The present research was conducted by the Research Grant of Kwangwoon University in 2019.

CAUTION: All appropriate safety practices must be followed when using lasers12 and chemical products, including the use of personal protective equipment such as safety goggles, glasses, gloves, and lab coats.
1. Content creation
<ol>
	<li>Model the different elements of the scene (character and background) with 3D computer graphics programs such as Blender, a free and open-source 3D software toolset.</li>
	<li>Create a 12-frame cyclic animation with the 3D computer graphics program.</li>
	<li>3D print and paint the different elements.
	<ol>
		<li>Print characters and background at the same scale using a fused deposition modeling (FDM) monochrome 3D printer13, with a white polylactic acid (PLA) filament.</li>
		<li>Use sandpaper to eliminate printing defects.</li>
		<li>Hand-paint the different elements with acrylic paint. 
		CAUTION: To avoid unpleasant odors, paint outdoors or use ventilation.</li>
	</ol>
	</li>
	<li>Set up the recording box. Fix the background in a rigid wooden box to avoid movement and place the different 3D printed characters inside one after another to allow the recording of the different 4 inch x 5 inch holograms. 
	NOTE: To avoid movement during hologram recording, firmly attach the individual elements using glue or plasticine, without applying stress.</li>
</ol>
2. Hologram recording
<ol>
	<li>On an optical table, assemble a Denisyuk single-beam full-color optical setup9,10 to record the holograms. 
	NOTE: To record the different holograms, the three RGB lasers used are a red HeNe, 633 nm, 20 mW; a green diode-pumped solid-state (DPSS), 532 nm, 100 mW adjusted to 20 mW; and a blue DPSS 473 nm 50 mW adjusted to 20 mW. The spatial filter is equipped with a 40x, 0.65 NA achromatic microscope objective and a 10 &#956;m pinhole.
	<ol>
		<li>Combine the 3 laser beams (red, green, and blue) with an X-cube prism to get a white laser beam that passes through the same spatial filter. 
		NOTE: Use two mirrors for the red and blue lasers to get four degrees of freedom and perfectly align the three beams.</li>
		<li>From a distance of 1 m and an angle of 45&#176;, illuminate the recording box with the divergent beam.</li>
		<li>Adjust the distance of the three lasers from the cube to get similar beam diameters projected on the object plane. 
		NOTE: The recording box has to be illuminated with a wide, clean and homogeneous divergent white beam.</li>
	</ol>
	</li>
	<li>Use a power meter to adjust the color balance and determine the exposure time.
	<ol>
		<li>Measure the intensity of each laser horizontally, at the position of the holographic plate (see Table of Materials). Since the plate material is isopanchromatic, adjust the color balance equally for the 3 lasers. 
		NOTE: The power-meter used allows direct reading of the power of the 633 nm red laser. For the 473 nm blue and 532 nm green lasers, it is necessary to apply a correction coefficient (x0.4 for blue and x0.6 for green).</li>
		<li>Determine the exposure time before recording the hologram, according to the following formula: 
		<img alt="Equation 1" src="/files/ftp_upload/60459/60459eq1.jpg" /> (1)</li>
		<li>where t is the exposure time (s), H the sensitivity of the material (J/cm2) and E the intensity of the laser (W/cm2). E is measured at the position of the holographic plate with a power meter. 
		NOTE: The sensitivity of the materials used here is 200 &#956;J/cm2 per laser for a full-color (RGB) hologram. The intensity of each laser at the position of the holographic plate, measured with the power-meter is 17 &#956;W/cm&#178; per laser, and the exposure time is 12 s according formula (1).</li>
	</ol>
	</li>
	<li>Close the laser beam with a shutter. 
	NOTE: Use an electronic shutter with a timer to control the exposure time precisely.</li>
	<li>Prepare plates. 
	CAUTION: Handle the plate edges using gloves, and do not allow skin contact with the emulsion at any time.
	<ol>
		<li>Remove holographic plates them from the refrigerator to avoid a shift and store them at room temperature (20&#8211;25 &#176;C) for 1 h before recording. 
		NOTE: The plates used here have to be refrigerated at 4 &#176;C.</li>
		<li>Darken the upper edge of the plate with a black marker to avoid internal reflection.</li>
	</ol>
	</li>
	<li>Set up the recording plate under a green safelight.
	<ol>
		<li>Blow onto the plate to determine the emulsion side. Steam appears only on the glass side.</li>
		<li>Place the holographic plate emulsion-side down on the recording box. Allow it to stabilize for 5 min before recording.</li>
	</ol>
	</li>
	<li>Open the shutter to expose the recording plate, during the time previously calculated with the formula (1).</li>
	<li>Keep the recorded plate in a closed box away from light.</li>
</ol>
3. Hologram development
NOTE: Holograms are developed with a safe and non-staining chemical process developed for the ultimate emulsions.
<ol>
	<li>Once the plate has been exposed, prepare 100 mL of developer for a 4 inch x 5 inch plate. Mix the developer at a ratio of 1 part developer to 10 parts distilled or demineralized water (1:10). 
	NOTE: The developer is stocked in a concentrated solution in a closed bottle to prevent oxidation and needs to be diluted with distilled or demineralized water just before processing.</li>
	<li>Heat the developer to 22 &#176;C precisely. 
	NOTE: The water temperature must be equal to or greater than 20 &#176;C for the developer to function properly. For repetitions, control the temperature before development with a thermometer.</li>
	<li>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 4 min precisely. At the end of the development, the plate attains a pale yellow/orange color. 
	NOTE: The development process becomes visible a few seconds after the plate is fully covered with the developer. Use an insulated tray with a lid to maintain a constant temperature during development. Further development to attempt to get a black density is not required.</li>
	<li>Remove the developer and wash the plate in its tray under running tap water for 30 s, allowing the water to overflow into a sink.</li>
	<li>Under normal light, place the developed plate in the tray and submerge it quickly, emulsion-side up, into the bleach without agitation until the plate becomes fully transparent. The bleaching process becomes visible a few seconds after the plate is fully submerged. 
	NOTE: The typical bleaching time is 3 to 5 min at room temperature (20&#8211;25 &#176;C).</li>
	<li>Remove the bleach and wash the plate in its tray under running tap water for 2 min, allowing the water to overflow into a sink. 
	NOTE: When the plate is still in a wet state after bleaching, a hologram can be observed by transmission with a halogen spot. When the hologram is successful, this image will appear very strong.</li>
	<li>Place the plate in the tray and submerge it, emulsion-side up, into a demineralized or distilled water solution with some drops of wetting agent without agitation for 1 min.</li>
	<li>Remove the plate from the tray and dry it vertically for 15-20 min.</li>
	<li>Repeat these operations for each of the 12 holograms. Before recording, in order to place the different objects in the recording box with great precision, apply a holographic onion-skin method by replacing the previous transparent hologram at its recording position, and observe both images at the same time under laser illumination to check that the new character is well-positioned. 
	NOTE: Onion skinning is a procedure usually used in stop-motion animation to see two different frames at the same time.</li>
</ol>
4. Hologram sealing
NOTE: Holograms are protected by a second clean glass plate sealed to the hologram using optical ultraviolet (UV) glue.
<ol>
	<li>Use a scalpel to scrape off 5 mm of the emulsion around the edges. 
	NOTE: This operation is easier when the plate is still wet.</li>
	<li>Laminate the hologram to a clean glass plate of equal size (4 inch x 5 inch), with 1 mL of UV glue. 
	NOTE: To facilitate lamination, pre-heat the glue, the hologram and the clean glass plate in an oven at 30 &#176;C for 10 min.</li>
	<li>Expose the clean glass side of the hologram to sunlight; the UV glue will harden within 5 min. 
	NOTE: It is also possible to use a UV lamp, but strong UV exposure should be avoided.</li>
	<li>Wash the sealed hologram with water and soap, dry it with tissue paper and blacken the back of it with matte black spray paint.</li>
</ol>
5. Fantatrope assembly and operation
<ol>
	<li>Mount the 12 holograms in chronological order in the regularly placed frames of a Fantatrope. 
	NOTE: Gentet et al. 20197 describe the manufacture and operation of a Fantatrope.</li>
	<li>Rotate the Fantatrope at constant speed. An RGB LED strobe light synchronized with the rotation speed successively illuminates the different frames to create a rapid succession of images and produce the illusion of movement. 
	NOTE: A rotation of one turn per second is enough to get the sense of a fluid motion.</li>
</ol>

<ol>
	<li>Geng, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-dimensional+display+technologies.">Three-dimensional display technologies.</a> Advances in Optics and Photonics. 5 (4), 456-535 (2013).</li><li>Lim, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=360-degree+tabletop+electronic+holographic+display.">360-degree tabletop electronic holographic display.</a> Optics Express. 24 (22), 2499 (2016).</li><li>Sugie, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-performance+parallel+computing+for+next-generation+holographic+imaging.">High-performance parallel computing for next-generation holographic imaging.</a> Nature Electronics. 1 (4), 254 (2018).</li><li>Ogle, K. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Some+aspects+of+stereoscopic+depth+perception.">Some aspects of stereoscopic depth perception.</a> JOSA. 57, 1073-1081 (1967).</li><li>Read, J. C. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Balance+and+coordination+after+viewing+stereoscopic+3D+television.">Balance and coordination after viewing stereoscopic 3D television.</a> Royal Society Open Science. 2, 140522 (2015).</li><li>Lambooij, M., Ijsselsteijn, W., Fortuin, M., Heynderickx, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visual+discomfort+and+visual+fatigue+of+stereoscopic+displays:+a+review.">Visual discomfort and visual fatigue of stereoscopic displays: a review.</a> Journal of Imaging Science and Technology. 53 (3), 1-14 (2009).</li><li>Gentet, P., Joung, J., Gentet, Y., Hamacher, A., Lee, S. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fantatrope,+a+moving+hologram+display:+design+and+implementation.">Fantatrope, a moving hologram display: design and implementation.</a> Optics Express. 27 (8), 11571-11584 (2019).</li><li>Denisyuk, Y. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+reproduction+of+the+optical+properties+of+an+object+by+the+wave+field+of+its+scattered+radiation.">On the reproduction of the optical properties of an object by the wave field of its scattered radiation.</a> Optics and Spectroscopy. 14, 279-284 (1963).</li><li>Bjelkhagen, H. I., Brotherton-Ratcliffe, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Ultra-realistic imaging: advanced techniques in analogue and digital colour holography. , (2013).</li><li>Graham, S., Zacharovas, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Practical Holography, Fourth Edition. , (2015).</li><li>Gentet, P., Gentet, Y., Lee, S. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultimate+04+the+new+reference+for+ultra-realistic+color+holography.">Ultimate 04 the new reference for ultra-realistic color holography.</a> 2017 International Conference on Emerging Trends &amp; Innovation in ICT (ICEI). , 162-166 (2017).</li><li>International Electrotechnical Commission. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=IEC+60825-1:+2014.+Safety+of+laser+products-Part+1:+Equipment+classification+and+requirements.">IEC 60825-1: 2014. Safety of laser products-Part 1: Equipment classification and requirements.</a> IEC Geneva. 3, (2014).</li><li>Kun, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reconstruction+and+development+of+a+3D+printer+using+FDM+technology.">Reconstruction and development of a 3D printer using FDM technology.</a> Procedia Engineering. 149, 203-211 (2016).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Covestro Deutschland AG, Bayfol HX200 Datasheet. , (2018).</li><li>Bjelkhagen, H. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Silver+Halide+Recording+Materials+for+Holography+and+Their+Processing.">Silver Halide Recording Materials for Holography and Their Processing.</a> Springer Series in Optical Sciences. 66, (1993).</li></ol>

Philippe Gentet, Lyoung-Hui Kim, Kwang-Jib Kim and Seung-Hyun Lee declare that they have no conflict of interest. Yves Gentet is the manufacturer of the emulsion used here.

Traditionally, stop-motion film uses puppets or clay models. To avoid movement and obtain a bright image at the time of hologram recording, a set of 3D printed characters and backgrounds are chosen. Furthermore, the different elements are attached firmly and without stress in the box. If an element is fixed with constraint or moves during the recording, it will appear black or fringed in the final hologram. 3D printing is a very interesting new tool for creating original models for analog holography.
<p class="jove_c...

Three-dimensional (3D) displays are an important research topic1,2,3 and most of the current approaches use the stereoscopic principle4 that causes visual discomfort and fatigue5,6. The Fantatrope is a convenient new type of dynamic holographic 3D display that can show a short animation in full color without the need for special viewing aids7. A Fantatrope uses a series of twelve full-color holograms corresponding to the different phases of an animation. All holograms used in this device must be ultra-realistic and present the same brightness, transparency, and homogeneous colors. The recording of a single high-quality full-color hologram remains difficult even for experienced practitioners. While the choices of the recording technique and holographic material are important key points, there are several more details that are crucial to successfully record such holograms.
For this protocol, a cyclic sequence of twelve different images is first created with a 3D computer graphics program and all the elements are 3D printed to become hologram models. These holograms are recorded with the single-beam method8 introduced by Yuri Denisyuk in 1963 that allows the recording of ultra-realistic holograms with a 180&#176; full-parallax. A Denisyuk full-color setup uses three different lasers (red, green, and blue) combined to get a white laser beam. Silver-halide emulsions are the best choice of recording material9 and only a few silver-halide full-color emulsions are available9,10. Furthermore to record the blue wavelength without blur, an iso-panchromatic emulsion with a resolution of more than 10,000 lines/mm is required.
In this protocol, the set of holograms are recorded on 4 inch x 5 inch plates, using a material that is specially designed for recording full-color analog holograms without any diffusion and is made isopanchromatic for all the common visible lasers used in color holography (see Table of Materials). The grain is so fine (4 nm) that any visible wavelength can be recorded inside without any diffusion11. Furthermore, each hologram is developed using a safe, non-staining chemical process developed for the ultimate emulsions.
This detailed protocol is intended to help new and experienced practitioners in the field of analog holography to avoid many common pitfalls associated with recording full-color Denisyuk holograms; it can also provide an approach to learn how to use ultimate silver-halide holographic materials and chemicals to obtain reliable and reproducible results.

<table><tbody><tr><td>Black marker</td><td>Monami</td><td>Magic Cap</td><td></td></tr><tr><td>FDM monochrome 3D printer</td><td>Anet</td><td>A8</td><td></td></tr><tr><td>Holographic bleach</td><td>Ultimate Holography</td><td>BLEACH-1L</td><td>Non-toxic</td></tr><tr><td>Holographic developer</td><td>Ultimate Holography</td><td>REV-U08-1.2</td><td>Non-toxic</td></tr><tr><td>Holographic plates</td><td>Ultimate Holography</td><td>U04P-VICOL-4X5</td><td>Light-sensitive</td></tr><tr><td>Laser (DPSS 532 nm 100 mW)</td><td>Cobolt</td><td>Samba</td><td>Follow safety practices</td></tr><tr><td>Laser (DPSS 473 nm 50 mW)</td><td>Cobolt</td><td>Blue</td><td>Follow safety practices</td></tr><tr><td>Laser (HeNe 633 nm 21 mW)</td><td>Thorlabs</td><td>HNL210L</td><td>Follow safety practices</td></tr><tr><td>Laser power meter</td><td>Sanwa</td><td>LP1</td><td></td></tr><tr><td>Matte black spray paint</td><td>Plasti-kote</td><td>3101</td><td></td></tr><tr><td>Microscope objective</td><td>Edmund Optics</td><td>40X 0.65 NA</td><td></td></tr><tr><td>Pinhole</td><td>Edmund Optics</td><td>10 &amp;mu;m</td><td></td></tr><tr><td>Spatial Filter Movement</td><td>Edmund Optics</td><td>39-976</td><td></td></tr><tr><td>UV glue</td><td>Vitralit</td><td>6127</td><td>Use gloves</td></tr><tr><td>Wetting agent</td><td>Kodak</td><td>Photo-Flo</td><td></td></tr><tr><td>White PLA filament</td><td>Hatchbox</td><td>PLA-1KG1.75-BLK</td><td></td></tr><tr><td>X-cube</td><td>Edmund Optics</td><td>54-823</td><td></td></tr></tbody></table>

recording ultra-realistic full-color analog holograms for use in a moving hologram display

This paper demonstrates a method to record a set of twelve ultra-realistic full-color analog holograms presenting the same brightness, transparency and homogeneous colors for the fabrication of a Fantatrope, a dynamic holographic 3D display, without the need for special viewing aids. The method involves the use of 3D printer technology, a single-beam full-color Denisyuk optical setup with three low-power lasers (red, green, and blue) and an iso-panchromatic high-sensitive silver-halide holographic emulsion specially designed for recording analog holograms without any diffusion. A cyclic animation is created with a 3D computer graphics program and different elements are 3D printed to form models for the holograms. Holograms are recorded with a full-color holographic setup and developed using two simple chemical baths. To prevent any emulsion thickness variations, the holograms are sealed with optical glue. Results confirm that all holograms recorded with this protocol present the same characteristics, which allow them to be used in the Fantatrope.

3D content was created and a cyclic sequence of twelve images was imagined, and the different elements were then 3D printed and painted (Figure 1). A Denisyuk single-beam full-color optical setup was assembled to record holograms (Figure 2). After recording, the holograms were developed and sealed (Figure 3) to obtain a set of twelve ultra-realistic full-color analog holograms with a 180&#176; full-parallax, showing the same brightness, transparency and homogeneous color...

Watch this Scientific Journal Video about Recording Ultra-Realistic Full-Color Analog Holograms for Use in a Moving Hologram Display at JoVE.com

Recording Ultra-Realistic Full-Color Analog Holograms for Use in a Moving Hologram Display

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.

This paper demonstrates a method to record a set of twelve ultra-realistic full-color analog holograms presenting the same brightness, transparency and ...

recording-ultra-realistic-full-color-analog-holograms-for-use-moving

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9.6K Views.  Kwangwoon University. 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.

Video: Recording Ultra-Realistic Full-Color Analog Holograms for Use in a Moving Hologram Display

High-resolution, High-speed, Three-dimensional Video Imaging with Digital Fringe Projection Techniques

Digital fringe projection (DFP) techniques provide dense 3D measurements of dynamically changing surfaces.&#160;Like the human eyes and brain, DFP uses triangulation between matching points in two views of the same scene at different angles to compute depth.&#160;However, unlike a stereo-based method, DFP uses a digital video projector to replace one of the cameras1. The projector rapidly projects a known sinusoidal pattern onto the subject, and the surface of the subject distorts these patterns in the camera&#8217;s field of view. Three distorted patterns (fringe images) from the camera can be used to compute the depth using triangulation.
Unlike other 3D measurement methods, DFP techniques lead to systems that tend to be faster, lower in equipment cost, more flexible, and easier to develop.&#160;DFP systems can also achieve the same measurement resolution as the camera.&#160;For this reason, DFP and other digital structured light techniques have recently been the focus of intense research (as summarized in1-5). Taking advantage of DFP, the graphics processing unit, and optimized algorithms, we have developed a system capable of 30&#160;Hz 3D video data acquisition, reconstruction, and display for over 300,000 measurement points per frame6,7.&#160;Binary defocusing DFP methods can achieve even greater speeds8.
Diverse applications can benefit from DFP techniques. Our collaborators have used our systems for facial function analysis9, facial animation10, cardiac mechanics studies11, and fluid surface measurements, but many other potential applications exist.&#160;This video will teach the fundamentals of DFP techniques and illustrate the design and operation of a binary defocusing DFP system.

This video describes the fundamentals of digital fringe projection techniques, which provide dense 3D measurements of dynamically changing surfaces.&#160;It also demonstrates the design and operation of a high-speed binary defocusing system based on these techniques.

Digital fringe projection (DFP) techniques provide dense 3D measurements of dynamically changing surfaces.&#160;Like the human eyes and brain, DFP uses ...

Construction of a High Resolution Microscope with Conventional and Holographic Optical Trapping Capabilities

High resolution microscope systems with optical traps allow for precise manipulation of various refractive objects, such as dielectric beads 1 or cellular organelles 2,3, as well as for high spatial and temporal resolution readout of their position relative to the center of the trap. The system described herein has one such "traditional" trap operating at 980 nm. It additionally provides a second optical trapping system that uses a commercially available holographic package to simultaneously create and manipulate complex trapping patterns in the field of view of the microscope 4,5 at a wavelength of 1,064 nm. The combination of the two systems allows for the manipulation of multiple refractive objects at the same time while simultaneously conducting high speed and high resolution measurements of motion and force production at nanometer and piconewton scale.

The system described herein employs a traditional optical trap as well as an independent holographic optical trapping line, capable of creating and manipulating multiple traps. This allows for the creation of complex geometric arrangements of refractive particles while also permitting simultaneous high-speed, high-resolution measurements of the activity of biological enzymes.

High resolution microscope systems with optical traps allow for precise manipulation of various refractive objects, such as dielectric beads 1 or cellular ...

Compact Lens-less Digital Holographic Microscope for MEMS Inspection and Characterization

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and automotive. However, effective inspection and characterization metrology systems are needed to ensure the functional reliability of MEMS. This study presents a system based on digital holography as a tool for MEMS metrology. Digital holography has gained increasing attention in the past 20 years. With the fast development and decreasing cost of sensor arrays, resolution of such systems has increased broadening potential applications. Thus, it has attracted attention from both research and industry sides as a potential reliable tool for industrial metrology. Indeed, by recording the interference pattern between an object beam (which contains sample height information) and a reference beam on a CCD camera, one can retrieve the quantitative phase information of an object. However, most of digital holographic systems are bulky and thus not easy to implement on industry production lines. The novelty of the system presented is that it is lens-less and thus very compact. In this study, it is shown that the Compact Digital Holographic Microscope (CDHM) can be used to evaluate several characteristics typically consider as criteria in MEMS inspections. The surface profiles of MEMS in both static and dynamic conditions are presented. Comparison with AFM is investigated to validate the accuracy of the CDHM.

We present a compact reflection digital holographic system (CDHM) for inspection and characterization of MEMS devices. A lens-less design using a diverging input wave providing natural geometrical magnification is demonstrated. Both static and dynamic studies are presented.

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and ...

Characterization of Anisotropic Leaky Mode Modulators for Holovideo

Holovideo displays are based on light-bending spatial light modulators. One such spatial light modulator is the anisotropic leaky mode modulator. This modulator is particularly well suited for holographic video experimentation as it is relatively simple and inexpensive to fabricate1-3. Some additional advantages of leaky mode devices include: large aggregate bandwidth, polarization separation of signal light from noise, large angular deflection and frequency control of color1. In order to realize these advantages, it is necessary to be able to adequately characterize these devices as their operation is strongly dependent on waveguide and transducer parameters4. To characterize the modulators, the authors use a commercial prism coupler as well as a custom characterization apparatus to identify guided modes, calculate waveguide thickness and finally to map the device's frequency input and angular output of leaky mode modulators. This work gives a detailed description of the measurement and characterization of leaky mode modulators suitable for full-color holographic video.

This work describes fabrication and characterization of anisotropic leaky mode modulators for holographic video.

Holovideo displays are based on light-bending spatial light modulators.  One such spatial light modulator is the anisotropic leaky mode modulator.  This ...

Shaping the Amplitude and Phase of Laser Beams by Using a Phase-only Spatial Light Modulator

The aim of this article is to visually demonstrate the utilization of an interferometric method for encoding complex fields associated with coherent laser radiation. The method is based on the coherent sum of two uniform waves, previously encoded into a phase-only spatial light modulator (SLM) by spatial multiplexing of their phases. Here, the interference process is carried out by spatial filtering of light frequencies at the Fourier plane of certain imaging system. The correct implementation of this method allows arbitrary phase and amplitude information to be retrieved at the output of the optical system.
It is an on-axis, rather than off-axis encoding technique, with a direct processing algorithm (not an iterative loop), and free from coherent noise (speckle). The complex field can be exactly retrieved at the output of the optical system, except for some loss of resolution due to the frequency filtering process. The main limitation of the method might come from the inability to operate at frequency rates higher than the refresh rate of the SLM. Applications include, but are not limited to, linear and non-linear microscopy, beam shaping, or laser micro-processing of material surfaces.

We show how to encode the complex field of laser beams by using a single phase element. A common-path interferometer is employed to mix the phase information displayed into a phase-only spatial light modulator to finally retrieve the desired complex field pattern at the output of an optical imaging system.

The aim of this article is to visually demonstrate the utilization of an interferometric method for encoding complex fields associated with coherent laser ...

Demonstration of Spin-Multiplexed and Direction-Multiplexed All-Dielectric Visible Metaholograms

The optical holography technique realized by metasurfaces has emerged as a novel approach to projective volumetric display and information encryption display in the form of ultrathin and almost flat optical devices. Compared to the conventional holographic technique with spatial light modulators, the metahologram has numerous advantages such as miniaturization of optical setup, higher image resolution and larger field of visibility for holographic images. Here, a protocol is reported for the fabrication and optical characterization of optical metaholograms that are sensitive to the spin and direction of incident light. The metasurfaces are composed of hydrogenated amorphous silicon (a-Si:H), which has large refractive index and small extinction coefficient in the entire visible range resulting in high transmittance and diffraction efficiency. The device produces different holographic images when the spin or direction of incident light are switched. Therefore, they can encode multiple types of visual information simultaneously. The fabrication protocol consists of film deposition, electron beam writing and subsequent etching. The fabricated device can be characterized using a customized optical setup that consists of a laser, a linear polarizer, a quarter waveplate, a lens and a charge-coupled device (CCD).

We present a protocol for fabrication of spin- and direction-multiplexed visible metaholograms, then conduct an optical experiment to verify their function. These metaholograms can easily visualize encoded information, so they can be used for projective volumetric display and information encryption.

The optical holography technique realized by metasurfaces has emerged as a novel approach to projective volumetric display and information encryption ...

Uncovering Hidden Dynamics of Natural Photonic Structures Using Holographic Imaging

In this method, the potential of optics and holography to uncover hidden details of a natural system's dynamical response at the nanoscale is exploited. In the first part, the optical and holographic studies of natural photonic structures are presented as well as conditions for the appearance of the photophoretic effect, namely, the displacement or deformation of a nanostructure due to a light-induced thermal gradient, at the nanoscale. This effect is revealed by real-time digital holographic interferometry monitoring the deformation of scales covering the wings of insects induced by temperature. The link between geometry and nanocorrugation that leads to the emergence of the photophoretic effect is experimentally demonstrated and confirmed. In the second part, it is shown how holography can be potentially used to uncover hidden details in the chemical system with nonlinear dynamics, such as the phase transition phenomenon that occurs in complex oscillatory Briggs-Rauscher (BR) reaction. The presented potential of holography at the nanoscale could open enormous possibilities for controlling and molding the photophoretic effect and pattern formation for various applications such as particle trapping and levitation, including the movement of unburnt hydrocarbons in the atmosphere and separation of different aerosols, decomposition of microplastics and fractionation of particles in general, and assessment of temperature and thermal conductivity of micron-size fuel particles.

The paper is primarily focused on the combined power of optical (linear and nonlinear) and holographic methods used to reveal phenomena at the nanoscale. The results obtained from the biophotonic and oscillatory chemical reactions' studies are given as representative examples, highlighting holography's ability to reveal dynamics at a nanoscale.

In this method, the potential of optics and holography to uncover hidden details of a natural system's dynamical response at the nanoscale is exploited. ...

Chemistry

Transmission of Multiple Signals through an Optical Fiber Using Wavefront Shaping

The transmission of multiple independent optical signals through a multimode fiber is accomplished using wavefront shaping in order to compensate for the light distortion during the propagation within the fiber. Our methodology is based on digital optical phase conjugation employing only a single spatial light modulator, where the optical wavefront is individually modulated at different regions of the modulator, one region per light signal. Digital optical phase conjugation approaches are considered to be faster than other wavefront shaping approaches, where (for example) a complete determination of the wave propagation behavior of the fiber is performed. In contrast, the presented approach is time-efficient since it only requires one calibration per light signal. The proposed method is potentially appropriate for spatial division multiplexing in communications engineering. Further application fields are endoscopic light delivery in biophotonics, especially in optogenetics, where single cells in biological tissue have to be selectively illuminated with high spatial and temporal resolution.

We demonstrate the transmission of multiple independent signals through a multimode fiber using wavefront shaping employing a single spatial light modulator. By modulating the wavefront for each signal individually, spatially separated foci are transmitted. Potential applications are multiplexed data transfer in communications engineering and endoscopic light delivery in biophotonics.

The transmission of multiple independent optical signals through a multimode fiber is accomplished using wavefront shaping in order to compensate for the ...

Bioengineering

Quantifying Microorganisms at Low Concentrations Using Digital Holographic Microscopy (DHM)

Accurately detecting and counting sparse bacterial samples has many applications in the food, beverage, and pharmaceutical processing industries, in medical diagnostics, and for life detection by robotic missions to other planets and moons of the solar system. Currently, sparse bacterial samples are counted by culture plating or epifluorescence microscopy. Culture plates require long incubation times (days to weeks), and epifluorescence microscopy requires extensive staining and concentration of the sample. Here, we demonstrate how to use off-axis digital holographic microscopy (DHM) to enumerate bacteria in very dilute cultures (100-104 cells/mL). First, the construction of the custom DHM is discussed, along with detailed instructions on building a low-cost instrument. The principles of holography are discussed, and a statistical model is used to estimate how long videos should be to detect cells, based on the optical performance characteristics of the instrument and the concentration of the bacterial solution (Table 2). Video detection of cells at 105, 104, 103, and 100 cells/mL is demonstrated in real time using un-reconstructed holograms. Reconstruction of amplitude and phase images is demonstrated using an open-source software package.

Quantifying Microorganisms at Low Concentrations Using Digital Holographic Microscopy DHM

Digital holographic microscopy (DHM) is a volumetric technique that allows imaging samples 50-100X thicker than brightfield microscopy at comparable resolution, with focusing performed post-processing. Here DHM is used for identifying, counting, and tracking microorganisms at very low densities and compared with optical density measurements, plate count, and direct count.

Accurately detecting and counting sparse bacterial samples has many applications in the food, beverage, and pharmaceutical processing industries, in ...

Digital Inline Holographic Microscopy (DIHM) of Weakly-scattering Subjects

Weakly-scattering objects, such as small colloidal particles and most biological cells, are frequently encountered in microscopy. Indeed, a range of techniques have been developed to better visualize these phase objects; phase contrast and DIC are among the most popular methods for enhancing contrast. However, recording position and shape in the out-of-imaging-plane direction remains challenging. This report introduces a simple experimental method to accurately determine the location and geometry of objects in three dimensions, using digital inline holographic microscopy (DIHM). Broadly speaking, the accessible sample volume is defined by the camera sensor size in the lateral direction, and the illumination coherence in the axial direction. Typical sample volumes range from 200 &#181;m&#160;x 200 &#181;m&#160;x 200 &#181;m using LED illumination, to 5 mm&#160;x 5 mm&#160;x 5 mm or larger using laser illumination. This illumination light is configured so that plane waves are incident on the sample. Objects in the sample volume then scatter light, which interferes with the unscattered light to form interference patterns perpendicular to the illumination direction. This image (the hologram) contains the depth information required for three-dimensional reconstruction, and can be captured on a standard imaging device such as a CMOS or CCD camera. The Rayleigh-Sommerfeld back propagation method is employed to numerically refocus microscope images, and a simple imaging heuristic based on the Gouy phase anomaly is used to identify scattering objects within the reconstructed volume. This simple but robust method results in an unambiguous, model-free measurement of the location and shape of objects in microscopic samples.

Digital Inline Holographic Microscopy DIHM of Weakly-scattering Subjects

The three-dimensional locations of weakly-scattering objects can be uniquely identified using digital inline holographic microscopy (DIHM), which involves a minor modification to a standard microscope. Our software uses a simple imaging heuristic coupled with Rayleigh-Sommerfeld back-propagation to yield the three-dimensional position and geometry of a microscopic phase object.

Weakly-scattering objects, such as small colloidal particles and most biological cells, are frequently encountered in microscopy. Indeed, a range of ...