Engineering
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Recording Ultra-Realistic Full-Color Analog Holograms for Use in a Moving Hologram Display
Chapters
Summary January 14th, 2020
We present a protocol to record a set of ultra-realistic full-color analog holograms, showing the same brightness, transparency, and homogeneous colors, on ultra-fine-grain silver-halide holographic emulsions for the fabrication of a dynamic holographic 3D display.
Transcript
The recording of a single high-quality analog hologram remains difficult even for experienced practitioners. This protocol gives several crucial key points and details to successfully record such holograms. This protocol allows getting a set of ultra-realistic full-color holograms presenting the same brightness, transparency and homogenous colors with the use of the ultimate holographic material and chemicals.
This detailed protocol is intended to help new and also experienced practitioners in the field of analog holography to avoid many common pitfalls associated with recording full-color holograms. This visual demonstration of this method is critical to highlight all details that allow having reproducible results and get good holograms. To begin, model the different elements to the scene with 3D computer graphics program Blender, a free and open source 3D software tool set.
Create a 12-frame cyclic animation. Print characters and background at the same scale using a fused deposition modeling monochrome 3D printer with a white polylactic acid filament. Use sandpaper to eliminate printing defects.
Hand paint the different elements with acrylic paint. Set up the recording box and fix the background in a rigid wooden box to avoid movement. Using glue or plasticine, firmly attach the 3D printed character inside the box without applying stress.
On an optical table with green safelight, assemble a Denisyuk single beam full-color optical setup to record the holograms. Use a red helium neon laser 633 nanometers and 20 milliwatts, a green diode-pumped solid-state 532 nanometers and 20 milliwatts, and a blue diode-pumped solid-state 473 nanometers and 20 milliwatts. Position two mirrors for the red and blue lasers to get four degrees of freedom.
Combine the three laser beams with an X-cubed prism to get a white laser beam that passes through the same spatial filter. From a distance of one meter and an angle of 45 degrees, illuminate the recording box with the divergent beams. Use the red and blue mirrors to get a homogenous white beam projected on the object plane.
With a power meter, measure the intensity of each laser horizontally at the position of the holographic plate. Determine the exposure time according to the manuscript. Close the laser beam with a shutter.
The electronic shutter with a timer is able to control the exposure time precisely. To prepare plates under a green safelight, remove the holographic plates from the refrigerator and store them at room temperature in a closed black box for one hour before recording. Darken the upper edge of the plate with a black marker to avoid internal reflection.
Then set up the recording plate. Blow onto the plate to determine the emulsion side with no steaming appearing. Place the holographic plate emulsion side down on the recording box.
Allow it to stabilize for five minutes before recording. Open the shutter to expose the recording plate for the calculated amount of exposure time. Then keep the recorded plate in a closed box away from light.
Under normal light, mix 10 milliliters of developer with 90 milliliters of distilled or demineralized water in a tray. Heat the developer to 22 degrees Celsius precisely in a microwave and check with a thermometer. Under a green safelight, place the exposed plate in the tray and submerge it quickly emulsion side up into the developer and agitate slowly for four minutes precisely.
Remove the developer and wash the plate in its tray under running tap water for 30 seconds allowing the water to overflow into a sink. Under normal light, the plate has a pale yellow or orange color. Place the developed plate in the tray with bleach and submerge it quickly emulsion side up without agitation.
Keep the plate in the bleach until it becomes fully transparent. Remove the bleach and wash the plate in its tray under running tap water for two minutes allowing the water to overflow into a sink. Then fill the tray with demineralized or distilled water solution with some drops of wetting agent and submerge the plate in the tray emulsion side up without agitation for one minute.
Next, remove the plate from the tray and dry it vertically for 15 to 20 minutes. The hologram is visible under white light illumination. To place the next object in the recording box with great precision, use a holographic onion skin method under a green safelight by replacing the previous transparent hologram at its recording position and observing both images at the same time under laser illumination to check that the new character is well positioned.
While the plate is still wet, use a scalpel to scrape off five millimeters of the emulsion around the edges. Heat one milliliter of UV glue, the hologram, and a clean glass plate of the equal size in an oven at 30 degrees Celsius for 10 minutes. Laminate the hologram to the clean glass plate with a glue.
Expose the clean glass side of the hologram to sunlight and the UV glue hardens within five minutes. Then wash the sealed hologram with water and soap, dry it with tissue paper. Blacken the back of it with matte black spray paint.
Mount the 12 holograms in chronological order in the regularly placed frames in the cylinder of the Fantatrope. Rotate the Fantatrope gradually until it reaches a constant speed of two turns per second. An RGB LED strobe light synchronized with the rotation speed successfully illuminates the different frames to create a rapid succession of images and produce the illusion of movement.
In this protocol, a Denisyuk single beam full-color optical setup was assembled to record analog holograms. After recording, the holograms were developed, bleached and sealed to obtain a set of 12 ultra-realistic full-color analog holograms with a 180 degree showing the same brightness, transparency, and homogenous colors. The Fantatrope with the 12 full-color analog holograms mounted in chronological order was successfully operated.
It generated the effect of a dynamic 3D display without the need for any special viewing aids. When rotation speed of the cylinder accelerated, the character appeared as if it was in motion. To get reproducible results, illuminate the plate with three homogenous beams, use a parameter to determine the exposure time and respect the same development times and temperature for each plate.
To prevent any image and thickness variations, holograms are sealed with glue. The sealed holograms can be flipped and used like masters to record H2 floating holograms with the same setup. The recording of holograms presenting the same brightness, transparency, and homogenous colors allow the creation of the phototrope, the first dynamic holographic display.
Ultimate holographic plates are developed with a safe and non-staining chemical process, but use personal protective equipment like goggles, glasses, gloves, and lab coats when using lasers, glue, and paint.
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