This work was financially supported by the National Research Foundation (NRF) grants (NRF-2019R1A2C3003129, CAMM-2019M3A6B3030637, NRF-2019R1A5A8080290) funded by the Ministry of Science and ICT of the Korean government. I.K. acknowledges the NRF Global Ph.D. fellowship (NRF-2016H1A2A1906519) funded by the Ministry of Education of the Korean government.

1. Device fabrication
NOTE: Figure 1 shows the fabrication process of a-Si:H metasurfaces17.
<ol>
	<li>Prepare a fused silica wafer piece (size = 2 cm x 2 cm, thickness = 500 &#181;m) as a substrate. Rinse the substrate with acetone and isopropyl alcohol (IPA) then blow nitrogen gas over the substrate to dry it.</li>
	<li>Deposit a 380 nm thick a-Si:H film on the substrate using plasma-enhanced chemical vapor deposition (PECVD) with the following settings: chamber temperature = 300 &#176;C; radio frequency power = 800 W; gas flow rate = 10&#160;sccm for SiH4 and 75 sccm for H2; process pressure = 25 mTorr; time = 30 s.</li>
	<li>Spin-coat an e-beam lithography photoresist. Drop polymethyl methacrylate (PMMA) A2 onto the substrate and spin-coat with a rotation speed of 2,000 rpm for 1 min.</li>
	<li>Bake the resist-coated substrate on a hotplate at 180 &#176;C for 5 min.</li>
	<li>Spin-coat a conductive polymer layer to prevent charge accumulation during the e-beam writing process. Drop the conductive polymer (e.g., Espacer) onto the substrate and spin-coat with a rotation speed of 2,000&#160;rpm for 1 min.</li>
	<li>Run e-beam lithography with an acceleration voltage of 80 kV and a current of 50 pA.</li>
	<li>Immerse the sample in deionized (DI) water for 2 min to remove the conductive polymer layer. Immerse the sample in 1:3 methyl isobutyl ketone (MIBK):IPA solution surrounded by an iced cup for 12 min to develop the exposed pattern. Then rinse the sample with IPA for 30 s.</li>
	<li>Deposit a 30 nm thick chromium (Cr) film by using an e-beam evaporator.</li>
	<li>Immerse the sample in acetone to remove the unexposed photoresist layer and transfer the Cr pattern onto the substrate. Sonicate for 1 min at 40 kHz, then rinse with IPA for 30 s.</li>
	<li>Etch the uncovered a-Si:H layer to transfer the Cr pattern into the a-Si:H layer using a dry etcher with a source power of 500 W, bias of 100 V, gas flow rates of 80 sccm for Cl2 and 120 sccm for HBr.</li>
	<li>Immerse the sample in a Cr etchant solution to remove the Cr etch mask. Then rinse the sample sequentially with acetone, IPA and DI water for 30 s, respectively.</li>
</ol>
2. Scanning electron microscope characterization
<ol>
	<li>Spin-coat a conductive polymer layer to prevent charge accumulation during the electron beam scanning process. Drop the conductive polymer onto the substrate and spin-coat at a rotation speed of 2,000 rpm for 1 min.</li>
	<li>Fix the substrate onto the sample holder using carbon tape. Vent the load lock chamber by pressing the AIR button.</li>
	<li>Put the holder onto the holding rod of the load-lock chamber. Evacuate the load lock chamber by pressing the EVAC button.</li>
	<li>Set the stage height and tilting angle by setting the Z sensor to 8 mm and the T sensor to 0&#176;.</li>
	<li>Open the load lock chamber door by pressing the OPEN button. Press the holding rod to transfer the holder to the main scanning electron microscope (SEM) chamber. Pull out the rod and press the CLOSE button.</li>
	<li>Check the vacuum state before turning on the electron gun. Execute the flashing function by pressing the FLASHING button to remove carbon or dust in the electron gun with an instant high voltage.</li>
	<li>Turn on the electron gun with an accelerating voltage of 5 kV by clicking the ON button in the SEM software.</li>
	<li>Adjust the beam alignment to precisely locate the electron beam in the center position by clicking the BEAM ALIGNMENT panel in the software. Using a stage controller, locate the beam in the center.</li>
	<li>Adjust the aperture alignment and stigma alignment to make a circular electron beam by clicking the APERTURE ALIGNMENT panel in the software. Using a stigma controller, make a stable beam to scan on the same spot.</li>
	<li>Capture SEM images with an appropriate focus and stigmator adjustment.</li>
	<li>Turn off the electron beam by clicking the OFF button in the software. Click the HOME button to return the stage to its original position.</li>
	<li>Open the door of the main chamber and push the rod to pick up the sample holder. Vent the load lock chamber by pressing the AIR button, then unload the holder.</li>
	<li>Rinse the sample with DI water to remove the conductive polymer layer.</li>
</ol>
3. Optical characterization of the spin-multiplexed metahologram
<ol>
	<li>Prepare optical components listed in Table of Materials.</li>
	<li>Attach the diode laser module to an adapter that can be plugged into a 1 inch optical mount. Adjust the height of the diode laser by using a post and a post holder, and fix the position by using a clamp. 
	NOTE: Every optical component should be mounted using a post and a post holder, then fixed in position by using a clamp.</li>
	<li>Assemble the half-wave plate by using a 1 inch rotational mount, then place the plate in front of the laser module to rotate the linearly-polarized light.</li>
	<li>Prepare two mirrors by mounting them on 1 inch kinematic mounts and one alignment disk to align the direction of initial beam.
	<ol>
		<li>Place the alignment disk in front of the laser and set the height. Place the two mirrors so that the beam bends twice at 90&#176; each to be alternating directions.</li>
		<li>Place the alignment disk near the second mirror and adjust the angle of the first mirror by rotating knobs to align the light in the center.</li>
		<li>Place the alignment disk far from the second mirror and adjust the angle of the second mirror by rotating knobs to align the light in the center.</li>
		<li>Repeat steps 3.4.2 and 3.4.3 until the light passes through the center of an alignment disk in both places.</li>
	</ol>
	</li>
	<li>Place a neutral density filter behind the mirror to control the intensity of light. Place an iris behind the neutral density filter to control the diameter of incident light.</li>
	<li>To make a circularly polarized light, place a linear polarizer and a quarter wave plate in order behind the iris. Mount each component on its own rotational mount.</li>
	<li>Attach the fabricated metasurface to a plate with a hole and mount the plate on the XY translation mount for rectangular optics. Adjust the XY translation mount so that light is directed to the pattern in the sample.</li>
	<li>Place a lens after the metasurface. Adjust the position of lens to be placed at the focal length. Place a CCD after the lens to capture a hologram image.</li>
</ol>
4. Optical characterization of the direction-multiplexed metahologram
<ol>
	<li>Prepare two beam splitters, two mirrors, lens and CCD. 
	NOTE: This setup can be built from the spin-multiplexed metahologram setup by adding additional components.</li>
	<li>Place a beam splitter between the quarter-wave plate and the XY translation mount to split the beam into two directions. Place another beam splitter between the XY translation mount and the lens. 
	NOTE: One beam path is the same as the previous spin-multiplexed metahologram setup. Here, another split beam will be aligned to illuminate a sample in the opposite direction to the previous setup.</li>
	<li>Place two mirrors so that the beam bends twice at 90&#176; each to form alternating directions and adjust the beam to be directed into the second beam splitter. Finely align the light so that the beam irradiates the sample correctly in the opposite direction.</li>
	<li>Place another lens at 90&#176; to the right of the first beam splitter and place a CCD to capture a hologram image from the opposite direction.</li>
</ol>

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The a-Si:H metasurfaces were fabricated in three major steps: a-Si:H thin film deposition using PECVD, precise EBL, and dry etching. Among these steps, the EBL writing process is the most important. First, the pattern density on metasurfaces is quite high, so the process requires precise control over the electron dose (energy) and scanning parameters such as number of dots per unit area. The development condition should also be chosen carefully. The density of the pattern is very high, so when the development process is ...

Optical metasurfaces composed of sub-wavelength nanostructures have enabled many interesting optical phenomena, including optical cloaking1, negative refraction2, perfect light absorption3, color filtering4, holographic image projection5, and beam manipulation6,7,8. Optical metasurfaces that have appropriately-designed scatterers can modulate the spectrum, wavefront and polarization of light. Early optical metasurfaces were mainly fabricated using noble metals (e.g., Au, Ag) due to their high reflectivity and ease of nanofabrication, but they have high Ohmic losses, so the metasurfaces have low efficiency at short visible wavelengths.
Development of nanofabrication techniques for dielectric materials that have low losses in visible light (e.g., TiO29, GaN10, and a-Si:H11) has enabled realization of highly efficient flat optical devices with optical metasurfaces. These devices have applications in optics and engineering. One intriguing application is optical holography for projective volumetric display and information encryption. Compared to conventional holograms that use spatial light modulators, the metahologram has numerous advantages such as miniaturization of optical setup, higher resolution of holographic images and larger field of visibility.
Recently, encoding of multiple holographic information in a single-layered metahologram device has been achieved. Examples include metaholograms that are multiplexed in spin12,13, orbital angular momentum14, incident light angle15, and direction16. These efforts have overcome the critical shortcoming of metaholograms, which is a lack of design freedom in a single device. Most conventional metaholograms could only produce single encoded holographic images, but multiplexed device can encode multiple holographic images in real time. Hence, the multiplexed metahologram is a crucial solution platform towards real holographic video display or multifunctional anticounterfeiting holograms.
Reported here are protocols to fabricate spin- and direction-multiplexed all-dielectric visible metaholograms, then to optically characterize them13,16. To encode multiple visual information in a single metasurface device, metaholograms are designed which show two different holographic images when the spin or direction of incident light are changed. To fabricate highly efficient holographic images in a manner comparable with CMOS technology, a-Si:H is used for the metasurfaces and dual magnetic resonances and antiferromagnetic resonances induced inside them are exploited. The fabrication protocol consists of film deposition, electron beam writing, and etching. The fabricated device is characterized using a customized optical setup composed of a laser, a linear polarizer, a quarter waveplate, a lens and a charge-coupled device (CCD).

<table border="0" cellpadding="0" cellspacing="0" style="width:881px;" width="880">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Aceton</td>
			<td style="width:187px;">J.T. Baker</td>
			<td style="width:201px;">925402</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Beam splitter</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">CCM1-BS013/M</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Chromium etchant</td>
			<td style="width:187px;">KMG</td>
			<td style="width:201px;">Cr-7</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Chromium evaporation source</td>
			<td style="width:187px;">Kurt J. Lesker</td>
			<td style="width:201px;">EVMCR35D</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Clamp</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">CP175</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Conducting polymer</td>
			<td style="width:187px;">Showa denko</td>
			<td style="width:201px;">E-spacer</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Diode laser</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">CPS635</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">E-beam evaporation system</td>
			<td style="width:187px;">Korea Vacuum Tech</td>
			<td style="width:201px;">KVE-E4000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">E-beam resist</td>
			<td style="width:187px;">Microchem</td>
			<td style="width:201px;">495 PMMA A2</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Electron beam lithography</td>
			<td style="width:187px;">Elionix</td>
			<td style="width:201px;">ELS-7800</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Half-wave plate</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">AHWP05M-600</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Inductively-coupled plasma reactive ion etching</td>
			<td style="width:187px;">DMS</td>
			<td style="width:201px;">-</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Iris</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">SM1D12</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Isopropyl alcohol</td>
			<td style="width:187px;">J.T. Baker</td>
			<td style="width:201px;">909502</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Kinematic mirror mount</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">KM100/M</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Lens</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">LB1630</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Lens Mount</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">LMR2/M</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Linear polarizer</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">GTH5-A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Mirror</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">PF10-03-G01</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Neutral density filter</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">NDC-50C-4</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Plasma enhanced chemical vapor deposition</td>
			<td style="width:187px;">BMR Technology</td>
			<td style="width:201px;">HiDep-SC</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Post</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">TR75/M</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Post holder</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">PH75E/M</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Quarter-wave plate</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">AQWP10M-580</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Resist developer</td>
			<td style="width:187px;">Microchem</td>
			<td style="width:201px;">MIBK:IPA=1:3</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Rotational mount</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">RSP1/M</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">Scanning electron microscopy</td>
			<td style="width:187px;">Hitachi</td>
			<td style="width:201px;">Regulus8100</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">XY translation mount</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">XYF1/M</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:327px;">1-inch adapter</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">AD11F</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:327px;">1-inch lens mount</td>
			<td style="width:187px;">Thorlabs</td>
			<td style="width:201px;">CP02/M</td>
			<td></td>
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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).

The a-Si:H metasurfaces enable high cross-polarization efficiency and can be fabricated using a method (Figure 1) that is compatible with CMOS; this trait may enable scalable fabrication and near-future commercialization. The SEM image shows the fabricated a-Si:H metasurfaces (Figure 2). Furthermore, a-Si:H has a larger refractive index than TiO2 and GaN, so even with low aspect ratio nanostructure of around 4.7, an a-SiH meta-hologram with high diffr...

Watch this Scientific Journal Video about Demonstration of Spin-Multiplexed and Direction-Multiplexed All-Dielectric Visible Metaholograms at JoVE.com

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

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 ...

demonstration-spin-multiplexed-direction-multiplexed-all-dielectric

Research

JoVE Journal

Engineering

5.6K Views.  Pohang University of Science and Technology (POSTECH). 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.

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

Construction and Testing of Coin Cells of Lithium Ion Batteries

Rechargeable lithium ion batteries have wide applications in electronics, where customers always demand more capacity and longer lifetime. Lithium ion batteries have also been considered to be used in electric and hybrid vehicles1 or even electrical grid stabilization systems2. All these applications simulate a dramatic increase in the research and development of battery materials3-7, including new materials3,8, doping9, nanostructuring10-13, coatings or surface modifications14-17 and novel binders18. Consequently, an increasing number of physicists, chemists and materials scientists have recently ventured into this area. Coin cells are widely used in research laboratories to test new battery materials; even for the research and development that target large-scale and high-power applications, small coin cells are often used to test the capacities and rate capabilities of new materials in the initial stage. 
 In 2010, we started a National Science Foundation (NSF) sponsored research project to investigate the surface adsorption and disordering in battery materials (grant no. DMR-1006515). In the initial stage of this project, we have struggled to learn the techniques of assembling and testing coin cells, which cannot be achieved without numerous help of other researchers in other universities (through frequent calls, email exchanges and two site visits). Thus, we feel that it is beneficial to document, by both text and video, a protocol of assembling and testing a coin cell, which will help other new researchers in this field. This effort represents the "Broader Impact" activities of our NSF project, and it will also help to educate and inspire students.
In this video article, we document a protocol to assemble a CR2032 coin cell with a LiCoO2 working electrode, a Li counter electrode, and (the mostly commonly used) polyvinylidene fluoride (PVDF) binder. To ensure new learners to readily repeat the protocol, we keep the protocol as specific and explicit as we can. However, it is important to note that in specific research and development work, many parameters adopted here can be varied. First, one can make coin cells of different sizes and test the working electrode against a counter electrode other than Li. Second, the amounts of C black and binder added into the working electrodes are often varied to suit the particular purpose of research; for example, large amounts of C black or even inert powder were added to the working electrode to test the "intrinsic" performance of cathode materials14. Third, better binders (other than PVDF) have also developed and used18. Finally, other types of electrolytes (instead of LiPF6) can also be used; in fact, certain high-voltage electrode materials will require the uses of special electrolytes7.

A protocol to construct and test coin cells of lithium ion batteries is described. The specific procedures of making a working electrode, preparing a counter electrode, assembling a cell inside a glovebox and testing the cell are presented.

Rechargeable lithium ion batteries have wide applications in electronics, where customers always demand more capacity and longer lifetime.  Lithium ion ...

Bringing the Visible Universe into Focus with Robo-AO

The angular resolution of ground-based optical telescopes is limited by the degrading effects of the turbulent atmosphere. In the absence of an atmosphere, the angular resolution of a typical telescope is limited only by diffraction, i.e., the wavelength of interest, &lambda;, divided by the size of its primary mirror's aperture, D. For example, the Hubble Space Telescope (HST), with a 2.4-m primary mirror, has an angular resolution at visible wavelengths of ~0.04 arc seconds. The atmosphere is composed of air at slightly different temperatures, and therefore different indices of refraction, constantly mixing. Light waves are bent as they pass through the inhomogeneous atmosphere. When a telescope on the ground focuses these light waves, instantaneous images appear fragmented, changing as a function of time. As a result, long-exposure images acquired using ground-based telescopes - even telescopes with four times the diameter of HST - appear blurry and have an angular resolution of roughly 0.5 to 1.5 arc seconds at best.
Astronomical adaptive-optics systems compensate for the effects of atmospheric turbulence. First, the shape of the incoming non-planar wave is determined using measurements of a nearby bright star by a wavefront sensor. Next, an element in the optical system, such as a deformable mirror, is commanded to correct the shape of the incoming light wave. Additional corrections are made at a rate sufficient to keep up with the dynamically changing atmosphere through which the telescope looks, ultimately producing diffraction-limited images.
The fidelity of the wavefront sensor measurement is based upon how well the incoming light is spatially and temporally sampled1. Finer sampling requires brighter reference objects. While the brightest stars can serve as reference objects for imaging targets from several to tens of arc seconds away in the best conditions, most interesting astronomical targets do not have sufficiently bright stars nearby. One solution is to focus a high-power laser beam in the direction of the astronomical target to create an artificial reference of known shape, also known as a 'laser guide star'. The Robo-AO laser adaptive optics system2,3 employs a 10-W ultraviolet laser focused at a distance of 10 km to generate a laser guide star. Wavefront sensor measurements of the laser guide star drive the adaptive optics correction resulting in diffraction-limited images that have an angular resolution of ~0.1 arc seconds on a 1.5-m telescope.

Light from astronomical objects must travel through the earth's turbulent atmosphere before it can be imaged by ground-based telescopes. To enable direct imaging at maximum theoretical angular resolution, advanced techniques such as those employed by the Robo-AO adaptive-optics system must be used.

The angular  resolution of ground-based optical telescopes is limited by the degrading  effects of the turbulent atmosphere. In the absence of an ...

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 ...

Spatial Separation of Molecular Conformers and Clusters

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold molecular beams. However, these beams often contain multiple conformers and clusters, even at low rotational temperatures. We present an experimental methodology that allows the spatial separation of these constituent parts of a molecular beam expansion. Using an electric deflector the beam is separated by its mass-to-dipole moment ratio, analogous to a bender or an electric sector mass spectrometer spatially dispersing charged molecules on the basis of their mass-to-charge ratio. This deflector exploits the Stark effect in an inhomogeneous electric field and allows the separation of individual species of polar neutral molecules and clusters. It furthermore allows the selection of the coldest part of a molecular beam, as low-energy rotational quantum states generally experience the largest deflection. Different structural isomers (conformers) of a species can be separated due to the different arrangement of functional groups, which leads to distinct dipole moments. These are exploited by the electrostatic deflector for the production of a conformationally pure sample from a molecular beam. Similarly, specific cluster stoichiometries can be selected, as the mass and dipole moment of a given cluster depends on the degree of solvation around the parent molecule. This allows experiments on specific cluster sizes and structures, enabling the systematic study of solvation of neutral molecules.

We present a technique that allows the spatial separation of different conformers or clusters present in a molecular beam. An electrostatic deflector is used to separate species by their mass-to-dipole moment ratio, leading to the production of gas-phase ensembles of a single conformer or cluster stoichiometry.

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold ...

Fabrication and Testing of Microfluidic Optomechanical Oscillators

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including microresonators. However, because of the increased acoustic radiative losses during direct liquid immersion of optomechanical devices, almost all published optomechanical experiments have been performed in solid phase. This paper discusses a recently introduced hollow microfluidic optomechanical resonator. Detailed methodology is provided to fabricate these ultra-high-Q microfluidic resonators, perform optomechanical testing, and measure radiation pressure-driven breathing mode and SBS-driven whispering gallery mode parametric vibrations. By confining liquids inside the capillary resonator, high mechanical- and optical- quality factors are simultaneously maintained.

Parametric optomechanical excitations have recently been experimentally demonstrated in microfluidic optomechanical resonators by means of optical radiation pressure and stimulated Brillouin scattering. This paper describes the fabrication of these microfluidic resonators along with methodologies for generating and verifying optomechanical oscillations.

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including ...

Preparation and Evaluation of Hybrid Composites of Chemical Fuel and Multi-walled Carbon Nanotubes in the Study of Thermopower Waves

When a chemical fuel at a certain position in a hybrid composite of the fuel and a micro/nanostructured material is ignited, chemical combustion occurs along the interface between the fuel and core materials. Simultaneously, dynamic changes in thermal and chemical potentials across the micro/nanostructured materials result in concomitant electrical energy generation induced by charge transfer in the form of a high-output voltage pulse. We demonstrate the entire procedure of a thermopower wave experiment, from synthesis to evaluation. Thermal chemical vapor deposition and the wet impregnation process are respectively employed for the synthesis of a multi-walled carbon nanotube array and a hybrid composite of picric acid/sodium azide/multi-walled carbon nanotubes. The prepared hybrid composites are used to fabricate a thermopower wave generator with connecting electrodes. The combustion of the hybrid composite is initiated by laser heating or Joule-heating, and the corresponding combustion propagation, direct electrical energy generation, and real-time temperature changes are measured using a high-speed microscopy system, an oscilloscope, and an optical pyrometer, respectively. Furthermore, the crucial strategies to be adopted in the synthesis of hybrid composite and initiation of their combustion that enhance the overall thermopower wave energy transfer are proposed.

A protocol for conducting thermopower wave experiments is presented. The synthesis of hybrid composites of a chemical fuel and micro/nanostructured material, manufacturing of a thermopower wave generator, and methods for measuring the corresponding physical phenomena are described.

When a chemical fuel at a certain position in a hybrid composite of the fuel and a micro/nanostructured material is ignited, chemical combustion occurs ...

Research and Development of High-performance Explosives

Developmental testing of high explosives for military applications involves small-scale formulation, safety testing, and finally detonation performance tests to verify theoretical calculations. For newly developed formulations, the process begins with small-scale mixes, thermal testing, and impact and friction sensitivity. Only then do subsequent larger scale formulations proceed to detonation testing, which will be covered in this paper. Recent advances in characterization techniques have led to unparalleled precision in the characterization of early-time evolution of detonations. The new technique of Photonic Doppler Velocimetry (PDV) for the measurement of detonation pressure will be shared and compared with traditional fiber-optic detonation velocity and plate-dent calculation of detonation pressure. In particular, the role of aluminum in explosive formulations will be discussed. Recent developments led to the development of explosive formulations that result in reaction of aluminum very early in the detonation product expansion. This enhanced reaction leads to changes in the detonation velocity and pressure due to reaction of the aluminum with oxygen in the expanding gas products.

Developmental testing of high explosives for military applications involves small-scale formulation, safety testing, and finally detonation performance tests to verify theoretical calculations. This paper will share typical development tests associated with the measurement of detonation velocity and detonation pressure.

Developmental testing of high explosives for military applications involves small-scale formulation, safety testing, and finally detonation performance ...

Visible-light Induced Reduction of Graphene Oxide Using Plasmonic Nanoparticle

Present work demonstrates the simple, chemical free, fast, and energy efficient method to produce reduced graphene oxide (r-GO) solution at RT using visible light irradiation with plasmonic nanoparticles. The plasmonic nanoparticle is used to improve the reduction efficiency of GO. It only takes 30 min&#160;at RT by illuminating the solutions with Xe-lamp, the r-GO solutions can be obtained by completely removing gold nanoparticles through simple centrifugation step. The spherical gold nanoparticles (AuNPs) as compared to the other nanostructures is the most suitable plasmonic nanostructure for r-GO preparation. The reduced graphene oxide prepared using visible light and AuNPs was equally qualitative as chemically reduced graphene oxide, which was supported by various analytical techniques such as UV-Vis spectroscopy, Raman spectroscopy, powder XRD and XPS. The reduced graphene oxide prepared with visible light shows excellent quenching properties over the fluorescent molecules modified on ssDNA and excellent fluorescence recovery for target DNA detection. The r-GO prepared by recycled AuNPs is found to be of same quality with that of chemically reduced r-GO. The use of visible light with plasmonic nanoparticle demonstrates the good alternative method for r-GO synthesis.

A simple protocol for the preparation of reduced graphene oxide using visible light and plasmonic nanoparticle is described.

Present work demonstrates the simple, chemical free, fast, and energy efficient method to produce reduced graphene oxide (r-GO) solution at RT using ...

Fabrication and Characterization of Superconducting Resonators

Superconducting microwave resonators are of interest for a wide range of applications, including for their use as microwave kinetic inductance detectors (MKIDs) for the detection of faint astrophysical signatures, as well as for quantum computing applications and materials characterization. In this paper, procedures are presented for the fabrication and characterization of thin-film superconducting microwave resonators. The fabrication methodology allows for the realization of superconducting transmission-line resonators with features on both sides of an atomically smooth single-crystal silicon dielectric. This work describes the procedure for the installation of resonator devices into a cryogenic microwave testbed and for cool-down below the superconducting transition temperature. The set-up of the cryogenic microwave testbed allows one to do careful measurements of the complex microwave transmission of these resonator devices, enabling the extraction of the properties of the superconducting lines and dielectric substrate (e.g., internal quality factors, loss and kinetic inductance fractions), which are important for device design and performance.

Superconducting microwave resonators are of interest for detection of light, quantum computing applications and materials characterization. This work presents a detailed procedure for fabrication and characterization of superconducting microwave resonator scattering parameters.

Superconducting microwave resonators are of interest for a wide range of applications, including for their use as microwave kinetic inductance detectors ...

Reaction Kinetics and Combustion Dynamics of I4O9 and Aluminum Mixtures

Tetraiodine nonoxide (I4O9) has been synthesized using a dry approach that combines elemental oxygen and iodine without the introduction of hydrated species. The synthesis approach inhibits the topochemical effect promoting rapid hydration when exposed to the relative humidity of ambient air. This stable, amorphous, nano-particle material was analyzed using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) and showed an exothermic energy release at low temperature (i.e., 180 &#176;C) for the transformation of I4O9 into I2O5. This additional exothermic energy release contributes to an increase in overall reactivity of I4O9 when dry mixed with nano-aluminum (Al) powder, resulting in a minimum of 150% increase in flame speed compared to Al + I2O5. This study shows that as an oxidizer, I4O9 has more reactive potential than other forms of iodine(V) oxide when combined with Al, especially if I4O9 can be passivated to inhibit absorption of water from its surrounding environment.

Reaction Kinetics and Combustion Dynamics of I4O9 and Aluminum Mixtures

A protocol for measuring flame speeds of a reactive mixture composed of tetraiodine nonoxide (I4O9) and aluminum (Al) is presented. A method for resolving reaction kinetics using differential scanning calorimetry (DSC) is also presented. It was found that I4O9 is 150% more reactive than other iodine(V) oxides.

Tetraiodine nonoxide (I4O9) has been synthesized using a dry approach that combines elemental oxygen and iodine without the introduction of hydrated ...