DE102009030912A1 - Terahertz lens e.g. flat-convex lens, for guiding electromagnetic waves in e.g. airport, has space ring provided between plate and foil, and lens volume filled with liquid, where curvature of surfaces and length of lens are adjusted - Google Patents

Abstract

The lens has a space ring provided between a planar plate and a plastic foil (1). The lens is formed as a flat-convex lens and as a flat-concave lens in which the plastic foil is replaced by the planar plate. Lens volume (4) is filled with transparent liquid e.g. paraffin oil such as medical white oil, for producing terahertz electromagnetic waves, and a curvature of breaking lens surfaces and focal length of the lens are adjustable by changing the filling volume. The medical white oil is transparent in a visible spectral region. The planar plate is made of glass or plastic.

Description

introduction

The The invention relates to a component according to the preamble of Claim 1.

to Guiding electromagnetic waves at terahertz (THz) frequencies currently plastic lenses and metallic concave mirrors are used. THz frequencies include the frequency range between 50 GHz and 30 THz, preferably the range between 100 GHz and 10 THz. This must be for any desired focal length or shape a separate THz lens or a separate mirror can be made. THz waves will be for example, in basic research, for quality control industrial products or for security checks of persons z. B. used at airports.

It is known that due to their low absorption non-polar plastics, preferably polyolefins are suitable for the construction of lenses for THz frequencies. EP 1 505 382 shows, for example, the use of Topas and Zeonex as suitable THz lens materials. After the production of a plastic THz lens, its focal length is fixed and can no longer be changed. If other focal lengths or a change in the lens shape (concave, convex) is desired, a new THz lens must be designed and manufactured. The newly manufactured THz lens is to be installed in the existing THz structure, which is associated with corresponding adjustment effort with each focal length change.

task The invention is to provide a simple device that allows variable adjustment of the lens focal length and lens shape.

These The object is achieved by a component having the features of the claim 1 solved.

Two Plastic films are placed on top of each other and between clamped two rings. The gap between both slides will with a transparent to electromagnetic waves at THz frequencies Liquid filled. This way arises the ideal lens body. By the amount of fluid volume can the focal length and shape (concave, convex) set the THz lens arbitrary.

By increased the use of a THz lens with variable focal length the flexibility of a THz system. By filling or draining the liquid can be lens-shaped and focal length are changed.

The Using a THz lens with variable focal length saves costs, because fewer THz lenses need to be kept at a fixed focal length. The Different focal lengths can be achieved with a single THz lens variable focal length can be realized. An additional one Adjustment effort as when changing THz lenses with fixed focal length deleted as well.

THz systems in which THz lenses with variable focal length can be used be built more compact and easier, as the focal length and Change the shape of the THz lenses. A THz lens with variable focal length replaced in the structure of several THz lenses with fixed focal length.

It it is also advantageous to choose a liquid which is also transparent in the visible spectral range and there has the same refractive index as in the THz range. This transparency allows an optical pre-adjustment of the THz lenses and facilitates installation of the components in a THz system.

Description:

embodiments The invention are illustrated in the drawings and are in Described in more detail below.

1 : A top view of the THz lens with variable focal length (in the propagation direction of the electromagnetic radiation)

2 : A longitudinal section through a THz lens with variable focal length: realization of a biconvex lens

3 : A longitudinal section through a THz lens with variable focal length: realization of a biconcave lens

4 : A longitudinal section through a THz lens with variable focal length: realization of a plano-convex lens

5 : A longitudinal section through a THz lens with variable focal length: realization of a plano-concave lens

6 : A longitudinal section through a THz lens with variable focal length: Realization of a Bestformlinse with different radii of curvature on both lens surfaces

7 : A longitudinal section through a THz lens with variable focal length: realization of an F-theta lens with concave-convex-shaped lens surfaces

8th : Refractive index of a medicinal white oil that can be used as a lens fluid

9 : Absorption coefficient of a medicinal white oil that can be used as a lens fluid

10 : Relationship between focal length and filling volume using the example of a THz lens with a diameter of 100 mm when using a liquid with a refractive index of 1.49.

For producing a THz lens with variable focal length according to 1 to 7 two plastic films ( 1 ) and between two rings ( 2 ) braced. The tension ( 3 ) can be realized for example by means of screws and nuts. The transparent THz-wave liquid is located between the two plastic films and forms the lens volume ( 4 ). It can be connected via a supply line ( 5 ) the lens volume ( 4 ) or drained from it. With a stopcock ( 6 ), the supply line is closed as soon as the desired lens volume and thus the desired focal length is reached.

The simplest form of realization is the biconvex shaped THz lens 2 If the space between the two plastic films is filled with a transparent liquid for THz waves, the two films bulge spherically on both sides (solid line). Will the lens volume ( 4 ) increases, the curvature of the lens surface increases (dotted line). If the volume is increased even further, the curvature of the lens surface (dashed line) also increases. The greater the curvature, the smaller the radius of curvature r _{L of} the lens becomes. It stands for the volume V of the lens, for its aperture radius r _A and the height of the bulge h in the following context:

From the radius of curvature r _{L of} the lens and from the refractive index n, the focal length f of the lens is calculated using the known lens-maker formula for a biconvex lens:

For example, for a refractive index of n = 1.49 ( 8th ) and an aperture radius of r _A = 50 mm with a filling volume of V = 108 ml a focal length f = 100 mm. The entire course of the focal length as a function of the filling volume is in 10 shown.

As filling of the lens volume ( 4 ) are only liquids with high transparency in the THz range suitable. Liquids with a high transparency in the THz range have an absorption coefficient of less than 5 cm ^-1 at a frequency of 1 THz, preferably less than 1 cm ^-1 at a frequency of 1 THz. Especially suitable are paraffin oils, preferably medicinal white oils, since these have very low absorption coefficients and are also transparent in the visible frequency range, which permits optical pre-adjustment of the components. The spectral profile of the absorption coefficient of an exemplary medicinal white oil is in 9 shown. Water is hereby completely excluded for use as a lens fluid.

One between the plastic films ( 1 ) mounted spacer ring ( 7 ) according to 3 allows the representation of a concave shaped lens. In this design, the existing liquid from the lens volume ( 4 ) sucked off. The more fluid from the lens volume ( 4 ), the stronger the two lens surfaces bulge inward.

Will one of the plastic films ( 1 ) in 2 and 3 through a plane plate ( 8th ) of a dielectric material, preferably made of glass or plastic, can according to 4 and 5 a plano-convex or a plano-concave lens are shown.

On the other hand, it allows one between the two plastic films ( 1 ) mounted plane plate ( 8th ), the filling volumes and thus the radii of curvature on both lens halves set separately. This construction allows the fabrication of F-theta lenses (shown in FIG 7 ) or Bestformlinsen (shown in 6 ). The latter are characterized by particularly low aberrations.

In the context of the invention numerous refinements are possible. In particular, lenses with spacer ring ( 7 ), as in the 3 and 5 are represented by additional filling with the transparent liquid for THz waves also form a convex shape. In the 6 and 7 can between plastic film ( 1 ) and adjacent plane plate ( 8th ) a spacer ring ( 7 ) are used.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 1505382 [0003]

Claims (13)

THz lens for electromagnetic waves at THz frequencies, characterized in that the lens volume is filled with a transparent liquid for THz waves and the curvature of the refractive lens surfaces and thus the focal length of the lens is adjustable by changing the filling volume. Component according to Claim 1, characterized that the THz-wave transparent liquid located between two stretchable plastic films, which in turn are clamped between two rings and via a supply line can be filled or emptied. Component according to Claim 1 or 2, characterized that the liquid transparent to THz waves in the THz lens is a paraffin oil, preferably a medical one White oil. Component according to one of the preceding claims, characterized in that the medicinal white oil Also in the visible spectral range is transparent and so an optical Pre-adjusting the THz lenses allowed. Component according to one of the preceding claims, characterized in that the lens is a biconvex Lens with two identical radii of curvature is. Component according to one of the preceding claims, characterized in that it is a biconcave lens with two identical radii of curvature, in which a Spacer ring is located between the plastic films. Component according to one of the preceding claims, characterized in that it is a plano-convex lens, in which one of the plastic films has been replaced by a plane plate. Component according to one of the preceding claims, characterized in that it is a plano-concave lens, in which one of the plastic films has been replaced by a plane plate and in which a spacer ring between flat plate and plastic film located. Component according to one of the preceding claims, characterized in that the plane plate between the plastic films is so that there are two separate lens volumes, the can be filled and emptied separately, what the Realization a Bestformlinse allows. Component according to one of the preceding claims, characterized in that the plane plate between the plastic films is so that there are two separate lens volumes, the can be filled and emptied separately, and a additional spacer ring, the realization of a concave convex lens allows. Component according to one of the preceding claims, characterized in that the plane plate of a for THz-wave transparent dielectric material is, preferably made of glass or plastic. Component according to one of the preceding claims, characterized in that the concave lenses by additional Filling can also assume a convex shape. Component according to one of the preceding claims, characterized in that also in the convex lenses between the two plastic films or between plastic film and flat plate a spacer ring can be used.