Traditional Culture Encyclopedia - Photography and portraiture - Conclusion of holography experiment

Conclusion of holography experiment

(1) The light source must be a coherent light source

As we know from the previous analysis, holography is based on the principle of light interference, so the light source must have good coherence. The emergence of laser provides an ideal light source for holography. This is because laser has good spatial coherence and temporal coherence. In the experiment, He-Ne laser was used, which can be used to shoot small diffuse objects, and good holograms can be obtained.

(2) The holographic photography system must be stable

Since interference fringes are recorded on the holographic film, and they are thin and dense interference fringes, it is extremely difficult to process during the photography process. Small interference will cause the interference fringes to be blurred, or even make the interference fringes impossible to record. For example, if the film is displaced by one micron during the shooting process, the stripes will be unclear. For this reason, the holographic experimental platform is required to be shockproof. All optics on the holographic table are securely attached to the worktop steel plate with magnetic material. In addition, air flow through the optical path, sound wave interference and temperature changes will cause changes in the density of the surrounding air. Therefore, during exposure, it is forbidden to make loud noises or move around at will, and 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 table, stabilize for one minute, and then expose the light at the same time to get better results.

(3) The object light and the reference light should meet the requirements.

The optical path difference between the object light and the reference light should be as small as possible. It is best that the optical path lengths of the two beams of light are equal, and at most they cannot exceed 2cm, use a thin string to measure when adjusting the light path; the angle between the two beams of light should be between 30° and 60°, preferably around 45°. Because the angle is small, the interference fringes will be thin, which will affect the system. The requirements for stability and photosensitive material resolution are low; the light intensity ratio of the two beams of light must be appropriate, generally between 1:1 and 1:10. The light intensity ratio is measured with a silicon photocell.

(4) Use high-resolution holographic films

Because holographic films record thin and dense interference fringes, high-resolution photosensitive materials are required. The photosensitive film used for ordinary photography can only record 50 to 100 stripes per millimeter due to the coarse grains of silver compounds. The type I holographic dry plate produced by Tianjin Photosensitive Film Factory has a resolution of up to 3,000 stripes per millimeter. Meet the requirements for holography.

(5) The development process of holograms

The development process is also very critical. We prepare the developer, stopper, fixer and bleach according to the formula requirements. The above-mentioned prescriptions all require the use of distilled water, but experiments have proven that they can also be prepared with pure tap water. The rinsing process should be carried out in a dark room, and the medicinal solution must not be exposed to light. It should be kept at room temperature of 20°C for rinsing. Once the medicinal solution is prepared, it can be used for about a month if properly stored.