What is laser holography? Shooting requirements for holograms

Laser holographic photography is a new technology, and it has been hailed as a miracle of the 20th century. Its principle was discovered in 1947 by the Hungarian British physicist Dennis Gäbor, and it is completely different from ordinary photographic principles. It wasn't until more than 10 years later, when American physicists Reiff and Jupat Nyx invented lasers, that holographic photography was put into practice.

It can be said that holographic photography is the product of the combination of information storage and laser technology. Laser holography consists of two steps: recording and reproduction.

The holographic recording process is: divide the laser beam into two beams; A laser beam is projected directly onto a photosensitive negative, called a reference beam; Another laser beam is projected on an object, and when it is reflected or transmitted by the object, it carries the relevant information of the object, which is called the object beam. The object beam is also processed and projected on the same area of the photosensitive negative.

On the photosensitive negative, the object beam and the reference beam are coherently superimposed, forming interference fringes, which completes a hologram. Holographic reproduction is done by illuminating a hologram with a laser beam that should be transmitted exactly the same frequency and direction as the reference beam, so that a stereoscopic image of the object can be reproduced.

When people look at different angles, they can see different sides of an object, as if they are seeing a real object, but they can't touch the real object. The difference between holographic photography and ordinary photography: In ordinary photography, the scene captured by the camera only records the intensity of the reflected light of the scene, that is, the amplitude information of the reflected light, but cannot record the stereoscopic information of the scene.

Holographic technology, on the other hand, is able to record the amplitude and phase of the reflected light from the scene. When a hologram is taken, the light wave itself and the relative phase of the two beams of light are recorded, which is caused by the difference in position between the object and the reference light. We cannot see the image of the object from the interference fringes on the hologram**, and a cohesive laser must be used to accurately aim at the target and irradiate the hologram to reproduce the entire information of the object light.

Hologram Hologram refers to a new photographic technique that records all information such as the amplitude and phase of the reflected waves of the subject. Ordinary photography is to record the distribution of light intensity on the surface of the object, and it cannot record the phase information of the reflected light of the object, so it loses the three-dimensional sense. Hologrammetry uses a laser as the illumination source and divides the light emitted by the light source into two beams, one directed at the photoreceptor and the other beam reflected by the subject and then directed at the photosensor.

The two beams of light are superimposed on the photosensitive film to produce interference, and the degree of light sensitivity of each point on the photosensitive film varies not only with the intensity but also with the phase relationship of the two beams. So holographic photography not only records the intensity of reflections on the object, but also records the phase information. If the human eye looks directly at this light-sensitive negative, it can only see interference fringes like fingerprints, but if it is irradiated with a laser, the human eye can see through the negative film a three-dimensional image of the original photographed object is exactly the same.

A holographic photo** can reproduce the entire scene even if only a small part of it remains. Holographic photography can be applied to many aspects of non-destructive testing, ultrasound holography, holographic microscope, holographic memory, holographic film and television in industry. In the early 80s, the French Holographic Exhibition was exhibited all over the world, and people enjoyed the magical holographic photography.

On the wall, it seems that a faucet is stretched out, and he raises his hand to twist it, but it turns out to be empty; A frame, in which there was no image, but when a beam of light came, a beautiful girl appeared in the frame, slowly taking off her glasses and smiling at the person; A glass cover, which was empty, but in the light of the light immediately appeared a statue of Venus; On the frame, inside the glass cover, the image is constantly changing.

1. The holographic photography system should be stable. Because the interference fringes on the holographic film are fine and dense, the slightest interference during the photographic process will cause the interference fringes to blur. Therefore, holographic camera systems need to be resistant to shocks, acoustic interference, and temperature changes.

2. The light source must be a coherent light source. Hologram is based on the principle of light interference, so the light source must have good coherence. The laser light source has good spatial and temporal coherence, which can obtain a good hologram.

3. The optical path difference between the object light and the reference light should be as small as possible. It is best to have equal optical paths of two beams of light, no more than 2cm at most, and use a thin rope to measure the dimming path; The angle between the two beams of light should be between 30° and 60°, preferably around 45°.

4. The holographic film has high resolution. Fine, dense interference fringes are recorded on holographic films, so high-resolution photosensitive materials are required. The general resolution is 3000 strips per millimeter, which can meet the requirements of hologram.

Holographic image technology can project three-dimensional images through the principle of interference and diffraction, and use laser as the illumination source, which is a next-generation display technology.

The types of hologram technology include transmissive, reflective, image-surface, rainbow-based, compositive, molded, and arithmetic. Transmissive is one of the most common technologies.

Features of holographic image technology: it can quickly restore the three-dimensional image of the object, with the manuscript book with stereo sound, which can bring an immersive sense of realism, and can be used in museums to display collections, compared with VR and other technologies, holograms do not need to wear glasses**, **The experience is more excellent, and the cost is lower.

Hologram technology products: holograms, hologram display devices, holographic displays. Derivative technology: 360 holographic phantom imaging system, holographic projection technology, fog curtain Yun Jingnai stereoscopic imaging.

Data expansion: Holographic image technology is also known as virtual imaging technology or holographic imaging, and its imaging principle is to record the phase and amplitude of the object's light wave by light wave interference, and at the same time, the light wave information of the object is displayed by the principle of diffraction, so as to achieve the imaging effect. Holographic image technology has developed rapidly since the advent of lasers in the 60s of the 20th century.

The principle of holography is applicable to various forms of fluctuations, such as X-rays, microwaves, sound waves, electron waves, etc.

HolographyIt is a technology that uses the principle of coherent optics to make three-dimensional optical images.

The principle of holography can be simply explained as the fact that the information of the subject is cross-interfered with a reference light wave to form an image called a hologram. In this image, each pixel contains all the information about the object, which can be used to reproduce the three-dimensional image of the object.

Expansion:

The basic principle of holography is the Raleigh-Sommerfeld Diffraction, which is when a light source emits light waves, and the wavefront is affected by diffraction and interference during propagation. In hologram, the receiving light source and cross-interfering with the reference light wave can encode the morphological information of the subject in the interference fringes. This encoding process is done by combining the optical amplitude of the subject and the phase information of the interferometric reference light onto the pure light field, which is then recorded with a mask to become a hologram.

The optical equipment of holographic photography is mainly composed of five parts: light source, reference light, object, camera and holographic recording material. Lasers and high-resolution CCD cameras are often used for light sources and cameras, which can capture more detailed three-dimensional images. A certain degree of coherence between the reference light and the object needs to be ensured to establish the conditions for cross-interference, so that interference fringes can be generated on the reflected beam and the object.

The holographic recording material can be ordinary color film, fused silica glass, etc., and they can record this complex interference fringe to form a hologram.

Holographic technology has the advantages of efficient optical image recording performance and highly restored three-dimensional images. It is used in various computer equipment, optical testing, and scientific research. In the field of computing, holograms can be used to create ultra-high-resolution model images, which play a significant role in industrial design and quality control.

In terms of scientific research, holographic photography is widely used in non-destructive testing technology, three-dimensional construction, physical optics, etc.

Laser holography is optical holography, which is an effective means to record the amplitude and phase information of light waves on the surface of the subject in the form of interference fringes by using the interference phenomenon of light waves, which is an effective means to record all the information of light waves. Optical holography is widely used in precision metrology, information storage and processing, and biomedicine.

It is a photographic method that records and reproduces three-dimensional (stereoscopic) images of objects without lenses. It is a technology that records information about the amplitude and phase of the wavefront of a light wave from an object, and reproduces this light wave when needed.

Ordinary photography is based on the principle of geometric optics, using lens imaging to record the light intensity distribution of each point, the image is a two-dimensional plane image, the relationship between objects and images is corresponding to the points, as long as the negative is damaged, the image can not be reproduced. Moreover, the requirements of ordinary photos are not high compared to the external environment, and the general conditions can be met. Hologram is different, it is based on the laws of physical optics such as light interference and diffraction, and introduces an appropriate coherent reference wave, which not only records the amplitude information of the object light, but also records the phase information lost in the ordinary photographic process.

What is obtained on the photosensitive substrate is not the image of the object, but the interference fringes between the object light and the reference light, and the chiaroscuro of these fringes, the shape and density of the fringes reflect the amplitude and phase distribution of the object light wave. After development and fixing, a hologram was obtained. It is equivalent to a complex grating, and the original object light wave can only be reconstructed under proper light wave illumination.

Holograms give a three-dimensional real image. The relationship between objects and images is corresponding to the point and surface, and each point on the hologram records all the object and light information, whether worn or damaged, as long as a small piece of hologram is obtained, the original object can be truly reproduced. Of course, the shooting requirements of laser holography are also much stricter than ordinary photography.

First of all, the light source must be a coherent light source, and holographic photography is based on the interference principle of light, so the light source must have good coherence [5]. The advent of lasers provides an ideal light source for holograms. Secondly, the holographic photographic system should have stability, because the holographic negative is recorded on the fine and dense interference fringes, so the very small interference in the photographic process will cause the blurring of the interference fringes, and even make the interference fringes unable to record, for this reason, the holographic experimental bench is required to be shockproof, all the optical devices on the holographic table are firmly sucked on the steel plate of the working table with magnetic materials, in addition, the air flow through the optical path, sound wave interference and temperature changes will cause the change of the density of the surrounding air, therefore, in the first Loud noises should not be allowed, no random movement should be allowed, and the entire laboratory should be absolutely quiet.

Thirdly, the optical path difference between the object light and the reference light should be as small as possible, not more than 2 cm at most. In addition, it is necessary to use high-resolution holographic negatives, because holographic negatives are recorded with fine and dense interference fringes, so high-resolution photosensitive materials are required. Ordinary photographic photosensitive negatives can only record 50 100 fringes per millimeter due to the coarse silverization particles, while laser holographic dry plates can have a resolution of up to 3000 stripes per millimeter, which can meet the requirements of holographic photography [6].

Finally, the flushing process of holographic ** The flushing process is also very critical. In general, the requirements for the relative conditions of laser holography are still very demanding.

Laser holography**, also known as rainbow holography**, is to make the image onto the plastic film through laser plate making, resulting in a colorful diffraction effect, so that ** has a sense of two-dimensional and three-dimensional space. In normal light, the hidden images and information in ** will be reproduced, and when the light shines from a certain angle, a new image will appear on **.

1. Holographic ** and ordinary popular science ** are different, under the appropriate lighting, the scene displayed on the holographic ** is three-dimensional, and all sides of the scene can be seen.

2. The difference between holographic photography and conventional photography is that conventional photography only records the change of light intensity on the surface of the photographed object, that is, only the amplitude of the light is recorded; Whereas, holograms record all the information of the light waves, and in addition to the amplitude, they also record the phase of the light waves. In this way, all the information about the light wave field of the space object is stored and recorded. Then use the diffraction of holographic ** to a specific wavelength monochromatic illumination light to reveal the original space scene.

It can "resurrect" a "frozen" scene and appear in front of people's eyes.

3. Ordinary photography can only store the spatial distribution of the light intensity of the photographed object, which cannot meet the requirements of people who hope to perceive the real 3D scene in a specific environment; Holographic photography is to record the interference fringes of the object light wave and the corresponding reference light wave irradiating the object, so as to record all the light field information including the object amplitude (light intensity) and phase, so it is called "holographic".