Holography and holographic technology

Holography refers to a new photography technology, which records all the information of the amplitude and phase of the reflected wave of the object being photographed. Ordinary photography records the light intensity distribution on the surface of the object, but it can't record the phase information of the reflected light of the object, so it loses its three-dimensional sense. Holography uses laser as the illumination source, and divides the light emitted by the light source into two beams, one of which is directly directed at the photosensitive plate, and the other is reflected by the subject and then directed at the photosensitive plate. The superposition of two beams of light on the photosensitive plate produces interference, and the sensitivity of each point on the photosensitive plate changes not only with the intensity, but also with the phase correlation of the two beams of light. Therefore, holography not only records the reflection intensity on the object, but also records the phase information. When the human eye directly looks at this photosensitive film, it can only see interference fringes like fingerprints, but if it is irradiated by laser, the human eye can see the three-dimensional image of the original object through the film. Even if only a small part of the holographic image remains, it can still reproduce the whole scene. Holography can be applied to nondestructive testing, ultrasonic holography, holographic microscope, holographic storage, holographic film and television and many other aspects in industry.

Shooting requirements: In order to shoot satisfactory holograms, the shooting system must meet the following requirements:

The light source must be a coherent light source

From the previous analysis, we know that holography is based on the interference principle of light, so the light source must have good coherence. The appearance of laser provides an ideal light source for holography. This is because laser has good spatial and temporal coherence. In the experiment, a good hologram can be obtained by shooting small diffuse objects with He-Ne laser. Holographic system should have stability.

Because the interference fringes are recorded on the holographic negative, and they are thin and dense, the smallest interference will blur the interference fringes in the process of photography, and even the interference fringes cannot be recorded. For example, if the film is displaced by one micron during shooting, the stripes will not be clearly distinguished. Therefore, the holographic experimental platform is required to be shockproof. All optical devices on the holographic table are firmly attached to the steel plate of the table with magnetic materials. In addition, air flowing through the optical path, acoustic interference and temperature changes will all cause changes in the surrounding air density. Therefore, it is forbidden to talk loudly and walk around at will during the exposure period to ensure the absolute silence of the whole laboratory. Our experience is that after each group adjusts the light path, students leave the experimental platform, stabilize for one minute, and then expose at the same time, which is better. ?

Object light and reference light shall meet the following requirements

The optical path difference between the object light and the reference light should be as small as possible, and the optical paths of the two beams should be equal at most, not exceeding 2cm, and the amount of lines should be better when adjusting the optical paths; The included angle between the two beams should be between 30 and 60, preferably around 45. Because the included angle is small, the interference fringes will be fine, which does not require high stability of the system and resolution of photosensitive materials. The light intensity ratio of the two beams should be appropriate, which is generally required to be between1:1~1:10. The light intensity ratio is measured by a silicon photocell.

Using high-resolution holographic negatives

Because thin and dense interference fringes are recorded on the holographic negative, high-resolution photosensitive materials are needed. Because silver compounds particles are coarse, ordinary photographic plates can only record 50 ~ 100 stripes. The resolution of type I holographic plate produced by Tianjin Photographic Film Factory can reach 3000 lines per millimeter, which can meet the requirements of holographic photography.

Development process of hologram

The flushing process is also critical. We prepare the medicine according to the prescription requirements, and prepare the developer, fixer and bleach solution. All the above prescriptions need distilled water, but the experiment proves that it is also successful to prepare with pure tap water. The washing process should be carried out in a dark room, and the liquid medicine must not be illuminated. Room temperature of about 20℃ should be maintained during washing. If the primary potion is properly preserved, it can be used for about a month.