What Is a Virtual Hologram?
Specifically refers to a technology that allows the diffracted light emitted from an object to be reproduced in the same position and size as before.
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- In 1947, British physicist Denise Gabor (1900-1979) discovered the hologram
- Ordinary photography, can only record the intensity of the object's light field (the square of the complex amplitude mode)
- The first virtual singer concert
- The production process is as follows.
- A beam of coherent light (with exactly the same frequency and showing obvious interference effects) is subjected to a 1: 1 beam splitting. The object beam is called the object light, and the other beam is called the reference light. Under the condition that the optical path (light travel distance) is approximately the same, the object light and the reference light reflected on the object interfere with each other on the crystal (or holographic film).
- When observing the holographic negative with reference light, you can observe the original three-dimensional object on the holographic negative.
- This is the simplest hologram principle. In addition, there are holograms that can be reproduced by white light (referring to non-coherent light sources, such as lights and sunlight) (widely used in anti-counterfeiting signs), and color holograms (which can reproduce the subject with white light) Color) and so on. The process of making these holograms is quite complicated.
- Although holograms are often referred to as three-dimensional optical holograms, this is a misunderstanding. In addition, the sound field can also be made into a hologram.
- Holographic applications
- projection
- Holographic projection is
- Holographic projection
- 360 degree phantom imaging system
- 360-degree phantom imaging is a kind of mid-air imaging in which three-dimensional images are suspended in the real scene, creating an illusion and real atmosphere with strange effects and a strong sense of depth. The real object can be combined in the middle of forming an aerial illusion to realize the combination of the image and the real object. Can also be equipped with a touch screen to achieve interaction with the audience. It can be made into four windows according to requirements, with a maximum of 2-11 meters on each side. It can be made into a holographic phantom stage, a three-dimensional 360-degree demonstration of the product; real and illusionist performing on the same stage; fantasy dance of the science and technology museum, etc.
- It is suitable for expressing individual items with rich details or internal structures, such as watches, cars, jewelry, industrial products, and characters, cartoons, etc., giving the audience a completely three-dimensional impression.
- Photographing requirements
- In order to take a satisfactory hologram, the shooting system must have the following requirements:
- According to the previous analysis, holography is based on the interference principle of light, so the light source must be very coherent. The advent of lasers provides an ideal light source for holography. This is because the laser has good spatial coherence and time coherence. In the experiment, a He-Ne laser was used, and a small diffusive object was taken with it to obtain a good hologram.
- Because interference fringes are recorded on the holographic negative, and they are thin and dense interference fringes, even the smallest interference during the photographing process will cause the interference fringes to be blurred, and even make the interference fringes unrecordable. For example, if the film is shifted by one micrometer during the shooting, the fringes will be indistinguishable. For this reason, the holographic laboratory bench is required to be shockproof. All optical devices on the holographic stage are firmly fixed on the work surface steel plate with magnetic material. In addition, the air flow through the optical path, acoustic interference and temperature changes will cause changes in the surrounding air density. Therefore, no loud noises should be prohibited during exposure, and random walks should not be allowed to ensure that the entire laboratory is absolutely quiet. Our experience is that after each group has adjusted the light path, the students leave the experimental platform, stabilize for one minute, and then expose at the same time to get better results.
- The difference between the path lengths of the object light and the reference light should be as small as possible. The light path length of the two beams is the best, and the maximum cannot exceed 2cm. Use a string to measure the light path; 60 °, it is best to be about 45 °, because the interference angle is small, the interference fringes are thin, so the requirements for the stability of the system and the resolution of the photosensitive material are relatively low; It is required to be between 1: 1 and 1:10, and the light intensity ratio is measured by a silicon photocell.
- Because fine and dense interference fringes are recorded on holographic negatives, high-resolution photosensitive materials are required. Photographic negatives for general photography can only record 50 to 100 stripes per millimeter due to the coarse silver particles. The type I holographic dry plate produced by Tianjin Photographic Film Factory has a resolution of 30,000 per millimeter and can meet holographic Photo requirements.
- The rinsing process is also critical. We formulate according to the formulation requirements, and formulate the developing solution, stopping solution, fixing solution and bleaching solution. The above-mentioned several prescriptions require the preparation with distilled water, but experiments have proved that the preparation with pure tap water has also been successful. The rinsing process should be carried out in a dark room. The medicinal solution must not be exposed to light. Rinse at a room temperature of about 20 ° C. Once prepared, the medicinal solution can be used properly for about one month.
- Related applications
- In summary, holography is a video recording method that does not use ordinary optical imaging systems. It is a new technology of stereo photography and wavefront reconstruction developed in the 1960s. Because holography can record all the information (i.e., the amplitude and phase of light waves) emitted from the surface of the object, and can completely reproduce all the information of the light wave of the object, holography has a wide range of applications in production practice and scientific research [2, 3]. For example: holographic film and holographic television, holographic storage, holographic display and holographic anti-counterfeiting trademarks.
- In addition to optical holography, infrared, microwave, and ultrasonic holographic technologies have also been developed, which are of great significance in military reconnaissance and surveillance. We know that general radar can only detect the target's orientation and distance, while holography can give a three-dimensional image of the target, which has a great effect on the timely identification of aircraft and ships. Therefore, it has attracted much attention. However, since visible light decays rapidly when it travels through the atmosphere or water, it is even impossible to work in bad weather. In order to overcome this difficulty, infrared, microwave and ultrasonic holographic technologies have been developed. That is, coherent infrared light, microwave and ultrasonic are used to take holographic photos, and then visible light is used to reproduce the object image. This holographic technology has the same principle as ordinary holographic technology. The key of the technology is to find a sensitive recording medium and a suitable reproduction method.
- Ultrasound holography can reproduce three-dimensional patterns of underwater objects, so it can be used for underwater reconnaissance and surveillance. Figure (3). Because objects that are opaque to visible light are often transparent to ultrasonic waves, ultrasonic holography can be used for military operations underwater, as well as medical perspectives and industrial non-destructive testing.