This work was supported by National Natural Science Foundation of China (grant no. 11772045) and Education and Teaching Reform Project of University of Science and Technology Beijing (grant no. JG2017M58).

1. Experimental setup and procedures
NOTE: Set up the experimental system as shown in Figure 2.
<ol>
	<li>Preparation of the vibration system
	<ol>
		<li>Prepare three 1.0-mm-thickness mirrored circular acrylic plates with diameter of 150 mm, 200 mm and 250 mm respectively. Drill a hole of 3 mm in diameter at the center of each plate. Mark several black points every 5 mm along an arbitrary radius.</li>
		<li>Attach each plate to the actuate bar of the vibrator with a bolt in the middle point. Drive the vibrator with a sine wave using a waveform generator, and default settings will be enough for the resonance experiment. 
		NOTE: The excitation direction of the vibrator is horizontal for the convenience of moving the screen afterwards.</li>
		<li>Acquisition of the resonance frequency
		<ol>
			<li>Place the laser pen to project the laser beam to the vibrating plate perpendicularly such that the beam is reflected to the light screen in the distance. The distances between the laser pen and the plate and the light screen are 120 mm and 500 mm, respectively. 
			NOTE: The farther the distance between the light screen and the vibrating plate, the more obvious the phenomenon appears. It is also noted that the present method can be used to measure either axisymmetric or non-axisymmetric mode shapes. Due to the consideration of simplicity and convenience, the present manuscript only demonstrates the application in determining axisymmetric mode shapes of three circular plates. Then we just need to measure the vibration amplitude along any radial direction to reconstruct the two-dimensional mode shape of the plate.</li>
			<li>Move the laser pen along the direction perpendicular to its length direction to make the incident point scan over a diameter while the signal generator changing its frequency continuously. Do it quickly until the spot length is significantly stretched along the diameter when scanning in a certain frequency range, and some spots with almost no expansion appear. For the plate with a diameter of 150 mm, 200 mm and 250 mm, the frequency ranges swept are 200-400 Hz, 100-300 Hz and 50-250 Hz, respectively.</li>
			<li>Scan this certain frequency range slowly and pick out the frequency at which the spot expands most obviously. It is found that for the plate with a diameter of 150 mm, 200 mm and 250 mm, the resonance frequencies are 346 Hz, 214 Hz and 150 Hz, respectively.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Preparation of the light path and measurement system
	<ol>
		<li>Place the light screen parallel to the vibrating plate. Mark the distance with a meter ruler, and use 500 mm as the starting distance.</li>
		<li>Place the laser pen to project the beam perpendicularly on the plate such that the beam is reflected to the light screen in the distance. Make sure that the mark made before can be scanned while the laser pen is moving. 
		NOTE: The laser beam light must be projected perpendicularly on the plate.</li>
	</ol>
	</li>
	<li>Experimental measurement
	<ol>
		<li>Turn on the signal generator and set the excitation frequency to be the same as the resonance frequency obtained in step 1.1.3.3. The signal intensity should as small as possible once the light spot on the light screen is large enough to be recorded.</li>
		<li>Adjust the laser pen to make the incident point coincide with the first marker, which is the nearest marker to the fixed point of the plate.</li>
		<li>Move the screen from a distance D of 500 mm to 1000 mm and measure the spot length L on the screen every 50 mm. Record data in tabular form.</li>
		<li>Adjust the laser pen to make the incident point adjacent to the next marker in turn and repeat step 1.3.3 until all the markers have been measured. 
		NOTE: Since acrylic plates are easily deformed plastically under excitation, the experimental measurement process of one plate cannot be paused for a long time.</li>
		<li>Replace the former plate with the next one and repeat steps 1.3.1 to 1.3.4.</li>
	</ol>
	</li>
</ol>
2. Data processing
<ol>
	<li>Determine the angle &#952; between the incident and reflected light with relationship: 
	<img alt="Equation 1" src="/files/ftp_upload/61020/61020equ01.jpg" /> 
	where D is the distance between the rest position of the vibrating plate and the light screen, w is vibrating amplitude of the plate, and L is the length of the light spot on the light screen. Several pairs of D and L are obtained in step 1.3.3.</li>
	<li>Determine the slope <img alt="Equation 2" src="/files/ftp_upload/61020/61020equ02v3.jpg" /> of the mode shape by: 
	<img alt="Equation 3" src="/files/ftp_upload/61020/61020equ03.jpg" /> 
	NOTE: The obtained slope is always positive with Eqs.(1) and (2).</li>
	<li>Use a minus sign between two zero points to obtain the true slope distribution. 
	NOTE: It does not matter whether the revision begins from the first or the second zero point.</li>
	<li>Integrate the slope distribution of each plate and determine the integral constant by the nodes to obtain the mode shape with: 
	<img alt="Equation 4" src="/files/ftp_upload/61020/61020equ04.jpg" /> 
	NOTE: Nodes correspond to the largest slope of the mode shape. is a constant determined by the location of the nodal lines of the Chladni pattern shown in Figure 2.</li>
	<li>Compute the uncertainty of the slope12 with: 
	<img alt="Equation 5" src="/files/ftp_upload/61020/61020equ05.jpg" /> 
	NOTE: t0.95(n &#8211; 2) is the t distribution factor with 95% confidence and degrees of freedom n-2, and it is about 2 here. Sr is the standard error of the linear regression with D and L, Um denotes the uncertainty of the measured distance Di, and is 0.5 mm here. The average measured distance is defined by <img alt="Equation 6" src="/files/ftp_upload/61020/61020equ06v3.jpg" />, and n denotes the total number of measured Di.</li>
</ol>

<ol>
	<li>Waller, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vibrations+of+free+circular+plates.+Part+1:+Normal+modes.">Vibrations of free circular plates. Part 1: Normal modes.</a> Proceedings of the Physical Society. 50 (1), 70-76 (1938).</li><li>Waller, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vibrations+of+free+square+plates:+part+I.+Normal+vibrating+modes.">Vibrations of free square plates: part I. Normal vibrating modes.</a> Proceedings of the Physical Society. 51 (5), 831-844 (1939).</li><li>Waller, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vibrations+of+free+plates:+isosceles+right-angled+triangles.">Vibrations of free plates: isosceles right-angled triangles.</a> Proceedings of the Physical Society. 53 (1), 35-39 (1941).</li><li>Waller, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vibrations+of+Free+Rectangular+Plates.">Vibrations of Free Rectangular Plates.</a> Proceedings of the Physical Society Section B. 62 (5), 277-285 (1949).</li><li>Waller, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vibrations+of+Free+Elliptical+Plates.">Vibrations of Free Elliptical Plates.</a> Proceedings of the Physical Society Section B. 63 (6), 451-455 (1950).</li><li>Tuan, P. H., Wen, C. P., Chiang, P. Y., Yu, Y. T., Liang, H. C., Huang, K. F., 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=Exploring+the+resonant+vibration+of+thin+plates:+Reconstruction+of+Chladni+patterns+and+determination+of+resonant+wave+numbers.">Exploring the resonant vibration of thin plates: Reconstruction of Chladni patterns and determination of resonant wave numbers.</a> The Journal of the Acoustical Society of America. 137 (4), 2113-2123 (2015).</li><li>Tuan, P. H., Lai, Y. H., Wen, C. P., Huang, K. F., Chen, Y. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Point-driven+modern+Chladni+figures+with+symmetry+breaking.">Point-driven modern Chladni figures with symmetry breaking.</a> Scientific Reports. 8 (1), 10844 (2018).</li><li>Castellini, P., Martarelli, M., Tomasini, E. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laser+Doppler+Vibrometry:+Development+of+advanced+solutions+answering+to+technology's+needs.">Laser Doppler Vibrometry: Development of advanced solutions answering to technology's needs.</a> Mechanical Systems and Signal Processing. 20 (6), 1265-1285 (2006).</li><li>Sels, S., Vanlanduit, S., Bogaerts, B., Penne, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-dimensional+full-field+vibration+measurements+using+a+handheld+single-point+laser+Doppler+vibrometer.">Three-dimensional full-field vibration measurements using a handheld single-point laser Doppler vibrometer.</a> Mechanical Systems and Signal Processing. 126, 427-438 (2019).</li><li>Georgas, P. J., Schajer, G. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simultaneous+Measurement+of+Plate+Natural+Frequencies+and+Vibration+Mode+Shapes+Using+ESPI.">Simultaneous Measurement of Plate Natural Frequencies and Vibration Mode Shapes Using ESPI.</a> Experimental Mechanics. 53 (8), 1461-1466 (2013).</li><li>Luo, Y., Feng, R., Li, X. D., Liu, D. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+simple+approach+to+determine+the+mode+shapes+of+Chladni+plates+based+on+the+optical+lever+method.">A simple approach to determine the mode shapes of Chladni plates based on the optical lever method.</a> European Journal of Physics. 40, 065001 (2019).</li><li>Coleman, H. W., Steele, W. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Experimentation and uncertainty analysis for engineer. , (1999).</li></ol>

The authors have nothing to disclose.

The optical lever method is adopted in this paper to determine the mode shape of a plate, since the Chladni pattern can only show the nodal lines of a vibrating plate. To determine the mode shape of the plate, the relationship between the slope and distance of the light screen and spot length should be obtained in advance. Then through definite integration calculation, the mode shape of the Chladni pattern could be quantitatively determined.
Generally, the whole process of the present approach...

Chladni mode shapes are of great interest in both science and engineering applications. Chladni patterns are reactions of physical waves, and one can illustrate the wave pattern with various methods. It is a well-known method to show the various modes of vibration on an elastic plate by outlining the nodal lines. Small particles are always employed to show the Chladni patterns, since they can stop at the nodes where the relative vibrating amplitude of the plate is zero, and the positions of the nodes vary with resonant mode to form various Chladni patterns.
Many researchers have paid attention to various Chladni patterns, but they only show the nodal lines of the mode shapes, the mode shapes (i.e., vibration amplitude) between the nodal lines are not illustrated. Waller investigated the free vibrations of a circle1, a square2, an isosceles right angled triangles3, a rectangular4, elliptical5 plates, and different Chladni patterns are illustrated therein. Tuan et al. reconstructed different Chladni patterns through both experimental and theoretical approaches, and the inhomogeneous Helmholtz equation is adopted during the theoretical modeling6,7. It is a popular method of using Laser Doppler Vibrometer (LDV) or Electronic Speckle Pattern Interferometry (ESPI) to quantitatively measure the mode shapes of the Chladni patterns8,9,10. Although LDV enables femtometer amplitude resolution and very high frequency ranges, unfortunately, the price of LDV is also a little expensive for classroom demonstration and/or college physics education. With this consideration, the present paper proposed a simple approach to quantitatively determine the mode shapes of a Chladni pattern with low cost, since only an extra laser pen and a light screen are needed here.
The present measurement method is illustrated in Figure 111. The vibrating plate has three different positions: the rest position, position 1 and position 2. Position 1 and 2 represent the two maximum vibrating places of the plate. A laser pen projects a straight beam on the surface of the plate, and if the plate locates at the rest position, the laser beam will be directly reflected to the light screen. While the plate locates at position 1 and 2, then the laser beam will be reflected to point A and B on the light screen, respectively. Due to the effect of persistence of vision, there will be a bright straight line on the light screen. The length of the bright light L is related to the distance D between the light screen and the location of the laser point. Different points on the plate have different slopes, which could be determined by the relationship between L and D. After obtaining the slope of the mode shape at different points on the plate, the problem turns into a definite integral. With the help of the boundary vibration amplitude of the plate and the discrete slope data, the mode shape of the vibrating plate can be obtained easily. The whole experimental setup is given in Figure 211.
This paper describes the experimental setup and procedure for the optical lever method to measure the Chladni mode shapes. Some typical experimental results are also illustrated.

<table>
	<tbody>
		<tr>
			<td>Acrylic plates</td>
			<td>Dongguan Jinzhu Lens Products Factory</td>
			<td></td>
			<td>Three 1.0-mm-thickness mirrored circular acrylic plates with diameter of 150 mm, 200 mm and 250 mm respectively. They are easily deformed.</td>
		</tr>
		<tr>
			<td>Laser pen</td>
			<td>Deli Group</td>
			<td>2802</td>
			<td>Red laser is more friendly to the viewer. The finer the laser beam, the better.</td>
		</tr>
		<tr>
			<td>Light screen</td>
			<td>Northern Tempered Glass Custom Taobao Store</td>
			<td></td>
			<td>Several layers of frosted stickers can be placed on the glass to achieve the effect of frosted glass.</td>
		</tr>
		<tr>
			<td>Ruler</td>
			<td>Deli Group</td>
			<td>DL8015</td>
			<td>The length is 1m and the division value is 1mm.</td>
		</tr>
		<tr>
			<td>Signal generator</td>
			<td>Dayang Science Education Taobao Store</td>
			<td>TFG6920A</td>
			<td>Common ones in university laboratories are available.</td>
		</tr>
		<tr>
			<td>Vibrator</td>
			<td>Dayang Science Education Taobao Store</td>
			<td></td>
			<td>The maximum amplitude is 1.5cm.The power is large enough to cause a noticeable phenomenon when the board vibrates. Otherwise, add a power amplifier.</td>
		</tr>
	</tbody>
</table>

measurement of chladni mode shapes with an optical lever method

Quantitatively determining the Chladni pattern of an elastic plate is of great interest in both physical science and engineering applications. In this paper, a method of measuring mode shapes of a vibrating plate based on an optical lever method is proposed. Three circular acrylic plates were employed in the measurement under different center harmonic excitations. Different from a traditional method, only an ordinary laser pen and a light screen made of ground glass are employed in this novel approach. The approach is as follows: the laser pen projects a beam to the vibrating plate perpendicularly, and then the beam is reflected to the light screen in the distance, on which a line segment made of the reflected spot is formed. Due to the principle of vision persistence, the light spot could be read as a bright straight line. The relationship between the slope of the mode shape, length of the light spot and the distance of the vibrating plate and the light screen can be obtained with algebraic operations. Then the mode shape can be determined by integrating the slope distribution with suitable boundary conditions. The full-field mode shapes of Chladni plate could also be determined further in such a simple way.

The excitation frequency that can excite axisymmetric Chladni pattern is determined through the frequency sweeping test. Three circular acrylic plates with diameters of 150 mm, 200 mm and 250 mm are tested, and results show that the first order axisymmetric resonance frequencies are 346 Hz, 214 Hz and 150 Hz for the three plates respectively. It is concluded that with larger diameter, the plate is more flexible, and the corresponding resonance frequency will be smaller. The Chladni patterns of the acrylic plate with diff...

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Measurement of Chladni Mode Shapes with an Optical Lever Method

A simple method of measuring the Chladni mode shape on an elastic plate by the principle of an optical lever is proposed.

Quantitatively determining the Chladni pattern of an elastic plate is of great interest in both physical science and engineering applications. In this ...

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5.0K Views.  University of Science and Technology Beijing. A simple method of measuring the Chladni mode shape on an elastic plate by the principle of an optical lever is proposed.

Video: Measurement of Chladni Mode Shapes with an Optical Lever Method

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 ...

Development of Whispering Gallery Mode Polymeric Micro-optical Electric Field Sensors

Optical modes of dielectric micro-cavities have received significant attention in recent years for their potential in a broad range of applications. The optical modes are frequently referred to as "whispering gallery modes" (WGM) or "morphology dependent resonances" (MDR) and exhibit high optical quality factors. Some proposed applications of micro-cavity optical resonators are in spectroscopy1, micro-cavity laser technology2, optical communications3-6 as well as sensor technology. The WGM-based sensor applications include those in biology7, trace gas detection8, and impurity detection in liquids9. Mechanical sensors based on microsphere resonators have also been proposed, including those for force10,11, pressure12, acceleration13 and wall shear stress14. In the present, we demonstrate a WGM-based electric field sensor, which builds on our previous studies15,16. A candidate application of this sensor is in the detection of neuronal action potential.
The electric field sensor is based on polymeric multi-layered dielectric microspheres. The external electric field induces surface and body forces on the spheres (electrostriction effect) leading to elastic deformation. This change in the morphology of the spheres, leads to shifts in the WGM. The electric field-induced WGM shifts are interrogated by exciting the optical modes of the spheres by laser light. Light from a distributed feedback (DFB) laser (nominal wavelength of ~ 1.3 &mu;m) is side-coupled into the microspheres using a tapered section of a single mode optical fiber. The base material of the spheres is polydimethylsiloxane (PDMS). Three microsphere geometries are used: (1) PDMS sphere with a 60:1 volumetric ratio of base-to-curing agent mixture, (2) multi layer sphere with 60:1 PDMS core, in order to increase the dielectric constant of the sphere, a middle layer of 60:1 PDMS that is mixed with varying amounts (2% to 10% by volume) of barium titanate and an outer layer of 60:1 PDMS and (3) solid silica sphere coated with a thin layer of uncured PDMS base. In each type of sensor, laser light from the tapered fiber is coupled into the outermost layer that provides high optical quality factor WGM (Q ~ 106). The microspheres are poled for several hours at electric fields of ~ 1 MV/m to increase their sensitivity to electric field.

A high-sensitivity photonic micro sensor was developed for electric field detection. The sensor exploits the optical modes of a dielectric sphere. Changes in the external electric field perturb the sphere morphology leading to shifts in its optical modes. The electric field strength is measured by monitoring these optical shifts.

Optical modes of dielectric micro-cavities have received significant attention in recent years for their potential in a broad range of applications. The ...

Quantum State Engineering of Light with Continuous-wave Optical Parametric Oscillators

Engineering non-classical states of the electromagnetic field is a central quest for quantum optics1,2. Beyond their fundamental significance, such states are indeed the resources for implementing various protocols, ranging from enhanced metrology to quantum communication and computing. A variety of devices can be used to generate non-classical states, such as single emitters, light-matter interfaces or non-linear systems3. We focus here on the use of a continuous-wave optical parametric oscillator3,4. This system is based on a non-linear &#967;2 crystal inserted inside an optical cavity and it is now well-known as a very efficient source of non-classical light, such as single-mode or two-mode squeezed vacuum depending on the crystal phase matching. 
Squeezed vacuum is a Gaussian state as its quadrature distributions follow a Gaussian statistics. However, it has been shown that number of protocols require non-Gaussian states5. Generating directly such states is a difficult task and would require strong &#967;3 non-linearities. Another procedure, probabilistic but heralded, consists in using a measurement-induced non-linearity via a conditional preparation technique operated on Gaussian states. Here, we detail this generation protocol for two non-Gaussian states, the single-photon state and a superposition of coherent states, using two differently phase-matched parametric oscillators as primary resources. This technique enables achievement of a high fidelity with the targeted state and generation of the state in a well-controlled spatiotemporal mode.

We describe the reliable generation of non-Gaussian states of traveling optical fields, including single-photon states and coherent state superpositions, using a conditional preparation method operated on the non-classical light emitted by optical parametric oscillators. Type-I and type-II phase-matched oscillators are considered and common procedures, such as the required frequency filtering or the high-efficiency quantum state characterization by homodyning, are detailed.

Engineering non-classical states of the electromagnetic field is a central quest for quantum optics1,2. Beyond their fundamental significance, such states ...

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.

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 ...

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One of the limiting steps to detecting traces of explosives at screening venues is effective collection of the sample. Wipe-sampling is the most common procedure for collecting traces of explosives, and standardized measurements of collection efficiency are needed to evaluate and optimize sampling protocols. The approach described here is designed to provide this measurement infrastructure, and controls most of the factors known to be relevant to wipe-sampling. Three critical factors (the applied force, travel distance, and travel speed) are controlled using an automated device. Test surfaces are chosen based on similarity to the screening environment, and the wipes can be made from any material considered for use in wipe-sampling. Particle samples of the explosive 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) are applied in a fixed location on the surface using a dry-transfer technique. The particle samples, recently developed to simulate residues made after handling explosives, are produced by inkjet printing of RDX solutions onto polytetrafluoroethylene (PTFE) substrates. Collection efficiency is measured by extracting collected explosive from the wipe, and then related to critical sampling factors and the selection of wipe material and test surface. These measurements are meant to guide the development of sampling protocols at screening venues, where speed and throughput are primary considerations.

Optimized sampling protocols and the development of new wipe materials can be facilitated by standardized measurements of collection efficiency from wipe-sampling. Our approach for sampling trace explosives uses an automated device to control speed, force, and distance during wipe-sampling followed by extraction of collected explosives.

One of the limiting steps to detecting traces of explosives at screening venues is effective collection of the sample. Wipe-sampling is the most common ...

Design and Fabrication of an Optical Fiber Made of Water

In this report, an optical fiber of which the core is made solely of water, while the cladding is air, is designed and manufactured. In contrast with solid-cladding devices, capillary oscillations are not restricted, allowing the fiber walls to move and vibrate. The fiber is constructed by a high direct current (DC) voltage of several thousand volts (kV) between two water reservoirs that creates a floating water thread, known as a water bridge. Through the choice of micropipettes, it is possible to control the maximal diameter and length of the fiber. Optical fiber couplers, at both sides of the bridge, activate it as an optical waveguide, allowing researchers to monitor the water fiber capillary body waves through transmission modulation and, therefore, deducing changes in surface tension.
Co-confining two important wave types, capillary and electromagnetic, opens a new path of research in the interactions between light and liquid-wall devices. Water-walled microdevices are a million times softer than their solid counterparts, accordingly improving the response to minute forces.

This protocol describes the design and manufacture of a water bridge and its activation as a water fiber. The experiment demonstrates that capillary resonances of the water fiber modulate its optical transmission.

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A protocol for fabricating a device for simultaneously drying multiple optical cells is presented.

Optical cells, which are experimental instruments, are small, square tubes sealed on one side. A sample is placed in this tube, and a measurement is ...

Measuring the Complete-arch Distortion of an Optical Dental Impression

Digital workflows have actively been used to produce dental restorations or oral appliances since dentists started to make digital impressions by acquiring 3D images with an intraoral scanner. Because of the nature of scanning the oral cavity in the patient&#39;s mouth, the intraoral scanner is a handheld device with a small optical window, stitching together small data to complete the entire image. During the complete-arch impression procedure, a deformation of the impression body can occur and affect the fit of the restoration or appliance. In order to measure these distortions, a master specimen was designed and produced with a metal 3D printer. Designed reference geometries allow setting independent coordinate systems for each impression and measure x, y, and z displacements of the cylinder top circle center where the distortion of the impression can be evaluated. In order to evaluate the reliability of this method, the coordinate values of the cylinder are calculated and compared between the original computer-aided design (CAD) data and the reference data acquired with the industrial scanner. The coordinate differences between the two groups were mostly less than 50 &#181;m, but the deviations were high due to the tolerance of 3D printing in the z coordinates of the obliquely designed cylinder on the molar. However, since the printed model sets a new standard, it does not affect the results of the test evaluation. The reproducibility of the reference scanner is 11.0 &#177; 1.8 &#181;m. This test method can be used to identify and improve upon the intrinsic problems of an intraoral scanner or to establish a scanning strategy by measuring the degree of distortion at each part of the complete-arch digital impression.

Here, we present a protocol to measure the degree of distortion at each part of the compete-arch digital impression acquired from an intraoral scanner with 3D-printed metal phantom with standard geometries.

Digital workflows have actively been used to produce dental restorations or oral appliances since dentists started to make digital impressions by ...

Measuring the Interaction Force Between a Droplet and a Super-hydrophobic Substrate by the Optical Lever Method

The goal of this paper is to investigate the interaction force between droplets and super-hydrophobic substrates in the air. A measurement system based on an optical lever method is designed. A millimetric cantilever is used as a force sensitive component in the measurement system. Firstly, the force sensitivity of the optical lever is calibrated using electrostatic force, which is the critical step in measuring interaction force. Secondly, three super-hydrophobic substrates with different grid fractions are prepared with nanoparticles and copper grids. Finally, the interaction forces between droplets and super-hydrophobic substrates with different grid fractions are measured by the system. This method can be used to measure the force on the scale of sub-micronewton with a resolution on the scale of nanonewton. The in-depth study of the contact process of droplets and super-hydrophobic structures can help to improve the production efficiency in coating, film and printing. The force measurement system designed in this paper can also be used in other fields of microforce measurement.

The protocol aims to investigate the interaction between droplets and super-hydrophobic substrates in the air. This includes calibrating the measurement system and measuring the interaction force at super-hydrophobic substrates with different grid fractions.

The goal of this paper is to investigate the interaction force between droplets and super-hydrophobic substrates in the air. A measurement system based on ...

Method Development for Contactless Resonant Cavity Dielectric Spectroscopic Studies of Cellulosic Paper

The current analytical techniques for characterizing printing and graphic arts substrates are largely ex situ and destructive. This limits the amount of data that can be obtained from an individual sample and renders it difficult to produce statistically relevant data for unique and rare materials. Resonant cavity dielectric spectroscopy is a non-destructive, contactless technique which can simultaneously interrogate both sides of a sheeted material and provide measurements which are suitable for statistical interpretations. This offers analysts the ability to quickly discriminate between sheeted materials based on composition and storage history. In this methodology article, we demonstrate how contactless resonant cavity dielectric spectroscopy may be used to differentiate between paper analytes of varying fiber species compositions, to determine the relative age of the paper, and to detect and quantify the amount of post-consumer waste (PCW) recycled fiber content in manufactured office paper.

A protocol for the non-destructive analysis of the fiber content and relative age of paper.

The current analytical techniques for characterizing printing and graphic arts substrates are largely ex situ and destructive. This limits the amount of ...