All work performed under the support of the National Institute of Standards and Technology. Certain commercial equipment, instruments, or materials are identified to foster understanding of this protocol. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.

Caution: Please consult all relevant safety programs before the experiment. All the experimental procedures described in this protocol are performed in accordance with the NIST LASER safety program as well as other applicable regulations. Please be sure to select and wear proper personal protective equipment (PPE) such as laser protection glasses designed for the specific wavelength and power. Handling dry nano/microparticles may require additional respiratory protection.
1. Design and Fabrication of a PZT Holder and a Sample Enclosure
<ol>
	<li>Design a PZT holder and a sample enclosure 
	NOTE: Particular design values vary depending on the selection of a PZT.
	<ol>
		<li>Open the computer-aided design (CAD) software package. Draw a two-dimensional (2D) sketch of a holder for a given PZT dimension. Develop the 2D sketch to volumetric features using combinations of Extrude/Extrude-cut.</li>
		<li>Click Sketch, draw a rectangle and extrude it to make a rectangular cube.</li>
		<li>Sketch a disk on the top surface of the cube to define a circularly recessed feature to cover and hold the ring-type PZT.</li>
		<li>Define a central hole to have an optical access for both real-time imaging and trapping.</li>
		<li>Define a circular guide along the rim of the central hole to insert a flat metallic (copper) ring to concentrate the ultrasonic power toward the center area as shown in Figure 2a.</li>
		<li>Create two bore holes for M6 screws on the PZT holder to be assembled with a bottom plate (purchased, 4 mm thick bottom aluminum plate with a hole in the center), as shown in Figure 2c and 2d.</li>
		<li>In a similar manner, design a rectangular frame of the sample enclosure. Click Sketch, and draw a rectangle, extrude the rectangle to make it a rectangular box.</li>
		<li>Draw a smaller rectangle on the top surface of the rectangular box and extrude-cut the rectangle to make it as a rectangular tube.</li>
		<li>Draw a smaller rectangle on the side wall of the tube and Extrude-cut to transform it into the frame of sample enclosure box.</li>
		<li>Convert these three-dimensional (3D) models into a stereolithography (STL) file format for a 3D printing process (Figure 2b).</li>
	</ol>
	</li>
	<li>3D printing of the designed objects
	<ol>
		<li>Open the design file (&#34;-.STL&#34;) from the 3D printer operating software. Lay the object flat 0/.and center the object on (0, 0, 0) by clicking the object to select it and using the alignment functions: &#34;Move&#34;, &#34;On Platform&#34;, and &#34;Center&#34;. Orient the PZT holder to face the delicate features upward. The recessed surface will be faced upward.</li>
		<li>In the menu go to the &#34;Settings&#34; and the &#34;Quality&#34; tab. Set the printing values as following, Infill: 100%, Number of shells: 2, and Layer height: 0.2 mm.</li>
		<li>Preview the objects to check the total print time and make sure the layered objects will be printed as desired. Export the 3D print file in a &#34;.x3g&#34; format and save it to use in the 3D printer.</li>
		<li>Turn on the 3D printer and warm it up until the temperature of the extrusion nozzle reaches an operating temperature, 230 &#176;C. Load the design file from a memory card or network drive.</li>
		<li>During the warm up, place the Build platform with blue painter&#39;s tape to help objects adhere securely. As a thermoplastic material for the printing job, use a polylactic acid (PLA) filament for both objects.</li>
		<li>Print the designed objects. Once the printing job is finished, turn off the printer after it has cooled down.</li>
		<li>Detach the printed object from the platform using a chisel. Straighten up the printed objects. If the orientation is appropriately chosen, the PZT holder can be directly used without further post-processing.</li>
		<li>For the sample enclosure, prepare one pair of indium tin oxide (ITO) coated coverslips and three glass coverslips to cover the frame. Use a diamond cutter to fit the coverslip to the enclosure.</li>
		<li>Wire the two parallel conducting plates using a fast drying silver paint to supply voltage across two plates. Glue these five windows onto the sample enclosure using an instant adhesive glue. 
		NOTE: The one pair of ITO coated coverslips are installed on the sample enclosure in parallel (facing each other) to provide uniform electric field and to generate ballistic motion of the naturally charged particle along the electric field. The three conventional coverslip cover the rest of sample enclosure surfaces (top and two other sides) to protect the trapped particle from the external flow of air</li>
	</ol>
	</li>
</ol>
2. Optical Trap Loading of a Selected Microparticle
<ol>
	<li>Sample preparation
	<ol>
		<li>Store the microparticles in an evacuated desiccator to reduce contact with moisture in the air before the experiment.</li>
		<li>Pour out a small portion of microparticles onto a glass slide and immediately put the manufacture&#39;s bottle back in the desiccator.</li>
		<li>Pick up some of the microparticles with a glass capillary tube. Scatter the particles over the substrate by gently tapping on the capillary while holding the capillary over the coverslip.</li>
		<li>Verify the quantity and distribution of deposited particles on the substrate using a dark-field microscope. 
		Note: In the sample preparation step, the particle is just scattered on a coverslip and imaged with an optical microscope to verify overall arrangement before inserting them (a coverslip with scattered microparticles) between the PZT and PZT holder. Since the surface adhesion is strong enough to hold individual microparticles on the substrate, the adhered particles are firmly fixed unless significant external force is applied.</li>
	</ol>
	</li>
	<li>Piezoelectric launcher assembly
	<ol>
		<li>Obtain all the components of the piezoelectric launcher: the flat bottom plate, insulating film, the PZT, the glass coverslip, a copper ring, the PZT holder, two M6 screws, and the sample enclosure.</li>
		<li>Apply a thin film (or tape) on the bottom plate to insulate the PZT. The glass coverslip isolates the top of the stack.</li>
		<li>Assemble the stack by centering the PZT on top of the flat plate now insulated with tape, followed by the coverslip, the copper ring, and the PZT holder. Screw the stack together maintaining the centering of the PZT to avoid shorting the PZT to the holder if the holder is conducting as shown in Figure 2c and 2d. The copper ring provides an evenly distributed mechanical preload on the stack for plastic PZT holders.</li>
		<li>Finally, glue the sample enclosure onto the stack and mount the assembly on an XYZ translational stage in the microscope.</li>
	</ol>
	</li>
	<li>Configuration of the PZT launcher 
	NOTE: Driving the PZT with a high voltage signal has potential electrical hazards. Please consult with safety personnel before the experiment. All the electrical connections should be secured before the experiment. Turn off the amplifier and disconnect PZT leads whenever possible.
	<ol>
		<li>Connect the PZT leads to the voltage amplifier and connect the function generator to an input port of the voltage amplifier.</li>
		<li>Turn on the function generator and configure it to generate continuous square waves with an output voltage of 1 V. Do not generate the voltage signal until all the connections are verified and secured.</li>
		<li>Turn on the voltage amplifier and generate the square wave of output voltage 1 V by enabling the output.</li>
		<li>Connect the monitoring output port (output voltage 200 V) of the amplifier to an oscilloscope. Configure the amplifier to have gain of 200 V/V by turning the gain knob on the front panel. Verify that the monitoring output voltage has an amplitude of 1 V as measured by the oscilloscope.</li>
		<li>Once the function generator and the amplifier are configured, find the resonant frequency of the PZT launcher by scanning the modulation frequency of the driving signal while the real-time video microscope images adhered particles. Repeat the scanning until the microparticle motion is a maximum. Use this frequency (64 kHz here) to release particles. 
		NOTE: The modulation frequency is manually changed (scanned) from zero to 150 kHz to find the resonant frequency.</li>
		<li>Configure the function generator to generate a square wave with a specified number of cycles in burst mode. Press the &#34;Burst&#34; button on the front panel and select &#34;N Cycle Burst&#34;.</li>
		<li>Choose the burst count by pressing &#34;# Cycles&#34; soft key and set the count to 10 or 20.</li>
		<li>Configure the square waveform to generate voltage signals with an amplitude of 600 V (three times the voltage used for continuous excitation) at the resonant frequency of 64 kHz which has found from the previous step. Verify that the pulsing signal releases the target particle in a repeatable manner by ensuring particles move after each pulse.</li>
	</ol>
	</li>
	<li>Selective optical trap loading 
	NOTE: The PZT launcher assembly is installed on a manual linear translation xy stage. The particles can be translated relative to the fixed beam focus by moving the translational stage.
	<ol>
		<li>Remove the laser line filter to identify the focus of the trapping beam by rotating the microscope turret (Figure 3a). Move the motorized focusing block back and forth vertically around the best focus of the visible image to optimize focus.</li>
		<li>Once the focus position is verified, put the filter back to give a clear real-time video without interference from the trapping beam.</li>
		<li>Translate the sample to place a selected particle at the focus position of the trapping laser. Focus on the particle to image the center of a selected particle, which places the nominal trapping position below the particle center by about one half radius while leaving the levitation position above the particle.</li>
		<li>Adjust the power supply connected to the electro-optic modulator (EOM) driver to set the optical trapping power. The optimal power depends on particle size and material. The optical power was found through repeated trials to determine the power sufficient to levitate the particle without ejecting it from the beam. Here, use an optical power of 140 mW at the back focal plane of the objective to trap the 20 &#181;m diameter polystyrene (PS) particles.</li>
		<li>After the center of the selected particle is aligned, actuate the piezoelectric launcher with several pulses. The change of the particle image from a static focused image to a moving blurred image indicates successful loading to the levitation position.</li>
		<li>Translate the levitated particle vertically about a millimeter above the substrate by moving the objective lens up to prevent possible surface interactions. Then reduce the optical power to transition the levitated particle (Figure 3b) into the nominal trapping position (Figure 3c) which is more stable. 
		NOTE: The optical power of trapping laser can be modulated by an electro-optic modulator (EOM). The EOM regulates the output power with a bias voltage supplied through a digital power supply. One can observe the transition from the levitation to trapping position through the CCD while slowly reduces the optical power.</li>
		<li>For the position measurement, as depicted in Figure 3c to 3d, carefully move the center of the PZT holder to the optical axis and then move the objective lens up (vertically) to translate the particle into the middle of sample enclosure (9 mm above the substrate) where the fringe electric field is minimized.</li>
		<li>After performing the measurement as described below, place the particle on the substrate by moving the objective down until the particle touches the substrate. Since most of the particles are applied near the corners, the trapped particle can be easily recognized and re-trapped when it is placed in the central area. This enables reversible trap loading to measure changes occurring beyond a single trapping event such as contact interactions of the particle and substrate.</li>
	</ol>
	</li>
</ol>
3. Data Acquisition
<ol>
	<li>Align the condenser and the focusing lens to maximize the QPD &#34;SUM&#34; signal with a particle in the trap.</li>
	<li>Align the focusing lens to nominally zero the X and Y channels of the QPD, as shown in Figure 4c.</li>
	<li>Repeat the adjustment of the condenser and the focusing lens until the Fourier transformed position signals (or power spectrum density (PSD) plots) of the X and Y channels superimpose to show balanced sensitivity. Properly aligned QPD signals (X and Y) show almost identical behavior, as shown in Figure 4b.</li>
	<li>Once the QPD alignment is verified, connect the voltage amplifier to the two ITO plates. Connect the voltage monitoring output signal of the amplifier to the DAQ system to record the step excitation signal and the induced particle trajectory synchronously.</li>
	<li>Supply a continuous square wave of 400 V to generate an electric field (Figure 4d) that moves the particle transversely to the optical axis by about 500 nm (Figure 4e). Measure the step response of the trapped particle using the QPD.</li>
	<li>Average multiple periods as necessary to reduce the effects of Brownian motion. The induced motion can be used to measure the optical force over a wider range of motion than that of thermal fluctuations.12,17 Figure 4d and 4e shows averaged signals of applied voltage and the induced particle trajectory over 50 iterations of step excitation.</li>
</ol>

<ol>
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Phys. 9 (12), 806-810 (2013).</li><li>Gieseler, J., Deutsch, B., Quidant, R., Novotny, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Subkelvin+Parametric+Feedback+Cooling+of+a+Laser-Trapped+Nanoparticle.">Subkelvin Parametric Feedback Cooling of a Laser-Trapped Nanoparticle.</a> Phys. Rev. Lett. 109 (10), 103603 (2012).</li><li>Chang, D. E., 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=Cavity+opto-mechanics+using+an+optically+levitated+nanosphere.">Cavity opto-mechanics using an optically levitated nanosphere.</a> Proc. Natl. Acad. 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Protoc. 2 (12), 3226-3238 (2007).</li><li>Pesce, G., 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=Step-by-step+guide+to+the+realization+of+advanced+optical+tweezers.">Step-by-step guide to the realization of advanced optical tweezers.</a> J. Opt. Soc. Am. B. 32 (5), B84 (2015).</li><li>Thornton, S. T., Marion, J. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Classical Dynamics of Particles and Systems. , (2003).</li><li>Ashkin, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stability+of+optical+levitation+by+radiation+pressure.">Stability of optical levitation by radiation pressure.</a> Appl. Phys. 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The authors declare no competing financial interest.

The piezoelectric launcher is designed to optimize the dynamic performance of a selected PZT. Proper selection of PZT materials and management of ultrasonic vibrations are the key steps to yield a successful experiment. PZTs have different characteristics depending on the type of transducer (bulk or stacked) and component materials (hard or soft). A bulk type PZT made of a hard piezoelectric material is chosen for the following reasons. First, hard piezoelectric materials have lower dielectric losses and higher mechanica...

Ashkin reported the acceleration and trapping of microparticles by radiation pressure in 1970.1 His novel achievement promoted the development of optical trapping techniques as a primary tool for fundamental studies of physics and biophysics.2,3,4,5 To date, the application of optical trapping has focused mainly on liquid environments, and been used to study a very wide range of systems, from the behavior of colloids to the mechanical properties of single biomolecules.6,7,8 Application of optical trapping to gaseous media, however, requires resolving several new technical issues.
Recently, optical trapping in air/vacuum has been increasingly applied in fundamental research. Since optical levitation potentially provides nearly-complete isolation of a system from the surrounding environment, the optically levitated particle becomes an ideal laboratory for studying quantum ground states in small objects,4 measuring high-frequency gravitational waves,9 and searching for fractional charge.10 Moreover, the low viscosity of air/vacuum allows one to use inertia to measure the instantaneous velocity of a Brownian particle11 and to create ballistic motion over a wide range of motion beyond the linear spring-like regime.12 Therefore, detailed technical information and practices for optical traps in gaseous media have become more valuable to the broader research community.
New experimental techniques are required to load nano/microparticles into optical traps in gaseous media. A piezoelectric transducer (PZT), a device that converts electric energy into mechano-acoustic energy, has been used to deliver small particles into optical traps in air/vacuum5,12 since the first demonstration of optical levitation.1 Since then, several loading techniques have been proposed to load smaller particles using volatile aerosols generated by a commercial nebulizer13 or an acoustic wave generator.14 The floating aerosols with solid inclusions (particles) randomly pass near the focus and are trapped by chance. Once the aerosol is trapped, the solvent evaporates out and the particle remains in the optical trap. However, these methods are not well suited to identify desired particles from within a sample, load a selected particle and to track its changes if released from the trap. This protocol is intended to provide details to new practitioners on selective optical trap loading in air, including the experimental setup, fabrication of a PZT holder and sample enclosure, trap loading, and data acquisition associated with the analysis of particle motion in both the frequency and time domains. Protocols for trapping in liquid media have also been published.15,16
The overall experimental setup is developed on a commercial inverted optical microscope. Figure 1 shows a schematic diagram of the setup used to demonstrate steps of the selective optical trap loading: freeing the resting microparticles, lifting the chosen particle with the focused beam, measuring its motion, and placing it onto the substrate again. First, translational stages (transverse and vertical) are used to bring a selected microparticle on the substrate to the focus of a trapping laser (wavelength 1064 nm) focused by an objective lens (near-infrared corrected long-working distance objective: NA 0.4, magnification 20X, working distance 20 mm) through the transparent substrate. Then, a piezoelectric launcher (a mechanically pre-loaded ring-type PZT) generates ultrasonic vibrations to break the adhesion between microparticles and a substrate. Thus, any freed particle can be lifted by the single-beam gradient laser trap focused on the selected particle. Once the particle is trapped, it is translated to the center of the sample enclosure containing two parallel conducting plates for electrostatic excitation. Finally, a data acquisition (DAQ) system simultaneously records the particle motion, captured by a quadrant-cell photodetector (QPD), and the applied electric field. After finishing the measurement, the particle is controllably placed onto the substrate so that it can be trapped again in a reversible manner. This overall process can be repeated hundreds of times without particle loss to measure changes such as contact electrification occurring over several trapping cycles. Please refer to our recent article for details.12

<table border="0" cellpadding="0" cellspacing="0" width="1124">
	<tbody>
		<tr height="26">
			<td height="26" style="height:27px;width:319px;">ScotchBlue Painter&#39;s Tape Original</td>
			<td style="width:177px;">3M</td>
			<td style="width:216px;">3M2090</td>
			<td style="width:413px;"></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;width:319px;">Scotch 810 Magic Tape</td>
			<td style="width:177px;">3M</td>
			<td style="width:216px;">3M810</td>
			<td></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;width:319px;">Function/Arbitrary Waveform generator</td>
			<td style="width:177px;">Agilent</td>
			<td style="width:216px;">HP33250A</td>
			<td></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;width:319px;">Power supply/Digital voltage supplier</td>
			<td style="width:177px;">Agilent</td>
			<td style="width:216px;">E3634A</td>
			<td></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;width:319px;">Ring-type piezoelectric transducer</td>
			<td style="width:177px;">American Piezo Company</td>
			<td style="width:216px;">item91</td>
			<td></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;width:319px;">Electro-optic modulator</td>
			<td style="width:177px;">Con-Optics</td>
			<td style="width:216px;">350&#8722;80-LA</td>
			<td></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;width:319px;">Amplifier for Electro-optic modulator</td>
			<td style="width:177px;">Con-Optics</td>
			<td style="width:216px;">302RM</td>
			<td></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;width:319px;">Mitutoyo NIR infinity Corrected Objective</td>
			<td style="width:177px;">Edmund optics</td>
			<td style="width:216px;">46-404</td>
			<td>Manufactured by Mitutoyo and Distributed by Edmund optics</td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;width:319px;">LOCTITE SUPER GLUE LONGNECK BOTTLE</td>
			<td style="width:177px;">Loctite</td>
			<td style="width:216px;">230992</td>
			<td></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;">3D printer</td>
			<td style="width:177px;">MakerBot</td>
			<td style="width:216px;">Replicator 2</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Polylactic acid (PLA) filament</td>
			<td style="width:177px;">MakerBot</td>
			<td style="width:216px;">True Red PLA Small Spool</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Data Acquisition system</td>
			<td style="width:177px;">National Instruments</td>
			<td style="width:216px;">780114-01</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Quadrant-cell photodetector</td>
			<td style="width:177px;">Newport</td>
			<td style="width:216px;">2031</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Translational stage</td>
			<td style="width:177px;">Newport</td>
			<td style="width:216px;">562-XYZ</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Inverted optical microscope</td>
			<td style="width:177px;">Nikon Instruments</td>
			<td style="width:216px;">EclipsTE2000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Fluorescence filter (green)</td>
			<td style="width:177px;">Nikon Instruments</td>
			<td style="width:216px;">G-2B</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Flea3/CCD camera</td>
			<td style="width:177px;">Point Grey</td>
			<td style="width:216px;">FL3-U3-13S2M-CS</td>
			<td>Trapping laser</td>
		</tr>
		<tr height="46">
			<td height="46" style="height:46px;width:319px;">Diode pumped neodymium yttrium vanadate(Nd:YVO4)</td>
			<td style="width:177px;">Spectra Physics</td>
			<td style="width:216px;">J20I-8S-12K/ BL-106C</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Indium tin oxide (ITO) Coated coverslips</td>
			<td style="width:177px;">SPI supplies</td>
			<td style="width:216px;">06463B-AB</td>
			<td>Polystyrene microparticles</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Fast Drying Silver Paint</td>
			<td style="width:177px;">Tedpella</td>
			<td style="width:216px;">16040-30</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Dri-Cal size standards</td>
			<td style="width:177px;">Thermo Scientific</td>
			<td style="width:216px;">DC-20</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Optical Fiber</td>
			<td style="width:177px;">Thorlabs</td>
			<td style="width:216px;">P1&#8722;1064PM-FC-5</td>
			<td>bottom plate</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Aluminium plate&#160;</td>
			<td style="width:177px;">Thorlabs</td>
			<td style="width:216px;">CP4S</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">High voltage power amplifier</td>
			<td style="width:177px;">TREK</td>
			<td style="width:216px;">PZD700A M/S</td>
			<td></td>
		</tr>
	</tbody>
</table>

optical trap loading of dielectric microparticles in air

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly scattered dielectric microparticles adhered to a glass substrate are momentarily detached using ultrasonic vibrations generated by a piezoelectric transducer (PZT). Then, the optical beam focused on a selected particle lifts it up to the optical trap while the vibrationally excited microparticles fall back to the substrate. A particle may be trapped at the nominal focus of the trapping beam or at a position above the focus (referred to here as the levitation position) where gravity provides the restoring force. After the measurement, the trapped particle can be placed at a desired position on the substrate in a controlled manner. 
In this protocol, an experimental procedure for selective optical trap loading in air is outlined. First, the experimental setup is briefly introduced. Second, the design and fabrication of a PZT holder and a sample enclosure are illustrated in detail. The optical trap loading of a selected microparticle is then demonstrated with step-by-step instructions including sample preparation, launching into the trap, and use of electrostatic force to excite particle motion in the trap and measure charge. Finally, we present recorded particle trajectories of Brownian and ballistic motions of a trapped microparticle in air. These trajectories can be used to measure stiffness or to verify optical alignment through time domain and frequency domain analysis. Selective trap loading enables optical tweezers to track a particle and its changes over repeated trap loadings in a reversible manner, thereby enabling studies of particle-surface interaction.

The PZT launcher is designed using a CAD software package. Here, we use a simple sandwich structure for the preloading (a PZT clamped with two plates), as shown in Figure 2. The PZT holder and the sample enclosure can be fabricated from a variety of materials and methods. For a quick demonstration, we choose 3D printing with thermoplastic as illustrated in Figure 2d. Based on the fabricated components, optical trap loading is shown in Figure 3</st...

Watch this Scientific Journal Video about Optical Trap Loading of Dielectric Microparticles In Air at JoVE.com

Optical Trap Loading of Dielectric Microparticles In Air

A protocol for launching and stably trapping selected dielectric microparticles in air is presented.

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly ...

optical-trap-loading-of-dielectric-microparticles-in-air

Research

JoVE Journal

Engineering

9.0K Views.  National Institute of Standards and Technology. A protocol for launching and stably trapping selected dielectric microparticles in air is presented.

Video: Optical Trap Loading of Dielectric Microparticles In Air

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 ...

Fabricating Metamaterials Using the Fiber Drawing Method

Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate 1. They owe their electromagnetic properties to the structure of their constituents, instead of the atoms that compose them. For example, sub-wavelength metal wires can be arranged to possess an effective electric permittivity that is either positive or negative at a given frequency, in contrast to the metals themselves 2. This unprecedented control over the behaviour of light can potentially lead to a number of novel devices, such as invisibility cloaks 3, negative refractive index materials 4, and lenses that resolve objects below the diffraction limit 5. However, metamaterials operating at optical, mid-infrared and terahertz frequencies are conventionally made using nano- and micro-fabrication techniques that are expensive and produce samples that are at most a few centimetres in size 6-7. Here we present a fabrication method to produce hundreds of meters of metal wire metamaterials in fiber form, which exhibit a terahertz plasmonic response 8. We combine the stack-and-draw technique used to produce microstructured polymer optical fiber 9 with the Taylor-wire process 10, using indium wires inside polymethylmethacrylate (PMMA) tubes. PMMA is chosen because it is an easy to handle, drawable dielectric with suitable optical properties in the terahertz region; indium because it has a melting temperature of 156.6 &deg;C which is appropriate for codrawing with PMMA. We include an indium wire of 1 mm diameter and 99.99% purity in a PMMA tube with 1 mm inner diameter (ID) and 12 mm outside diameter (OD) which is sealed at one end. The tube is evacuated and drawn down to an outer diameter of 1.2 mm. The resulting fiber is then cut into smaller pieces, and stacked into a larger PMMA tube. This stack is sealed at one end and fed into a furnace while being rapidly drawn, reducing the diameter of the structure by a factor of 10, and increasing the length by a factor of 100. Such fibers possess features on the micro- and nano- scale, are inherently flexible, mass-producible, and can be woven to exhibit electromagnetic properties that are not found in nature. They represent a promising platform for a number of novel devices from terahertz to optical frequencies, such as invisible fibers, woven negative refractive index cloths, and super-resolving lenses.

Metamaterials at terahertz frequencies offer unique opportunities, but are challenging to fabricate in bulk. We adapt the fabrication procedure for microstructured polymer optical fibers to inexpensively fabricate metamaterials potentially on an industrial scale. We produce polymethylmethacrylate fibers containing ~10 &mu;m diameter indium wires separated by ~100 &mu;m, which exhibit a terahertz plasmonic response.

Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate 1. They owe ...

Optical Trapping of Nanoparticles

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping and manipulating small biological particles. Ashkin and co-workers first demonstrated optical tweezers using a single focused beam1. The single beam trap can be described accurately using the perturbative gradient force formulation in the case of small Rayleigh regime particles1. In the perturbative regime, the optical power required for trapping a particle scales as the inverse fourth power of the particle size. High optical powers can damage dielectric particles and cause heating. For instance, trapped latex spheres of 109 nm in diameter were destroyed by a 15 mW beam in 25 sec1, which has serious implications for biological matter2,3.
A self-induced back-action (SIBA) optical trapping was proposed to trap 50 nm polystyrene spheres in the non-perturbative regime4. In a non-perturbative regime, even a small particle with little permittivity contrast to the background can influence significantly the ambient electromagnetic field and induce a large optical force. As a particle enters an illuminated aperture, light transmission increases dramatically because of dielectric loading. If the particle attempts to leave the aperture, decreased transmission causes a change in momentum outwards from the hole and, by Newton's Third Law, results in a force on the particle inwards into the hole, trapping the particle. The light transmission can be monitored; hence, the trap can become a sensor. The SIBA trapping technique can be further improved by using a double-nanohole structure.
The double-nanohole structure has been shown to give a strong local field enhancement5,6. Between the two sharp tips of the double-nanohole, a small particle can cause a large change in optical transmission, thereby inducing a large optical force. As a result, smaller nanoparticles can be trapped, such as 12 nm silicate spheres7 and 3.4 nm hydrodynamic radius bovine serum albumin proteins8. In this work, the experimental configuration used for nanoparticle trapping is outlined. First, we detail the assembly of the trapping setup which is based on a Thorlabs Optical Tweezer Kit. Next, we explain the nanofabrication procedure of the double-nanohole in a metal film, the fabrication of the microfluidic chamber and the sample preparation. Finally, we detail the data acquisition procedure and provide typical results for trapping 20 nm polystyrene nanospheres.

The following setup approach details low power optical trapping of dielectric nanoparticles using a double-nanohole in metal film.

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping ...

Fabrication of VB2/Air Cells for Electrochemical Testing

A technique to investigate the properties and performance of new multi-electron metal/air battery systems is proposed and presented. A method for synthesizing nanoscopic VB2 is presented as well as step-by-step procedure for applying a zirconium oxide coating to the VB2 particles for stabilization upon discharge. The process for disassembling existing zinc/air cells is shown, in addition construction of the new working electrode to replace the conventional zinc/air cell anode with a the nanoscopic VB2 anode. Finally, discharge of the completed VB2/air battery is reported. We show that using the zinc/air cell as a test bed is useful to provide a consistent configuration to study the performance of the high-energy high capacity nanoscopic VB2 anode.

Fabrication of VB2/Air Cells for Electrochemical Testing

A protocol is presented to study multi-electron metal/air battery systems by using previous technology developed for the zinc/air cell. Electrochemical testing is then performed on fabricated batteries to evaluate performance.

A technique to investigate the properties and performance of new multi-electron metal/air battery systems is proposed and presented. A method for ...

The Preparation of Electrohydrodynamic Bridges from Polar Dielectric Liquids

Horizontal and vertical liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields (8-20 kV/cm) and polar dielectric liquids. These bridges are unique from capillary bridges in that they exhibit extensibility beyond a few millimeters, have complex bi-directional mass transfer patterns, and emit non-Planck infrared radiation. A number of common solvents can form such bridges as well as low conductivity solutions and colloidal suspensions. The macroscopic behavior is governed by electrohydrodynamics and provides a means of studying fluid flow phenomena without the presence of rigid walls. Prior to the onset of a liquid bridge several important phenomena can be observed including advancing meniscus height (electrowetting), bulk fluid circulation (the Sumoto effect), and the ejection of charged droplets (electrospray). The interaction between surface, polarization, and displacement forces can be directly examined by varying applied voltage and bridge length. The electric field, assisted by gravity, stabilizes the liquid bridge against Rayleigh-Plateau instabilities. Construction of basic apparatus for both vertical and horizontal orientation along with operational examples, including thermographic images, for three liquids (e.g., water, DMSO, and glycerol) is presented.

Horizontal and vertical electrohydrodynamic liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields and polar dielectric liquids. The construction of basic apparatus and operational examples, including thermographic images, for three liquids (e.g., water, DMSO, and glycerol) is presented.

Horizontal and vertical liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields (8-20 kV/cm) and ...

Writing Bragg Gratings in Multicore Fibers

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong suppression at a single wavelength requires that all cores have matching transmission profiles. These gratings cannot be inscribed using the same method as for single-core fibers because the curved surface of the cladding acts as a lens, focusing the incoming UV laser beam and causing variations in exposure between cores. Therefore we use an additional optical element to ensure that the beam shape does not change while passing through the cross-section of the multicore fiber. This consists of a glass capillary tube which has been polished flat on one side, which is then placed over the section of the fiber to be inscribed. The laser beam enters the fiber through the flat surface of the capillary tube and hence maintains its original dimensions. This paper demonstrates the improvements in core-to-core uniformity for a 7-core fiber using this method. The technique can be generalized to larger multicore fibers.

We describe a technique for inscribing identical fiber Bragg gratings into each core of a multicore fiber. This is achieved by introducing an additional surface into the optical path to mitigate lensing by the curved surface of the fiber cladding.

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong ...

Fabrication Process of Silicone-based Dielectric Elastomer Actuators

This contribution demonstrates the fabrication process of dielectric elastomer transducers (DETs). DETs are stretchable capacitors consisting of an elastomeric dielectric membrane sandwiched between two compliant electrodes. The large actuation strains of these transducers when used as actuators (over 300% area strain) and their soft and compliant nature has been exploited for a wide range of applications, including electrically tunable optics, haptic feedback devices, wave-energy harvesting, deformable cell-culture devices, compliant grippers, and propulsion of a bio-inspired fish-like airship. In most cases, DETs are made with a commercial proprietary acrylic elastomer and with hand-applied electrodes of carbon powder or carbon grease. This combination leads to non-reproducible and slow actuators exhibiting viscoelastic creep and a short lifetime. We present here a complete process flow for the reproducible fabrication of DETs based on thin elastomeric silicone films, including casting of thin silicone membranes, membrane release and prestretching, patterning of robust compliant electrodes, assembly and testing. The membranes are cast on flexible polyethylene terephthalate (PET) substrates coated with a water-soluble sacrificial layer for ease of release. The electrodes consist of carbon black particles dispersed into a silicone matrix and patterned using a stamping technique, which leads to precisely-defined compliant electrodes that present a high adhesion to the dielectric membrane on which they are applied.

This manuscript shows the fabrication process for the manufacture of dielectric elastomer soft actuators based on silicone membranes. The three key stages of production are presented in detail: blade casting of thin silicone membranes; pad printing of compliant electrodes; and the assembly of all the components.

This contribution demonstrates the fabrication process of dielectric elastomer transducers (DETs). DETs are stretchable capacitors consisting of an ...

Measurement of Quantum Interference in a Silicon Ring Resonator Photon Source

Silicon photonic chips have the potential to realize complex integrated quantum information processing circuits, including photon sources, qubit manipulation, and integrated single-photon detectors. Here, we present the key aspects of preparing and testing a silicon photonic quantum chip with an integrated photon source and two-photon interferometer. The most important aspect of an integrated quantum circuit is minimizing loss so that all of the generated photons are detected with the highest possible fidelity. Here, we describe how to perform low-loss edge coupling by using an ultra-high numerical aperture fiber to closely match the mode of the silicon waveguides. By using an optimized fusion splicing recipe, the UHNA fiber is seamlessly interfaced with a standard single-mode fiber. This low-loss coupling allows the measurement of high-fidelity photon production in an integrated silicon ring resonator and the subsequent two-photon interference of the produced photons in a closely integrated Mach-Zehnder interferometer. This paper describes the essential procedures for the preparation and characterization of high-performance and scalable silicon quantum photonic circuits.

Silicon photonic chips have the potential to realize complex integrated quantum systems. Presented here is a method for preparing and testing a silicon photonic chip for quantum measurements.

Silicon photonic chips have the potential to realize complex integrated quantum information processing circuits, including photon sources, qubit ...

Fabrication of Polymer Microspheres for Optical Resonator and Laser Applications

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, interface precipitation, and mini-emulsion. In all methods, well-defined, micrometer-sized spheres are obtained from a self-assembling process in solution. The vapor diffusion method can result in spheres with the highest sphericity and surface smoothness, yet the types of the polymers able to form these spheres are limited. On the other hand, in the mini-emulsion method, microspheres can be made from various types of polymers, even from highly crystalline polymers with coplanar, &#960;-conjugated backbones. The photoluminescent (PL) properties from single isolated microspheres are unusual: the PL is confined inside the spheres, propagates at the circumference of the spheres via the total internal reflection at the polymer/air interface, and self-interferes to show sharp and periodic resonant PL lines. These resonating modes are so-called "whispering gallery modes" (WGMs). This work demonstrates how to measure WGM PL from single isolated spheres using the micro-photoluminescence (&#181;-PL) technique. In this technique, a focused laser beam irradiates a single microsphere, and the luminescence is detected by a spectrometer. A micromanipulation technique is then used to connect the microspheres one by one and to demonstrate the intersphere PL propagation and color conversion from coupled microspheres upon excitation at the perimeter of one sphere and detection of PL from the other microsphere. These techniques, &#181;-PL and micromanipulation, are useful for experiments on micro-optic application using polymer materials.

Protocols for the synthesis of microspheres from polymers, the manipulation of microspheres, and micro-photoluminescence measurements are presented.

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, ...

Application of Design Aspects in Uniaxial Loading Machine Development

In terms of accurate and precise mechanical testing, machines run the continuum. Whereas commercial platforms offer excellent accuracy, they can be cost-prohibitive, often priced in the $100,000 - $200,000 price range. At the other extreme are stand-alone manual devices that often lack repeatability and accuracy (e.g., a manual crank device). However, if a single use is indicated, it is over-engineering to design and machine something overly elaborate. Nonetheless, there are occasions where machines are designed and built in-house to accomplish a motion not attainable with the existing machines in the laboratory. Described in detail here is one such device. It is a loading platform that enables pure uniaxial loading. Standard loading machines typically are biaxial in that linear loading occurs along the axis and rotary loading occurs about the axis. During testing with these machines, a load is applied to one end of the specimen while the other end remains fixed. These systems are not capable of conducting pure axial testing in which tension/compression is applied equally to the specimen ends. The platform developed in this paper enables the equal and opposite loading of specimens. While it can be used for compression, here the focus is on its use in pure tensile loading. The device incorporates commercial load cells and actuators (movers) and, as is the case with machines built in-house, a frame is machined to hold the commercial parts and fixtures for testing.

Here we present a protocol to develop a pure uniaxial loading machine. Critical design aspects are employed to ensure accurate and reproducible testing results.

In terms of accurate and precise mechanical testing, machines run the continuum. Whereas commercial platforms offer excellent accuracy, they can be ...