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Homemade holograms

S.P. Vorobyov and S.M. Zharkiy, Moscow


Display holograms attract people because of their unusual properties. Many enthusiasts are interested in holography. Usually, amateur holographers face the problem of purchasing of the necessary equipment. This article describes the simple holographic setup and processing, which allow to record small reflection holograms in domestic conditions even by children.

Design of the holographic setup is based on four principles:
1. Use of laser pointer, as a source of coherent light.
2. Use of Denisyuk's holographic scheme.
3. Use of holographic photoplates PFG-03m for recording of reflection holograms.
4. Use of a free-flowing material for installation of parts of the holographic scheme.

Laser pointer

Simple laser pointer contains the low-power semi-conductor laser, which radiates red light and focusing lens. The divergent beam is necessary for hologram recording, therefore lens should be extracted, and then laser pointer will radiate a wide beam of light, sufficient for illumination of small objects, see fig.

Denisyuk’s hologram recording scheme

Holographic scheme of Yuri Denisyuk (see fig.) is widely known, its basic advantages - simplicity of the design and high quality of holograms recorded. Narrow light beam 2 from the laser 1 is directed by the mirror 3 to spatial filter 4, which expands the beam up to the necessary size and simultaneously improves its homogeneity. Expanded beam 5 exposes photoplate 6 and the object 7, which is fixed on a rigid base 8. Laser light is reflected from the object to the photo plate from the reverse side. Two beams meet each other in the photo plate's plane: the first beam goes from the laser and it is called a "reference beam" and the second one, which goes from the object, is called a "signal beam". These beams create an interference pattern, which is registered on the photo plate. If we use a laser pointer, even the spatial filter, which raises uniformity of a beam and an expanding lens are not required, as the semi-conductor laser itself radiates quite homogeneous, divergent beam of light. Therefore for assembly of the Denisyuk's scheme, one should have a laser diode, the rigid support for photo plate fastening and the object itself. If it's necessary, one should use a rotary mirror 3, which directs a beam in a required direction.

Holographic plates

Holographic plates PFG-03m - transparent silver halide photo plates with very high resolution - more than 5000 lines/mm. They are used for recording reflection holograms in Denisyuk's scheme. They are sensitized to red spectrum to record holograms by He-Ne laser. These photoplates are suitable for hologram recording by laser diode as well.

Fastening of holographic scheme parts

It is known, the sand or fine gravel suppresses well mechanical oscillation and vibration. This property of fine gravel is valuable at creation of domestic holographic setup, as free-flowing materials are available in many shops. The phototray is filled with the gravel, see fig. avove. A clothes-pin is used for fastening of laser pointer, see fig. This allows placing the laser on gravel and at the same time pressing the button, so the laser constantly radiates a beam of light. The object (medal, coin or other small object) is put directly on gravel, which was condensed beforehand in an area of installation.

The photoplate is put up on three screws partially buried in gravel, since it is known, that the system with three basic points is steadiest. To direct a laser beam to the object under the necessary angle and to make the holographic scheme more compact, the large rotary mirror is installed under the angle about 45 degrees. Two simple forks are used as support for a mirror, see fig. The sequence of hologram recording is (white light is switched off), see fig. below.
1. A sheet of a white paper is put on the supporting screws; its size is equal to the size of a photoplate. Changing a position of laser pointer, one should achieve uniform illumination of a sheet of a paper.
2. Next step: a beam of the laser should be blocked by a sheet of black paper, then accurately replace a sheet of a white paper with a photoplate PFG-03m on the supporting screws. End face of a photoplate should be covered by a strip of black paper, in order to avoid exposure of end face by reference beam.
3. One should reserve time 1-2 minutes for complete stabilization of all elements of the scheme.
4. Then cautiously lift sheet of a black paper and expose photoplate 5-10 sec. Note: exact time of exposure should be found out before the procedure (see the article "Determination of exposing time of holograms").
5. Then there is a standard chemical photographic processing of a photoplate in a developer GP-3 and fixing solution.
6. If a grey veil is visible on the hologram and the image is not bright, this means the exposition is insufficient and it is necessary to increase exposure time. If the hologram has a dark brown color and the image is dim, this means, the hologram is overexposed and it's necessary to reduce exposure. If some dark strips are visible on the hologram, this means some of part of the scheme was displaced during hologram recording. It is necessary to check up carefully stability of a placement of all elements of the scheme, and then repeat procedure of hologram recording.

The holograms

Authors of this article have recorded several small reflection holograms of satisfactory quality using described scheme (see the photos).

Mentioned method of hologram recording, certainly does not allow obtaining holograms of high quality and big size. Its basic purpose is educational, in order to teach basics of applied holography to beginners and inspire them to start mastering of serious trends of a modern holography.