DE2324381A1 - FOURIER SYNTHETIC TRANSFORM HOLOGRAM - Google Patents

Description

Turlabor AG, Geissacherstrasse B, 8126 Zumikon (Switzerland)

Synthetic Fourier transform hologram

The invention relates to a synthetic Fourier transform hologram, in which a basic pattern is modulated by an image to be displayed.

The well-known synthetic Fourier transform holograms of this type have a checkerboard-like basic pattern. In order to generate the specified image by means of such a filter, a monochromatic parallel beam and an optical system are required. This optical system is required to have a high resolution and is therefore expensive. In addition, the adjustment of the optical system is difficult and time-consuming and there are light losses due to the same.

The invention makes it possible to dispense with this optical system in that, according to the invention, the frequency of the basic pattern is linear increases with the distance from the optical axis. The invention also relates to the use of this Fourier transform hologram for material processing.

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3098A7 / 0953

An exemplary embodiment of the subject matter of the invention is shown schematically in the drawing. In perspective Show illustration:

Fig. 1 shows the beam path through a Fresnel zone plate

2 shows the beam path through a Fourier transform hologram according to the invention;

Also show

3 and 4 the transmission of the Fresnel zone plate according to Fig. 1 or the Fourier transform hologram according to Fig. 2.

The Fresnel zone plate shown in Fig. 1 (Fresnel diffraction lens) 1v consists in the known manner of a transparent plate on which concentric, opaque circles are drawn with the distance between the circles decreasing towards the outside. If you illuminate the plate 1 with a point-like monochromatic light source 2, so that is diffracted light focused in a point 3 of a ξ- Π image plane, which is parallel to the x-y plane of the plate 1. In FIG. 1, the transmission t of the plate 1 is a function of the radius r shown. It is a square wave that changes between the values t = 1 and t = 0 and its spatial frequency increases linearly with the radius, its "pulses" 4 becoming narrower with increasing radius.

The Fourier transform hologram shown in FIG one can imagine that it emerged from the plate 1 that its square wave spatially corresponds to the Fourier transform of a given image has been modulated, i.e. that the individual "pulses" 4 'in relation to the pulses 4 in their position

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and width have been changed. The spatial modulation can calculated in such a way, in particular by means of a computer, that a certain figure is created in the ^ ~ ^ "image plane; in the present case In this case, the light emanating from the monochromatic light source 2 is focused on a concentric circle 6. If, for example, there is a metal plate in the plane of the picture, a hole with the radius of the circle can be made in this way .6 cut out.

Instead of a circle, the light could also point to any one or several other closed or open lines are concentrated are, depending on the desired application for drilling, cutting, welding and the like.

The basic pattern of the Fourier transformation hologram must does not necessarily correspond to that of the Fresnel zone plate. In general, the basic pattern can be represented by the following equation will:

t (x, y) = V ^-1 C _n * Bxp.jnoc. 4 (xu) ² + (yv) ² V

Therein mean:

t (x, y) is the transmission at each point on the x-y plane

C _n coefficients of the series expansion

© £, u and ν constants.

The basic modulated pattern is then represented by the equation

t (x, y) = p (x, y) · \ _c · exp.jnoC 4 (xu) ² + (yv) ² r

n = - oc

309847/0953

where p (x, y) is the Fourier transform of the given Image is at every point in the .x-y plane.

The above general equation also includes basic patterns in which the transmission is not just two extreme values t = 1 and assumes t = 0 ("binary pattern"), but also those in which the transmission varies continuously in a wavy manner, Extreme values of the transmission are t = +1 and t = -1, where one As usual, negative transmission means a phase shift of 180 °.

In contrast to the well-known synthetic Fourier transform hollograms is there no optical system for generating the image 6 between the hologram 5 and the ^ ~ ^? Image layer necessary. To change the scale of Figure 6, it is sufficient to measure the distance between the hologram 5 and the light source 2, while using the known holograms this requires a different optical system. Another The advantage is that the wavelength of the monochromatic light is within fairly wide limits ("Fresnel range") can vary without distorting the image.

3098 ^ 770953

Claims (2)

Claims ) Synthetic Fourier transform hologram in which a basic pattern is modulated by an image to be displayed, characterized in that the frequency of the basic pattern increases linearly with the distance from the optical axis. 2. Use of the filter according to claim 1 for material processing. 309847/0953 Blank page