CN203164205U - Surface plasma longitudinal field scanning near-field optic microscope device - Google Patents

Abstract

The utility model provides a surface plasma longitudinal field scanning near-field optic microscope device. The device is provided with a surface plasma excitation unit (1), a scanning control unit (2) and a detection unit (3); after being focused through a high numerical aperture objective lens (6), incident light excites an SPP field on an interface of a metal membrane and air, raman signals and the SPP field interfere with each other to form a stationary field of the SPP field around a focus; the scanning control unit (2) can achieve three-dimensional scanning and positioning for an atomic force microscope (AFM) metal probe (5) by means of an AFM controller (4); and the detection unit (3) achieves three-dimensional measurement and analysis for a longitudinal field component of a surface plasma field.

Description

A kind of surface plasma longitudinal field optical microscope for scanning near field device

Technical field

The utility model belongs to optical sensing and the technical field of imaging that near field optic is surveyed, particularly a kind of pick-up unit of surface plasma longitudinal field.

Background technology

In the prior art, object is closely related with the non radiation field that is strapped in body surface less than fine structure and the fluctuating information of diffraction limit under Near Field, on the one hand, is in the detailed information of the interior inclusion body structure of non radiation field of near-field region; On the other hand, because this field intensity is exponential damping along with leaving surface distance, so in the far field is traditional optical detective technology, can't detect.This contradiction concentrates on the key problem of near field optic and surveys the non radiation field that is strapped in body surface, and non radiation field is blazed abroad with the form of radiation field without distortion, and received technical.Because surface plasma body resonant vibration can effectively strengthen the intensity of local fields and have the characteristic of a series of novelties, therefore (Surface Plasmons Polaritons, near-field detection SPPs) is a major issue of present near field optic for surface plasma.The SPPs that is in near-field region has comprised abundant reflection object fine structure and the information of optical characteristics, therefore the detection technique of SPPs exciting and propagation characteristic of right solution surface plasma itself not only, and to the SPPs sensing, imaging technique etc. all have great directive significance.Because the surface wave characteristic of SPPs, its electric field intensity is presenting the exponential damping form perpendicular to the interface direction, so traditional optical microphotograph means can't be carried out imaging to it.

The instrument of at present comparatively common measurement near field distribution is optical microscope for scanning near field (SNOM), but the near-field detection of utilizing the surface plasma of SNOM exists some defectives and deficiency: at first, because it utilizes optical fiber probe that the near field is detected, can only detect the cross stream component of light field in the near-field region in the ordinary course of things.Studies show that and have only when longitudinal component to be measured during greater than 30 times of cross stream components, could detect the longitudinal component near field effectively.For SPPs, its longitudinal component is occupied an leading position, but the ratio difference of the shared resultant field of longitudinal field under the different condition, but in general, and still there is gap in the longitudinal field component with 30 times of transverse field component, so can't carry out effective detection of longitudinal field with SNOM.Secondly, transmitted light has very big influence to the result of imaging.Because transmitted light also can effectively be coupled to the optical fiber probe of SNOM, therefore the near field distribution of utilizing SNOM to obtain is the stack of SPPs and transmitted light, and this has influenced the detection quality of SPPs light field to a certain extent.Especially under the situation that high-NA focuses on, therefore its transmission light intensity even greater than the intensity of the SPPs that produces greatly reduces the reliability of detection.Near special light field focus does not also have to such an extent that be very perfectly SPPs optical field imaging at present.Therefore research and develop out a cover and can effectively detect the near field longitudinal component, the ultrahigh resolution imaging technique that simultaneously can fine elimination sees through influence of light has special profound significance.

The utility model content

The utility model improves at the problem that above-mentioned prior art exists, be that the technical problems to be solved in the utility model provides a kind of surface plasma longitudinal field optical microscope for scanning near field device, when utilizing this device, realized the near field electric field longitudinal component scanning probe of ultrahigh resolution.

Surface plasma longitudinal field pick-up unit of the present utility model comprises: a kind of surface plasma longitudinal field optical microscope for scanning near field device has surface plasma and excites unit 1, scan control unit 2 and detecting unit 3; Surface plasma excites unit 1 to comprise: excitation source, beam splitter 7, high-NA objective 6, the slide that is coated with the 45nm silverskin, 3-D scanning platform; The slide that is coated with the 45nm silverskin is arranged on the 3-D scanning platform, is adsorbed with Raman molecular by self assembly on it; The light beam that excitation source sends passes beam splitter 7, high-NA objective 6 is radiated on the slide that is adsorbed with Raman molecular; Scan control unit 2 comprises: AFM metal probe 5, AFM controller 4, computing machine; AFM controller 4 control linkage AFM metal probes 5; Computer control connects AFM controller 4; Detecting unit 3 comprises: spectroanalysis instrument 11, photomultiplier 10, beam splitter 8, CCD and computing machine; Beam splitter 8 connects spectroanalysis instrument 11, photomultiplier 10; Spectroanalysis instrument 11 connects CCD; CCD is connected computing machine with photomultiplier 10; Spectrometer 11 connects CCD; CCD is connected computing machine with photomultiplier 10;

What spectroanalysis instrument (11) was analyzed is Raman spectrum;

Have surface plasma exciting step, scan control step and detect step; The surface plasma exciting step is by self assembly absorption Raman molecular on metal film and air interface, after focusing on, high-NA objective (6) produces SPP field at golden film and air interface at incident light, Raman molecular on golden film under the effect of SPP field sends Raman signal, it interferes near the stationary field that forms SPPs focus mutually, by analyzing the characteristics that Raman signal obtains the SPP field;

The scan control step utilizes AFM controller (4) can realize 3-D scanning and location to AFM metal probe (5);

Detect longitudinal field component three-dimensional measurement and analysis that step realizes the surface plasma field.

Have surface plasma exciting step, scan control step and detect step; The surface plasma exciting step is to apply Raman molecular at metal film and air interface, after focusing on, high-NA objective 6 produces SPP field at golden film and air interface at incident light, Raman molecular on golden film under the effect of SPP field sends Raman signal, it interferes near the stationary field that forms SPPs focus mutually, by analyzing the characteristics that Raman signal obtains the SPP field; The scan control step utilizes AFM controller 4 can realize 3-D scanning and location to AFM metal probe 5;

Detect longitudinal field component three-dimensional measurement and analysis that step realizes the surface plasma field.

Surface plasma excites the unit, the TM light wave that satisfies the surface plasma shooting conditions focuses on through high-NA (N.A=1.49) object lens, can form ATR (attenuated total reflection, Attenuated TotalReflection) structure, thus can be at silverskin (or golden film; From the worker, the average film thickness difference is 0.3nm) surface generation surface plasma, the exciting light of different polarization states distributes at the surface plasma that metallic film surface produces the different distributions pattern.

The scan control unit, utilize the AFM controller can realize 3-D scanning and location to the AFM metal probe, when controlling the SPPs of the close metallic film surface of AFM metal probe point, because the interaction energy of SPPs and metal probe point effectively excites local surface plasma (LSP), make the electric field at the most advanced and sophisticated place of metal needle point obtain great enhancing.When making that by self assembly the metal probe tip is adsorbed with Raman molecular, because height local and the significantly existence of the coupled field of enhancing, Raman signal obtains 10 ⁸Enhancing doubly; When considering that transmitted light influences, the Raman signal intensity that excites corresponding to SPPs is 20 times of the light activated signal intensity of transmission, and the Raman signal intensity of SPPs and LSP coupled field has improved nearly 2 orders of magnitude than the Raman signal intensity that is excited by SPPs merely, thereby the influence of penetrating light can be ignored substantially.

Detecting unit, the surface plasma that produces in metallic film surface comprises longitudinal component and cross stream component two parts, and the ratio of the longitudinal component of SPPs and cross stream component is that the ratio by metal and near dielectric specific inductive capacity thereof determines, that is: | E _z| ²/ | E _r| ²=| ε _m|/ε _dIn visible-range, for gold and the most frequently used metal of these two kinds of excitating surface plasmas of silver, this ratio is respectively 0.83,21.78 and 2.923,26.3 the size of this ratio does not satisfy 30 times of these lower limits that longitudinal field is transverse field, therefore can not directly use conventional method to detect.The utility model detecting unit realizes that by the interaction of SPPs and metal probe point Raman strengthens, by surface plasma coupled radiation (surface plasmon-coupled emission, SPCE) Raman signal is passed through high-NA oil immersion objective directional couple to beam splitter 1 from the metal film top, enter CCD and photomultiplier via beam splitter 2 respectively afterwards, by the collection of computer control Raman signal, and then obtain the single-point longitudinal field component measurement of surface plasma field.Control AFM metal probe carries out longitudinal field component three-dimensional measurement and the analysis that 3-D scanning can be realized the surface plasma field.The resolution of whole longitudinal field result of detection is below 50nm, and as long as the acquisition process time of the image of every longitudinal field distribution is 1-2 minute.The image that CCD is obtained carries out deconvolution processing can obtain intuitively that the longitudinal field distribution situation can form good complementation with the longitudinal field distribution situation of utilizing photomultiplier to obtain.

Surface plasma longitudinal field detection method of the present utility model comprises: be to apply the individual layer Raman molecular by self assembly on metal film and air interface, when incident light can excite SPPs at metal film and air interface after high-NA objective focuses on, it interferes near the stationary field that forms SPPs focus mutually.When the AFM metal probe point that is stained with Raman molecular during near the stationary field of SPPs, because the interaction energy of SPPs and metal probe point effectively excites local surface plasma (LSP), make the most advanced and sophisticated electric field of locating of metal needle point obtain great enhancing.Because the gap structure (metal film-gap-metal probe structure) of metal film-AFM metal probe orientation is consistent with the orientation of SPPs longitudinal field component, thereby can fully excite LSP, and transverse field does not participate in exciting of LSP, when Raman molecular sticked to the needle point tip, the Raman signal that the coupled field of SPPs and LSP excites had also obtained great enhancing.

$I_{\mathrm{RS}}\left(v_S\right)\∝{\mathrm{N\σ}}_{\mathrm{SERS}}\·\frac{{\left|E_{\mathrm{loc}}\right|}^4}{{\left|E_{\mathrm{SP}}\right|}^4}\·{\left|E_{\mathrm{SP}}\right|}^2={\mathrm{N\σ}}_{\mathrm{SERS}}\·\mathrm{RE}\·{\left|E_{\mathrm{SP}}\right|}^2---\left(1\right)$

I wherein _RSBe Raman signal intensity, E _LocBe the field intensity of SPPs and LSP coupled electromagnetic field, e _SpBe the field intensity of the SPPs field that excites LSP, RE is the Raman enhancer.

Can obtain from above-mentioned principle: the SPPs electric field intensity of Raman signal intensity and needle point present position is directly proportional, simultaneously because the cross stream component of SPPs is basic and LSP excite irrelevant, and the main body of SPPs electric field intensity is its longitudinal component, thereby according to the longitudinal electric field strength relationship of Raman signal intensity and needle point present position SPPs, can obtain the longitudinal field field strength distribution of corresponding position; And then experiment porch carried out high accuracy three-dimensional scanning, simultaneously Raman signal is imported photomultiplier and carries out secondary and amplify, just can realize to whole near field range inside surface plasma longitudinal component effectively, accurately and ten minutes measurement fast.

The utility model provides the method for the high precision of surface plasma longitudinal field, high-sensitivity measurement and device, by adopting SPPs and LSP coupling Raman spectrum to strengthen technology, effectively reduce the interference that the external environment factor is brought, improved longitudinal field measuring reliability and stability.The utility model can be expanded to the detection to the longitudinal component of common light field, is easy to be applied in the dissimilar SPR coupling schemes, and system's simplicity of design, easy to operate.

Description of drawings:

Fig. 1 surface plasma longitudinal field pick-up unit structural representation;

Fig. 2 Finite-Difference Time-Domain Method is at the analog result synoptic diagram of this experiment;

In Fig. 3 analog result the SPPs field with and laterally, longitudinal component and experimental result comparison synoptic diagram;

Near the scanning result of SPPs stationary field Fig. 4 focusing: it is that near SPPs longitudinal field focus that 1 vortex light beam excites distributes that a, b, c are respectively linearly polarized light, radial polarisation light topological charge.D, e, f is the analog result according to Richard-wolf vectorial method (Richard-Wolf vector Integral Theory);

The experimental result of Fig. 5-1 longitudinal field component center halfwidth;

The repeated experiment result schematic diagram of Fig. 5-2 longitudinal field component center halfwidth.

Embodiment:

The utility model is described in further detail below in conjunction with drawings and Examples.

Basic thought of the present utility model is the interaction realization Raman enhancing by SPPs and metal probe point,, surveys longitudinal field indirectly with Raman signal intensity and distributes with the proportional relation between the SPPs longitudinal component according to Raman signal intensity.

Embodiment: shown in Fig. 1,2,3,4,5-1,5-2,

A kind of surface plasma longitudinal field optical microscope for scanning near field device has surface plasma and excites unit 1, scan control unit 2 and detecting unit 3; Surface plasma excites unit 1 to comprise: excitation source, beam splitter 7, high-NA objective 6, the slide that is coated with the 45nm silverskin, 3-D scanning platform; The slide that is coated with the 45nm silverskin is arranged on the 3-D scanning platform, is adsorbed with Raman molecular by self assembly on it; The light beam that excitation source sends passes beam splitter 7, high-NA objective 6 is radiated on the slide that is adsorbed with Raman molecular; Scan control unit 2 comprises: AFM metal probe 5, AFM controller 4, computing machine; AFM controller 4 control linkage AFM metal probes 5; Computer control connects AFM controller 4; Detecting unit 3 comprises: spectroanalysis instrument 11, photomultiplier 10, beam splitter 8, CCD and computing machine; Beam splitter 8 connects spectroanalysis instrument 11, photomultiplier 10; Spectroanalysis instrument 11 connects CCD; CCD is connected computing machine with photomultiplier 10;

What spectroanalysis instrument (11) was analyzed is Raman spectrum;

Have surface plasma exciting step, scan control step and detect step; The surface plasma exciting step is by self assembly absorption Raman molecular on metal film and air interface, after focusing on, high-NA objective (6) produces SPP field at golden film and air interface at incident light, Raman molecular on golden film under the effect of SPP field sends Raman signal, it interferes near the stationary field that forms SPPs focus mutually, by analyzing the characteristics that Raman signal obtains the SPP field;

The scan control step utilizes AFM controller (4) can realize 3-D scanning and location to AFM metal probe (5);

Detect longitudinal field component three-dimensional measurement and analysis that step realizes the surface plasma field.

Have surface plasma exciting step, scan control step and detect step; The surface plasma exciting step is to apply Raman molecular at metal film and air interface, after focusing on, high-NA objective 6 produces SPP field at golden film and air interface at incident light, Raman molecular on golden film under the effect of SPP field sends Raman signal, it interferes near the stationary field that forms SPPs focus mutually, by analyzing the characteristics that Raman signal obtains the SPP field;

The scan control step utilizes AFM controller 4 can realize 3-D scanning and location to AFM metal probe 5;

Detect longitudinal field component three-dimensional measurement and analysis that step realizes the surface plasma field.

And being simplification device, is the silver nanoparticle bead replacement AFM metal scan head system of 60nm with diameter, and Raman molecular is placed between nanosphere and the metal film.Because the vertical Rankine-Hugoniot relations between nanosphere and the metal film has only the longitudinal component of electric field can effectively excite LSP, and electric field is strapped in the space of the residing nanosphere of Raman molecular and metal film.Therefore this method has with AFM metal scan head system and has identical function.By the analysis to this simplification device experimental result, can realize the feasibility to surface plasma longitudinal field scanning microscope system, validity, and the assessment of practicality.As can be seen from Figure 2, because the introducing of near field sniffer (prill, AFM metal probe 5), the field distribution of SPPs field does not change, and energy only occurs and assembles between sniffer and golden film.Adopt Finite-Difference Time-Domain Method that this experiment is simulated, and compare with experimental result, as shown in Figure 3, be without loss of generality, adopt said apparatus, be the actual measurement that 1 vortex light beam has carried out numerical simulation and corresponding SPPs longitudinal field to linearly polarized light, radial polarisation light and topological charge respectively, the result as shown in Figure 4.The SPPs stationary field of measuring according to this experimental program and the longitudinal electric field of numerical simulation distribute and fit like a glove, and have very high accuracy.For the light activated SPPs of the radial polarisation of wavelength 632.8nm, the center maximal value halfwidth of its longitudinal field component is 184.3nm in the laboratory test results, shown in Fig. 5-1 and 5-2, be one group with 50 samples and carry out repeated experiment, the gained result satisfies normal distribution substantially, and its longitudinal field center maximal value halfwidth mean value is 188.93nm (0.355 λ ₀, accordingly, 0.099 λ ₀ ²) than its representative value 0.16 λ ₀ ²Little by 38%, standard deviation is 6.76nm.This has significance for the resolution that improves system.Simultaneously, because the secondary amplification of significant Raman enhancement effect and photomultiplier, Raman signal is amplified significantly, thereby has effectively reduced scanning imagery required integral time, and this has improved the practicality of the utility model system greatly.In a word, according to our experimental result, the feasibility of the utility model system, validity, and practicality has all obtained checking.

Obviously, above-described embodiment of the present utility model only is for the utility model example clearly is described, and is not to be restriction to embodiment of the present utility model.For those of ordinary skill in the field, can also make other changes in different forms on the basis of the above description.Here need not also can't give all embodiments exhaustive.And these belong to apparent variation or the change that spirit of the present utility model extended out and still are among the protection domain of the present utility model.

Claims (2)

1. a surface plasma longitudinal field optical microscope for scanning near field device is characterized in that, has surface plasma and excites unit (1), scan control unit (2) and detecting unit (3); Described surface plasma excites unit (1) to comprise: excitation source, beam splitter (7), high-NA objective (6), the slide that is coated with the 45nm silverskin, 3-D scanning platform; The slide of the described 45nm of being coated with silverskin is arranged on the described 3-D scanning platform, is adsorbed with Raman molecular by self assembly on it; The light beam that described excitation source sends passes described beam splitter (7), high numerical aperture journey object lens (6) and is radiated on the described slide that is adsorbed with Raman molecular; Described scan control unit (2) comprising: AFM metal probe (5), AFM controller (4), computing machine; The described AFM metal probe of described AFM controller (4) control linkage (5); Described computer control connects described AFM controller (4); Described detecting unit (3) comprising: spectroanalysis instrument (11), photomultiplier (10), beam splitter (8), CCD and computing machine; Described beam splitter (8) connects described spectroanalysis instrument (11), photomultiplier (10); (11 connect described CCD to described spectroanalysis instrument; Described CCD is connected described computing machine with photomultiplier (10).

2. surface plasma longitudinal field optical microscope for scanning near field device according to claim 1 is characterized in that: what described spectroanalysis instrument (11) was analyzed is Raman spectrum.

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