DE3141789C2 - Solar ray concentrator and method for its manufacture - Google Patents

Abstract

The invention relates to heliotechnology. A sunbeam concentrator is designed in the form of a prism (1) which has surfaces (2, 3, 4) for the entry, reflection and exit of rays. The concentrator according to the invention is characterized in that a material layer (5) with a spatial hologram produced therein is arranged on the entry surface (2) and/or on the reflection surface (3). This hologram is of the transmission type if it is located on the entry surface (2) and of the reflection type if it is located on the reflection surface (3). The structure of the hologram is such that the radiation is introduced into the prism (1) at a total reflection angle. The manufacturing process for the sunbeam concentrator is based on the recording of an interference image of a reference beam (6) and an object beam (7) of a laser radiation in a light-sensitive layer (5). The light-sensitive layer (5) is applied to the entrance surface (2) and/or to the reflection surface (3) of the prism (1). The interference image is recorded by directing the reference beam (6) in the direction of the radiation to be concentrated and the object beam (7) at a total reflection angle (Θ) for the materials of the light-sensitive layer (5) and the prism (1). The concentrator is preferably intended for use in devices for converting solar energy into heat or electrical energy.

Description

The invention relates to a solar ray concentrator and a method for its manufacture, according to the preamble of claims 1 and 7.

The solar ray concentrator according to the invention can be used in heliotechnology to concentrate solar radiation incident on the working surface of a photoconverter.

It is a solar ray concentrator in the form of a Prisms with a triangular base made of a material with a high refractive index are known (DR Mills, JE Giurtronich, "Ideal prism solar concentrators", "Solar Energy", 1978, 21, N. 5, pp. 423-430), in which the radiation concentration is achieved by multiple total reflections.

The prism has surfaces for the entry, reflection and exit of rays. The lower reflection surface of the prism has a mirror coating, while the surface angle between the upper entry surface of the prism and the reflection surface is chosen with consideration for the total reflection of a light beam entering the prism and is approximately 20°. The rays that are reflected several times leave the exit surface of the prism opposite this surface angle.

The concentration multiplicity, which can be defined as the ratio of the area of the entrance surface to the exit surface, turns out to be low and amounts to approximately 3. The concentrator has large dimensions and dimensions. In addition, the entire spectrum of solar radiation is concentrated, which leads to an uneconomical conversion of solar energy by a selective receiver, e.g. a photoconverter, which reaches a sensitivity maximum in a certain spectral range.

DE-PS 26 29 641 discloses a selective solar ray concentrator in the form of a transparent prism - a plane-parallel plate - with luminescence centers dispersed in its volume, which re-emit radiation falling on them in a longer-wave spectral range. To increase the degree of concentration, a reflective layer is applied to the lower surface of the plate and to all side surfaces with the exception of the exit surface.

In this concentrator, the luminescence radiation spreads out in all directions within the plate, whereby the luminescence radiation striking the plate surfaces from the inside at a smaller solid angle than the limiting angle of total reflection leaves the plate and is lost. For a glass plate with a refractive index of 1.5, these losses amount to approximately 25%. Such losses are fundamentally impossible to eliminate. Significant losses also occur as a result of self-absorption and reflection at the reflective surfaces. Other shortcomings of this luminescence concentrator include difficulties in synthesizing a phosphor with suitable spectral characteristics, as well as its instability and short lifespan.

Finally, US-PS 40 54 356 discloses a sunbeam concentrator which is designed in the form of a lens or a hologram of a light point source. Such a concentrator is simple to manufacture; it is created by recording an interference pattern of a plane-parallel reference beam and a diverging object beam of laser radiation in a layer of a light-sensitive material. The focal length of this lens, however, turns out to be large and is determined by the position of the source of diverging radiation. To arrange a receiver for concentrated radiation at the focal point of the lens, an auxiliary device connecting the receiver to the lens is required. In addition, the energy distribution over the surface of the receiver is very uneven.

To concentrate solar radiation, concentrators are of interest that do not produce an image of a radiation source and ensure a uniform energy distribution directly over their exit surface.

From DE-OS 30 12 500, which deals with a reflector for light rays based on diffraction gratings, it is known to use diffraction gratings formed in a photosensitive material by holographic processes. Since there are two or three differently oriented, different diffraction gratings, the hologram is composite. One or all of the diffraction gratings can have focusing properties. When the reflector is illuminated, the radiation striking it is reflected and focused outside the reflector plate with the hologram.

The invention is based on the object of creating such a solar ray concentrator, the construction of which is able to ensure a reduction in energy losses during the concentration of solar radiation, an increase in the degree of concentration, an extension of the possibilities for concentrating different spectral ranges of solar radiation, the possibility of a simultaneous separate concentration of the different spectral ranges on different beam exit surfaces.

The invention is also based on the object of simplifying the manufacturing technology for solar ray concentrators.

The stated object is achieved in a solar ray concentrator having the features of claim 1.

In a solar ray concentrator according to the invention, the radiation is guided into the prism with the help of the hologram, spreads within it and is focused on one or more end faces of the prism.

In order to specify spectral characteristics of the solar ray concentrator over a wide range, it is advisable to choose the angle between the entrance surface and the reflection surface to be at least equal to half the angle value representing the angular difference between the Bragg angle and the angle of minimum diffraction efficiency.

To increase the degree of concentration of solar radiation, it is desirable to select the parameters of a hologram provided on one side of the prism in such a way that the radiation propagates in the prism parallel to the surface opposite to that on which the hologram is located.

If the prism has the shape of a parallelepiped, it is expedient to design the spatial hologram with an uneven structure to prevent diffraction of a beam propagating within the prism which is reflected by the hologram/air interface.

To expand the spectral range of solar radiation to be concentrated, the spatial hologram can be made up of multiple layers, with each layer containing information about a light source with a wavelength different from the wavelengths of the light sources used to generate the holograms in the other layers.

In order to make more effective use of solar radiation, it is desirable to select the number of layers of the spatial hologram equal to the number of exit surfaces and the structure of the hologram of each layer taking into account the direction of radiation to the corresponding exit surface.

The stated object is further achieved by the fact that in a manufacturing process for a solar ray concentrator with recording of an interference image from a reference and an object beam of laser radiation in a light-sensitive layer according to the invention, this light-sensitive layer is applied to the entrance surface and/or to the reflection surface of a prism and the recording of the interference image takes place by directing the reference beam in the direction of the radiation to be concentrated and the object beam at the total reflection angle against air of the materials of the light-sensitive layer and the prism.

To ensure greater freedom of choice for the spectral range to be concentrated when using a prism with a trapezoidal base, a light beam with a flat wavefront can be used as the object beam and directed onto one of non-parallel prism surfaces, which are selected as the entrance and reflection surfaces.

• R&min; ≤β + 2 φ&min;m,

zu wählen, wobei

• R&min; den Einfallswinkel des Objektbündels auf die Eintrittsfläche des Prismas,
• β den Grenzwinkel für eine Totalreflexion an der Trennfläche Prisma/Luft,
• φ&min; den Winkel zwischen der Eintrittsfläche und der Reflexionsfläche des Prismas und
• m die Höchstzahl von Mehrfachreflexionen eines Strahls einer zu konzentrierenden Strahlung innerhalb des Prismas bezeichnet.

In this case, the angle of incidence for the reference beam in the prism is conveniently determined according to the formula

• R &min; ? β + 2 ? &min; m ,

to choose, whereby

• R &min; the angle of incidence of the object beam on the entrance surface of the prism,
• β is the critical angle for total reflection at the prism/air interface,
• φ &min; is the angle between the entrance surface and the reflection surface of the prism and
• m is the maximum number of multiple reflections of a beam of radiation to be concentrated within the prism.

When manufacturing a solar ray concentrator based on a prism having a rectangular base, it is expedient to use as an object beam a light beam with a diverging wave front, the source of which is arranged in such a way that a section on the hologram/air interface between the point of entry of a beam and the point of its first reflection from the hologram/air interface is visible at the point of the above-mentioned first reflection at an angle corresponding to at least the angle amount representing the angular difference between the Bragg angle and the angle of minimum diffraction efficiency.

When manufacturing a solar ray concentrator with a multilayer hologram, it is advisable to apply at least one more photosensitive layer to the first photosensitive layer and to record an interference pattern on each of the layers using a light source having a wavelength different from the wavelengths of the light sources used to record the interference patterns on the other layers, and choosing the values of the wavelengths for all light sources taking into account the absence of the effect of cross-modulation.

Here, the number of layers of the spatial hologram can be selected according to the number of exit surfaces of the concentrator and an interference image can be recorded in each layer by directing the object beam towards an exit surface corresponding to the respective layer.

The solar ray concentrator designed according to the invention concentrates any region of the solar spectrum, reduces energy losses during concentration, and provides a high concentration level. The concentrator is simple in design and contains the smallest possible number of components. The process of manufacturing the concentrator is characterized by simplicity and the absence of labor-intensive operations for mechanical processing of the surfaces of the optical elements. By creating an appropriate structure of the diffraction grating of the spatial hologram by using light sources with different wavelengths, more effective use of the solar ray spectrum is ensured with the possibility of separate concentration of different spectral regions.

The invention will be explained in more detail below with reference to specific embodiments illustrated in the drawing.

Fig. 1 shows a solar ray concentrator and a device for producing a transmission-type spatial hologram on the entrance surface of a prism with a triangular base;

Fig. 2 shows a solar ray concentrator with a prism with a trapezoidal base and a spatial hologram of the transmission type on the entrance surface;

Fig. 3 shows a solar ray concentrator with a prism with a trapezoidal base and a spatial hologram of the reflection type on the reflection surface;

Fig. 4 shows a solar ray concentrator in the form of a parallelepiped and the radiation direction of an object beam during its manufacture;

Fig. 5 shows a solar ray concentrator in the form of a parallelepiped with a spatial hologram of the transmission type on the entrance surface and a spatial hologram of the reflection type on the reflection surface;

Fig. 6 shows a solar ray concentrator in the form of a parallelepiped with a two-layer transmission type hologram on the entrance surface and with two exit surfaces.

The solar ray concentrator shown in Fig. 1 consists of a prism 1 with a triangular base, which has an entrance surface 2 , a reflection surface 3 and an exit surface 4 for radiation, and a layer 5 of a photosensitive material applied to the entrance surface 2 with a spatial hologram of the transmission type created therein. The structure of the diffraction grating is such that the introduction of the radiation into the prism is ensured at an angle of total reflection R and when the concentrator is illuminated by a light beam identical to a reference beam 6 used in recording the hologram, the light rays propagate within the prism 1 parallel to the reflection surface 3 .

In another embodiment of the same concentrator, the spatial hologram can be located on the reflection surface 3 (not shown in the drawings). In this case, the structure of its diffraction grating provides the hologram with reflection properties and propagation of the radiation entering the prism 1 parallel to the beam entrance surface 2 .

The solar ray concentrator shown in Fig. 2 consists of a prism 1' with a trapezoidal base and with an entrance surface 2 and a reflection surface 3 , and with two exit surfaces 4 and 4'. and a material layer 5 with a spatial transmission hologram generated in it. The surfaces 2 and 3 are not parallel in the prism 1' . The parameters of the diffraction grating of the said hologram are such that when the concentrator is illuminated by the light beam identical to the reference beam 6 , the latter is introduced into the prism 1 at the total reflection angle R to the entrance surface 2 and continues in the direction of the exit surface 4. The direction of an object beam 7 to the prism 1' when the diffraction grating of the spatial hologram is formed is indicated by dots.

The concentrator shown in Fig. 3, in contrast to the one shown in Fig. 2, has a material layer 5' with a spatial reflection hologram on a reflection surface 3. The structure of the diffraction grating of the hologram is such that the light beam that has entered the prism 1' and is identical to the reference beam is reflected within the prism 1' at a total reflection angle R ' greater than the angle R and is directed in the direction of the smaller exit surface 4' of the prism 1' .

Another embodiment of a sunbeam concentrator consists, according to Fig. 4, of a prism 1" in the form of a rectangular parallelepiped with an entrance surface 2 , a reflection surface 3 and two exit surfaces 4 and 4" and of a material layer 5 with a spatial transmission hologram. In contrast to the concentrators shown in Figs. 1 to 3, the hologram mentioned has an irregular structure to prevent diffraction of a beam continuing within the prism 1" and reflected from the hologram/air-air interface.

Fig. 5 shows an embodiment of a concentrator, the difference from that shown in Fig. 4 is that a material layer 5' with a spatial reflection hologram is additionally applied to the reflection surface 3 of the prism 1" . The parameters of the diffraction gratings of the holograms are selected such that a spectral range with wavelengths close to λ ₁ is diffracted on the transmission type hologram (layer 5 ) and a spectral range with wavelengths close to λ ₂ is diffracted on the reflection type hologram (layer 5 ). The radiation from these two ranges is concentrated on the exit surface 4 .

Another embodiment of a solar ray concentrator is shown in Fig. 6. Its difference from the concentrator according to Fig. 4 is that the spatial transmission hologram in the layer 5" is multi-layered, the number of layers of the hologram being equal to the number of exit surfaces for the concentrated radiation. To illustrate this , Fig. 6 shows a two-layer hologram of the transmission type, one layer of which directs the concentrated radiation with wavelengths close to λ ₁ onto the exit surface 4 and the other layer of which directs the radiation with wavelengths close to λ ₂ onto the second exit surface 4' .

The manufacturing process for the solar ray concentrator shown in Fig. 1 is as follows. A layer 5 of a light-sensitive material, for example a photo emulsion, is applied to the entrance surface 2 of the prism 1. A layer 8 of an immersion liquid with a refractive index close to the refractive index of the light-sensitive material is applied to the layer 5 of the light-sensitive material and an auxiliary prism 9 is placed on top of it. The auxiliary prism 9 serves to direct the reference beam 6 in the direction of the radiation to be concentrated and the object beam 7 parallel to the reflection surface 3. An interference image from the reference beam 6 and the object beam 7 of the laser radiation is recorded in the light-sensitive layer 5. The transmission hologram proves to be homogeneous because the reference beam 6 and the object beam 7 each have a flat wave front. To obtain a reflection hologram in a concentrator based on a triangular prism 1 , the photosensitive layer 5 is applied to the reflection surface 3 , while the object beam 7 is directed parallel to the entrance surface 2 of the prism 1. In the sunbeam concentrator according to Fig. 1, the angle φ between the entrance surface 2 and the reflection surface 3 uniquely defines an angle between the reference beam 6 and the object beam 7 , which in turn determines spectral characteristics of a spatial hologram generated in the photosensitive layer 5 .

The embodiment according to Fig. 2 with a trapezoidal prism 1' offers a wide range of options for specifying the spectral characteristics of a concentrator. In the manufacture of such a concentrator, the object beam 7 is directed onto the prism 1' at an optional total reflection angle for the material of the prism 1' , starting with the limiting total reflection angle β , in contrast to the manufacturing process for the concentrator according to Fig. 1. In this case, a light beam with a flat wave front is used as the object beam 7. The angle φ ' between the entrance surface 2 and the reflection surface 3 can be selected within the limits of 45° to δ /2, where δ is the angular deviation from the Bragg angle at which the diffraction effectiveness of the spatial hologram is minimal. In order to achieve a high degree of concentration for the light beam, it is expedient to set the angle φ' equal to δ. /2. The object beam 7 is directed onto the prism 1' in the direction of the exit surface 4 .

• R&min; ≤β + 2 φ&min;m,

wobei

• R&min; den Einfallswinkel des Objektbündels auf die Eintrittsfläche 2 des Prismas 1&min;,
• β den Grenz-Totalreflexionswinkel an der Trennfläche Prisma/Luft,
• φ&min; den Winkel zwischen der Eintrittsfläche 2 und Reflexionsfläche 3 des Prismas 1&min; und
• m die Höchstzahl von Mehrfachreflexionen eines Strahls einer zu konzentrierenden Strahlung innerhalb des Prismas 1&min;

bezeichnet.The manufacturing process for the concentrator shown in Fig. 3 consists in applying a light-sensitive layer 5' to the reflection surface 3 and recording an interference image by directing the reference beam 6 and the object beam 7 onto the light-sensitive layer 5' from opposite sides thereof. The object beam 7 is introduced into the prism 1' at an angle R ' to the entrance surface 2 which exceeds the limiting total reflection angle β by at least an angle equal to a product of the number of reflections of a beam on the reflection surface 3 and twice the angle φ ' between the entrance surface 2 and the reflection surface 3 of the prism 1' . This condition is described by the following relationship:

• R &min; ? β + 2 ? &min; m ,

where

• R ' is the angle of incidence of the object beam on the entrance surface 2 of the prism 1' ,
• β is the limiting total reflection angle at the prism/air interface,
• φ ' is the angle between the entrance surface 2 and reflection surface 3 of the prism 1' and
• m is the maximum number of multiple reflections of a beam of radiation to be concentrated within the prism 1'

designated.

Furthermore, the described manufacturing method for the concentrator of Fig. 3 differs from the manufacturing method for the concentrator according to Fig. 2 in that the object beam 7 is introduced into the prism 1' in the direction of the exit surface 4' .

• 2 (d + d _l ) tg α ≤h [tg (α _o + δ _o-) - tg α _o ],

wobei

• d einen Abstand zwischen der Eintritts- und der Reflexionsfläche,
• d _I die Dicke des räumlichen Hologramms,
• h den Abstand von der Quelle für das Objektbündel bis zur Trennfläche Hologramm/Luft,
• α einen Totalreflexionswinkel an der Trennfläche Prisma-Luft,
• α _o einen mit α durch das Brechungsgesetz verbundenen Einfallswinkel eines Strahls des Objektbündels und
• δ _o eine Winkelabweichung vom α _o /2 gleichen Bragg- Winkel, bei der die Beugungseffektivität des räumlichen Hologramms minimal ist,

bezeichnet.In the method of manufacturing the concentrator according to Fig. 4, a prism 1" in the form of a rectangular parallelepiped is selected, on the entrance surface 2 of which a photosensitive layer 5 is applied, and an object beam 7 with a diverging wave front is used when recording an interference image. In this case, the position of the source P for the object beam 7 with respect to the entrance surface 2 is selected in such a way that a section on the hologram/air interface between the point of entry of the beam and the point of its first reflection on the hologram/air interface is seen at an angle of not less than half an angular deviation from the Bragg angle at the point of the above-mentioned first reflection, at which the diffraction efficiency of the spatial hologram is minimal. Compliance with this condition in the case of the arrangement of the spatial transmission hologram on the entrance surface 2 is ensured by observing the following ratio:

• 2 (d + d _l ) tg ? ? h [ tg ( α _o + δ _{o -} ) - tg α _o ],

where

• d a distance between the entrance and the reflection surface,
• d _I is the thickness of the spatial hologram,
• h is the distance from the source of the object beam to the hologram/air interface,
• α is a total reflection angle at the prism-air interface,
• α; _o an angle of incidence of a ray of the object bundle related to α; by the law of refraction and
• δ _o is an angular deviation from α _o /2 equal Bragg angle at which the diffraction efficiency of the spatial hologram is minimal,

designated.

In deriving this ratio, the refractive indices of the material layer with the spatial hologram and that of the prism are assumed to be equal, because they usually differ only slightly from each other. The refractive index of the medium in which the source P of the object beam 7 is located is assumed to be different from the refractive index of the prism 1' .

In the special case of equal refractive indices , the angle α is to be set equal to the angle α _o . In addition, the thickness d _I of the spatial hologram is generally much smaller than the distance d between the entrance surface 2 and the reflection surface 3 and can be neglected. The steering of the object beam 7 at a required angle can be ensured, for example, with the aid of a corresponding auxiliary prism and a layer of an immersion liquid on the entrance surface 2 .

The manufacturing process for the embodiment of the concentrator shown in Fig. 5 consists in first applying a light-sensitive layer 5 to a surface, for example to the entrance surface 2 , and in this a spatial transmission hologram from a light source with a wavelength λ _I is generated. This layer is then subjected to a corresponding photochemical treatment. Then a light-sensitive layer 5' is applied to the reflection surface 3 , in this a spatial reflection hologram from a light source with a different wavelength λ ₂ is generated and this layer is subjected to a corresponding photochemical treatment. When manufacturing such a concentrator, the wavelengths λ ₁ and λ ₂ of the light sources are selected with regard to the absence of cross-modulation. As an example , Fig. 5 shows a concentrator in which the two object beams are introduced into the prism 1" in the direction of the exit surface 4 .

In a similar way, the concentrator shown in Fig. 6 is manufactured, in which the number of layers of the spatial hologram is selected according to the number of exit surfaces. The layer of the spatial hologram is applied to the entrance surface 2. First, the first photosensitive layer is applied and a spatial hologram is generated therein by directing the object beam towards the first exit surface 4 and by using a light source with a wavelength λ ₁ . Then a second photosensitive layer is applied and a spatial hologram is generated therein by directing the object beam towards the second exit surface 4' and by using a light source with a different wavelength λ 2 . After that, further layers can be applied and the operations described repeated. Here, the wavelengths λ ₁ and λ ₂ are selected. ₂ of the light sources is also chosen taking into account a minimization of the effect of cross modulation, so that the light of one wavelength only diffracts at "its" diffraction grating and does not interact with other layers of the hologram formed by the light sources of the other wavelengths.

Structurally, all concentrators can have a prism made of an optically transparent solid material. In addition, the prism can be made in the form of a solid shell filled with a transparent liquid, for example, in order to improve the temperature conditions for the receiver of concentrated radiation.

During operation of the solar ray concentrator according to the invention, the spatial hologram represents a spatial diffraction grating which contains periodically arranged scattering surfaces. If a light wave identical to one of the two waves involved in the formation of the hologram is incident on such a grating at a Bragg angle, it diffracts there and recreates a wave identical to the second wave. Therefore, the spatial hologram formed by the plane-parallel reference beam 6 and by the object beam 7 introduced into the prism at the total reflection angle R recreates the object beam 7 when illuminated by the reference beam 6. As a result, a light beam from the air is introduced into the optically denser medium of the prism 1 at the total reflection angle.

The spatial hologram exhibits an angular selectivity, ie a dependence of the diffraction efficiency on the value of the angular deviation of the illumination beam from the Bragg angle, whereby the permissible angular deviation is smaller, the larger a Formation of the hologram is equal to twice the Bragg angle between the reference beam 6 and the object beam 7. In addition, the spatial hologram is selective for the wavelength of the illuminating radiation, which is why when illuminated by sunlight it can concentrate a certain spectral range depending on the conditions for forming the hologram.

The concentrator according to Fig. 1 has a spatial transmission hologram on the entrance surface 2 , which guides the radiation entering the prism 1 parallel to the reflection surface 3. Compared to the concentrators shown in Fig. 2 and 3, it concentrates a relatively narrower spectral range at the same angle between the entrance surface 2 and the reflection surface 3 because of a larger angle between the reference beam 6 and the object beam 7 of the radiation. In this case, no multiple reflections of the concentrated light radiation occur within the prism 1 .

The concentrator according to Fig. 2 works as follows. The light radiation identical to the reference beam 6 diffracts on a spatial transmission hologram by striking a material layer 5 with it, and enters the prism 1' at the angle of total reflection R. After being reflected back from the reflection surface 3 inclined to the entrance surface 2 at an angle of φ ', the beam strikes the hologram/air interface at an angle of R + 2 φ ' and undergoes total reflection. The angle φ ' is chosen to be no smaller than half an angular deviation from the Bragg angle at which the diffraction efficiency of the said hologram is equal to zero.

Since the beam reflected from the hologram/air interface does not hit the scattering surfaces of the spatial hologram at the Bragg angle, but with a deviation of the angle 2 φ ' from it, at which the diffraction efficiency of this hologram is zero, it does not diffract. Its direction therefore does not change, and after a series of multiple reflections it exits through the exit surface 4 .

In the embodiment of the concentrator corresponding to Fig. 3 with a prism 11' having a trapezoid as its base, the radiation is concentrated on the smaller exit surface 4' . As an example, an embodiment with a spatial reflection hologram lying on the reflection surface 3 in the layer 5' is shown. When generating the diffraction grating of the hologram mentioned, the object bundle 7 is introduced into the prism 1' through the reflection surface 3 at the angle R '. In contrast to the concentrator shown in Fig. 2, this angle is reduced by a value of 2 φ ' after each reflection from the surface 3. So that the beam does not leave the prism 1' through the entrance surface 2 or the reflection surface 3 , the angle R ' is compared to the limiting total reflection angle β. is chosen to be larger by an angle which is equal to the product of the number m of reflections of the beam from the reflection surface 3 and twice the angle between the entrance surface 2 and the reflection surface 3 of the prism 1. Such a concentrator can have a spatial transmission hologram with a similar effect on the entrance surface 2. In this embodiment of the concentrator, higher concentration levels for the light radiation and a narrower region of the concentrated radiation are obtained compared to the concentrator shown in Fig. 2. This is due to a smaller surface area of the exit surface 4' and to a larger angle between the reference beam 6 and the object beam 7 .

The sunbeam concentrator shown in Fig. 4 contains a prism 1" in the form of a parallelepiped and a material layer 5 with a spatial transmission hologram on the entrance surface 2 . The diffraction grating of the said hologram is formed by a plane-parallel reference beam 6 and by a diverging object beam 7 of the radiation. Because the diverging object beam 7 was guided into the prism 1" at an angle of total reflection during the manufacturing process for the concentrator, the introduction of a beam of rays identical to the reference beam 6 from the air into the optically denser medium of the prism 1" at an angle of total reflection is achieved. This is a necessary but not sufficient condition for the concentration of light radiation. The light beam diffracted by the spatial hologram enters the prism 1" at the angle of total reflection, undergoes total reflection on the reflection surface 3 and returns at a certain point to the material layer 5 with the spatial hologram. For concentration, it is sufficient that the beam after reflection from the spatial hologram/air interface does not satisfy the Bragg condition on this section of the hologram. Then it will not diffract on the spatial hologram and will leave the exit surface 4 after a series of total reflections. For this purpose, the structure of the diffraction grating of the spatial hologram is made inhomogeneous in the direction of propagation of the repeatedly reflected beam. This inhomogeneity is ensured by the divergence of the object beam 7 , the rays of which enter the material layer 5 at different angles when the hologram is formed.

By selecting the distance from the source P ( Fig. 4) for the object beam 7 to the entrance surface 2 and the distance between the entrance surface 2 and the reflection surface 3 , the incidence of the beam reflected from the hologram/air interface on the hologram is made possible with such an angular deviation from the Bragg angle on this section that the diffraction efficiency of the spatial hologram on this section is zero for it. Since the spatial hologram has angular selectivity, it does not exert a diffractive effect on the beam directed with a certain angular deviation from the Bragg angle.

Depending on the geometry of the diverging object beam with a given wavelength, the light radiation can be concentrated during the manufacturing process for the concentrator onto two or more exit surfaces of the prism, onto a part of the exit surface or onto any point on the prism.

The embodiments of concentrators shown in Fig. 5 and 6 work analogously to those described above with the only difference that in the embodiment according to Fig. 5 the radiation from the two holograms - the transmission hologram (layer 5 ) and the reflection hologram (layer 5' ) - is concentrated on the one exit surface 4 and in the embodiment according to Fig. 6 the radiation from each layer of the transmission hologram is concentrated on a corresponding exit surface 4 or 4' .

Since the spatial hologram, in addition to the angular selectivity also has spectral selectivity, its diffraction efficiency decreases with the deviation from the Bragg wavelength when illuminated at the Bragg angle. Therefore, in all the solar ray concentrators described above, a single-layer hologram of sufficient thickness can be used instead of the multilayer spatial hologram. The spatial diffraction gratings from different light sources are superimposed on each other, and when illuminated by white light at the Bragg angle, each diffraction grating separates its own spectral range. The effect of cross-modulation turns out to be minimal when the wavelengths of the light sources differ significantly from each other.

The listed embodiments of the solar ray concentrator do not limit the invention in any way and are given to illustrate the variety of possible designs and properties of a fundamentally new type of solar ray concentrator based on the use of spatial holograms and the effect of total reflection.

The solar ray concentrator, when designed according to the invention, allows higher concentration levels to be achieved compared to existing concentrators based on a prism with total reflection. The method of manufacturing the concentrator according to the invention makes it possible to obtain solar ray concentrators with a wide range of spectral selectivity, from narrow-band filter concentrators with a spectral range of a few nanometers to concentrators that have practically no spectral selectivity. The separate concentration of different spectral ranges on different exit surfaces allows one concentrator to simultaneously use several selective receivers for light radiation with sensitivity maxima at different wavelengths. This significantly increases the efficiency of the concentrator and expands its application possibilities. The concentrator is very simple in construction, has the smallest possible number of components and is very reliable in operation. Its manufacturing process is characterized by the absence of processes with labor-intensive mechanical processing and involves only a small number of operations that require only a short time (about a few minutes) to perform.

Claims (12)

1. Solar ray concentrator in the form of a prism with surfaces for entry, reflection and exit of rays, characterized in that a material layer ( 5 ) with a spatial hologram produced therein is arranged on the entry surface ( 2 ) and/or on the reflection surface ( 3 ), which is of the transmission type on the entry surface ( 2 ) and of the reflection type on the reflection surface ( 3 ), the hologram arranged on the entry surface ( 2 ) being constructed in such a way that the radiation to be concentrated is introduced into the prism at an angle which is greater than the critical angle of total reflection which the prism would have without a material layer containing a hologram. 2. Solar ray concentrator according to claim 1, characterized in that the angle ( φ &min;) between the entrance surface ( 2 ) and the reflection surface ( 3 ) corresponds to at least half the angle value which represents the angle difference between the Bragg angle and the angle of minimum diffraction effectiveness. 3. Solar ray concentrator according to claim 1, characterized in that in a prism ( 1 ) provided with a hologram on only one side, the parameters of the hologram are selected such that the radiation in the prism ( 1 ) spreads parallel to the surface which is opposite to that on which the hologram is located. 4. A solar ray concentrator according to claim 1, with a prism in the form of a parallelepiped, characterized in that the spatial hologram has an irregular structure to prevent diffraction of a beam propagating within the prism which is reflected by the hologram/air interface. 5. Solar ray concentrator according to one of claims 1 to 4, characterized in that the spatial hologram is designed in multiple layers and each layer contains information about a light source with a wavelength different from the wavelengths of the light sources used in the production of the holograms in the other layers. 6. Solar ray concentrator according to claim 5, characterized in that the number of layers of the spatial hologram is equal to the number of exit surfaces ( 4, 4' ) and the structure of the hologram of each layer is selected taking into account the direction of radiation onto the corresponding exit surface ( 4 or 4' ). 7. Method for producing a solar ray concentrator according to claim 1 with recording of an interference image in a light-sensitive layer from a reference and an object beam of a laser radiation, characterized in that the light-sensitive layer ( 5 ) is applied to the entrance surface ( 2 ) and/or to the reflection surface ( 3 ) of a prism ( 1 ) and the recording of the interference image takes place by directing the reference beam ( 6 ) in the direction of the radiation to be concentrated and the object beam ( 7 ) at the critical angle of total reflection ( R ) against air of the materials of the light-sensitive layer ( 5 ) and the prism ( 1 ). 8. Method according to claim 7, in which a prism with a trapezoidal base is used, characterized in that a light radiation with a flat wave front is used as the object beam ( 7 ) and is directed onto one of non-parallel prism surfaces which are selected as entrance and reflection surfaces ( 2 and 3 respectively). 9. Method according to claim 8, characterized in that the entrance angle ( R ) for the reference beam ( 7 ) in the prism ( 1 ) is selected according to the formula R &min; ≤ β + 2 φ &min; m , where
R &min; the angle of incidence of the object beam on the entrance surface ( 2 ) of the prism ( 1 ), β is the critical angle for total reflection at the prism/air interface, φ &min; is the angle between the entrance surface ( 2 ) and the reflection surface ( 3 ) of the prism ( 1 ) and m is the maximum number of multiple reflections of a beam of radiation to be concentrated within the prism ( 1 ).
10. Method according to claim 7, in which a prism with a rectangular base is used, characterized in that a light radiation with a diverging wave front is used as the object beam ( 7 ), the source (P) of which is arranged in such a way that a section on the hologram/air interface between the entry point of a beam and the point of its first reflection from the hologram/air interface is visible at the point of the above-mentioned first reflection at an angle corresponding to at least the angle amount representing the angular difference between the Bragg angle and the angle of minimum diffraction effectiveness. 11. A method according to claim 7, characterized in that at least one more photosensitive layer is applied to the first photosensitive layer and an interference image is recorded on each of the layers, for which purpose use is made of a light source with a wavelength different from the wavelengths of the light sources used to record the interference images on the other layers and the values of the wavelengths for all light sources are selected taking into account the absence of the effect of cross modulation. 12. Method according to claim 11, characterized in that the number of layers of the spatial hologram is selected according to the number of exit surfaces of the concentrator and an interference image is recorded in each layer by directing the object beam ( 7 ) in the direction of an exit surface corresponding to the respective layer.