JP2008077044A - Display apparatus, hologram reproducing apparatus and apparatus utilizing hologram - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel display apparatus, a hologram reproducing apparatus and an apparatus that utilizes holograms, using laser irradiation in a wavelength band equal to or longer than 190 nm and shorter than 380 nm. <P>SOLUTION: The display apparatus includes a display device 1190 having a layer constructed by including an alkali halide or alkaline earth halide of which the optical characteristics are changed by laser irradiation of a first wavelength region equal to or longer than 190 nm shorter than 380 nm; a first light source 1191 for emitting a laser beam 1192 of the first wavelength region, in order to write display data in the display device 1190; and a second light source for irradiating the display device 1190, in which the display data are written, with light of a second wavelength region in the range of 380 nm to 800 nm. The display device has a plurality of layers comprising materials having absorption peak wavelengths different from one another, and the first light source and the second light source are constituted by a single light source variable in wavelength. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a display device, a hologram reproducing device, and a device using a hologram. The present invention also relates to a hologram reproducing apparatus that can be used as a three-dimensional (hereinafter referred to as 3D) stereoscopic display.

  A cathode chromic storage tube called a dark trace tube is known as a display using an alkali halide or the like. The dark trace tube directly observes a colored image by an electron beam.

Patent Document 1 (Japanese Patent Laid-Open No. 2000-206858) also discloses a hologram reproducing apparatus using an electron beam.
JP 2000-206858 A

  When an electron beam is used, the inside of the display element that forms the hologram interference fringes needs to be a vacuum system.

  In addition, alkali halides and alkaline earth halides are electrically insulating materials, and by irradiating with an electron beam, charges are accumulated in a display element that is manually configured using the materials, and so-called charge-up may occur. .

  Therefore, the present invention provides a novel display device, a hologram reproducing device, and a device using a hologram using laser irradiation in a wavelength band of 190 nm or more and less than 380 nm.

A display device according to the first aspect of the present invention includes:
A display element having a layer configured to contain an alkali halide or an alkaline earth halide whose optical properties are changed by laser irradiation in a first wavelength region of 190 nm or more and less than 380 nm;
A first light source that outputs a laser in the first wavelength region to write display data to the display element;
A second light source for irradiating the display element in which the display data is written with light in a second wavelength region of 380 nm to 800 nm;
It is characterized by having.

The hologram reproducing apparatus according to the second aspect of the present invention is
A display element including an alkali halide or an alkaline earth halide whose optical properties change by laser irradiation in a first wavelength region of 190 nm or more and less than 380 nm;
Writing means for writing hologram interference fringes on the display element by laser irradiation in the first wavelength region;
Means for irradiating the hologram interference fringes with readout light in a second wavelength region having a wavelength region of 380 nm or more and 800 nm or less to reproduce a hologram three-dimensional image;
It is characterized by comprising.

  The hologram interference fringes can be formed by writing dot data to the display element based on hologram data.

  Further, by switching the pixel size based on the dot data, it is possible to switch between stereoscopic display and non-stereoscopic display.

A hologram reproducing apparatus according to a third aspect of the present invention is
The first, second, and third layers that are made of alkali halide or alkaline earth halide and whose optical characteristics are changed by laser irradiation in the first wavelength region having a wavelength region of 190 nm or more and less than 380 nm are laminated. Having a display element;
The first, second, and third layers are different from each other in absorption wavelength peak in a state in which optical characteristics are changed by laser irradiation in the first wavelength region,
The absorption wavelength peaks of the first, second, and third layers are 380 nm to 500 nm, 500 nm to 600 nm, and 600 nm to 800 nm, respectively.
Writing means for writing hologram interference fringes on the display element by laser irradiation in the first wavelength region;
The display element on which the hologram interference fringes are written has a reproducing means for irradiating readout light to reproduce a hologram three-dimensional image.

The apparatus using the hologram according to the fourth aspect of the present invention is:
A volume hologram recording medium comprising an alkali halide or an alkaline earth halide whose optical properties are changed by laser irradiation in a first wavelength region of 190 nm or more and less than 380 nm;
A first light source for irradiating the volume hologram recording medium with laser light in the first wavelength region;
A second light source for irradiating the volume hologram recording medium with readout light in a second wavelength region of 380 nm to 800 nm;
The volume hologram recording medium and the first light source are relatively three-dimensionally scanned,
A volume hologram interference fringe based on bit data is formed on the volume hologram recording medium.

  The volume hologram recording medium is composed of a plurality of layers made of an alkali halide or an alkali halide earth, and the optical characteristics of the plurality of layers are changed by laser irradiation in the first wavelength region, and the optical characteristics It is also possible to make the absorption wavelength peaks different in the state where is changed.

  The present invention has the following features.

  Specifically, the hologram reproducing apparatus of the present invention is configured using an alkali halide or alkaline earth metal whose optical characteristics are changed by laser irradiation in a first wavelength region having a wavelength region of 190 nm or more and 380 nm or less. Means for writing, on the display surface, hologram interference fringes based on hologram data by laser irradiation of the first wavelength region as dot data, and readout light of the second wavelength region having a wavelength region of 380 nm to 800 nm on the hologram interference fringe And a means for reproducing a hologram three-dimensional image.

  Further, in the present invention, the optical characteristics are changed by laser irradiation of the first wavelength region having a wavelength region of 190 nm or more and 380 nm or less, the absorption wavelength peak in the state where the optical property is changed is 380 nm or more and 500 nm or less, and the absorption wavelength peak is 500 nm. More than 600 nm and an absorption wavelength peak of 600 nm or more and 800 nm or less, each display surface of the laminated display surface in which display surfaces made of three kinds of alkali halides or alkaline earth halides are laminated, Means for writing hologram interference fringes based on hologram data by laser irradiation with different dot intervals, and a wavelength peak selected from a second wavelength region having a wavelength region of 308 nm to 800 nm in the hologram interference fringes 380 nm to 500 nm, wavelength peak 00nm or 600nm or less, is characterized in that it comprises a means for reproducing the hologram stereoscopic image peak wavelength is irradiated with reading light of a wavelength 800nm or 600nm.

  Furthermore, the present invention relates to a volume hologram recording medium using an alkali halide or an alkaline earth halide whose optical characteristics are changed by laser irradiation in a first wavelength region having a wavelength region of 190 nm or more and 380 nm or less, and the recording medium And a means for forming a volume hologram interference fringe based on bit data on the display surface of the recording medium by relatively three-dimensionally scanning dot positions of the laser light in the first wavelength region, and the volume hologram interference fringe And a means for performing readout by irradiating readout light in a second wavelength region having a wavelength region of 380 nm or more and 800 nm or less.

  Further, in the present invention, the optical characteristics are changed by laser irradiation of the first wavelength region having a wavelength region of 190 nm or more and 380 nm or less, the absorption wavelength peak in the state where the optical property is changed is 380 nm or more and 500 nm or less, and the absorption wavelength peak is 500 nm. A volume hologram recording medium on which display surfaces made of three kinds of alkali halides or alkaline earth earths having an absorption wavelength peak of 600 nm or more and 600 nm or less and 800 nm or less are laminated, the recording medium, and the first wavelength region Means for relatively three-dimensionally scanning the laser light irradiation position of the recording medium to form volume hologram interference fringes based on bit data at different interference fringe pitches on each display surface of the recording medium; The wavelength peak selected from the first wavelength region is not less than 380 nm and not more than 500 nm. Click is 500nm or 600nm or less, it is characterized in that it comprises a means for reading wavelength peak was irradiated with reading light of a wavelength 800nm or 600nm.

  ADVANTAGE OF THE INVENTION According to this invention, the novel display apparatus, the hologram reproduction apparatus, and the apparatus using a hologram are provided.

  First, the background that led to the present invention will be described. As a result of diligent research, the inventor of the present application has applied laser irradiation in a first wavelength region having a wavelength region of 190 nm or more and 380 nm or less to a material made of alkali halide or alkaline earth halide (because the wavelength region is in the ultraviolet region). In the following, the optical characteristics may be changed due to abbreviated as “ultraviolet laser”), which led to the recognition that the change state of the material is relatively stable.

  And, using the alkali halide or alkaline earth halide, recognizing that it is possible to realize a highly useful new display device and hologram reproducing device by utilizing reversibility with respect to changes in optical properties. The present invention has been achieved.

(First embodiment: display device)
The display device (FIG. 9) according to this embodiment has the following features. First, a display element 1190 including a layer including an alkali halide or an alkaline earth halide whose optical characteristics are changed by irradiation with a laser 1192 in a first wavelength region of 190 nm to less than 380 nm is provided.

  Here, with respect to the material constituting the layer, the contents described in the later-described embodiments are applied as they are.

  Further, in order to write display data to the display element, the first light source 1191 that outputs the laser 1192 in the first wavelength region and the display element in which the display data is written are 380 nm to 800 nm. The second light source (not shown) for irradiating light in the second wavelength region is provided to constitute the display device according to this embodiment.

  Here, regarding the first and second light sources, the contents described in the later-described embodiments are applied as they are.

  Although the second light source is not illustrated in FIG. 9, the second light source may be provided on the same surface side as the first light source with respect to the display element 1190 or on the opposite side.

  The display element in the present embodiment includes at least the following two concepts.

a first concept, that is, an image or character data is written by the first light source on a display element comprising a specific material such as an alkali halide, and the light having the second wavelength band In this case, the light is incident on an element and the display element is used as a filter.

  In this case, whether the incident light is transmitted or not varies depending on whether or not the position is written by the first light source. By utilizing such a phenomenon, the display element can be used as a light modulation element for displaying a non-stereoscopic image as in a liquid crystal display.

  In addition, although the use as transmission (so-called transmissive display device) has been described in the case where transmission of incident light is used, the display element according to the present invention can also be applied to a reflective display device.

b Second concept This is a case where a three-dimensional image display is realized by inputting readout light to the display element.

  In the following embodiments, a detailed description is given regarding displaying a stereoscopic image using a hologram. However, the present invention is not necessarily limited to a display device using a hologram.

(Second Embodiment: Hologram Reproducing Device)
The hologram reproducing apparatus will be described. FIG. 1 shows a display surface 1 of a display element including an alkali halide or an alkaline earth halide whose optical characteristics are changed by irradiation with a laser 2 in a first wavelength region of 190 nm or more and less than 380 nm.

  An ultraviolet laser irradiation means 4 is shown for performing laser 2 irradiation in the first wavelength region. As the ultraviolet laser irradiation means 4, a gas laser such as an excimer laser or a solid-state laser using a semiconductor can be applied.

  Hologram interference fringes 3 are written on the display element by irradiation with the laser 2 in the first wavelength region.

  The hologram interference fringes 3 are irradiated with the readout light 5 in the second wavelength region having a wavelength region of 380 nm or more and 800 nm or less to reproduce a hologram three-dimensional image. For example, the reading light 5 irradiates the hologram interference fringe 3 with a visible laser included in the above-described wavelength range through a magnifying lens 9 used as necessary. In this way, a hologram reproduction stereoscopic image 6 is obtained as shown in FIG.

  The hologram interference fringes herein can be written as dot data on the display element by the ultraviolet laser irradiation means 4 based on hologram data input from the outside (or previously input) to the apparatus.

  Of course, the hologram reproducing apparatus can be provided with an erasing means for erasing the hologram interference fringes.

  The hologram stereoscopic image can be continuously reproduced by repeating the hologram interference fringe writing step by the writing means, the hologram stereoscopic image reproducing step by the reproducing means, and the hologram interference fringe erasing step by the erasing means. .

  The erasing method is not particularly limited, and may be performed by applying laser irradiation, electromagnetic waves, or heat to the display element.

  When erasing by laser irradiation, a laser light source having a wavelength of 700 nm or more is used. Note that the writing laser light source, the reproducing light source, and the erasing light source can be realized by a single light source as long as they are variable light sources.

  As shown in FIG. 1, the irradiation of the readout light 5 in the second wavelength region can be performed from the same surface side as the laser irradiation in the first wavelength region on the display element. In addition, the writing unit 4 can form the hologram interference fringes on a virtual plane defined in the depth direction of the display element.

  Furthermore, it is possible to switch between stereoscopic display and non-stereoscopic display by switching the pixel size written by the dot data (details will be described later).

  Next, the best mode for carrying out the invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a configuration of an embodiment of a hologram reproducing apparatus according to the present invention. The volume hologram reproduction according to the present invention will be described later.

  In the figure, reference numeral 1 denotes a display surface whose optical characteristics are changed by ultraviolet laser irradiation. The ultraviolet laser irradiation means 4 condenses the ultraviolet laser 2 on the display surface 1 and radiates the luminance modulation while performing two-dimensional scanning according to the digital hologram data, and writes the hologram interference fringes 3 necessary for reproducing the three-dimensional image. A method for creating digital hologram data will be described later.

  The readout light irradiation means irradiates the hologram interference fringe 3 written on the display surface 1 with the readout light 5 in the second wavelength region having a wavelength region of 380 nm or more and 800 nm or less to reproduce the hologram reproduction stereoscopic image 6. is there. The display surface 1 is configured using an alkali halide or an alkaline earth halide.

  The reading light irradiating means includes a visible laser 7 and a magnifying lens 9 that magnifies and irradiates the visible laser beam emitted from the visible laser on the display surface 1. As the reading light irradiation means, white light can also be used in order to devise the hologram.

  Here, the wavelength of the ultraviolet laser 2 is 380 nm or less, which is shorter than the visible wavelength of human beings, preferably 360 nm or less, which is defined as an ultraviolet region in the international unit system (SI). Further, the wavelength of 190 nm or less is known as vacuum ultraviolet, and the absorption loss due to the atmosphere increases, and the advantage of the laser with respect to the electron beam cannot be utilized because it is necessary to use a lens system made of a special material because of the relationship between the wavelength and the refractive index.

  Therefore, in the present invention, it is preferable to use an ultraviolet wavelength region of 190 nm or more and 360 nm or less. For example, pulse lasers such as YAG third harmonic (355 nm), YAG fourth harmonic (266 nm), KrF excimer (248 nm), and ArF excimer (193 nm) can be used. Furthermore, an ultraviolet wavelength semiconductor laser or surface emitting laser currently under development can be used.

  The reason for using the laser is that the energy density is high and the beam convergence necessary for writing the hologram is high. The ultraviolet laser irradiation means 4 includes a lens for condensing the ultraviolet laser, an ultraviolet mirror for defining the irradiation position of the ultraviolet laser, a galvano for scanning the ultraviolet laser, a polygon, and the like. If necessary, erasing means 8 for erasing the interference fringes 3 written on the display surface 1 may be provided.

  Next, the digital hologram data described above will be described. This is described in Japanese Patent Laid-Open No. 2000-206858 previously proposed by the present inventor. Digital hologram data is prepared in advance by the following method. Similar to general hologram recording, the object is irradiated with coherent light (waves), and the scattered, reflected, and transmitted light interferes with the reference light.

  As this wave, a laser beam or an electron beam is generally used. For the purpose of the present invention, since it is necessary to record the interference pattern as a binary or multi-value electric signal, an image sensor is used as means for recording the interference pattern. The interference fringes may be taken directly or imaged with a diffusion plate. Alternatively, it is possible to read the light-sensitive material pattern once.

  A general image sensor has a density of several tens of microns per pixel, and an interference pattern is usually several microns or less. Therefore, an interference fringe is enlarged and projected by a magnifying lens or the like. Further, even if an actual object is not used, data called a CG hologram obtained by calculating interference fringes using a computer graphic technique can be used.

  FIG. 2 shows a state in which hologram interference fringes are displayed. As shown in FIG. 2, an ultraviolet laser 2 is irradiated on the display surface 1 by an ultraviolet laser irradiation means 4 to form dot-shaped color centers in the alkali halide constituting the display surface 1. That is, the luminance modulation of the ultraviolet laser 2 is performed by the ultraviolet laser irradiation means 4 while performing two-dimensional scanning according to the digital hologram bit data, thereby forming the hologram interference fringes 3 composed of dot groups.

  FIG. 3 shows a state of hologram reproduction. As shown in FIG. 3, the hologram reproduction three-dimensional image 6 is formed by diffracting and interfering the readout light 5 with the hologram interference fringe 3. Further, the hologram interference fringe 3 is returned to the ground state by irradiation of the laser beam or heating by the erasing means 8, and the hologram reproduction three-dimensional image is continuously reproduced by repeating the display of the hologram interference fringe and the reproduction of the hologram reproduction three-dimensional image again. Of course, the same applies to color display.

  Here, for the digital hologram display surface 1 of the present invention, a material composed of a combination of the following cations and anions is used as an alkali halide or alkaline earth halide.

  The cation is one or more kinds of cations among lithium, sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, and radium. As an anion, the salt which consists of a combination with 1 or more types of anions among fluorine, chlorine, bromine, iodine, and astatine can be used.

  Moreover, the mixture which consists of said several cation and several anion can also be used. Further, a perhalogenate salt by a combination of a perchlorate anion or a perbromate anion and an alkali or alkaline earth cation can also be used. Hereinafter, these are collectively referred to as substances having a color center.

  Since the substance having the color center has no optical absorption in the visible wavelength region, the single crystal is generally colorless and transparent. A substance having a color center is colored at a site irradiated with an ultraviolet laser, and at the same time, the refractive index changes in a specific wavelength region.

  It is a readout light including this coloring wavelength / refractive index change wavelength region (generally referred to as a visible laser beam for reproduction since a coherent laser beam is used). Further, in the region not irradiated with the ultraviolet laser, there is no absorption and refractive index change in the visible region, and it is transparent or white and has high laser light transmittance / reflectance. By utilizing this property as a diffraction filter for visible laser light for reproduction and by forming an appropriate hologram interference fringe 3 shape, it is possible to reproduce a hologram reproduction stereoscopic image.

  It is described that a substance having a color center generates excitons (a pair of electrons and holes) when irradiated with an ultraviolet laser, and the electrons are trapped in the trap level to become a color center. In other words, the color center is described in “Optical Physical Property Handbook” (pages 228 and 398).

  FIG. 4A and FIG. 4B are diagrams showing the coloring principle of a substance having a color center in terms of structure and energy. The coloring mechanism is said to be due to the fact that electrons are trapped in the halogen vacancies of the ionic crystal as shown in FIG.

  In terms of energy, there is a trap level between the conduction band and the valence band as shown in FIG. 4B, and electrons are excited from the valence band to the trap level by an electromagnetic wave such as an ultraviolet laser ( Hereinafter, this is referred to as primary excitation, and a state in which electrons are excited in the trap level is referred to as an excited state). The lifetime of electrons in this trap level is characterized by being relatively long at temperatures near room temperature.

  The trapped electrons are re-excited from the trap level to the conduction band by visible light (laser) or by heat (hereinafter referred to as secondary excitation), and then return from the conduction band to the valence band. At the same time, the color disappears.

  Such a coloring phenomenon is applied to a dark trace tube using an electron beam. A dark trace tube irradiates an alkali halide with an electron beam, colors it, and directly observes it. In the dark trace tube, since the colored part is directly observed, the spot diameter of the electron beam is large.

  On the other hand, in the invention according to this embodiment, an ultraviolet laser is used as means for forming the color center.

  Further, instead of displaying an image to be observed directly on the display surface, a hologram interference fringe is displayed. Therefore, the ultraviolet laser spot diameter is small, and image formation can be performed by applying not only the ultraviolet laser but also reading light, erasing light or heat to the display surface.

  A general phosphor can also be excited by an ultraviolet laser from the valence band, which is the ground level, to the conduction band or trap level, which is the excitation level, but has a short lifetime at the excitation level near room temperature. Many. Furthermore, the purpose of using fluorescent light, which is a general phosphor, is that there is no change in the color itself, or even if there is a change in color, it is not used as a filter.

  In general phosphors, electrons are released by thermal motion / diffusion at the excitation level and return to the ground state while emitting fluorescence, and the excitation (fluorescence) lifetime is short.

  The display surface of the present invention is characterized in that the excited state is thermally stable and continues to maintain a colored state until an ultraviolet laser irradiation for one frame and visible laser light for reproduction (and further erase light) are applied. To do.

  In the present invention, an alkali halide or earth alkali which is colorless and transparent or white in the ground state is used.

  As described above, the present invention is such that a substance having a color center such as an alkali halide or an alkaline earth halide is colored at a site irradiated with an ultraviolet laser, and the transmittance of visible laser light for reproduction of this colored wavelength is obtained. The reflectivity is low, and the refractive index changes at the same time. On the other hand, in the region not irradiated with the ultraviolet laser, there is no absorption in the visible region, it is transparent or white, the laser has high transmittance and reflectance, and there is no change in refractive index.

  Utilizing this fact, this is used as a reproduction visible laser light filter or a spatial optical modulator (SLM), and a hologram hologram image is reproduced by forming an appropriate hologram interference fringe shape.

  Absorption in the visible wavelength region in the ultraviolet laser excited state is thought to be due to (re) excitation from the trap level to the valence band by light of a wavelength corresponding to the energy gap between the trap level and the valence band. ing. The display surface made of a material having a color center in the present invention functions as a filter for reproducing visible laser light, and displays an appropriate hologram interference fringe shape, thereby reproducing and reproducing the hologram by diffracting and interfering with the reproducing visible laser light. To do.

  Further, as the reading light irradiating means, one that irradiates reading light with wavelengths of three colors R, G, and B is used. Further, as a UV laser irradiation means, a plurality of hologram interference fringes having different spectral absorption changes and / or refractive index changes in specific wavelength ranges and / or different hologram interference fringe pitches corresponding to each of the three colors of readout light are written. Is used. Thus, simultaneous reproduction of the three primary color hologram images can be performed.

  A surface coating treatment may be applied to the outside of the display surface to prevent moisture and scratches. In addition, a substance having a color center can be formed on the surface of a transparent substrate such as glass, and the glass surface can be used as the outside to prevent moisture and scratches.

  There are a transmissive arrangement in which the reproduction light is opposite to the reading light irradiation and a reflection arrangement in which the reproduction light is on the same side with respect to the reading light irradiation. As the hologram erasing means, a device that erases hologram interference fringes by applying light, electromagnetic waves, or heat can be used.

  Further, the present invention will be described in detail. An object of the present invention is to provide a stereoscopic display that continuously reproduces a transmittable image without using a master that causes image quality degradation based on the principle of hologram. The present invention relates to a three-dimensional display (hologram continuous reproduction apparatus), that is, a reproduction apparatus.

  At the time of imaging, the object is irradiated with coherent (coherent) light (waves) as in general hologram recording, and the scattered, reflected, and transmitted light interferes with the reference light. As this wave, a laser beam or an electron beam is generally used. For the purpose of the present invention, it is necessary to record the interference pattern as a binary or multi-value electric signal, and therefore an image sensor is used as means for recording the interference pattern. A hologram interference fringe may be directly photographed or formed with a diffusion plate. Alternatively, the light-sensitive pattern of the photosensitive material may be enlarged and read once.

  When photographing hologram interference fringes directly, the linearity with respect to the spectral sensitivity and light intensity of the image sensor is taken into consideration, as in general photography. Since a general imaging device has a density of several tens of microns per pixel and an interference pattern is usually several microns or less, hologram interference fringes are magnified and recorded by a magnifying lens or the like.

  In addition to the above method, as a method not using an actual object, CGH (computer generated hologram) data obtained by calculating hologram interference fringes using a computer graphic method can be used.

  The interference pattern obtained by the above-described known method is subjected to image processing or electrical transmission, and the position of the ultraviolet laser and the hologram display surface are relative to each other as an ultraviolet laser deflection signal or irradiation coordinate signal and an ultraviolet laser output modulation signal. Then, scanning and intensity modulation are performed to irradiate the hologram display surface. As a scanning method of the ultraviolet laser, a scanning method (raster scanning) is generally performed in which the luminance (intensity) modulation of the ultraviolet laser is performed while scanning in the main scanning direction X and sequentially shifting in the sub-scanning direction Y orthogonal thereto. .

  Alternatively, it is possible to modulate the intensity (intensity) of the ultraviolet laser while moving the display surface and shifting the position relative to the ultraviolet laser. For luminance modulation of the ultraviolet laser, control of an input signal (voltage, current, pulse width, etc.) to the laser, or a mechanical blanking technique such as a galvano mirror or TI DLP can be used.

  The display surface is characterized in that its physical properties are changed by an ultraviolet laser to diffract light. That is, the display resolution is preferably equal to the wavelength of visible light, that is, 20 microns or less, particularly 1 micron or less. The ultraviolet laser is capable of condensing to 1 micron or less using a high NA ultraviolet lens and scanning the scanner or stage with high accuracy. Light can be diffracted by forming interference fringes formed of light transmittance or refractive index change on the display surface.

  Holograms are mainly classified into two types: amplitude type and phase type. The amplitude type includes silver salt films and photochromic materials, and the theoretical diffraction efficiency is 6.25%. Phase types include dichromated gelatin and polymer liquid crystal, and the theoretical diffraction efficiency is 34%.

  A substance having a color center is used as a substance capable of causing such a physical property change by an ultraviolet laser.

  For a substance having a color center, as described above, an ultraviolet laser having a first wavelength used for excitation for forming a color center, and a visible light for reproduction having a second wavelength that is irradiated and diffracted in this excited state. Acts with laser light. Then, if necessary, excitation light or heat of the third wavelength is applied to irradiate the excited state and return to the ground state. This third excitation light is generally longer in wavelength than the visible visible laser light. In addition, when the period of continuous reproduction is long, it is preferably erased by heating.

  Since conventional televisions display images directly on the display surface, a display resolution that is about the resolution of the human eye is sufficient. In the present invention, the hologram interference fringes that can diffract light are displayed on the display surface, and display with higher resolution than the conventional cathode ray tube phosphor is required. In the present invention, a display surface having a display resolution of about 1 micron using a substance having a color center is preferable. The color center is one in which one electron is trapped in the halogen defect lattice of the ionic crystal as described above, and therefore the resolution of the display surface using this is very high in the order of tens of angstroms in principle. The display resolution of the hologram depends on the ultraviolet laser to be exposed.

  As the ultraviolet laser, a pulse laser such as a single mode YAG third harmonic (355 nm), YAG fourth harmonic (266 nm), KrF excimer (248 nm), or ArF excimer (193 nm) can be used as appropriate. Furthermore, a semiconductor laser or a surface emitting laser in the ultraviolet wavelength region such as an aluminum nitride system currently under development can be used. The ultraviolet laser can focus the spot diameter to 10 μm to 1 μm or less using a high NA ultraviolet objective lens.

  A substance having a color center has different transmittance, reflectance, and refractive index in a specific wavelength region between a portion excited by an ultraviolet laser and a ground state portion. Therefore, it is necessary to consider not only the pitch of the hologram interference fringes but also the wavelength of the visible laser beam that is the hologram reproduction light. For example, rubidium chloride absorbs near 640 nm and corresponds to the wavelength of the helium-neon laser. ing.

  The change in transmittance depends on the ultraviolet laser energy density, pulse width, number of pulses, and repetition frequency, but in the above-mentioned example of rubidium chloride, the reflectance at 640 nm is about 50% to 80% compared to before ultraviolet laser excitation. Sufficient contrast can be obtained. Even in the transmittance, a change of about 50% to 80% is recognized compared with that before the excitation with the ultraviolet laser. At the same time, the refractive index is changed, and the hologram of the present invention is an amplitude / phase hybrid type, so that high diffraction efficiency can be realized.

  As a display surface for reproducing a hologram, mechanical strength, ultraviolet laser shock resistance, environmental stability, and the like are required as in a general television. Some of the alkali halides mentioned above are not very hard or have high hygroscopicity, so surface coating is applied to the alkali halide, or an alkali halide is formed on the glass substrate and the glass substrate surface is directed to the outside. It is preferable. The ultraviolet laser is desirably exposed from the alkali halide surface side.

  Since coloring by the ultraviolet laser is derived from a micro ionic crystal structure, the crystal used for the display surface does not need to be a single crystal or a molten single crystal, and may be a polycrystal or a powder. Single crystallization eliminates scattering and provides a transparent display surface in the visible wavelength range, so that it can be used as a transmission type.

  In the case of a reflection type hologram reproducing apparatus that utilizes diffraction / interference of laser reflected light from the display surface, the substrate does not have to be transparent, and an alumina or silicon substrate can also be used. Depending on whether the hologram continuous reproduction apparatus is a transmission type or a reflection type, the crystal transparency can be controlled by a method for producing a substance having a color center constituting the display surface and single crystallinity.

  In such a single crystal, it is possible to improve the transparency by applying a smoothing process in the polishing step to obtain an optical element. However, the remaining surface roughness and surface scattering may cause problems. In addition, Fresnel reflection is unavoidable for light incident on an interface having a different refractive index on the surface, and may be observed as noise light with respect to diffracted light from a hologram.

  In such a case, it is preferable to display the hologram not on the surface but on a virtual surface having a constant depth. In order to realize this, it is desirable to collect light with a lens having an NA of 0.3 or more and a focal depth of 10 μm or less in consideration of the wavelength of the ultraviolet laser and the hologram bit size.

  By focusing on the inside of the display surface using this lens and exposing with the ultraviolet laser while moving the display surface relative to the ultraviolet laser, a hologram can be formed on a virtual surface with a constant depth.

  As a method for forming a crystal on a substrate, crystallization by evaporation of a solvent from a concentrated solution, formation of a molten salt, and various coating methods of a solution can be used. Moreover, polyvinyl alcohol etc. can be added as needed, and the coating property to a board | substrate and adhesive strength can also be improved. In addition, various additives can also be used. Alternatively, a substance having a color center can be formed on the substrate by vapor deposition.

  When the material having the color center is formed on the substrate in this way, the substrate is directed to the outside (outside) of the hologram reproducing apparatus so that the material having the color center does not cause mechanical defects or defects due to moisture absorption. At the same time, it is preferable that the ultraviolet laser is directly applied.

  Furthermore, in the case of colorization, it is necessary to make the absorption wavelength correspond to the three primary colors of R, G, and B. For example, lithium bromide and calcium chloride are yellow and absorb blue laser light, potassium chloride and the like are red and absorb green laser, and cesium bromide and the like are blue and absorb red laser. If these are mixed, the laser light of each wavelength can be absorbed independently, and the transmittance and reflectance can be changed.

  When substances having three kinds of color centers are mixed, substances having three kinds of color centers are mixed on the display surface, but each particle size is fine and at least one third of the beam diameter of the ultraviolet laser. It is as follows. Therefore, three kinds of substances are colored simultaneously in the ultraviolet laser beam.

  However, among the R, G, and B visible laser beams for reproduction, only one type of material has the uniqueness that satisfies the diffraction condition for light of one wavelength. For example, in the case of the color display surface of Example 4 described later, the 633 nm laser beam is transmitted through the hologram interference fringes of potassium bromide and potassium fluoride, and is absorbed only by the hologram interference fringes formed in rubidium chloride. Diffracted.

  Also, the 633 nm light diffracted only when the pitch of the hologram interference fringes satisfies the interference condition interferes to form a hologram reproduction stereoscopic image. In reality, the color resolution of a substance having three types of color centers is not perfect, and it is difficult to completely separate the interference condition from the resolution of the ultraviolet laser, and optical noise is generated.

  The first object of the present invention is stereoscopic display, but it can also be applied to non-stereoscopic display. Hologram interference fringes when performing stereoscopic display are Fourier-transformed and have a high spatial frequency, and thus cannot be recognized as a significant image even if they are directly observed by humans.

  In the present invention, non-stereoscopic display is also possible by expanding the colored portion to a spot diameter that can be directly observed using a stereoscopic display ultraviolet laser.

  As described above, since the alkali halide is colored itself, it is commercialized as a display called a dark trace tube. Even in the present invention, it is obvious that it can be used as a non-stereoscopic display by increasing the pixel size.

  In addition to using an ultraviolet laser instead of the electron beam of the dark trace tube, in the present invention, the pixel size (dot) is reduced when used as a three-dimensional display. Further, when used as a non-stereoscopic display, the pixel size is increased to such a level that a human can visually recognize it.

  Since the pixel size that can be visually recognized by humans is said to be about 2400 dpi in binary display, any pixel size of 10 μm × 10 μm or more can be recognized as an image. Thereby, 3D or 2D can be switched and displayed.

  As a method of switching the pixel size, for example, the laser output of the ultraviolet laser irradiation means 4 in FIG. 1 is changed, the scanning speed at the time of writing the hologram interference fringe is changed, or the pulse laser is used to change the ultraviolet laser irradiation energy density. There are ways to change it. As described above, when switching to a pixel size of 10 μm × 10 μm or more, if the laser output of the ultraviolet laser irradiation means 4 is increased, the scanning speed at the time of writing the hologram interference fringes is decreased, or the ultraviolet laser irradiation energy density is increased. good.

  Further, by stacking alkali halide display surfaces corresponding to the three primary colors of RGB, aligning the laser focal point on one of the stacked display surfaces and forming dots by color center coloring according to non-stereoscopic image data, the color non-coloration is achieved. A stereoscopic image can be displayed.

  The difference from the dark trace tube is that there is no charge-up because no electron beam is used, and no metal back is required. Therefore, in the dark trace tube, the penetration depth of the electron beam is so shallow that it is virtually impossible to multiplex in the thickness direction of the display surface. It is necessary to precisely irradiate the section with an electron beam.

  In the present invention, it is possible to color each layer even if they are stacked. Therefore, a pixel is selected by stacking three types of colored layers and addressing the ultraviolet laser to the (X, Y, Z) coordinates. And can be colored.

  In this case, by using a lens with a high NA and a shallow depth of field, the energy density distribution of the laser can be set high in a narrow range, so that addressing in the thickness direction is easy. In addition, since the laser can be used in the atmosphere as compared with the electron beam used in the vacuum system, the apparatus is simple.

  As described above, the reproduction visible laser beam having a wavelength satisfying the interference condition is irradiated on the entire surface of the hologram interference fringe display surface displayed by the ultraviolet laser scanning. Then, the transmittance and refractive index of the reproducing visible laser beam are different between the portion that is excited and colored by the ultraviolet laser and the portion that is not, and diffraction / interference occurs, and a hologram reproduction stereoscopic image is reproduced. The diffracted light from each point on the display surface is recombined in space and a hologram image can be formed in the same manner as a general hologram, and a stationary stereoscopic image is obtained.

  Depending on the positional relationship between the visible laser beam for reproduction and the display surface, the hologram reproduction stereoscopic image appears differently from the display surface or at the back. However, when the reproduction visible laser light source is positioned opposite to the observer side with respect to the display surface (when the reproduction light has a positional relationship that must pass through the display surface), the display surface uses this reproduction light. Must be transparent to

  A conventional cathode ray tube is an opaque scatterer. However, a material having a color center can be made transparent, which satisfies the above-mentioned requirements. In addition, since the substance having a color center in the present invention has a long excited state life and a stable colored state, a visible laser beam for reproduction is displayed on the entire surface after displaying a hologram interference fringe for one frame with an ultraviolet laser. Can be irradiated.

  In addition, the scanning time required for one frame can be shortened by irradiating an ultraviolet laser whose intensity is modulated from a plurality of ultraviolet laser light sources, rather than scanning with one ultraviolet laser. It is more preferable to use a planar VCSEL ultraviolet laser because scanning is unnecessary. As a multi-ultraviolet laser source, one using a semiconductor has been proposed.

  A substance having a color center may return to the ground state by a reproducing laser beam, but is often not perfect. For example, when some electrons are re-trapped at a level called F ′ center. In that case, it is preferable to irradiate the entire surface with incoherent long wavelength light for erasure. This is erasure by the secondary excitation light described above.

  It is also preferable to promote erasing by raising the display surface to several hundred degrees Celsius if necessary. The erasing speed has a temperature dependency. For example, in the case of potassium bromide crystals, the half-life τ at room temperature is several seconds, less than 1 second at 100 ° C., and several tens of milliseconds at 500 ° C.

  A three-dimensional image can be observed as a moving image by repeating these operations at a constant period. When this period is long, the screen appears to flicker, and the value is generally said to be about 1/30 second. However, in the case of a hologram, it is not necessarily in this range.

  As is apparent from the principle of the substance having a color center in the present invention, coloring is extremely sensitive, and the display and erasing speed is extremely fast. Photochromic substances and electrochromic substances are slow to be colored / decolored because energy and time are required for ion transfer accompanying molecular structure change and oxidation-reduction reaction. On the other hand, the coloring of a substance having a color center is an electron transfer similar to semiconductor switching, so that a high-speed response is possible. Furthermore, it has the characteristic that the repeated durability is very good as well as semiconductor switching.

  As described above, when a color image is displayed by the hologram reproducing device, it can be realized by the following configuration.

  First, a first layer, a second layer, and a third layer, which are made of an alkali halide or an alkaline earth halide and whose optical characteristics are changed by laser irradiation in a first wavelength region having a wavelength region of 190 nm or more and less than 380 nm, are laminated. A display element is prepared.

  Here, the first, second, and third layers have different absorption wavelength peaks in a state where optical characteristics are changed by laser irradiation in the first wavelength region, and the first, second, and third layers are different from each other. The absorption wavelength peaks in the range of 380 nm to 500 nm, 500 nm to 600 nm, and 600 nm to 800 nm, respectively.

  Then, a writing means for writing a hologram interference fringe on the display element by laser irradiation in the first wavelength region, and a reading light is irradiated on the display element on which the hologram interference fringe is written. By providing a reproducing means for reproducing an image, a hologram reproducing apparatus corresponding to a color image is provided.

  As the readout light, the wavelength peak selected from the second wavelength region having a wavelength region of 380 nm to 800 nm is 380 nm to 500 nm, and the wavelength peak is 500 nm to 600 nm on the display element in which the hologram interference fringes are written. In the following, three kinds of readout light having a wavelength peak of 600 nm or more and 800 nm or less can be used.

  According to the invention of this embodiment, the display surface is configured using an alkali halide or an alkaline earth halide, that is, a substance having a color center. Therefore, the optical characteristics in the visible region are reversibly changed by the ultraviolet laser, and the hologram reproduction stereoscopic image can be continuously reproduced on the display surface having a relatively stable characteristic and a long life after the change.

  In other words, a hologram interference fringe is formed on such a display surface with an ultraviolet laser, and a reproduction stereoscopic laser beam is diffracted and interfered with the hologram interference fringe to reproduce a three-dimensional hologram image. The ground state is restored by heat or infrared laser light irradiation. Then, by repeating the display of the hologram interference fringes and the reproduction of the hologram reproduction stereoscopic image again, the hologram reproduction stereoscopic image can be continuously reproduced.

(Third embodiment: volume hologram)
Next, the volume hologram reproducing apparatus according to the present invention will be described. The reproduction of the volume hologram according to the present invention is preferable for realizing a high-quality and high-contrast hologram reproduction stereoscopic image because the diffraction efficiency is higher.

  In the case of volume hologram reproduction, as shown in FIG. 1, the ultraviolet laser 2 is focused on the display surface 1 whose optical characteristics are changed by the ultraviolet laser irradiation means 4. At this time, luminance modulation irradiation is performed while two-dimensional scanning is performed according to digital hologram data, and hologram interference fringes 3 necessary for stereoscopic image reproduction are written. Since the configuration of the display surface 1 is the same as that in the case of the hologram reproduction, a detailed description is omitted.

  The volume hologram can be used not only as an image display device but also as an information recording / reproducing device.

  The volume hologram means a hologram recorded three-dimensionally on a relatively thick recording medium. For example, the hologram described in the first embodiment is recorded as f (x, y) data in a two-dimensional plane, whereas in the present embodiment, it is recorded as f (x, y, z) data. It is different in point.

  The reading light irradiating means irradiates the hologram interference fringe 3 written on the display surface 1 with the reading light 5 in the second wavelength region having a wavelength region of 380 nm or more and 800 nm or less to form a hologram reproduction stereoscopic image 6.

  As the reading light irradiating means, a visible laser 7 and a magnifying lens 9 for magnifying and irradiating the visible laser beam emitted from the visible laser beam on the display surface 3 are usually used. As the reading light irradiation means, it is possible to use white light by adding a device to the hologram.

  The wavelength of the ultraviolet laser 2 is the same as described in the case of hologram reproduction, and is 380 nm or less, which is not more than the visible wavelength of human beings, particularly preferably 360 nm or less defined as the ultraviolet region in the international unit system (SI). On the other hand, when the wavelength is 190 nm or less, it is known as vacuum ultraviolet, and the absorption loss due to the atmosphere increases, and the advantage of the laser with respect to the electron beam cannot be utilized because it is necessary to use a lens system made of a special material because of the relationship between wavelength and refractive index. Therefore, an ultraviolet wavelength region of 360 nm or less and 190 nm or more is particularly preferable.

  In the case of volume hologram reproduction, the ultraviolet laser irradiation means 4 is composed of a lens for condensing the ultraviolet laser. Further, it is composed of an ultraviolet mirror for defining the three-dimensional irradiation position of the ultraviolet laser, a galvano or polygon for XY scanning the ultraviolet laser, an XY stage moving means, and a Z moving means. If necessary, an erasing unit 8 for erasing interference fringes written on the display surface may be provided.

  In this configuration, as shown in FIG. 5, a dot-shaped color center is formed on the alkali halide constituting the display surface 1 by irradiating the display surface 1 with the ultraviolet laser 2 by the ultraviolet laser irradiation means 4. Then, the luminance modulation of the ultraviolet laser 2 is performed while three-dimensionally scanning in accordance with the digital hologram bit data to form the volume hologram interference fringes 3 composed of dot groups. Subsequently, as shown in FIG. 3, the hologram reproduction fringe image 6 is formed by diffracting and interfering with the reading light 5 by the hologram interference fringes 3.

  Further, the hologram interference fringe 3 is returned to the ground state by irradiating the laser beam or heating by the erasing means 8, and the hologram reproduction fringe display and the hologram reproduction stereoscopic image reproduction are repeated again, thereby continuously reproducing the hologram reproduction stereoscopic image. Do.

  The materials used for the display surface in the case of volume hologram reproduction according to the present invention are as described above. Similarly, these are collectively referred to as substances having a color center.

  Since a substance having a color center has no optical absorption in the visible wavelength region as described above, a single crystal is generally colorless and transparent. A substance having a color center is colored in a portion irradiated with an ultraviolet laser, and at the same time, the refractive index changes in a specific wavelength region.

  Transmission of reading light of this colored wavelength / refractive index change wavelength (in general, coherent visible laser light is used for reproduction, but white light may be used. Hereinafter, it is referred to as “reproduction light” in volume hologram reproduction). The refractive index changes at the same time as the refractive index / reflectance decreases. And in the site | part which is not irradiated with an ultraviolet laser, there is no absorption and refractive index change in a visible region, it is transparent or white, and the transmittance | permeability and reflectance of a laser beam are high. By utilizing this property as a diffraction filter for reproduction light and by forming an appropriate hologram interference fringe 3 shape, it is possible to reproduce a hologram reproduction stereoscopic image.

  In volume hologram reproduction according to the present invention, a material having a color center is irradiated with an ultraviolet laser to form a pixel bit composed of the color center, and the material having the color center and the ultraviolet laser are relative to each other in a two-dimensional plane. To form a two-dimensional general hologram. In reproducing the volume hologram according to the present invention, in order to further improve the diffraction efficiency, a three-dimensional volume hologram is formed by relatively moving a substance having a color center and an ultraviolet laser in a three-dimensional space.

  Further, as the reading light irradiating means, the one that irradiates the reading light of the three colors R, G, and B as described above is used. Further, as the ultraviolet laser irradiation means, a device for writing a plurality of hologram interference fringes having different spectral absorption changes corresponding to the three colors of readout light, changes in the refractive index in a specific wavelength range, or hologram interference fringe pitches are different. As a result, the three primary color hologram images can be reproduced simultaneously.

  Further, in the volume hologram reproduction according to the present invention, a surface coating treatment may be applied to the outside of the display surface to prevent moisture and scratches. Further, by forming a substance having a color center on the surface of a transparent support substrate such as glass and setting the glass surface to the outside, it is possible to prevent moisture and scratches.

  Further, there are a transmission type arrangement in which the reproduction light is opposite to the reading light irradiation and a reflection type arrangement in which the reproduction light is on the same side with respect to the reading light irradiation. As a hologram erasing means, a device that erases hologram interference fringes by applying light, electromagnetic waves or heat can be used.

  Furthermore, the volume hologram reproduction according to the present invention provides a three-dimensional display that continuously reproduces a transmittable image without using a master that causes image quality degradation based on the principle of the hologram as described above. is there. The present invention relates to a three-dimensional display (hologram continuous reproduction apparatus), that is, a reproduction apparatus.

  At the time of imaging, as in the case of general hologram recording as described above, the object is irradiated with coherent (coherent) light (wave), and the scattered / reflected / transmitted light interferes with the reference light. In general, a laser beam or an electron beam is used as the wave. In the case of a volume hologram, the volume hologram can be obtained by making the scattered, reflected, transmitted light from the object and the reference light incident on the thick film photosensitive member for the volume hologram from the front and back sides.

  For the purpose of the present invention, it is necessary to record the interference pattern as a binary or multi-value electric signal, and therefore an image sensor is used as means for recording the interference pattern. Hologram interference fringes may be directly photographed or imaged with a diffusing plate, or the light-sensitive pattern of the photosensitive material may be enlarged and read once.

  When photographing a hologram interference fringe directly, taking into account the spectral sensitivity of the image sensor and the linearity with respect to the light intensity are the same as in general photographing. Since a general imaging device has a density of several tens of microns per pixel and an interference pattern is usually several microns or less, hologram interference fringes are magnified and recorded by a magnifying lens or the like. The depth information of the volume hologram can be obtained by adjusting the focal length of the imaging system.

  In addition to the above method, as a method that does not use an actual object, CGH (computer generated hologram) data obtained by calculating volume hologram interference fringes using a computer graphic technique can also be used.

  The interference pattern obtained by such a known method is subjected to image processing or electrical transmission, and the position of the ultraviolet laser and the hologram display surface is relatively set as a deflection signal or irradiation coordinate signal of the ultraviolet laser and an output modulation signal of the ultraviolet laser. Scanning and intensity modulation are performed and the hologram display surface is irradiated. As a scanning method of the ultraviolet laser, a scanning method (raster scanning) is generally performed in which the luminance (intensity) modulation of the ultraviolet laser is performed while scanning in the main scanning direction X and sequentially shifting in the sub-scanning direction Y orthogonal thereto. .

  A scanning method using vector scanning is also suitable. Mechanical scanning means such as a galvanometer mirror or a polygon mirror can be used as a method of scanning the ultraviolet laser. The brightness (intensity) of the ultraviolet laser is modulated while shifting the relative position between the display surface and the ultraviolet laser.

  In addition to the hologram formation by these two-dimensional scanning, a volume hologram is formed by scanning in the depth direction Z. For luminance modulation of the ultraviolet laser, control of an input signal (voltage, current, pulse width, etc.) to the laser, or a mechanical blanking technique such as a galvano mirror or TI DLP can be used.

  As described above, the physical properties of the display surface are changed by the ultraviolet laser, and light can be diffracted. That is, the display resolution is preferably equal to the wavelength of visible light, that is, 20 microns or less, particularly 1 micron or less. The ultraviolet laser is capable of condensing to 1 micron or less using a high NA ultraviolet lens and scanning the scanner or stage with high accuracy.

  As described above, it is possible to diffract light by forming interference fringes composed of changes in light transmittance or refractive index on the display surface. Holograms are mainly classified into two types: amplitude type and phase type. The amplitude type includes silver salt films and photochromic materials, and the theoretical diffraction efficiency is 6.25%. Phase types include dichromated gelatin and polymer liquid crystal, and the theoretical diffraction efficiency is 34%. Compared to these, the theoretical diffraction efficiency of the volume hologram of the present invention is 100%, and it is possible to realize a high diffraction efficiency of 3 times to 10 times the conventional one.

  Note that the liquid crystal panel and AOM used for the digital hologram display medium cannot display a volume hologram due to its principle. A substance having a color center is used as a substance capable of causing such a physical property change by an ultraviolet laser. For a substance having a color center, as described above, an ultraviolet laser having a first wavelength used for excitation for forming a color center, and readout light having a second wavelength that is irradiated and diffracted in the excited state. Is used. Further, in order to irradiate the excited state and return to the ground state, the third wavelength of excitation light or heat is applied. In general, the third excitation light has a longer wavelength than the readout light. In addition, when the period of continuous reproduction is long, it is preferably erased by heating.

  In the present invention, hologram interference fringes capable of diffracting light are displayed on the display surface, and as described above, display with higher resolution than that of a conventional cathode ray tube phosphor is required. In the present invention, a display surface having a display resolution of about 1 micron using a substance having a color center is preferable. Since the color center is one in which one electron is captured in the halogen defect lattice of the ionic crystal as described above, the resolution of the display surface using this is very high in the order of tens of angstroms in principle. The display resolution of the hologram depends on the ultraviolet laser to be exposed.

  As described above, a single mode YAG third harmonic, YAG fourth harmonic, pulse laser such as KrF excimer or ArF excimer, or the like is appropriately used as the ultraviolet laser. Further, a semiconductor laser or a surface emitting laser in an ultraviolet wavelength region such as an aluminum nitride system can be used. A single-mode ultraviolet laser has a short wavelength and thus has a high resolution limit, and a spot diameter can be condensed to 10 μm to 1 μm or less using an ultraviolet objective lens having a high NA.

  As described above, a substance having a color center has different transmittance, reflectance, and refractive index in a specific wavelength region between a portion excited by an ultraviolet laser and a ground state portion. Therefore, it is necessary to consider not only the pitch of the hologram interference fringes but also the wavelength of the visible laser beam that is the hologram reproduction light. For example, the color center absorption of rubidium chloride is around 640 nm and corresponds to the wavelength of the helium-neon laser. is doing.

  The change in transmittance depends on the ultraviolet laser energy density, pulse width, number of pulses, and repetition frequency as described above. In the example of rubidium chloride, the reflectivity at 640 nm is about 50% to 80% compared to before the excitation with the ultraviolet laser, and a sufficient contrast can be obtained. Even in the transmittance, a change of about 50% to 80% is recognized compared with that before the excitation with the ultraviolet laser. At the same time, since the refractive index is changed, the hologram of the present invention is an amplitude / phase hybrid type, so that high diffraction efficiency can be realized.

  Here, the absorption wavelength of rubidium chloride is around 640 nm, sodium bromide is around 540 nm, and potassium fluoride is around 450 nm. Therefore, the inventors of the present application fabricated a volume hologram recording medium by processing these three types of single crystals to a thickness of 1 mm and further laminating mirror-finished surfaces. FIG. 10 shows the reflection spectrum after each ultraviolet laser irradiation.

  The order of lamination was set to be rubidium chloride, sodium bromide, and potassium fluoride from the ultraviolet laser side. The order of stacking is not necessarily this order. As an example of the writing pitch, interference fringes were written at different pitches on the volume hologram recording medium (an example of writing is a method described in Example 7 described later).

  A 266 nm YAG laser is focused to focus on the rubidium chloride layer, step-scanned at regular intervals in the plane direction (X and Y) and the layer thickness direction (Z), and according to CGH (computer generated hologram) data The binary hologram was written by turning on / off the laser. The step pitch at this time was 13 μm.

  Similarly, the light was focused so as to focus on the sodium bromide layer, and a hologram was written by step scanning at a pitch of 11 μm in the surface direction (X and Y) and the layer thickness direction (Z). Similarly, the light was focused so as to focus on the potassium fluoride layer, and a hologram was written by step scanning at a pitch of 9 μm in the surface direction (X and Y) and the layer thickness direction (Z).

  Next, the volume hologram is irradiated with readout light having a wavelength of three colors: blue having a wavelength peak of 380 nm to 500 nm, green having a wavelength peak of 500 nm to 600 nm, and red having a wavelength peak of 600 nm to 800 nm. did.

  Examples of the blue laser having a wavelength peak of 380 nm to 500 nm include the following. Argon (488 nm), He—Cd (441.6 nm), gallium nitride laser diode (400 nm to 500 nm or less), infrared semiconductor laser SHG (425 nm and 410 nm), and the like.

  A green laser having a wavelength peak of 500 nm or more and 600 nm or less can be selected from YAG-SHG (532 nm), argon (514.5 nm), and the like. The red laser having a wavelength peak of 600 nm or more and 800 nm or less can be selected from He—Ne 633 nm, AlGaInP laser diode (630 to 680 nm), krypton (647 nm), and the like.

  Next, using bromide bromide (absorption wavelength around 630 nm) as a volume hologram recording medium, holograms were written at a pitch of 12 μm by the same method as described above. During writing, it was performed at liquid nitrogen temperature, and after hologram reproduction, it was heated to 100 ° C. to erase the hologram. Other than the heater heating, any heating means such as a far infrared (wavelength of 800 nm or more) of a carbon dioxide laser (10.6 μm) may be used.

  Regarding the elimination of hologram interference fringes, an example of a volume hologram recording medium using potassium bromide has been shown. However, as described above, a volume hologram recording medium in which rubidium chloride, sodium bromide and potassium fluoride are laminated is used. The same applies when used. Also, writing is the same as above.

  For example, Mitutoyo UV × 50 (NA 0.4) can be used as a lens for condensing the laser in the first wavelength region (190 nm to 380 nm). If the NA is smaller than this, the intensity ratio in the Z-axis direction is small (the light condensing rate is small), so that it becomes difficult to write at a specific Z-axis position of the volume hologram recording medium.

  The display surface for reproducing the volume hologram according to the present invention is required to have mechanical strength, ultraviolet laser shock resistance, environmental stability and the like, as in a general television. Since the above-mentioned alkali halides do not have high hardness or have high hygroscopicity, surface coating is applied to the alkali halide, or an alkali halide is formed on the glass support substrate, and the glass support substrate surface on the outside side Is preferably directed. The ultraviolet laser is desirably exposed from the alkali halide surface side.

  Since the coloring by the ultraviolet laser is derived from the micro ionic crystal structure as described above, the crystal used for the display surface does not need to be a single crystal or a molten single crystal, and may be a polycrystal or a powder. Single crystallization eliminates scattering and provides a transparent display surface in the visible wavelength range, so that it can be used as a transmission type.

  In addition, in the case of a reflection type hologram reproducing apparatus that utilizes diffraction / interference of laser reflected light from the display surface, the support substrate of the substance having the color center does not need to be transparent as described above, such as an alumina or silicon substrate. Can also be used. Depending on whether the hologram continuous reproduction apparatus is a transmission type or a reflection type, crystal transparency can be controlled by a method for producing a substance having a color center constituting the display surface and single crystallinity.

  In such a single crystal, in order to obtain an optical element as described above, the transparency can be improved by performing a smoothing process in the polishing step. A hologram is formed on a virtual surface having a constant depth from the surface of the single crystal, and further, the hologram is formed by moving the depth at a constant pitch. Finally, a volume hologram is formed.

  In order to realize this, it is desirable to collect light with a lens having an NA of 0.3 or more and a focal depth of 10 μm or less in consideration of the wavelength of the ultraviolet laser and the hologram bit size as described above. By focusing on the inside of the display surface using this lens and exposing with the ultraviolet laser while moving the display surface relative to the ultraviolet laser, a hologram can be formed on a virtual surface with a constant depth.

  As a method for forming a crystal on a support substrate, crystallization by evaporation of a solvent from a concentrated solution, formation of a molten salt, and various coating methods of a solution can be used. If necessary, polyvinyl alcohol or the like can be added to improve the coatability and adhesion strength to the support substrate. In addition, various additives can also be used. Alternatively, a substance having a color center can be formed on the support substrate by vapor deposition.

  As described above, when the material having the color center is formed on the support substrate in this way, the support substrate is directed to the outside (outside) of the hologram reproducing device, and the material having the color center is mechanically defective or absorbs moisture. Do not cause defects due to. At the same time, it is preferable that the ultraviolet laser is directly applied.

  In the volume hologram reproduction according to the present invention, the entire surface is irradiated with readout light having a wavelength satisfying the interference condition on the hologram interference fringe display surface displayed by the ultraviolet laser scanning as described above. Then, the transmittance and refractive index of the readout light are different between the portion that is excited / colored by the ultraviolet laser and the portion that is not, and diffraction / interference occurs, and a hologram reproduction stereoscopic image is reproduced. The diffracted light from each point on the display surface is recombined in space and a hologram image can be formed in the same manner as a general hologram, and a stationary stereoscopic image is obtained.

  In addition, depending on the positional relationship between the readout light and the display surface, the hologram reproduction three-dimensional image appears differently from the display surface or from the back. However, when the readout light source is positioned opposite to the observer side with respect to the display surface (when the readout light has a positional relationship that must pass through the display surface), the display surface is It needs to be transparent.

  A conventional cathode ray tube is an opaque scatterer. However, as described above, a material having a color center can be made transparent, and satisfies the above-mentioned requirements. In addition, since the substance having a color center in the present invention has a long lifetime at the transition time from the excited state to the ground state at room temperature and the colored state is stably maintained, one frame of hologram interference fringes is displayed by an ultraviolet laser. Then, the reading light can be irradiated to the entire surface.

  Further, as described above, the scanning time required for one frame can be shortened by irradiating the intensity-modulated ultraviolet laser from a plurality of ultraviolet laser light sources rather than scanning with one ultraviolet laser. It is more preferable to use a planar VCSEL ultraviolet laser because scanning is unnecessary. As a multi-ultraviolet laser source, one using a semiconductor as described above has been proposed.

  Note that as described above, a substance having a color center may return to the ground state by a laser beam of readout light, but is often not perfect. For example, when some electrons are re-trapped at a level called F ′ center. In that case, it is preferable to irradiate the entire surface with incoherent long wavelength light for erasure. This is erasure by the secondary excitation light described above.

  It is also preferable to promote erasing by raising the display surface to several hundred degrees Celsius if necessary. The erasing speed has a temperature dependency. For example, in the case of potassium bromide crystals, the half-life τ at room temperature is several seconds, less than 1 second at 100 ° C., and several tens of milliseconds at 500 ° C.

  As described above, it is possible to observe a stereoscopic image as a moving image by repeating these operations at a constant cycle. When this period is long, the screen appears to flicker, and the value is generally said to be about 1/30 second.

  As is apparent from the principle of a substance having a color center in reproducing a volume hologram according to the present invention, coloring is highly sensitive and display and erasing speed are fast. Compared to photochromic materials and electrochromic materials that require energy and time for ion transfer associated with molecular structure changes and oxidation-reduction reactions, the coloring of materials with color centers of the present invention is similar to semiconductor switching, so it responds quickly. Is possible. In addition, the durability is good as well as semiconductor switching.

  The hologram according to the present invention described in the first to third embodiments can be used as an information recording / reproducing apparatus instead of a display for displaying characters and images.

  Such an apparatus includes, for example, a hologram data encoding unit, a hologram recording unit, a hologram reading / reproducing unit, and a hologram data decoding unit. The hologram data encoding unit converts information data into two-dimensional or three-dimensional hologram data. The hologram recording unit writes a hologram on a substance having a color center which is the recording medium of the present invention. The hologram reading / reproducing unit reads data from the hologram using reproducing light. The hologram data decoding unit decodes the read data into original information data.

  Next, examples of the present invention will be described.

(Example 1)
In Example 1, as the alkali halide constituting the display surface, a potassium bromide single crystal for infrared optical crystal, a circle having a diameter of Φ30 mm, and a thickness of 3 mm was used. The hologram was written on the cleavage (100) plane. FIG. 6 shows transmission spectra of potassium bromide used for the display surface before and after irradiation with ultraviolet laser.

  A Spectra Physics HIPPO-355Q (YAG third harmonic 355 nm) pulse laser was used as the hologram writing ultraviolet laser, and was oscillated at a frequency of 40 kHz. The spot diameter is an ellipse of 2.5 mm × 3.5 mm. The applied power of DPSS (diode pumping) was adjusted so that the energy of one pulse was 0.54 μJ.

  Using a Mitutoyo MPlunUV50x, the light was condensed to a spot diameter of 1.13 μm × 0.89 μm on the surface of the display surface. The display surface was fixed to the XY stage, the ellipse direction was the main scanning direction, and a width of 10 mm was scanned at a speed of 1 mm per second to write dots. Since the repetition frequency of the ultraviolet laser is 40 kHz, 40 dots are written redundantly while shifting the position in 1 μm. With the short circle direction as the sub-scanning direction, it was sent at a pitch of 10 μm, and the main scanning was reciprocated 100 times to draw 200 lines of about 1 μm line & 9 μm space.

  A helium neon laser (wavelength 633 nm, spot diameter 2 mm) was vertically incident as read visible light on the drawn diffraction grating (a kind of interference fringes). At that time, diffraction spots were observed up to the 5th order and the diffraction intensity was 10% or more at the peak, but the diffraction grating disappeared in about 20 seconds and the diffraction intensity gradually decreased, and only the 0th order light was diffracted. Has been found to be disallowed.

  The optical absorption spectrum of the color center forming portion on the display surface of this example has a wide absorption band extending from about 500 nm to about 700 nm, and the absorption peak is around 630 nm. Found from exposure experiments. In this example, verification was performed using a diffraction grating in order to clarify the basic physical properties of the hologram.

(Example 2)
In Example 2, as the alkali halide constituting the display surface, a potassium bromide single crystal for infrared optical crystal, a circle having a diameter of Φ30 mm, and a thickness of 3 mm was used. The hologram was written on the cleavage (100) plane.

  A Spectra Physics HIPPO-266Q (YAG 4th harmonic 266 nm) pulse laser was used as the hologram writing ultraviolet laser, and was oscillated at a frequency of 40 kHz. The spot diameter is an ellipse of 2.2 mm × 3.3 mm. The applied power of DPSS (diode pumping) was adjusted so that the energy of one pulse was 0.21 μJ.

  Using a Mitutoyo MPlunUV50x, the light was condensed to a spot diameter of 0.95 μm × 0.66 μm on the surface of the display surface.

  The display surface was fixed to the XY stage, the ellipse direction was the main scanning direction, and a dot group was written by scanning a width of 10 mm at a speed of 1 mm per second. Since the repetition frequency of the ultraviolet laser is 40 kHz, 40 dots are written redundantly while shifting the position in 1 μm. With the short circle direction as the sub-scanning direction, it was sent at a pitch of 10 μm, and the main scanning was reciprocated 100 times to draw 200 lines of about 1 μm line & 9 μm space.

  When a helium neon laser (wavelength 633 nm, spot diameter 2 mm) was vertically incident on the drawn diffraction grating (a kind of interference fringes), diffraction spots were observed up to the fifth order and the diffraction intensity was 10% or more at the peak. It has been found that when writing to potassium bromide with an ultraviolet laser of 266 nm, the time until erasure is increased to several hours. In this example, verification was performed using a diffraction grating in order to clarify the basic physical properties of the hologram.

(Example 3)
In Example 2, a diffraction grating was formed with an ultraviolet laser, a diffraction spot was regenerated with a helium neon laser, and hot air at 300 ° C. was blown. As a result, the diffraction grating disappeared in about 10 seconds and gradually diffracted. The strength was weakened. Further, it has been found that only the 0th order light is present and diffraction is not recognized.

  In addition, it was said that by adjusting the temperature of the display surface to 300 ° C. from the beginning, the diffraction grating disappears within one second, and the disappearance speed of the color center is said to be temperature dependent. I found out.

  As a result of earnest research, the inventor of the present application has confirmed that the formation of the color center has no temperature dependence from another experiment using an unfocused ultraviolet laser. Therefore, even if the temperature of the display surface is adjusted to 300 ° C. from the beginning, the peak value of the diffraction intensity is 15% and does not change, but disappears within 1 second, indicating the possibility of a moving image hologram.

  Further, when 355 nm is used as the ultraviolet laser of Example 1, the diffraction grating disappears within 1 second only by raising the temperature to 100 ° C., and the diffraction spot is instantaneously confirmed at a temperature higher than that, and measurement is performed. It became difficult.

Example 4
In Example 2, scanning was performed while performing luminance modulation of the ultraviolet laser based on the data of the computer generated hologram instead of the diffraction grating, and hologram interference fringes were written on the display surface. When a helium neon laser (wavelength 633 nm, spot diameter 2 mm) was vertically incident on the drawn hologram interference fringes, a three-dimensional still image was reproduced.

(Example 5)
In Example 5, the (100) surface of NaBr (sodium bromide) was used as the display surface. FIG. 7 shows the transmission spectrum of this display surface after irradiation with ultraviolet laser. Three hologram interference fringes were synthesized in which the pitch of the hologram interference fringes corresponded to 514 nm and 488 nm of the argon laser in addition to the wavelength of 633 nm of the helium-neon laser. Then, the ultraviolet laser beam was converged to a spot diameter of 0.95 μm × 0.66 μm, and the resultant hologram interference fringe was scanned to display the hologram interference fringe.

  In Example 1 and Example 2, scanning was performed at a pitch of 10 μm, but in this example, scanning was performed at a pitch of 1 μm.

  Next, visible light for reproduction of 633 nm, 514 nm, and 488 nm was magnified with a lens and collectively irradiated. Since sodium bromide has an absorption in a relatively wide wavelength range, these three laser wavelengths also have transmittance and refractive index changes, thereby reproducing a color hologram.

(Example 6)
In Example 6, a hologram was formed at the depth of the display surface. The working distance of Mitutoyo MPluna UV 50x used in Example 2 is 12 mm, and the focal length is 4 mm. In the configuration of Example 2, the Mitutoyo MPlunUV50x lens was moved in the Z-axis direction (the crystal stacking thickness direction), and the focal position was adjusted to a position of 100 μm from the surface of the display surface.

  The light was condensed to a spot diameter of 0.95 μm × 0.66 μm. At this focal position, a hologram is formed on a virtual plane constituted by XY two dimensions. This virtual plane is the (100) plane, similar to the cleaved surface. When the same diffraction grating as in Example 2 was formed, the diffraction efficiency of He—Ne was improved to 15%.

(Example 7)
In Example 7, three kinds of crystals of rubidium chloride (for 633 nm), potassium chloride (for 514 nm), and potassium fluoride (for 488 nm) were sliced to a thickness of 1 mm as a substance having a color center, and this was polished. A display surface was formed by laminating and joining in the above order. The transmission spectrum after each ultraviolet laser irradiation is shown in FIG.

  The laminated display surface is laminated as follows in a state where the optical characteristics are changed by laser irradiation. That is, a display surface made of three types of alkali halides or alkaline earth halides having absorption wavelength peaks of 380 nm to 500 nm, 500 nm to 600 nm, and 600 nm to 800 nm is preferably stacked.

  Moreover, the working distance of Mitutoyo MPluna UV50x used in Example 2 is 12 mm, and the focal length is 4 mm. This lens was moved in the Z-axis direction (in the direction of the crystal lamination thickness), and the focal position was adjusted 100 μm deep from the surface of one rubidium chloride on the display surface. The light was condensed to a spot diameter of 0.95 μm × 0.66 μm. An ultraviolet laser was scanned, and hologram interference fringes were formed at a pitch of 3 μm (dot interval) for R based on the hologram data as described above.

  Similarly, for G, interference fringes were formed at a pitch of 2 μm at a depth of 100 μm from the surface of potassium chloride, and for B at a pitch of 1 μm at a depth of 100 μm from the surface of potassium fluoride. 190 nm to 380 nm).

  Next, visible light for reproduction of 633 nm, 514 nm, and 488 nm was magnified with a lens and collectively irradiated. Visible light for reproduction was diffracted and interfered by hologram interference fringes having a refractive index change and absorption at the wavelength, thereby reproducing a color hologram.

  Visible light for reproduction is irradiated with readout light of three colors of wavelength: blue having a wavelength peak of 380 nm to 500 nm, green having a wavelength peak of 500 nm to 600 nm, and red having a wavelength peak of 600 nm to 800 nm. Good to do.

(Example 8)
In the configuration of the seventh embodiment, all RGB are scanned at a pitch of 1 μm, and one pixel size is set to a maximum of 20 μm × 20 μm, and the size of pixel dots is modulated to 16 gradations according to non-stereoscopic bitmap data. Was displayed.

Example 9
Examples 9 to 11 are examples in the case of volume hologram reproduction. As the alkali halide constituting the display surface, a potassium bromide single crystal for infrared optical crystal, a circle having a diameter of 30 mm and a thickness of 3 mm was used. The hologram was written on the cleavage (100) plane.

  A Spectra Physics HIPPO-266Q (YAG 4th harmonic 266 nm) pulse laser was used as the hologram writing ultraviolet laser, and was oscillated at a frequency of 40 kHz. The spot diameter is an ellipse of 2.2 mm × 3.3 mm. The applied power of DPSS (diode pumping) was adjusted so that the energy of one pulse was 0.21 μJ.

  Using a Mitutoyo MPlunUV50x, the light was condensed to a spot diameter of 0.95 μm × 0.66 μm from the surface to a depth of 2 mm.

  At this focal position, a hologram was formed on a virtual plane composed of XY two dimensions. This virtual plane is the (100) plane, similar to the cleaved surface.

  The display surface was fixed to an XY stage, the oval direction was the main scanning direction, and a dot group was written by scanning a width of 10 mm at a speed of 1 mm per second. Since the repetition frequency of the ultraviolet laser was 40 kHz, 40 dots were written in 1 μm while shifting the position. The short circle direction is set as the sub-scanning direction, the feed is performed at a pitch of 10 μm, and main scanning is reciprocated 100 times to draw 200 lines of about 1 μm line & 9 μm space.

  When a helium neon laser (wavelength 633 nm, spot diameter 2 mm) was perpendicularly incident on the drawn diffraction grating (a kind of interference fringes), diffraction spots were observed up to the fifth order and the diffraction intensity was 10% or more.

  Further, the display surface was moved at a pitch of 10 μm in the depth direction on the Z-axis stage, and a volume hologram in which 100 diffraction gratings by the XY scanning exposure were recorded in the depth direction was obtained.

  The diffraction intensity of helium neon laser (wavelength 633 nm, spot diameter 2 mm) normal incidence light by the volume hologram of the present invention is improved to 30% or more, and it became clear that the volume hologram has a higher diffraction efficiency than the two-dimensional hologram. . In this example, verification was performed using a diffraction grating in order to clarify the basic physical properties of the hologram.

(Example 10)
In Example 9, while controlling the temperature of the volume display medium at 100 ° C., a diffraction grating was formed with an ultraviolet laser, and at the same time, a diffraction spot was reproduced with a helium neon laser. As a result, it was found that the diffraction grating disappeared in about 30 seconds and the diffraction intensity gradually decreased, and only the 0th order light was found and diffraction was not recognized.

  As a result of diligent research, the inventor of the present application has confirmed from a separate experiment using an unfocused ultraviolet laser that the formation of the color center is not temperature-dependent, while the disappearance of the color center is temperature-dependent. Therefore, even if the volume type display medium is temperature-controlled at 100 ° C. from the beginning, the peak value of diffraction intensity does not change at 30%, but disappears within 30 seconds, indicating the possibility as a moving image hologram.

(Example 11) Hologram In Example 9, hologram interference fringes were written by scanning while performing luminance modulation of an ultraviolet laser based on data of a computer generated hologram instead of a diffraction grating. When a helium neon laser (wavelength 633 nm, spot diameter 2 mm) was vertically incident on the drawn hologram interference fringes, a three-dimensional still image was reproduced.

It is a schematic diagram for demonstrating this invention. It is a schematic diagram which shows a mode that the display of a hologram interference fringe is performed in the apparatus of FIG. It is a schematic diagram which shows a mode that hologram reproduction is performed in the apparatus of FIG. It is explanatory drawing which shows the coloring principle of the substance which has a color center used for the display surface of the apparatus of FIG. 1 structurally and in energy. It is a schematic diagram which shows a mode that the volume type interference fringe is displayed in the volume type hologram reproduction which concerns on this invention. It is a graph which compares and shows the transmission spectrum before and behind ultraviolet laser irradiation of the potassium bromide used for the display surface in Example 1 of this invention. It is a graph which shows the transmission spectrum after ultraviolet laser irradiation of NaBr used for the display surface in Example 5 of this invention. It is a graph which shows the transmission spectrum after electron beam irradiation of the rubidium chloride used for the display surface in Example 7 of this invention, potassium chloride, and potassium fluoride. 1 is a conceptual diagram of a display device according to the present invention. It is a figure which shows the reflection spectrum after ultraviolet laser irradiation of the rubidium chloride, sodium bromide, and potassium fluoride in the volume type hologram reproduction which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Display surface 2 Ultraviolet laser 3 Hologram interference fringe 4 Ultraviolet laser irradiation means 5 Reading light 6 Hologram reproduction three-dimensional image 7 Visible laser 8 Erasing means 9 Magnifying lens 1190 Display element 1191 1st light source 1192 Laser of 1st wavelength region

Claims (21)

A display device,
A display element having a layer configured to contain an alkali halide or an alkaline earth halide whose optical properties are changed by laser irradiation in a first wavelength region of 190 nm or more and less than 380 nm;
A first light source that outputs a laser in the first wavelength region to write display data to the display element;
A second light source for irradiating the display element in which the display data is written with light in a second wavelength region of 380 nm to 800 nm;
A display device comprising: The display device according to claim 1, wherein the display element includes a plurality of the layers made of materials having different light absorption wavelength peaks. The display device according to claim 1, wherein the first light source and the second light source are configured by a single light source having a variable wavelength. The display device according to claim 1, wherein the display data is hologram data. A hologram reproducing device,
A display element including an alkali halide or an alkaline earth halide whose optical properties change by laser irradiation in a first wavelength region of 190 nm or more and less than 380 nm;
Writing means for writing hologram interference fringes on the display element by laser irradiation in the first wavelength region;
Means for irradiating the hologram interference fringes with readout light in a second wavelength region having a wavelength region of 380 nm or more and 800 nm or less to reproduce a hologram three-dimensional image;
A hologram reproducing apparatus comprising: 6. The hologram reproducing apparatus according to claim 5, wherein the hologram interference fringes are written in the display element as dot data based on hologram data. An erasing unit for erasing the hologram interference fringes, and repeating the writing of the hologram interference fringes by the writing unit, the reproduction of the hologram stereoscopic image by the reproducing unit, and the elimination of the hologram interference fringes by the erasing unit; The hologram reproducing apparatus according to claim 5, wherein the image is continuously reproduced. The hologram reproducing apparatus according to claim 7, wherein the erasing unit erases the hologram interference fringes by applying laser irradiation, electromagnetic waves, or heat. 9. The hologram reproducing apparatus according to claim 8, wherein the laser irradiation wavelength is 700 nm or more. 6. The hologram reproducing apparatus according to claim 5, wherein the irradiation of the readout light in the second wavelength region is performed from the same side as the laser irradiation of the first wavelength region on the display element. The hologram reproducing apparatus according to claim 5, wherein the writing unit forms the hologram interference fringes on a virtual plane defined in a depth direction of the display element. The hologram reproducing apparatus according to claim 5, wherein the stereoscopic display and the non-stereoscopic display are switched by switching a pixel size based on the dot data. A hologram reproducing device,
The first, second, and third layers that are made of alkali halide or alkaline earth halide and whose optical characteristics are changed by laser irradiation in the first wavelength region having a wavelength region of 190 nm or more and less than 380 nm are laminated. Having a display element;
The first, second, and third layers are different from each other in absorption wavelength peak in a state in which optical characteristics are changed by laser irradiation in the first wavelength region,
The absorption wavelength peaks of the first, second, and third layers are 380 nm to 500 nm, 500 nm to 600 nm, and 600 nm to 800 nm, respectively.
Writing means for writing hologram interference fringes on the display element by laser irradiation in the first wavelength region;
A hologram reproducing apparatus comprising: reproducing means for reproducing the hologram stereoscopic image by irradiating the display element on which the hologram interference fringes are written with reading light. The hologram reproducing apparatus according to claim 13, wherein the hologram interference fringes are written in the display element as dot data based on hologram data. In the display element in which the hologram interference fringes are written, a wavelength peak selected from a second wavelength region having a wavelength region of 380 nm to 800 nm is 380 nm to 500 nm, a wavelength peak is 500 nm to 600 nm, and a wavelength peak The hologram reproduction apparatus according to claim 13, wherein the hologram three-dimensional image is reproduced using three kinds of readout lights having a wavelength of 600 nm to 800 nm. An erasing unit for erasing the hologram interference fringes, and repeating the writing of the hologram interference fringes by the writing unit, the reproduction of the hologram stereoscopic image by the reproducing unit, and the elimination of the hologram interference fringes by the erasing unit; The hologram reproducing apparatus according to claim 13, wherein the image is continuously reproduced. 17. The hologram reproducing apparatus according to claim 16, wherein the erasing unit erases the hologram interference fringes by applying laser irradiation, electromagnetic waves, or heat. The hologram reproducing apparatus according to claim 16, wherein a wavelength for the laser irradiation is 700 nm or more. The hologram reproducing apparatus according to claim 13, wherein a stereoscopic display and a non-stereoscopic display are switched by switching a pixel size to be written according to the dot data. A device using a hologram,
A volume hologram recording medium comprising an alkali halide or an alkaline earth halide whose optical properties are changed by laser irradiation in a first wavelength region of 190 nm or more and less than 380 nm;
A first light source for irradiating the volume hologram recording medium with laser light in the first wavelength region;
A second light source for irradiating the volume hologram recording medium with readout light in a second wavelength region of 380 nm to 800 nm;
A volume hologram interference fringe based on bit data is formed on the volume hologram recording medium by relatively three-dimensionally scanning the volume hologram recording medium and the first light source. Equipment that uses the. The volume hologram recording medium is composed of a plurality of layers made of an alkali halide or an alkali halide earth, and the plurality of layers change in optical characteristics by laser irradiation in the first wavelength region, and 21. The apparatus using a hologram according to claim 20, wherein the absorption wavelength peaks in a state where the optical characteristics are changed are different from each other.