DE102019104835B4 - Method and device for generating a three-dimensional image - Google Patents

Abstract

Method for generating a three-dimensional image, with the method steps:
- Generating laser radiation (9);
- Focusing the laser radiation in a working medium (4) which converts the laser radiation in the focus (7) at least partially into secondary light (6);
- Guiding the focus (7) along a trajectory running through the working medium (4) with simultaneous modulation of the laser radiation, whereby a self-illuminating image (8) is generated in the working medium (4); and
- optical imaging of the self-illuminating image (8), a real, three-dimensional image (13) of the self-luminous image (8) positioned freely in space being generated in an imaging volume outside of the working medium (4), the direction of the optical imaging being different from the direction of incidence of the laser radiation in the working medium (4).

Description

The invention relates to a method and a device for generating a three-dimensional image.

Various approaches to generating three-dimensional images exist in the prior art. All known solutions have disadvantages.

For example, stationary holograms are known. As is well known, holograms use the wave character of light to achieve three-dimensional representations. The motifs shown seem to float freely in space when viewed. It is also possible to see around an imaged object when moving laterally, and a full three-dimensional impression is created when viewing with binoculars. In holographic imaging, light from a coherent light source is modulated in phase and/or amplitude by a holographic element in such a way that it corresponds to the light field of a real, three-dimensional object. The holographic element is usually implemented as a micro- or nano-structured optical element, the illumination is provided by a laser, which is reflected by this element or transmitted through it. The disadvantage of this method is that the holographic element cannot be reconfigured, so that only a stationary image can be generated. At the same time, the size of the image is limited by the size of the holographic element. The costs per element are usually very high due to the complex production.

Adaptable holograms are also known. In these, instead of the static holographic element, a programmable phase-active display (an SLM, engl.: "spatial light modulator") is used to generate a variable hologram. However, with the technology available today, this solution is limited to very small images and low resolutions compared to the stationary holograms described above. Larger images would require larger SLMs, which are not available on the market.

In the case of static and adaptable holograms, it is in any case disadvantageous that an extremely high resolution is required when structuring the holographic element, since the light wave front generating the image and not the image itself has to be synthesized. In particular for adaptable holograms, this means a cost disadvantage. The computing effort for data preparation in real-time applications is extremely high.

Furthermore, object-writing methods are known from the prior art (cf. OCHIAI, Y. [et al.]: Fairy lights in femtoseconds: aerial and volumetric graphics rendered by focused femtosecond laser combined with computational holographic fields. ACM Transactions on Graphics, Vol. 35 (2), 2016, Article 17, pp. 1 - 14, DOI: 10.1145/2850414 With these, a three-dimensional image is composed directly from light-emitting points generated freely in space. For this purpose, a strong continuous-wave laser source, a pulsed laser source or an ultrashort-pulse laser system is focused in a working medium and the focus is guided through the working medium by suitable beam-deflecting optics along a trajectory, from which the self-luminous image is composed. The laser radiates through the working medium, which absorbs part of the directed energy of the laser radiation and emits it non-directionally as secondary radiation in the form of visible light. The light conversion process in the working medium is designed in such a way that the probability of conversion increases non-linearly with the light intensity. The consequence of this is that the laser radiation is only converted into secondary radiation in a spatially restricted manner in the area of the focus. For example, the conversion into secondary light can take place by means of a plasma excited to glow by the laser radiation in fluid working media (gases or liquids) or by two-photon fluorescence or also by local thermal emission. The laser radiation is modulated along the trajectory with regard to its amplitude and/or the movement speed of the focus in order to achieve a brightness variation. Such a method disclosed, for example, the U.S. 2017/0293259 A1 as well as the DE 198 37 425 A1 . This method has the disadvantage that the working medium has to be excited by high-energy laser radiation, so that there is generally no eye safety. In addition, the well-known light-converting processes go hand in hand with the generation of potentially harmful substances. A practical application of the known approach, for example for the realization of a three-dimensional display, has therefore not taken place to date.

Against this background, it is the object of the invention to specify a method and a device for generating a self-illuminating, three-dimensional image. The image should be able to be freely positioned in the room in a way that is eye-safe.

• - Erzeugen von Laserstrahlung;
• - Fokussieren der Laserstrahlung in ein Arbeitsmedium, das die Laserstrahlung in dem Fokus zumindest zum Teil in Sekundärlicht umwandelt;
• - Führen des Fokus entlang einer durch das Arbeitsmedium verlaufenden Trajektorie unter gleichzeitiger Modulation der Laserstrahlung, wodurch ein selbstleuchtendes Bild in dem Arbeitsmedium erzeugt wird; und
• - optisches Abbilden des selbstleuchtenden Bildes, wobei ein reelles, dreidimensionales, frei im Raum positioniertes Bild des selbstleuchtenden Bildes in einem Abbildungsvolumen außerhalb des Arbeitsmediums erzeugt wird, wobei sich die Richtung der optischen Abbildung von der Einstrahlrichtung der Laserstrahlung in das Arbeitsmedium unterscheidet.

The invention solves this problem by a method for generating a three-dimensional image, with the method steps:

• - Generation of laser radiation;
• - Focusing the laser radiation in a working medium that converts the laser radiation in the focus at least partially into secondary light;
• - Guide the focus along a running through the working medium trajectory with simultaneous modulation of the laser radiation, whereby a self-illuminating image is generated in the working medium; and
• - optical imaging of the self-illuminating image, with a real, three-dimensional, freely positioned image of the self-illuminating image being generated in an imaging volume outside of the working medium, the direction of the optical imaging being different from the direction of incidence of the laser radiation into the working medium.

• - einem Laser, der Laserstrahlung erzeugt;
• - einem Modulator, der die Laserstrahlung moduliert;
• - einem Arbeitsmedium, das die Laserstrahlung zumindest zum Teil

in Sekundärlicht umwandelt;

• - einem ersten optischen System, das die Laserstrahlung in das Arbeitsmedium fokussiert und ablenkt und so den Fokus entlang einer durch das Arbeitsmedium verlaufenden Trajektorie unter gleichzeitiger Modulation der Laserstrahlung führt, wobei in dem Arbeitsmedium durch das im Fokus abgestrahlte Sekundärlicht ein selbstleuchtendes Bild entsteht; und
• - ein zweites optisches System, das durch optische Abbildung des selbstleuchtenden Bildes ein reelles, dreidimensionales, frei im Raum positioniertes Bild des selbstleuchtenden Bildes in einem Abbildungsvolumen außerhalb des Arbeitsmediums erzeugt, wobei sich die Richtung der optischen Abbildung von der Einstrahlrichtung der Laserstrahlung in das Arbeitsmedium unterscheidet.

In addition, the invention solves the problem with a device for generating a three-dimensional image

• - a laser that generates laser radiation;
• - a modulator which modulates the laser radiation;
• - A working medium, the laser radiation at least in part

converted to secondary light;

• - A first optical system that focuses and deflects the laser radiation into the working medium and thus guides the focus along a trajectory running through the working medium while simultaneously modulating the laser radiation, a self-luminous image being produced in the working medium by the secondary light emitted in the focus; and
• - a second optical system that generates a real, three-dimensional image of the self-luminous image that is positioned freely in space in an imaging volume outside of the working medium by optical imaging of the self-luminous image, with the direction of the optical imaging being different from the direction of incidence of the laser radiation in the working medium .

The method according to the invention adopts the object-writing method described above for generating the self-illuminating image in the working medium.

The method of the invention is preferably based on the use of a strong continuous wave laser, a pulsed laser or an ultrashort pulse laser to generate the laser radiation.

The conversion of the laser radiation into secondary light is expediently carried out, as in the known method, by a non-linear optical process in the working medium (e.g. by a plasma excited by the laser radiation to glow in a fluid working medium, by two- or multi-photon fluorescence or also by local thermal emission ).

The use of laser radiation at different wavelengths is also conceivable (e.g. from several laser sources operated in parallel), with the laser radiation at the different wavelengths being modulated independently in order to produce the secondary light in different colors (e.g. red, green, and blue spectral range). In this way, the three-dimensional image can be generated in color.

The laser radiation is focused into the working medium, e.g. by a first optical system with scanner optics. In this case, the first optical system can be implemented by means of lenses or by means of mirrors or by means of micro-optical elements or a combination of these components. The scanner optics can be realized by one or more movable or deformable mirrors or lenses or by a phase-active element or a micromirror array or a combination of these components. The scanner optics must be designed in such a way that the focus of the laser beam is moved with sufficient speed and through a sufficiently large volume of the working medium. It is also conceivable for the laser beam to be split into several partial beams by suitable optics in order to scan the volume of the working medium in parallel along several trajectories. Beam shaping is also conceivable, so that patterned foci are created in the working medium.

The working medium can advantageously be enclosed in a media chamber with a wall that is transparent to the laser radiation or the secondary light. This chamber serves to provide the appropriate working medium for the light-converting process and to condition it appropriately, for example to increase the light yield. It also serves to isolate process media and by-products from the environment. The condition of the working medium can be checked by sensors built into the media chamber or by external sensors and can be influenced and adjusted by suitable actuators.

The unconverted part of the laser radiation is expediently safely absorbed in an absorber element arranged behind the focus in the direction of the beam and dissipated as heat. The absorber element can be designed as part of the media chamber.

The converted, non-directional secondary light is expediently cleaned of undesired light components by means of an optical filter. This includes e.g. B. Residual or scattered light of the laser radiation or light components with undesired wavelengths, for example, in the ultraviolet spectral range, but also too high intensity peaks in the visible spectral range.

According to the invention, the (corrected) secondary light is imaged by means of a second optical system in an imaging volume outside of the working medium. By imaging the self-luminous image created in the working medium, a real image is created in the imaging volume. The second optical system can be implemented using lenses or using (curved) mirrors or using micro-optical elements or a combination of these components. The second optical system performs point-to-point imaging of the self-luminous image into the imaging volume. The mapping can be designed according to the application and can contain, for example, distortions or enlargements or reductions.

According to the invention, the direction of the optical imaging differs from the direction of incidence of the laser radiation in the working medium. For example, the direction of the optical imaging and the direction of incidence of the laser radiation into the working medium can be essentially orthogonal. In this way, the laser radiation can be kept particularly safely away from the viewer of the image in the imaging volume.

The order of the optical filter and the second optical system can be interchanged in the beam path or form a constructive unit. The second optical system and/or the optical filter can also be structural components of the media chamber.

The method according to the invention makes it possible to implement large-volume, three-dimensional images positioned freely in space, with the maximum imaging volume, i.e. the maximum image size, being limited only by the power of the laser radiation and the optical systems. The components used according to the invention have significantly more favorable scaling properties than micro-optical elements conventionally used for holograms. In addition, the invention is suitable for generating moving images. High-resolution objects (resolution in the range of the focus diameter) can be displayed in large volumes and data preparation and processing is easy, since no conversion from the image to the wave field space is necessary. A real-time application is therefore possible.

In contrast to the conventional object-writing method, the invention enables the optical overall arrangement to be designed in an eye-safe manner by generating the real image as an image of the self-illuminating image generated by the laser radiation in the imaging volume. The working medium is shielded from the user, the laser radiation is absorbed and thus also kept away from the user. A suitable working medium can be selected independently of the observer. For example, gas composition and pressure can be varied in plasma processes, multi-photon fluorescence processes can be freely adapted and optimized with regard to dye, color, efficiency, concentration and long-term stability. Any potentially harmful substances that may be produced during the light-converting process remain in the media chamber and can be safely discharged from there. An extension to multicolored applications, e.g. by using at least three dyes or three different fluorescence processes, is conceivable, as already indicated above.

• 1 schematische Darstellung einer erfindungsgemäßen Vorrichtung.

An exemplary embodiment of the invention is explained in more detail below with reference to the drawing. It shows:

• 1 schematic representation of a device according to the invention.

In the embodiment of 1 an ultra-short pulse laser 1 is used to generate laser radiation. The laser radiation is modulated using an intensity modulator 2 . The modulated laser radiation passes through a first optical system 3 which focuses the laser radiation into a working medium 4 . For this purpose, the first optical system 3 has a lens arrangement with a variable focus length and movable mirrors. These scanner optics of the first optical system 3 are designed in such a way that the focus 7 of the laser beam is moved along a definable trajectory with sufficient speed and through a sufficiently large volume of the working medium 4 . The working medium 4 is located in a media chamber 5 with a wall that is transparent to the laser radiation or the secondary light.

The laser radiation radiates through the working medium 4, which absorbs part of the energy of the laser radiation and emits it non-directionally as secondary radiation 6 in the form of visible light. The light conversion process in the working medium 4 is non-linear, so that the laser radiation is only converted into secondary radiation in a spatially narrowly limited manner in the area of the focus 7 . The amplitude of the laser radiation is modulated along the trajectory by means of the modulator 2 in order to achieve a brightness variation. To this way, a self-illuminating image 8 is created in the working medium 4.

The non-converted part 9 of the laser radiation is safely absorbed in an absorber element 10 arranged behind the focus 7 in the beam direction and dissipated as heat. The unconverted laser radiation 9 is separated from the secondary light 6 by a dichroic mirror 11 functioning as a filter.

The secondary light 6 cleaned in this way is imaged in an imaging volume outside of the working medium by means of a second optical system 12 . By imaging the self-luminous image 8, a real image 13 is generated in the imaging volume. The second optical system 12 is realized by means of lenses. It performs a point-to-point mapping of the luminescent image 8 onto the real image 13.

A computer-based control device 14 controls the intensity modulator 2 and the first optical system 3 on the basis of the three-dimensional image data to be displayed in order to correspondingly control the focus 7 of the laser radiation in the working medium 4 and at the same time to modulate the intensity of the laser radiation so that the the self-illuminating image 8 corresponding to the image data is created. For example, the image data can be defined as brightness values on a three-dimensional grid. The control device 14 controls the intensity modulator 2 and the first optical system 3 in such a way that the focus 7 sequentially scans the coordinates of the grid and modulates the intensity of the laser radiation according to the brightness values assigned to the grid points.

Claims (14)

Method for generating a three-dimensional image, with the method steps: - Generating laser radiation (9); - Focusing the laser radiation in a working medium (4) which converts the laser radiation in the focus (7) at least partially into secondary light (6); - Guiding the focus (7) along a trajectory running through the working medium (4) with simultaneous modulation of the laser radiation, whereby a self-illuminating image (8) is generated in the working medium (4); and - optical imaging of the self-illuminating image (8), a real, three-dimensional image (13) of the self-luminous image (8) positioned freely in space being generated in an imaging volume outside of the working medium (4), the direction of the optical imaging being different from the direction of incidence of the laser radiation in the working medium (4). procedure after claim 1 , characterized in that the laser radiation is continuous wave laser radiation or pulsed laser radiation. procedure after claim 1 or 2 , characterized in that the laser radiation is converted into secondary light (6) by a non-linear optical process in the working medium (4). Procedure according to one of Claims 1 until 3 , characterized in that the laser radiation is absorbed behind the focus (7) in the beam direction. Procedure according to one of Claims 1 until 4 , characterized in that the optical imaging of the self-illuminating image (8) takes place by point-to-point imaging. Procedure according to one of Claims 1 until 5 , characterized in that the secondary light (6) of the self-luminous image (8) is optically filtered. Procedure according to one of Claims 1 until 6 , characterized in that the direction of the optical image and the direction of incidence of the laser radiation in the working medium (4) are essentially orthogonal. Device for generating a three-dimensional image, with - A laser (1) which generates laser radiation; - A modulator (2) which modulates the laser radiation; - A working medium (4) which converts the laser radiation at least partially into secondary light (6); - A first optical system (3), which focuses and deflects the laser radiation into the working medium (4) and thus guides the focus (7) along a trajectory running through the working medium (4) while simultaneously modulating the laser radiation, wherein in the working medium ( 4) a self-illuminating image (8) is created by the secondary light emitted in the focus (7); - a second optical system (11), which generates a real, three-dimensional image 13 of the self-luminous image (8) positioned freely in space by optical imaging of the self-luminous image (8) in an imaging volume outside of the working medium (4), the Direction of optical imaging differs from the direction of incidence of the laser radiation in the working medium (4). device after claim 8 , characterized in that the laser (1) is a continuous wave laser, a pulsed laser or a short-pulse laser. device after claim 8 or 9 , characterized in that the working medium (4) converts the laser radiation into secondary light (6) by a non-linear optical process. Device according to one of Claims 8 until 10 , characterized in that the working medium (4) is gaseous or liquid and is located in a media chamber (5) with walls that are transparent for the laser radiation and/or the secondary light. Device according to one of Claims 8 until 11 characterized by sensors that detect the status parameters of the working medium (4). Device according to one of Claims 8 until 12 , characterized by an absorber element (10) which is arranged behind the focus (7) in the path of the laser radiation and which absorbs the non-converted laser radiation (9). Device according to one of Claims 8 until 13 , characterized by an optical filter (11) which filters the secondary light (6).

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