Cherry Optical Holography
What is Holography?
By Nancy Gorglione
A Hologram is a three-dimensional photograph recorded through the positive interference of waves of laser light. Clear film windows of space, holograms can contain projected images, floating out in front of the hologram. Receding background images mark depth in space, while parallax - the ability to see around objects to objects placed behind, reinforces the true three dimensional effect for the viewer. Moving Holograms portray moments in time. And, Holograms can be breathtakingly beautiful.
Holography as Art Form is a profound media which allows the artist to record a three dimensional image that can contain aspects of both time and space, on a single, flat film plane. Moving, kinetic colorations; additive color mixture; time smear; space within space, and parallax plays; depth and projection; overlapping of imagery; all can produce stunning effects unique to the media.
A Hologram is a diffraction record of the positive interference of two wave fronts of laser light. Originally recorded on a photosensitive emulsion, the hologram is composed of a series of very fine lines which diffract or bend the reconstruction light back on the path of the original object. A hologram is a diffraction record of the in-phase light waves that reached the holographic film during its exposure.
Holography Graphics developed for Forsyth Gallery at Texas A & M University by N. Gorglione. Copyright 2017The Object Light is the light that illuminates the object, then bounces off the object and strikes the film. The Reference Beam is a clean spread of collimated laser light covering the film. Where the Object Beam and the Reference Beam meet on the film, they record the image in all its true three-dimensional glory. We Reconstruct the original holographic image by shining a light through the holographic film at the same angle as the original Reference Beam. This angle is called the reconstruction angle. Read more about it on our Transmission Hologram Art Page and Reflection Hologram Art Page.
All waves obey all ways
The positive interference of the Object and Reference Beams record the holographic image. An analog is ocean waves, which can be observed reinforcing each other to grow larger, or splashing into each other to diminish in size. Where the peaks or troughs of our laserâs waves meet in the holographic film, the parts that reinforce each other -called Positive Interference, are bright enough and energized enough to start an energy transition in the holographic film. Since a laser used for holography is coherent in time and space, it emits a continuous stream of light waves whose peaks and troughs travel on the same paths together, in-phase.
Holography continuous wave lasers emit a clean single mode or stream of in-phase photons, coherent in time and space. Pulsed lasers emit very bright brief coherent flashes to record animate objects, portraiture; while multiple pulses can produce interferograms.
The most common holographic film contains very fine resolution grains of silver halide evenly distributed throughout a binding and adhering gelatin. The basic exposure formula is
âabsorption of the photon supplies energy to free an electron which can move through the crystal latticeâ (of the silver halide gelatin film.) At one of the evenly distributed crystal imperfections, the freed electron is trapped. This further attracts interstitial ions (charged particles) of silver which continue to build up throughout the exposure. âA latent image spec of of at least 3 or 4 silver atoms is necessary for catalyzing development.â
Quotes and paraphrasing of: Silver Halide Photographic Materials, by K. Biedermann, in Holographic Recording Materials in Topics in Applied Physics, Vol. 20. Edited by H.M. Smith Spinger-Verlag, Berlin Heidelberg, New York.
After exposure, the film is developed, stopped, and then bleached, which re-halogenates the silver and turns it into a salt which kind of acts like a series of miniature lenses. The Reconstruction Light bends around or through these holographic lenses, called Zone Plates, to reconstruct the original object. A series of Zone Plates creates the Diffraction Matrix of our Hologram. If both Object and Reference beams are more fully collimated, ( minimal or no spread as the beams travel through space) the Diffraction Matrix can resemble microscopic lateral lines rather than overlapping circles. The middle of the page on Reflection Hologram Art illustrates zone plates and interference.
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