Holographic printers

There is a very interesting method of recording multiplex holograms consisting of miniature elements called holopixels.

Holopixels – these are tiny Fourier images of the angles of a synthesized hologram obtained from frames of multi-angle shooting of a three-dimensional scene. The method is based on the same principle as Lippman's integral photography. The elements of Lippman's optical raster are replaced by miniature holograms with a diameter of 0.5 mm, simulating the work of a photographic lens raster.

A fragment of the optical part of a digital holoprinter. A pulsed tricolor laser forms coherent pulses of red, green, and blue, which are used to record color holopixels on photographic material.

In order to understand how holographic printing occurs, imagine that we cut all the frames of multi-angle shooting into tiny squares. Then we assemble new matrices from the first, second, third and so on elements of the angles. The images of the matrices, built on a computer, are reproduced on a liquid crystal monitor (3), located in the focal plane of the lens (2). A laser beam of light, having passed through a liquid crystal modulator, is focused by the lens (2) on a photosensitive emulsion (4) into a spot with a diameter of about 0.5 mm. From the back of the photo emulsion, a narrow reference laser beam (5) of the same diameter is directed to the point being recorded. Thus, a sequential recording of many holopixels occurs, corresponding to each point of the synthesized reflective hologram.

Scheme of transformation (shown in color) of photographic angles into holopixel matrices.

Display synthesis is usually performed by three lasers with radiation of red, green and blue colors. By precisely combining color-separated holopixels on the photo emulsion, a full-color volumetric image is obtained.

The figure shows a diagram of a holographic printer developed in 1999 by employees of the Geola laboratory.

The setup utilizes three pulsed lasers emitting red (R), blue (B), and green (G). Each laser beam is split by a semitransparent mirror (1) into two components. One component forms an object beam and is directed by prisms (2) and (3) into an expander consisting of lenses (4) and (5). The expanded beam of laser light passes through a digital LCD modulator (6). A short-focus lens (7) collects the modulated light beam into a small spot with a diameter of 1 to 0.5 mm. The second beam is reflected from the semitransparent mirror (1) toward the mirror (10), which directs it to the same point (but from the reverse side) of the photosensitive film, into which the holopixel is focused by the lens (7). The holographic photographic material moves from point to point in the horizontal direction as the holopixels are printed, and is rewound from the feed reel (8) to the receiving reel (9) at the moment of transition to a new line. This is how digital printing of multiplex holographic displays occurs.

Digital three-colour hologram of the Fabergé Coronation Easter Egg, produced by CERESHOLOGRAPHICS (UK, 2015)

Colored holograms synthesized by this method amaze the viewer with their large size, depth of space and dynamic effects. Digital hologram 3×1.5 m by RabbitHoles (Canada).

There are practically no size limitations for such holograms, since they can be manufactured and assembled in parts. But here difficulties arise with the sources of restoration of such holograms. It is advisable to view printed holographic displays from a fairly large distance. At close range, our eye begins to distinguish “pixelation”.

An important advantage of this technology is that the synthesis process is one-step and does not require subsequent copying in order to obtain a reflective hologram.

Colored holographic displays synthesized from photographic angles are produced by such companies as: “Geola” (Vilnius, Lithuania), “ZebraImaging” (USA), “Yves Gente Holographic Studio” (Bordeaux, France), the domestic enterprise “SmirnHolo” and others.

Thanks to the existence of this method, photographers today have fantastic opportunities to create their works in three dimensions using computers.