盒的下基板的上表面镀一层低折射率耦合层,材料取熔石英,折射率1.457,厚度为500nm。然后再在其上镀制过渡层,分别为石英,熔石英,氟化镁,熔石英,石英,折射率分别为1.52,1.457,1.30, 1.45,1.52,厚度分别为500,500,100,200,100nm。再沉积一层透明导电膜 (ITO)层,折射率为1.9,厚度为100nm,然后旋涂一层液晶定向层(PI),折射率1.54,厚度100nm。两者的损耗取值为均10-5。液晶盒上基板取材玻璃,折射率1.52,厚度为1mm。其表面先后镀制ITO 层和液晶定向层PI,参数与下基板相同。取反平行的方向,摩擦液晶定向层。完成上述工艺后,液晶盒成盒,并灌注液晶。 液晶取材5CB,其寻常光和非寻常光的折射率分别为1.532和1.692,厚度为5μm。液晶盒上表面的倏逝场区域为待测样品区域,设为水溶液环境,折射率为1.33。Select a laser working wavelength for the collimated laser light source, such as: 632.8nm, select the coupling prism material such as flint glass, the refractive index is 1.778, and the lower substrate of the liquid crystal cell is also selected to match the coupling prism. The upper surface of the lower substrate of the liquid crystal cell is coated with a low refractive index coupling layer, the material is fused silica, the refractive index is 1.457, and the thickness is 500 nm. Then, a transition layer is plated on it, which are quartz, fused silica, magnesium fluoride, fused silica, quartz, the refractive index is 1.52, 1.457, 1.30, 1.45, 1.52, and the thickness is 500, 500, 100, 200 , 100nm. A layer of transparent conductive film (ITO) was deposited again with a refractive index of 1.9 and a thickness of 100 nm, and then a liquid crystal alignment layer (PI) was spin-coated with a refractive index of 1.54 and a thickness of 100 nm. The loss value of both is 10 -5 . The upper substrate of the liquid crystal cell is made of glass with a refractive index of 1.52 and a thickness of 1 mm. The ITO layer and the liquid crystal alignment layer PI are successively plated on its surface, and the parameters are the same as those of the lower substrate. Take the anti-parallel direction and rub the liquid crystal alignment layer. After the above process is completed, the liquid crystal cell is formed into a cell, and the liquid crystal is poured. The liquid crystal is made of 5CB, the refractive indices of ordinary light and extraordinary light are 1.532 and 1.692, respectively, and the thickness is 5 μm. The evanescent field area on the upper surface of the liquid crystal cell is the sample area to be tested, set as an aqueous solution environment, and the refractive index is 1.33.
根据上述结构参数,耦合棱镜对低折射率耦合层的全反射临界角为46.984°。取准直光的入射角为51.817°。TM入射光将会以倏逝波的形式耦合入液晶结构中,并在液晶层中传导至其上表面,并在上表面外形成表面倏逝波场。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°. Take the incident angle of the collimated light as 51.817°. The TM incident light will be coupled into the liquid crystal structure in the form of an evanescent wave, and conducted in the liquid crystal layer to its upper surface, and form a surface evanescent wave field outside the upper surface.
对平行排列的液晶层施加一法向的驱动电压,在电压有效值大于其取向阈值后,正性液晶分子会发生趋向电场方向的倾斜,倾角的大小取决于驱动电压的有效值。根据液晶的弹性连续体理论,(详见D.K.Yang and S.T.Wu,Fundamentals of Liquid CrystalDevices Wiley 2006),以及液晶材料的弹性参数,可以求得不同驱动电压下液晶分子的倾斜角分布,从而可以求得液晶层的折射率的在液晶盒厚度方向上的空间分布。在此基础上,利用光学传输矩阵的计算方法,可以计算上述结构中TM光波的波场的空间分布。具体方法可以参考我们发表的论文:Opt. Express 25(11), 12121-12130 (2017))。在此,我们关注倏逝波场中最靠近玻璃板表面的光场强度,其定义为光场振幅的平方与折射率的乘积。(详见M. Born, and E. Wolf, Principles of Optics, 7th ed. (Cambridge Univ. Press,2007))。A normal driving voltage is applied to the parallel-aligned liquid crystal layers. After the effective value of the voltage is greater than its orientation threshold, the positive liquid crystal molecules will tilt toward the direction of the electric field. The magnitude of the tilt 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 liquid crystal materials, the tilt angle distribution of liquid crystal molecules under different driving voltages can be obtained, which can be obtained The spatial distribution of the refractive index of the liquid crystal layer in the thickness direction of the liquid crystal cell. On this basis, using the calculation method of the optical transmission matrix, the spatial distribution of the wave field of the TM light wave in the above structure can be calculated. For specific methods, please refer to our published paper: Opt. Express 25(11), 12121-12130 (2017)). Here, we focus on the intensity of the light field in the evanescent wave field closest to the surface of the glass plate, which is defined as the product of the square of the light field amplitude and the refractive index. (See M. Born, and E. Wolf, Principles of Optics, 7th ed. (Cambridge Univ. Press, 2007)).
在不同的驱动电压下,液晶分子的不同取向,造成液晶层的折射率的变化,从而改变液晶层的导光性质,最终影响表面倏逝波的场强。根据上述理论,我们可以计算出驱动电压与表面倏逝波场强的对应关系。在准直光的入射角为51.817°的情况下,图2显示了驱动电压为零时的液晶盒厚度方向的折射率空间分布。图3 为图2 的液晶盒厚度方向的局部放大,以显示液晶盒内部沿法线方向的折射率空间分部。在相同的入射角下,图4为对液晶盒施加3.6-4.7伏的驱动电压情况下在图3中的液晶盒内及外侧沿液晶盒法线(Z)方向的折射率的空间分布。Under different driving voltages, the different orientations of the liquid crystal molecules cause changes in the refractive index of the liquid crystal layer, thereby changing the light-guiding properties of the liquid crystal layer, and ultimately affecting the field strength of the surface evanescent waves. According to the above theory, we can calculate the corresponding relationship between the driving voltage and the surface evanescent wave field strength. In the case of the incident angle of collimated light being 51.817°, Fig. 2 shows the spatial distribution of the refractive index in the thickness direction of the liquid crystal cell when the driving voltage is zero. FIG. 3 is a partial enlargement of the thickness direction of the liquid crystal cell of FIG. 2 to show the spatial division of the refractive index inside the liquid crystal cell along the normal direction. Under the same incident angle, Fig. 4 shows the spatial distribution of the refractive index along the normal (Z) direction of the liquid crystal cell inside and outside the liquid crystal cell in Fig. 3 when a driving voltage of 3.6-4.7 volts is applied to the liquid crystal cell.
保持准直光的入射角,图5为对液晶盒施加4.7伏的驱动电压情况下在液晶盒上基板的外表面处产生的表面倏逝场的强度沿液晶盒外法线(Z)方向变化的情况。图6 为对液晶盒施加3.6-4.7伏的驱动电压情况下在液晶盒上基板的外表面处产生的表面倏逝场的强度随驱动电压变化的情况。这个强度是一个相对于耦合层内的光场强度的比值。因此也称为光场强度的增强因子。它随驱动电压变化而连续单调变化。即实现了强度可电调节的表面倏逝波场。Keeping the incident angle of the collimated light, Fig. 5 shows the intensity of the surface evanescent field generated at the outer surface of the upper substrate of the liquid crystal cell under the condition of applying a driving voltage of 4.7 volts to the liquid crystal cell along the direction of the outer normal (Z) of the liquid crystal cell. Case. FIG. 6 shows the intensity of the surface evanescent field generated at the outer surface of the upper substrate of the liquid crystal cell as a function of the driving voltage when a driving voltage of 3.6-4.7 volts is applied to the liquid crystal cell. This intensity is a ratio relative to the intensity of the optical field within the coupling layer. Therefore, it is also called the enhancement factor of the light field intensity. It varies continuously and monotonically with the driving voltage. That is, a surface evanescent wave field with an electrically tunable intensity is realized.
在耦合角度的精度达到(1/1000)°的条件下,表面倏逝波强度的增强可达到70倍。这个增强是相对于耦合层中光场强度的比率。这个比率的最小到最大的范围即为倏波强度的可调节范围。选择其他耦合角,倏逝波的强率增强因子还有可能有更大的增强率。另外,若能进一步提高耦合角的控制精度,倏逝场的强度最高增强范围可达到多个数量级。本装置在表面显微测量,生物学,表面化学,显微光谱等领域有重要应用前景。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 a ratio relative to the intensity of the light field in the coupling layer. The minimum to maximum range of this ratio is the adjustable range of the surge intensity. Selecting other coupling angles, the intensity enhancement factor of evanescent wave may have a larger enhancement rate. In addition, if the control accuracy of the coupling angle can be further improved, the maximum enhancement range of the evanescent field intensity can reach several orders of magnitude. The device has important application prospects in the fields of surface microscopic measurement, biology, surface chemistry, and microscopic spectroscopy.
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