DE102013203761A1 - Magneto-optics with structured non-magnetic metals - Google Patents

Abstract

The invention describes the design of an arrangement of a regularly structured non-magnetic single or multi-layer system with several basic elements in the unit cells, in which a certain polarization of the reflected or transmitted wave is achieved for a given wavelength of the incident electromagnetic wave depending on an externally applied magnetic field .

Description

Technical area

The invention relates to an arrangement of a structured, non-magnetic single and multi-layer system, especially for the magneto-optical coupling of electromagnetic waves to the structured, non-magnetic single and multi-layer system, as well as its production and use.

State of the art

Structured non-magnetic metals, such as wire grid polarizers (WGP), which are metal wires with sub-wavelength periodicity, are known for their extreme polarization sensitivity.

The WGPs exhibit high reflectivity when the incident electromagnetic wave is polarized such that the component of the electric field is parallel to the WPG wires, and high transmission when the incident electromagnetic wave is polarized such that the component of the electric field perpendicular to the wires of the WPG shows.

Due to their special properties and compactness, WGPs are currently of particular application interest in projection and display devices.

Charge density waves (surface plasmons) are observed at the interface between metal layers and the surrounding medium, for example, air or other non-metallic material having a positive sign of the real part of the dielectric function.

Phenomenologically, no magneto-optical effects have been found in (structured) non-magnetic single or multi-layer systems.

Presentation of the invention

Technical task

The object of the invention is to provide an arrangement of a structured, non-magnetic single or multi-layer system, in which for a given wavelength of the incident electromagnetic wave and a certain strength of the magnetic field at the location of each single layer of the structured, non-magnetic single and multi-layer system, a certain polarization reflected or transmitted electromagnetic wave is achieved. The invention describes the design and manufacture of the structured, non-magnetic system to achieve the "target" polarization of the reflected or transmitted electromagnetic wave.

Furthermore, possible applications for this structured, non-magnetic single or multi-layer system are given.

Under electromagnetic waves are not only white light, monochromatic visible, ultraviolet or infrared light to understand, but the totality of all electromagnetic waves of different energies or frequencies or wavelengths.

Nanostructured metal films exhibit localized surface plasmons at resonant wavelengths with greatly exaggerated near field amplitude as the localized surface plasmons are optically excited.

The resonant wavelengths of the localized surface plasmons of nanostructured gold, copper, silver and platinum are in the visible spectral range. Optically excitable localized surface plasmons of nanostructured aluminum are in the UV spectral range.

In the following, any magnetic field-dependent change in the polarization properties of transmitted or reflected electromagnetic waves is referred to as a magneto-optical effect in structured non-magnetic single or multi-layer systems, the magneto-optical effects depending on the size and direction of the magnetic field at the location of the individual layers of the structured non-magnetic single or multi-layer system.

In vacuum, the ratio of the alternating electric and magnetic field components of electromagnetic waves c ₀ , where c ₀ corresponds to the propagation velocity of electromagnetic waves in vacuum, c ₀ = 3 × 10 ⁸ ms ^-1 . In the visible spectral range, the amplitude of the alternating electric field component is 2.7 × 10 ^-3 Vm ^-1 and the alternating magnetic field component 9 × 10 ^-12 T.

Detailed drawing description

The arrangement according to the invention will be described with drawings.

1 shows on both sides the structure of a structured single-layer system P of thickness d _P on a boundary layer or an interface G, wherein these are applied to a magnetizable or non-magnetizable support material T of thickness d _T. The magneto-optical effects depend on the dielectric properties ε ^{P of} the Single layer P of the structured single-layer system, the angle of incidence α, under which hit the electromagnetic waves on the structured single-layer system, and the magnetic field H at the location of the structured single layer.

For individual uses, for example, for use in determining magnetic gradient fields, it may be useful to use only monochromatic light in a monochromator 10 is generated, and optionally in the polarizer 11 was polarized, is used.

The two parts of the 1 should clarify that the thickness d _{P of} the layer P is relevant to the polarization result of the reflected electromagnetic wave.

2 shows on both sides the structure of a structured multi-layer system. The structured multilayer system comprises an optional carrier T and at least two structured non-magnetic monolayers P _i . When using a carrier T, as in 2 is shown formed between the carrier T and the adjacent to the carrier single layer P _n, a boundary layer or an interface G from. The thicknesses of these layers and of the carrier are denoted by d _Pi , d _G , d _T.

Analogous to 1 Electromagnetic waves at the angle of incidence α impinge on the structured single layer P _i and are reflected at the reflection angle α 'and transmitted at the angle of refraction β through the multilayer system.

The two parts of the 2 should clarify that the order of the individual layers P _{i is} relevant to the polarization result of the reflected wave.

3 presents various regularly structured basic forms of structured monolayers P with a base element in the unit cell in a structured single or multilayer system 2 in plan view, wherein the interface G in structured areas without single layer P can be seen. The left area illustrates a grid of the period p _y , the middle area a herringbone pattern of the periods p _x and d _y and the right area a circular antenna with the period d _r . These structured single layers with a base element in the unit cell show only a small coupling of incident electromagnetic waves to the plaques of the structured single layer.

4 provides various regularly structured basic shapes with two elements in the unit cell in the structured monolayers P in a structured single or multi-layer system 2 in plan view, wherein the interface G in structured areas without single layer P can be seen. The left area illustrates a grid of the period p _y ', the middle area a herringbone pattern of the periods d _x ' and d _y 'and the right area a circular antenna with the period d _r '. These structured individual layers show a large coupling of incident electromagnetic waves to the plasmon of the structured single layer and thus a high magnetic field dependence of the polarization state of the transmitted or reflected electromagnetic wave.

5 shows a possible a) series connection or b) parallel connection of individual structured single or multi-layer systems, which can be extended arbitrarily and used in plasmonic nanophotonics. A combination of series connections with parallel connections is also possible.

Main features of the solution

Electron mobility in structured non-magnetic metal layers is anisotropic and also depends on a static or dynamically changing magnetic field at the location of the patterned nonmagnetic metal layers.

The main driving force for electrons in structured metal layers with impinging electromagnetic waves is the drift along the direction of the alternating electric field component.

On the other hand, electrons in patterned metal layers in a large statically fixed or dynamically changing magnetic field, for example of 4 × 10 ^-4 T, have a strong Lorentz force in the plane perpendicular to the direction of the statically fixed or dynamically changing magnetic field and the electrons follow helical paths along the magnetic field lines.

Joule heating of the patterned metal layers is expected when a static or dynamically changing magnetic field is applied to the position of the nanostructured metal films.

The change in the polarization properties of the transmitted or reflected electromagnetic waves depends on both the electron mobility and plasmon effects in the structured, non-magnetic single or multi-layer systems.

The cause of these magneto-optical effects is a magnetic-field-dependent plasmonic dispersion of metal lattices and a broadening of the resonance frequencies at which the in-plane Wavelength vector of the incident electromagnetic wave can couple to the in-plane wave number vector of the metal lattice.

Plasmonic dispersion in structured, nonmagnetic metal layers depends on the properties of the dielectric tensor of the patterned, non-magnetic metal layers and on the properties of the dielectric tensor of the surrounding medium.

The magnetic field at the location of the structured, non-magnetic individual layers of the single or multi-layer system can be, for example, an external magnetic field and / or magnetic gradient fields from a surrounding magnetic and / or current-carrying medium.

Thus, the magneto-optic effect is 1 ° in nanostructured aluminum lattices with two elements in the unit cell and a lattice periodicity of 200 nm in a dc magnetic field of 0.4 T.

For example, air, Al ₂ O ₃ and / or AlN can be used as the surrounding medium for nanostructured aluminum layers.

Aluminum is the most abundant metal in the Earth's crust, accounting for 8% by weight of the Earth's solid surface, and is the most widely used non-ferrous metal in various areas of transportation and structural materials. It has already been shown that aluminum is superconducting up to a temperature of 1.2 K.

The physical cause for a fundamentally weak optical excitation of localized surface plasmons is the mismatch of the in-plane wave vector of incident electromagnetic waves and the in-plane wave vector of the nanostructured metal layers, where the in-plane wave vector of the incident electromagnetic wave is from the angle of incidence of the electromagnetic wave depends. Excluded are strong optical excitations of localized surface plasmons for certain resonance energies of the electromagnetic wave.

The use of multiple base elements in the unit cell of nanostructured non-magnetic metal layers can improve the optical excitability of localized surface plasmons in these nanostructured non-magnetic metal layers.

The magnetic field dependence of plasmon in nanostructured non-magnetic metal layers depends on the sudden change in the permittivity of the localized surface plasmons across the interface between the nanostructured metal layers and the surrounding medium.

Localized surface plasmons result from the electromagnetic boundary conditions at the surface of the nanostructured nonmagnetic metal layers and the effective restoring forces on the electrons driven by the alternating electric field component of the incident electromagnetic wave.

Additional local magnetic fields, eg. B. an external magnetic field, magnetic gradient fields from the surrounding magnetizable and / or current-carrying medium also exert driving forces on the electrons in the nanostructured non-magnetic metal layers and thus change the resonance energy of the optically excitable localized Oberflächenplasmonen, which propagate in the form of electromagnetic waves.

Mueller-Matrix Polarimetry, an extension of standard spectral ellipsometry, can be used to demonstrate the magneto-optic effects in nanostructured non-magnetic single-layer or multi-layer systems.

Mueller matrix polarimetry makes it possible to distinguish between polarization and depolarization and to detect any polarization state of the transmitted or reflected electromagnetic waves.

The magneto-optic effects provide a new link between the optical excitation of localized surface plasmons in nanostructured non-magnetic metal layers with controllable magnetic fields at the nanostructured metal layers.

The structuring with more than one base element in the unit cell improves the optical excitability of localized surface plasmons in nanostructured nonmagnetic metal layers. The physical cause for this is the mismatch of the in-plane wavenumber vector of the propagating electromagnetic wave, the in-plane wavenumber vector of the lattice vectors of nanostructured metal films except at certain resonance energies for different angles of incidence of the electromagnetic wave.

A magnetic field at the position of the structured nonmagnetic metal layers controls the plasmon dispersion in the structured non-magnetic metal layers.

The object is achieved by using a structured nonmagnetic single or multi-layer system 2 optional on one magnetizable or non-magnetizable carrier material T, the defined magnetic field-dependent change in the polarization state of the incident electromagnetic wave after transmission or reflection by the single or multi-layer system 2 ,

The arrangement according to the invention comprises at least one structured nonmagnetic single layer P _i with a thickness d _i , which can optionally be applied to a magnetizable or non-magnetizable carrier material T, for defined magnetic field-dependent coupling of the incident electromagnetic wave to the structured single or multi-layer system 2 in which the polarization state of the reflected or transmitted electromagnetic waves is manipulated or modulated as a function of their energy by the structuring and the material of the individual layers of the single or multilayer system and by the magnetic field H _i at the location of the structured single layer P _i .

The processing of the arrangement according to the invention takes place on the micro or nanometer scale.

The structured single layer P _i has localized surface polarites SP _i in the spectral range of the incident electromagnetic waves and the properties of the localized surface polarites SP _i depend on the magnetic field H _i at the location of the structured single layer P _i . The magnetic field H _i can be constant over time or variable.

The dielectric tensor ε ^SP _i determines the properties of the localized surface plasmons of the structured (non-magnetic) single layer P _i and depends on the magnetic field H _i at the location of the structured single layer P _i .

The spectral range of the localized surface polarites SP _i is determined by the structuring and by the properties of the surface plasmons of the structured single layer P _i .

The structured multilayer system 2 comprises at least one structured non-magnetic individual layers P _i with different magnetic field dependence of the surface polarites SP _i and at least one magnetizable single layer S _j with magneto-optical coupling constant Q _j .

The inventive arrangement can for non-destructive measurement of the magnetic field H _i in all structured individual layers P, P _{i of} the structured single or multi-layer system 2 using the measured properties (polarization states 12 and 13 and the wavelength λ) of the incident electromagnetic waves or of the structured single or multilayer system 2 reflected or transmitted electromagnetic wave can be used.

Furthermore, with the structured single or multi-layer system 2 using the dielectric tensor ε ^SP , ε ^SP _{i of} each individual layer P, P _{i of} the structured single or multi-layer system 2 and the characteristics of the incident electromagnetic waves (wavelength λ and polarization state 12 ) the polarization state of the reflected and transmitted electromagnetic wave can be determined.

Another use is the temporally constant or variable modulation of the polarization properties of the incident electromagnetic wave by the magnetic field H _{i is} controlled to be temporally variable at the location of the structured individual layers P _i .

The structured single or multi-layer system can thus be used as a magneto-optical sensor, memory or modulator.

Advantageous effects

With the arrangement according to the invention, magneto-optical effects can be controlled in structured non-magnetic single or multi-layer systems. A major advantage is that in the applications of the arrangement produced by this method, the requirements for the specific magneto-optical effects of the single or multilayer system with respect to angle of incidence of the light, polarization state of the light, frequency of light, magnetic field at the location of the non-magnetic single or multi-layer system be taken into account.

The inventive method allows easy adjustment of the desired target polarization.

The arrangement according to the invention can be used to measure the magnetic field at the location of the structured non-magnetic single layer and to determine the magnetization of individual structured non-magnetic individual layers.

Another possible use of the method is the targeted magneto-optical modulation of individual wavelengths and the magneto-optical modulation of several wavelengths of the incident light by series or parallel connection of several of these arrangements for individual wavelength ranges.

The inventive method enables the optimal design of structured single or multi-layer systems.

embodiments

New security features for banknotes

A nanostructured aluminum grid represents a new security feature for banknotes. The application of the nanostructured aluminum grid on banknotes makes banknote counterfeiting considerably more difficult or even impossible.

The nanostructure of the aluminum grid with respect to base, grid width and grid height of the base elements, periodicity and material of the surrounding medium determine the change in the polarization state of an electromagnetic wave reflected at the nanostructured aluminum grid, wherein at least the illuminated area of the nanostructured aluminum grid lies in a homogeneous magnetic field.

For example, the magnetic field can be generated in a miniaturized electromagnet, wherein the banknotes are brought into the center of the electromagnet for testing and irradiated with an electromagnetic wave at an angle of incidence α at the location of the nanostructured aluminum grid.

It is also possible to use other nanostructured nonmagnetic metal lattices, for example Au, Ag, Cu, Pt, or structured multilayer systems consisting of nonmagnetic and magnetic individual layers.

New means of communication in transport

Nanostructured aluminum grilles can be attached to the bodywork of vehicles below the door handle. In the countries with right-hand traffic, it is advisable to attach the nanostructured aluminum grid on the right side of the body and a detector system on the left side of the body.

The local magnetic field H _i at the location of the nanostructured non-magnetic single layer P _i is determined by the magnetizable and / or current-carrying material of the surrounding medium. By changing the direction of the current flow to generate the local magnetic field H _i , the magneto-optical effects of the nanostructured aluminum grid are electromagnetically switched. The detector system mounted on the left side of the body of another vehicle used for detection preferably operates with an IR diode laser.

The observing vehicle detects the reflection of the IR light on the nanostructured aluminum grid of the vehicle to be observed, preferably at an angle of incidence and reflection of 45 °.

Other applications

Plasma nanophotonics has implications for a variety of fields, including electronics, photonics, chemistry, biology and medicine.

For example, another application is the nanostructuring of differently shaped (concave, convex, parabolic) metal mirrors with multiple base elements in the unit cell.

The non-contact sensor principle of magneto-optics opens up possibilities for cost reduction for the areas of system installation and maintenance in information technology, vehicle technology, mechanical engineering and medical technology.

The magneto-optic effect in nanostructured non-magnetic metal layers also enables the optimization of polarizing optical elements in transmission and in reflection.

LIST OF REFERENCE NUMBERS

1

 Magnetisable single or multi-layer system

2

 Structured non-magnetic single or multi-layer system

10

 monochromator

11

 polarizer

12

Polarization state before interaction with 1

13

Polarization state after interaction with 1

14

 Analyzer or other applications

20

 Magnetizable material with non-plane-parallel interfaces

21

Material into which the magnetizable material 22 is embedded

22

 Segment with plane-parallel interfaces

G

 interface

T

 support material

S, S _i

 Magnetizable layer

P, P _i

Textured non-magnetic layer with localized surface plasmons

x, y, z

 Cartesian coordinate system

d _T

 Thickness of the carrier material

d _G

 Thick interface

d _i

 Thick magnetizable layer

α, α '

 Incidence, reflection angle

Β

 angle of refraction

H, H _i

 External magnetic field

M, M _i

Magnetization of the layer S _i

ε _i ^p

 Magneto-optic dielectric tensor layer S

ε _i ^P

 Dielectric tensor of layer P

ε _T

 Dielectric tensor of carrier T

N _i , K _i

Refractive index and absorption index of the layer S _i

Q _i

Magneto-optic coupling constant of the layer S _i

Claims (11)

Structured, non-magnetic single or multi-layer system 2 for the magnetic-field-dependent manipulation or modulation of incident electromagnetic waves, comprising at least one structured non-magnetic single layer P _i with a thickness d _i , which may optionally be applied to a magnetizable or non-magnetizable carrier material T, for the defined magnetic field-dependent coupling of the incident electromagnetic wave to the structured Single or multi-layer system 2 , characterized in that the polarization state of the reflected or transmitted electromagnetic waves as a function of their energy by the structuring and the material of the individual layers of the single or multi-layer system and by the magnetic field H _i at the location of the structured single layer P _{i can be} manipulated or modulated. Structured single or multi-layer system 2 according to claim 1, characterized in that the patterned single layer P _i has localized Oberflächenpolaritonen SP _i in the spectral range of the incident electromagnetic waves and that the properties of the localized Oberflächenpolaritonen SP _i of the magnetic field H _i depend on the location of the patterned single layer P _i, wherein the magnetic field H _i can be constant or variable over time. Structured single or multi-layer system 2 according to the preceding claims, characterized in that the periodicity of structuring on the micro or Nanometerskale lie and that the unit cell contains a plurality of basic elements. Structured single or multi-layer system 2 according to preceding claims, characterized in that the Dielektrizitätstensor ε ^SP _i and that the properties of the localized surface plasmons of the patterned single layer P _i of the magnetic field H _i depend on the location of the patterned single layer P _i. Structured single or multi-layer system 2 according to the preceding claims, characterized in that the spectral range with localized Oberflächenpolaritonen SP _{i is} determined by the structuring and by the properties of the surface plasmons of the structured single layer P _i . Structured single or multi-layer system 2 according to the preceding claims, characterized in that the structured multilayer system 2 at least one structured nonmagnetic single layer P _i with different magnetic field dependence of the surface polarites SP _i and at least one magnetizable single layer S _j with magneto-optical coupling constant Q _j . Method for predicting the polarization state of the reflected or transmitted electromagnetic wave of the structured single or multi-layer system 2 using the dielectric tensor ε ^SP , ε ^SP _{i of} each individual layer P, P _{i of} the structured single or multi-layer system 2 depending on the characteristics wavelength λ and polarization state 12 the incident electromagnetic waves. Use of the structured single or multi-layer system 2 for non-destructive measurement of the magnetic field H _i in all structured individual layers P, P _{i of} the structured single or multi-layer system 2 using the measured properties (polarization states 12 and 13 and the wavelength λ) of the incident electromagnetic waves or of the structured single or multilayer system 2 reflected or transmitted electromagnetic wave. Use of the structured single or multi-layer system 2 for temporally constant or variable modulation of the polarization properties of the incident electromagnetic wave. Use of the structured single or multi-layer system 2 for magneto-optical storage by manipulating the propagation of electromagnetic waves, characterized in that a static magnetic field H _i in the structured non-magnetic single layer P _{i of} the single or multi-layer system 2 is generated by the stray magnetic field of a magnetizable single layer S _j in the vicinity of the structured nonmagnetic single layer P _i . Use of the arrangement according to one of claims 1 to 3 as a magneto-optical sensor, magneto-optical modulator or as a magneto-optical memory.

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