DE1911801C3 - Procedure to expand the possibility of information transmission in the case of images by means of waves - Google Patents

Description

ft

according to Arcpnri. 1, dad, «* ge J.

tt Λ

WeU «nl _äog e

Size t | be modulated.

3. The method according to claim 2, characterized in that that the modulation on the carrier frequency done with optical grids.

4. The method according to claim 2, characterized in that that the modulation on the carrier frequency takes place in a holographic way.

5. The method according to claim 1, characterized in that that the spatial frequency spectrum of the structure to be examined in spatial frequency bands is decomposed, several of which are in the sub-wavelength range and in the image space for Image of the structure to be composed.

6. The method according to claim 5, characterized in that that the composition of the various frequency bands in the image space takes place in a holographic way.

7. The method according to claim 1, characterized in that that the information about the object contained in subwaves is initially holographic and then to normal by diffraction of sub-waves at the hologram structure Waves is transmitted.

8. The method according to claim 1, characterized in that that the sub-waves are generated by total internal reflection

9. The method according to claim 1, characterized in that that the sub-waves are generated by the diffraction of normal waves at a grating, the grating constant of which is smaller than that Wavelength of normal waves.

10 arrangement for carrying out the method according to claim 9, characterized in that the substructure _comprises at least one grid

11. The method according to claim 9, characterized in that that the sub-waves are generated on a grating with a phase structure.

12. The method according to claim 9, characterized in that the sub-waves on a grating can be generated with an amplitude structure.

they should be referred to as "subwaves" for short.

In contrast, ^we r ^the ^ [^ **** 1 ^uer fdämpften progressive waves as a "normal"

* «> Denotes waves.

Sub-waves arise 2: .B with total reflection at the interface of two media 1 and 2 with the refractive indices n. And η where / I ₁ > n, should be. If the angle of incidence φ of a plane wave in,

a ₅ Medium 1 greater than the critical angle of total reflection

30 , in the optically thinner medium 2 in the vicinity of the interface, a wave that progresses along the interface and is strongly attenuated perpendicular to the interface is formed. The wavelength of this sub-wave is

sin 91

40

The invention relates to a method for expanding the possibility of information transmission

forming systems in which the information 1 object space to image space is transferred by waves ; en will.

iei optical systems that use a conventional formation process (lens optics) is where K _{1 is} the length of the propagating waves in medium 1. It can therefore be seen that at the critical angle <p _er, the wavelength of this wave _{is equal to A 2.} As the angle of incidence increases, the wavelength becomes

Weiner and, finally, at conflicting incidence, X _s = X ₁ , ie equal to the wavelength in the denser medium 1. Sub-waves of a much smaller wavelength can e.g. B. by irradiating through a grating, for example with sinusoidal amplitude permeability and a grating constant a, which is small compared to the wavelength of the radiation. Sub-waves then arise that progress in the lattice plane and are strongly attenuated perpendicular to the lattice plane. The wavelength of these sub-waves is equal to the grating constant a of the grating irradiated through. .....

The invention is based on the object To develop a process that extends the possibility of information transmission in the case of images permitted by means of waves. Below images are not only geometrically similar images to understand. In particular, optical systems should be rounded, the resolution of which the above exceed specified limits.

According to the invention, this object is achieved in that the spatial frequencies are determined by the diffraction of sub-waves of the structure to be investigated, which is of the order of magnitude of the reciprocal sub-wavelength

Are transformed into a range of lower spatial frequency will.

In the following, a structure whose dimensions are smaller than the wavelength of the radiation used will be referred to for short as a "substructure" in relation to this radiation. It has been shown that by diffraction _e in <; r sub-wave at a sub-structure one again receives advancing waves. It is now particularly important that a transformation of the spatial frequencies occurs here. If you irradiate ir one-dimensional grid

f lattice constant a, spatial frequency k _a = -Λ

with a subwave of wavelength L ·, i.e. the wavenumber

this creates a diffraction spectrum with spatial frequencies k _b = mk _a - k _s (m = O ₁ +1, ± 2, ...).

By diffraction of sub-waves, spatial frequencies k _a that were previously inaccessible can be transformed into the conventional range if | A ₆ 1 <| k "\.

To do this, the wave number of the sub-wave must be selected accordingly: \ mk _a —k _s \ <\ k “\. A conventional imaging system (e.g. a Luise) then receives the same light distribution as a grating with the grating constant b ~ -. ' with vertical radiation with the wavelength! would cause. To generate an object-like image, however, a multiplicative transformation of the type

necessary; M is the magnification here. Let us first assume an object whose essential information is contained in a spatial frequency spectrum of width 2 k " (see FIG. 1). In the spatial frequency space, it must then be stated immediately how to get from Jk ₆ to k _b ^x :

M "

The structure must therefore be irradiated with sub-waves; the diffracted advancing waves are used to form an image enlarged by M times used; through modulation to a carrier frequency

quenz rl according to known methods finally an M-times enlarged image of the structure is produced, in which, however, the details corresponding to the spatial frequencies k _{a are resolved.}

The use and diffraction of subwaves thus provides for the increase in the resolving power the following advantages:

1. The shorter wavelength of the sub-waves is equivalent in terms of the resolution to be achieved an irradiation with the otherwise difficult to handle shorter waves (e.g. short-wave Ultraviolet or X-rays) for which there are no satisfactory imaging systems eibt.

2. The one when the sub-waves are diffracted at the substructure resulting homogeneous waves with the normal wavelength allow the further Processing with the highly developed means (lenses * etc.) of the conventional ones Optics.

Since the decisive physical quantity of a wave is the frequency, with this method ip the properties of the substructure, which are decisive for the wavelength X ₀ or Jl _n, are now displayed with a resolution that corresponds to _{a wavelength i s.}

There are two ways of carrying out the procedure in practice:

1. One generates, e.g. B. by diffraction of a progressing wave, which is expediently generated with a laser, at a generator grid with the grid constant j a sub-wave with the wave number k _s . The structure k _a to be examined is in direct contact with the grid . By a conventional optical system, e.g. B. a microscope

a5 lens, becomes an M-times enlarged image of the

Structure generated. This is converted into the final image k _b ^x .

2. The sequence given above can also be reversed: Instead of a generator grid for generating the subwaves, an analyzer grid k "is used to analyze the sub-waves with the wave numbers k _tt caused by the diffraction of a normal wave at the structure to be examined k _a .

An arrangement for carrying out the method mentioned under 1, which shows the individual steps particularly clearly, is shown in FIG. 2: The laser radiation 1 falls on the generator grid 2 and there generates sub-waves of the wave number k _s . These are bent at the object structure 3 spatial frequency k _a and generate normal waves of wave number k _b . The lens 4 generates the Fourier spectrum of k _b in its focal plane f and in the image plane (

an M-times enlarged and distorted image of the structure k _tt , corresponding to the spatial frequency spectrum k _b . The spatial frequency spectrum corresponding to this enlarged structure is generated in level 8 by the Luise 7. The aperture 9 blocks out the zero diffraction order and the negative spatial frequency corresponding to the undiffracted light passing through. About prism 11 and lens 12 wire at the angle

a shifted zeroth order 13 was introduced. To adjust amplitude and phase (this zero part Order), absorption and phase plates can be introduced into the side beam path.

In its rear focal plane, the lens 10 produces an M-times magnified image of the structure, the quality of which is comparable to an image that may be obtained from a conventional image with oblique lighting. Microscope, since here as there only the zeroth and a first order of diffraction contribute to the image.
An improvement in the image quality through Ausnut

tion of the positive and negative diffraction order the short-wave light of the wavelength of the

voltages can be z. B. would be used by holographic method subwaves,

to achieve. An example of this is shown in FIG. 3, the The inventive method can be applied to the

largely the arrangement according to FIG. 2 corresponds. Mapping of two-dimensional structures

On the photo plate 15 is created by superimposition 5 wear. Appropriate cross-

the first order of diffraction and the shifted grating are used.

zeroth order with the coherent reference beam. With the method according to the invention, one can 16 the hologram. If this hologram is also used in objects with a larger spatial frequency spectrum, the arrangement according to FIG. 4 reconstructed, so receive form and dissolve, e.g. For example, if the person who is remote from the image in the image plane 14 of the lens 17 contains the same image 10 frequency spectrum of the object only in certain intervals, as when viewed directly in the arrangement, all significant contributions. For this one has measured Fig. 2. However, the holography now offers this spectrum in bands of width <| k " | to dismantle several wave fields that lay one after the other; Several of these can now be generated by sub-recording and coherently overwave at the same time. One can store for this dismantling. So you can on the same photo plate 15 a 15 z. B. record several generator and analyzer grids for a second hologram, but in which now sub-waves of different wavelengths one after the other, the aperture 9 is arranged so that only use the negative. The spatial frequency bands obtained in this way wer-1. Order contributes to the picture. Prism 11 and lens then in the image space according to known methods 12 are changed so that the zeroth order now (W. Lukosz, Phys. Blätter, 24 [1968], 554) to the total image resulting from above at the same angle φ as before ao composed. Here comes from below. The angle of incidence of the reference beam is the application of photographic methods, anabündels is changed at the same time so that the angle of incidence as used above to compose the two angles between the reference beam and the zero order frequency-shifted spectra is the same for both recordings. It is particularly expedient in the reconstruction, since it allows the simultaneous overstructure of this double hologram in the arrangement of several recorded in succession according to FIG. 4 allow 18 mener wave fields with the reconstruction bundle,
one obtains an image of the structure which now contains the information about the spatial frequency range k _a contained in subwaves. If the object is first holographically registered in both recordings and the zero order is removed, the reconstruction then results in a dark-field image of the object structure through the diffraction of sub-waves at the structure. Transferring the hologram structure to normal waves.

Generator or analyzer grids, their grating sub-structures, are suitable for both amplitude constants that are significantly smaller than the wavelength of phase structures. Because of the coherence of its visible rays Is light, z. B. on electron- ion and its high spectral radiation intensity optical path (R. Speidel, Optik, 23 [1965], 35) is a laser as a radiation S in the optical field. 125) as an amplitude or phase grating. source preferred.

With the method according to the invention, in particular, the method described is preferably used in the particular by means of the arrangements described here in the optical wavelength region (ultraviolet, visible, a resolution that is far ultrared) can be achieved. In addition, however, it goes beyond what is required by Abbe's theory for electromagnetic waves with other wave resolution limits. In particular, structures can be resolved for length or for radiation of a different nature, which can be represented much smaller than waves (ζ. Β electrons, than λ / 4 , (λ = wavelength of the sound or ultrasonic waves used for imaging) , applicable. A used light). With regard to the special case of application, z. B. the Röntgenstrukmögens, the lens 4 acts as if for image analysis 45.

For this purpose 4 sheets of drawings

Claims (1)

Patent claims:
1. Method for expanding the information, the resolving power limited by diffraction. The principal limit of the resolving power is in the order of magnitude of 2IX if λ is the wavelength of the radiation used