M. S. P., D. G., D. V., and B. K. acknowledge support of the Biological and bioinspired structures for multispectral surveillance, funded by NATO SPS (NATO Science for Peace and Security) 2019-2022. B. K., D. V., B. B., D. G., and M. S. P. acknowledge funding provided bythe Institute of Physics Belgrade, through the institutional funding bythe Ministry of Education, Science, and Technological Development of theRepublic of Serbia. Additionally, B. K. acknowledges support from F R S - FNRS. M. P. acknowledges support from the Ministry of Education, Science and Technological Development of the Republic of Serbia, Contract number 451-03-9/2021-14/200026. S. R. M. was supported by a BEWARE Fellowship of the Walloon Region (Convention n&#176;2110034), as a postdoctoral researcher. T. V. acknowledges financial support from the Hercules Foundation. D.V., M.S.P., D.G., M.P., B.B., and B.K. acknowledge the support of the Office of Naval Research Global through the Research Grant N62902-22-1-2024.&#160;This study was conducted in partial fulfillment of the requirements for the PhD degree of Marina Simovi&#263; Pavlovi&#263; at the University of Belgrade, Faculty of Mechanical Engineering.

1. Precharacterization
<ol>
	<li>Perform a full precharacterization of the sample.
	<ol>
		<li>Perform all experiments on dry specimens purchased from a commercial source. Store the samples in the laboratory, in a dry and dark place, at room temperature.</li>
		<li>Prior to holographic measurements, perform a complete sample characterization by scanning electronic microscope (SEM), linear optical spectroscopy, and nonlinear optical microscopy (NOM)10 (Figure 1).</li>
		<li>In addition to the optical properties of samples measured by linear techniques, gather supplementary information with higher intensity laser beams that allow characterization of their nonlinear optical properties.</li>
		<li>Use the corresponding nonlinear optical susceptibilities to quantify the nonlinear optical response and form the basis of nonlinear optical techniques such as nondestructive multiphoton excitation fluorescence and second harmonic generation (SHG), which are used to characterize various biological samples.</li>
		<li>For the nonlinear chemical phenomena occurring in the oscillating BR reaction, carry out the study of interferometric monitoring of the in situ phase transition from state I to state II with the following concentrations of reactants: [CH2(COOH)2]0 = 0.0789 mol dm-3, [MnSO4]0 = 0.0075 mol dm-3, [HClO4]0 = 0.03 mol dm-3, [KIO3]0 = 0.0752 mol dm-3, and [H2O2]0 = 1.269 mol dm-3 (0 after the bracket stands for the initial concentration at the beginning of the process). Make the total volume used for the BR reaction equal to 2.5 mL. 
		NOTE: The concentration values used here are equal to the ones in the study by Pagnacco et al.8, but with reaction volume divided by 10.</li>
	</ol>
	</li>
	<li>Prepare the sample for the experiment.
	<ol>
		<li>Use wings of the Queen of Spain fritillary butterfly, I. lathonia, for this experiment. Place the wing on a hard surface and make a section with a 10 mm diameter cutter. Place the sample in the sample box, which can be any container with a lid.</li>
	</ol>
	</li>
</ol>
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/63676/63676fig01.jpg" /> 
Figure 1: Wavy cross-section of butterfly wing scale. The cross-section was recorded on a nonlinear optical scanning microscope (A,B). A SEM observation (C) of a wing of the Queen of Spain fritillary butterfly, I. lathonia,&#160;was also done. This figure has been modified from14. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/63676/63676fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
2. Experimental setup
<ol>
	<li>Holographic setup 
	NOTE: The holographic interferometry measurements were performed with a tailor-made optical setup (Figure 2).
	<ol>
		<li>Adjust the laboratory temperature to be 23 &#176;C &#177; 0.2 &#176;C. Turn the laser on. Use a laser (details given in the Table of Materials) with an excitation wavelength of 532 nm for these holographic observations.</li>
		<li>Check the alignment of the optical elements (Figure 2). First, check that setup is made according to the scheme in Figure 2.</li>
		<li>Align the laser beam perfectly with the concave mirror M. Check and adjust the position of the optical beam expander (L).</li>
		<li>Determine the beam part that impinges on sample S and ensure that it forms a reflex beam O. Check if the rest of the beam is collected on a spherical mirror CM, to be used to generate the reference beam R. Check if the detector C is placed within the interference zone of the two specified beams. 
		NOTE: A complementary metal oxide semiconductor (CMOS) sensor is used as detector.</li>
		<li>Set up the cameras according to the instructions for the camera used. Set up an optical/photographic camera for the holographic experiment as shown in Figure 2 (C is the camera; details given in the Table of Materials). Set up a second optical/photographic camera to view visible changes in BR reaction and a thermal camera with a thermal resolution of 50 mK and a focal length of 13 mm above the optical table. 
		NOTE: The camera used in the holographic experiment does not use an objective lens; the light directly impinges on the chip.</li>
	</ol>
	</li>
	<li>Prepare the sample into holographic setup.
	<ol>
		<li>Prepare the wing sample as in step 1.2.1. Place the prepared sample on a round metal support with a diameter of 15 mm. The support has three existing holes for the screws to which the metal ring holding the sample is attached.</li>
		<li>Attach the ring to the support. Place the attached sample in the part of the sample mount located on the optical table.</li>
		<li>Prepare the sample for chemical reaction monitoring. On the optical table, in the intended place, place a support with a flat adhesive surface on which the cuvette/vessel will be placed.</li>
		<li>Prepare the reagent used to initialize the reaction as in step 1.1.5. Fill the reactants into the cuvette, and mix in cuvette in the following order of volumes and concentrations: 0.7 mL of 0.2817 mol dm-3 CH2(COOH)2; 0.5 mL of 0.0375 mol dm-3 MnSO4; 0.5 mL of 0.15 mol dm-3 HClO4; 0.5 mL of 0.376 mol dm-3 KIO3 ; and 0.3 mL of 10.575 mol dm-3 H2O2.</li>
		<li>Ensure that the total volume in the cuvette is 2.5 mL, and place it on the support in the setup.</li>
		<li>Set up additional instruments if needed. For monitoring the photophoretic effect, use an additional laser (details given in Table of Materials) for local heating.</li>
	</ol>
	</li>
</ol>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/63676/63676fig02.jpg" /> 
Figure 2: The holographic setup. The figure shows how the various components are arranged for the holographic experiment. Abbreviations: L1 = laser at 532 nm, L = biconvex lens, A = aperture, M = a flat mirror used to deflect the laser beam, CM = concave mirror, C = CMOS camera, S = butterfly wing section, R = reference beam, O = object beam. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/63676/63676fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
3. Setup of the software used
NOTE: Home-built C++ software based on Fresnel approximation11 is used to analyze data from holographic experiments. The software developed for the presented study can be found at .12 The details of software cannot be published at the moment; however, additional information will be provided on request. Fresnel approximation is extremely useful in digital holography since it focuses on different surfaces and zooms in on the area of the first diffraction order, which contains complete information about the recorded scene.
<ol>
	<li>Turn on the computer and run the software. 
	NOTE: The step for running the software depends on the software itself. There is no commercial software for this purpose.</li>
</ol>
4. Perform the experiment
<ol>
	<li>Switch off the external lights. Carry out the whole experiment in a dark room.</li>
	<li>Synchronize the cameras by using a chosen interval. For this experiment, start the holographic camera after 60 s, and the two other cameras immediately after it, using either a software or manually.</li>
	<li>Press the recording buttons and define in the software when the recording starts.</li>
	<li>Induce dynamical changes in the system of interest. The method of initiation depends on the type of sample; in the case of photophoretic effect, externally heat the sample by using the available lasers: 450 nm, 532 nm, 660 nm, 980 nm. In the case of the BR reaction, start the reaction by mixing the chemical reactants. Observe the holographic experiment.</li>
	<li>Set the photographic and thermal camera to follow the whole experiment and determine the moment of the end of the holographic recording from the optical and thermal measurements.</li>
	<li>Pronounce the end of the process. The end of the recording is preprogrammed, according to the estimated duration of the process. For the BR reaction, use solidification as the end of the reaction. In the case of the photophoretic effect, there is no such specific moment. In any case, this step emphasizes the importance of triple recording.</li>
</ol>
5. Acquisition of results12
<ol>
	<li>Save the results. Precisely sort the files as a function of time for reconstructing holograms and deeper data analysis. 
	NOTE: In this step, the data is transferred from the camera used for holography to the computer (hard disk) in folders named after the shooting dates. Use copy/paste and rename buttons.</li>
	<li>Check the probe hologram for appropriate settings. In this way, the best settings are selected on the first hologram by looking at it, and then used for the reconstruction of all holograms.
	<ol>
		<li>Choose one hologram by clicking on one of them from the folder you previously made (step 5.1) and make a reconstruction by clicking on the Reconstruct button.</li>
		<li>Change the settings to achieve the best image and make the reconstruction again. Options for adjusting parameters such as sampling, offset, and Fresnel distance will appear on the screen (software menu). Repeat these steps until the best settings are defined.</li>
		<li>Perform the reconstructions. Choose all the holograms by clicking the Open File button and choosing all files. Apply the desired parameters for numerical reconstruction of holograms; they remain unchanged after the step 5.2.1, so do not perform any action this time.</li>
		<li>Carry out the reconstructions using the Reconstruct button, and the interferograms by inserting the file names in the start with/end with field and then by clicking the button Batch. The interferograms appear in the previously made folder (in step 5.1). 
		NOTE: After recording a series of holograms in time, the first hologram represents an unperturbed state, while the action of an external force causes subsequent holograms. It is necessary to reconstruct the holograms using shifted Fresnel transform13.</li>
		<li>Obtain the interferograms by subtraction (in terms of complex numbers) of a particular hologram in time with the first hologram obtained. 
		NOTE: This protocol allows observing the effect of the force on the object. The change in the interference pattern as a function of time is a consequence of deformation or displacement that occurs within the system during the measurement. These changes are used to monitor the system&#39;s dynamics at the nanoscale.</li>
	</ol>
	</li>
</ol>
6. Analyses of the results
<ol>
	<li>Perform a visual analysis as the first quality control step of the process. In this step, look for visible changes in interference pattern and try to match the changes in the interference pattern with results obtained by optical and thermal measurements.</li>
	<li>Perform a cross-examination of all recordings. In this second phase of the analysis, thoroughly analyze the images visually from both the optical and thermal cameras with the holographic reconstructions in order to reveal dynamics at the nanoscale. In this way, the reaction moment is seen simultaneously in holographic, thermal, and photographic images.</li>
	<li>Make a graphical representation of results based on numerical/software analysis and present them in the form of graphs (1D, 2D, or 3D), charts, histograms etc. After a complete analysis of results, draw conclusions and anticipate further research based on this.</li>
</ol>

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The authors declare no conflict of interests.

In the presented biophotonic study, it is shown that a novel holographic method can be used to detect minimal morphological displacement or deformation caused by low-level thermal radiation.
The most critical step in holographic measurement with biological samples is the preparation step. The preparation of the sample (cutting/gluing to match the size of the holder) depends on the sample&#39;s mechanical properties, and it is not possible to have a standard protocol for this step.
Regarding the BR study, it is vital to have a transparent reaction vessel and relatively clear optical path, since every obstacle during a chemical reaction, or physical transformation (like the release of oxygen, impurity) will affect interference pattern and therefore recorded results.
In general, the most significant limitation of the described method is the sample size that can be studied. The sample must have an appropriate dimension to be inserted within the optical setup. 
Here we show that holographic interferometry (HI) should be considered as an essential complementary tool for the characterization of samples. For example, a classic optical/IR image captures information only regarding the intensity, while the information about the phase is totally lost18. Holographic interferometry provides all information regarding the intensity and phase, and additionally can be used to monitor their changes in real time.
The importance of exploiting this method in condensed matter science is to reveal in situ the slightest changes in system dynamics. For example, the BR reaction can reveal the first cause of the symmetry-breaking process. Is the symmetry-breaking process predetermined by physical constraints connected with nonlinear dynamics, or is the process truly random? On the other hand, in another way, can the minor differences in BR oscillatory period duration cause a significant deviation in transition appearance?
The presented results are the first step that will lead to a deeper understanding of dynamics at the nanoscale. Since the potential of holography in condensed science research has still not been fully recognized, the purpose of this article is to highlight the power of holography for future material science research and applications; for example, particle trapping and levitation such as movement of unburnt hydrocarbons in the atmosphere or separation of various aerosols19, breaking down of microplastics in water and fractionation of particles in general20, and characterisation of temperature and thermal conductivity properties of micron-size fuel particles21.

To fully understand and notice all the unique phenomena in the nanoworld, it is crucial to employ techniques that are capable of revealing all details regarding structures and dynamics at the nanoscale. On this account, the unique combination of linear and nonlinear methods, combined with the power of holography to reveal the system&#39;s dynamics at the nanoscale are presented.
The described holographic technique can be viewed as the triple rec method (rec is the abbreviation for recording), since at a given time the signal is simultaneously recorded by a photographic camera, a thermal camera, and an interferometer. Linear and nonlinear optical spectroscopy and holography are well-known techniques, the fundamental principles of which are extensively described in the literature1,2.
To cut a long story short, holographic interferometry allows the comparison of wavefronts recorded at different moments in time to characterize the dynamics of the system. It was previously used to measure vibrational dynamics3,4. The power of holography as the simplest interferometry method is based on its ability to detect the smallest displacement within the system. First, we exploited holography to observe and reveal the photophoretic effect5 (i.e., the displacement of deformation of a nanostructure due to a light-induced thermal gradient), in different biological structures. For a true presentation of the method, representative samples were selected from a number of tested biological specimens6. Wings of the Queen of Spain fritillary butterfly, Issoria lathonia (Linnaeus, 1758; I. lathonia), were used in the framework of this study.
After having successfully demonstrated the occurrence of photophoresis at the nanoscale in biological tissues, a similar protocol was applied to monitor the spontaneous symmetry breaking process7 caused by a phase transition in an oscillatory chemical reaction. In this part, the phase transition from a low concentration of iodide and iodine (called state I) to a high concentration of iodide and iodine with solid iodine formation (defined as state II) that occurs in a chemically nonlinear BR reaction was studied8,9. Here, we reported for the first time a holographic approach that allows studying such a phase transition and spontaneous symmetry breaking dynamics at the nanoscale occurring in condensed systems.

<table><tbody><tr><td>Active Vibration Isolation, Four Optical Table Supports</td><td>Thorlabs</td><td>PTR502</td><td>High Load Capacity: 2,500 kg, Height 600 mm</td></tr><tr><td>Cuvette</td><td></td><td></td><td>Standard glass cuvette</td></tr><tr><td>Holographic camera (optical camera for holography)</td><td>Cannon</td><td>EOS 50D</td><td>Sensor Size 22.3 x 14.9 mm; Pixel pitch 4.69 &amp;micro;m; Max. resolution 4752 x 3168; JPEG file format</td></tr><tr><td>Hydrogen peroxide, H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt;</td><td>Merck (Darmstadt, Germany)</td><td></td><td></td></tr><tr><td>Laser</td><td>Laser Quantum</td><td>Torus 532 laser</td><td>Wavelength 532 nm; Power 390 mW; Coherence length 10 m</td></tr><tr><td>LED lasers</td><td></td><td></td><td></td></tr><tr><td>Malonic acid, C&lt;sub&gt;3&lt;/sub&gt;H&lt;sub&gt;4&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt;</td><td>Acr&lt;img alt=&quot;Equation 10&quot; src=&quot;/files/ftp_upload/63676/63676eq10.png&quot;/&gt;s Organics (Geel, Belgium)</td><td></td><td></td></tr><tr><td>Manganese sulphate,&amp;nbsp; MnSO&lt;sub&gt;4&lt;/sub&gt;</td><td>Fluka (Buchs, Switzerlend)</td><td></td><td></td></tr><tr><td>Nonlinear optical microscope</td><td>IPB</td><td></td><td></td></tr><tr><td>Optical accessories</td><td>Thorlab</td><td></td><td></td></tr><tr><td>Optical spectroscope</td><td></td><td></td><td></td></tr><tr><td>Optical table</td><td>Thorlabs</td><td>TOP450II PTR52509</td><td>dimensions 2000*1250*310 mm</td></tr><tr><td>Perchloric acid, HClO&lt;sub&gt;4&lt;/sub&gt;</td><td>Merck (Darmstadt, Germany)</td><td></td><td></td></tr><tr><td>Potassium iodate, KIO&lt;sub&gt;3&lt;/sub&gt;</td><td>Merck (Darmstadt, Germany)</td><td></td><td></td></tr><tr><td>Software</td><td></td><td></td><td>Home-build software made by one of the authors: Dusan Grujic. This software was conducted in partial fulfillment of the requirements for the PhD deegree of D.G.</td></tr><tr><td>Thermal camera</td><td>Flir</td><td>A65</td><td>640x512 pixel; Thermal resolution 50 mK</td></tr><tr><td>Video camera</td><td>Nikon</td><td>1v3</td><td>18.4 Mpixel; 60 fps</td></tr></tbody></table>

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.

A photophoretic effect was induced and monitored in a first experiment on the wing of a Morpho menelaus butterfly5. The effect was initiated by the action of LED lasers of different wavelengths (450 nm, 532 nm, 660 nm, and 980 nm). Here, the wings from an I. lathonia butterfly14 were used. After the recording procedure, the hologram image was reconstructed.
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/63676/63676fig03.jpg" /> 
Figure 3: I. lathonia wings&#39; holographic reconstructions. The reconstruction was done at 450 nm initiation (A), 532 nm initiation (B), and 980 nm initiation (C). The images show an obvious difference in the visual sense, where depending on the wavelength, the colored area appears in different sizes. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/63676/63676fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The fringes observed in Figure 3A-C are the consequence of the interference. This figure clearly shows that changes occur only during the irradiation of the sample with a second laser (placed to hit the sample with a beam that does not interfere with the beam from the primary laser; put into operation at any time during the recording), and confirms that holographic interferometry can be used to monitor the deformation or displacement of the biological tissues.
Figure 3A-C shows how different wavelengths between 450 nm (Figure 3A), 532 nm (Figure 3B), and 980 nm (Figure 3C) affect the interferometric pattern by causing different morphological displacements within the tissues.
In the second experiment regarding the oscillatory BR reaction, this reaction started immediately after the addition of hydrogen peroxide, producing a large amount of oxygen (Figure 4A). As the transition from state I to state II (Figure 4) is essentially irreproducible for an individual kinetic run8, the moment of transition is very difficult to monitor. Therefore, the presented results are the consequence of a large number of attempts. In the analysis of interferograms, a change in the fringe pattern was noticed at the exact moment when the reaction occurred (i.e., when transition from state I to state II occurred). Figure 4E shows a moment before the reaction occurred (left) and the exact moment (right). The wavelength used here is 573 nm. When calculating the displacement data from the amplitude image, the method of direct fringe counting was used. One fringe corresponds to a displacement of half the wavelength (i.e., 286.5 nm). If the displacement data is calculated from the phase, the following relation applies: &#916;l/&#955; = &#916;&#934;/2&#960;.
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/63676/63676fig04.jpg" /> 
Figure 4: The transition from state I to state II in Briggs-Rauscher (BR) reaction. The different recordings for the transition from state I to state II in Briggs-Rauscher (BR) reaction. (A) The beginning of the BR reaction with bubbles corresponds to oxygen and carbon dioxide formation. (B) The state I to state II reaction course. (C) The end of state I to state II transition. (D) Cuvette in setup. (E) Interferogram of the moment before reaction (left) and the moment of reaction (right). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/63676/63676fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Nonlinear chemical phenomena have been known for more than 100 years15, but despite this, there are still doubts about their full mechanism and dynamics16,17. The results obtained open new possibilities for the investigation and monitoring of such complex chemical phenomena in situ by a holographic technique.

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Uncovering Hidden Dynamics of Natural Photonic Structures Using Holographic Imaging

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. ...

uncovering-hidden-dynamics-natural-photonic-structures-using

Nanyang Technological University

Research

JoVE Journal

Chemistry

2.5K Views.  University of Belgrade. Dit is de eerste keer, voor zover we weten, dat holografische techniek werd gebruikt om foto's te controleren op rassen bij insectentweelingen en gezichtsovergang in niet-evenwichtsomstandigheden. Het voordeel van deze niet-invasieve techniek ligt in het feit dat het geen significante verstoring van het systeem veroorzaakt. Dit is bijvoorbeeld van groot belang voor niet-evenwichtsstudies.Niet-lineaire optica en holografie geven inzicht in complexe georganiseerde structuren die we in al...

Video: Uncovering Hidden Dynamics of Natural Photonic Structures Using Holographic Imaging

Fabrication And Characterization Of Photonic Crystal Slow Light Waveguides And Cavities

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view and for its considerable potential for practical applications. Slow light photonic crystal waveguides, in particular, have played a major part and have been successfully employed for delaying optical signals1-4 and the enhancement of both linear5-7 and nonlinear devices.8-11
Photonic crystal cavities achieve similar effects to that of slow light waveguides, but over a reduced band-width. These cavities offer high Q-factor/volume ratio, for the realization of optically12 and electrically13 pumped ultra-low threshold lasers and the enhancement of nonlinear effects.14-16 Furthermore, passive filters17 and modulators18-19 have been demonstrated, exhibiting ultra-narrow line-width, high free-spectral range and record values of low energy consumption.
To attain these exciting results, a robust repeatable fabrication protocol must be developed. In this paper we take an in-depth look at our fabrication protocol which employs electron-beam lithography for the definition of photonic crystal patterns and uses wet and dry etching techniques. Our optimised fabrication recipe results in photonic crystals that do not suffer from vertical asymmetry and exhibit very good edge-wall roughness. We discuss the results of varying the etching parameters and the detrimental effects that they can have on a device, leading to a diagnostic route that can be taken to identify and eliminate similar issues.
The key to evaluating slow light waveguides is the passive characterization of transmission and group index spectra. Various methods have been reported, most notably resolving the Fabry-Perot fringes of the transmission spectrum20-21 and interferometric techniques.22-25 Here, we describe a direct, broadband measurement technique combining spectral interferometry with Fourier transform analysis.26 Our method stands out for its simplicity and power, as we can characterise a bare photonic crystal with access waveguides, without need for on-chip interference components, and the setup only consists of a Mach-Zehnder interferometer, with no need for moving parts and delay scans.
When characterising photonic crystal cavities, techniques involving internal sources21 or external waveguides directly coupled to the cavity27 impact on the performance of the cavity itself, thereby distorting the measurement. Here, we describe a novel and non-intrusive technique that makes use of a cross-polarised probe beam and is known as resonant scattering (RS), where the probe is coupled out-of plane into the cavity through an objective. The technique was first demonstrated by McCutcheon et al.28 and further developed by Galli et al.29

Use of photonic crystal slow light waveguides and cavities has been widely adopted by the photonics community in many differing applications. Therefore fabrication and characterization of these devices are of great interest. This paper outlines our fabrication technique and two optical characterization methods, namely: interferometric (waveguides) and resonant scattering (cavities).

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view ...

Engineering

Using Microwave and Macroscopic Samples of Dielectric Solids to Study the Photonic Properties of Disordered Photonic Bandgap Materials

Recently, disordered photonic materials have been suggested as an alternative to periodic crystals for the formation of a complete photonic bandgap (PBG). In this article we will describe the methods for constructing and characterizing macroscopic disordered photonic structures using microwaves. The microwave regime offers the most convenient experimental sample size to build and test PBG media. Easily manipulated dielectric lattice components extend flexibility in building various 2D structures on top of pre-printed plastic templates. Once built, the structures could be quickly modified with point and line defects to make freeform waveguides and filters. Testing is done using a widely available Vector Network Analyzer and pairs of microwave horn antennas. Due to the scale invariance property of electromagnetic fields, the results we obtained in the microwave region can be directly applied to infrared and optical regions. Our approach is simple but delivers exciting new insight into the nature of light and disordered matter interaction.

Our representative results include the first experimental demonstration of the existence of a complete and isotropic PBG in a two-dimensional (2D) hyperuniform disordered dielectric structure. Additionally we demonstrate experimentally the ability of this novel photonic structure to guide electromagnetic waves (EM) through freeform waveguides of arbitrary shape.

Disordered structures offer new mechanisms for forming photonic bandgaps and unprecedented freedom in functional-defect designs. To circumvent the computational challenges of disordered systems, we construct modular macroscopic samples of the new class of PBG materials and use microwaves to characterize their scale-invariant photonic properties, in an easy and inexpensive manner.

Recently, disordered photonic materials have been suggested as an alternative to periodic crystals for the formation of a complete photonic bandgap (PBG). ...

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 ...

Demonstration of a Hyperlens-integrated Microscope and Super-resolution Imaging

The use of super-resolution imaging to overcome the diffraction limit of conventional microscopy has attracted the interest of researchers in biology and nanotechnology. Although near-field scanning microscopy and superlenses have improved the resolution in the near-field region, far-field imaging in real-time remains a significant challenge. Recently, the hyperlens, which magnifies and converts evanescent waves into propagating waves, has emerged as a novel approach to far-field imaging. Here, we report the fabrication of a spherical hyperlens composed of alternating silver (Ag) and titanium oxide (TiO2) thin layers. Unlike a conventional cylindrical hyperlens, the spherical hyperlens allows for two-dimensional magnification. Thus, incorporation into conventional microscopy is straightforward. A new optical system integrated with the hyperlens is proposed, allowing for a sub-wavelength image to be obtained in the far-field region in real time. In this study, the fabrication and imaging setup methods are explained in detail. This work also describes the accessibility and possibility of the hyperlens, as well as practical applications of real-time imaging in living cells, which can lead to a revolution in biology and nanotechnology.

The use of a hyperlens has been regarded as a novel super-resolution imaging technique due to its advantages in real-time imaging and its simple implementation with conventional optics. Here, we present a protocol describing the fabrication and imaging applications of a spherical hyperlens.

The use of super-resolution imaging to overcome the diffraction limit of conventional microscopy has attracted the interest of researchers in biology and ...

Spectral and Angle-Resolved Magneto-Optical Characterization of Photonic Nanostructures

Photonic crystals are periodic nanostructures that can support a variety of confined electromagnetic modes. Such confined modes are usually accompanied by local enhancement of electric field intensity that strengthens light-matter interactions, enabling applications such as surface-enhanced Raman scattering (SERS) and surface plasmon enhanced sensing. In the presence of magneto-optically active materials, the local field enhancement gives rise to anomalous magneto-optical activity. Typically, the confined modes of a given photonic crystal depend strongly on the wavelength and incidence angle of the incident electromagnetic radiation. Thus, spectral and angular-resolved measurements are needed to fully identify them as well as to establish their relationship with the magneto-optical activity of the crystal. In this article, we describe how to use a Fourier-plane (back focal plane) microscope to characterize magneto-optically active samples. As a model system, here we use a plasmonic grating built out of magneto-optically active Au/Co/Au multilayer. In the experiments, we apply a magnetic field on the grating in situ and measure its reciprocal space response, obtaining the magneto-optical response of the grating over a range of wavelengths and incident angles. This information enables us to build a complete map of the plasmonic band structure of the grating and the angle and wavelength dependent magneto-optical activity. These two images allow us to pinpoint the effect that the plasmon resonances have on the magneto-optical response of the grating. The relatively small magnitude of magneto-optical effects requires a careful treatment of the acquired optical signals. To this end, an image processing protocol for obtaining magneto-optical response from the acquired raw data is laid out.

Photonic band structure enables understanding how confined electromagnetic modes propagate within a photonic crystal. In photonic crystals that incorporate magnetic elements, such confined and resonant optical modes are accompanied by enhanced and modified magneto-optical activity. We describe a measurement procedure to extract the magneto-optical band structure by Fourier space microscopy.

Photonic crystals are periodic nanostructures that can support a variety of confined electromagnetic modes. Such confined modes are usually accompanied by ...

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.

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 ...

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 ...

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 ...

Bioengineering

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 ...

Biology

Evaluation and Manipulation of Neural Activity Using Two-Photon Holographic Microscopy

Recent advances in optical bioimaging and optogenetics have enabled the visualization and manipulation of biological phenomena, including cellular activities, in living animals. In the field of neuroscience, detailed neural activity related to brain functions, such as learning and memory, has now been revealed, and it has become feasible to artificially manipulate this activity to express brain functions. However, the conventional evaluation of neural activity by two-photon Ca2+ imaging has the problem of low temporal resolution. In addition, manipulation of neural activity by conventional optogenetics through the optic fiber can only simultaneously regulate the activity of neurons with the same genetic background, making it difficult to control the activity of individual neurons. To solve this issue, we recently developed a microscope with a high spatiotemporal resolution for biological applications by combining optogenetics with digital holographic technology that can modify femtosecond infrared laser beams. Here, we describe protocols for the visualization, evaluation, and manipulation of neural activity, including the preparation of samples and operation of a two-photon holographic microscope (Figure 1). These protocols provide accurate spatiotemporal information on neural activity, which may be useful for elucidating the pathogenesis of neuropsychiatric disorders that lead to abnormalities in neural activity.

We developed a two-photon holographic microscope that can visualize, assess, and manipulate neural activity using high spatiotemporal resolution, with the aim of elucidating the pathogenesis of neuropsychiatric disorders that are associated with abnormal neural activity.

Uncovering Hidden Dynamics of Natural Photonic Structures Using Holographic Imaging

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