This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 within the LDRD program.

1. Preparation of Polisher and Slurry
First prepare the Convergent Polishing System (specifically called Convergent, Initial Surface Independent, Single Iteration, Rogue Particle-Free Polisher or CISR (pronounced &#8216;scissor&#8217;))7,17 by installing the pad &#38; septum, conditioning the pad, diluting &#38; chemically stabilizing the slurry, and incorporating the slurry within the filtration system.
<ol>
	<li>On the CISR polisher, adhere a polyurethane pad onto the granite lap base. Adhere pad one edge first and apply pressure in the direction towards the opposing edge to minimize air gaps. Trim the overhanging pad and then use a razor blade and roller to puncture and remove air bubbles if necessary.</li>
	<li>For first time use and after every ~100 hr of polishing, diamond condition the pad using a CMP diamond conditioner (50 mm diameter; 0.6 psi applied pressure; 5 min dwell at each radial lap location with 25 mm spacing increments; lap rotation 25 rpm) with flowing DI water.</li>
	<li>Between polishing iterations, remove any residual slurry and glass products from the pad using an in-situ ultrasonic cleaner (~2 min dwell at each radial location; lap rotation 5 rpm) with flowing DI water.</li>
	<li>On the uniquely shaped septum weight, adhere double sided foam tape and then the septum material (e.g., pre-cut glass or other non-wearing material). Trim any overhanging foam tape to match the shape of the septum material and weight. Note the septum design (both shape and weight) changes for different sizes of the workpiece and lap7,17.</li>
	<li>Prepare polishing slurry to Baume 4 concentration (specifically mix by volume ~1 part cerium oxide polishing slurry and ~9 parts deionized (DI) water in a 11 L bucket). Check Baume using a Baume float. Add ~5 ml of KOH (10 M) to adjust pH to 9.5 and add ~120 ml (1 vol%) of proprietary surfactant19. Readjust pH and Baume every 24 hr of polishing.</li>
	<li>Install bucket with the prepared slurry into filtration system. Then install the desired CMP particle filters into filtration system. Let slurry recirculate within filtration system for several hours.</li>
	<li>Measure particle size distribution of slurry (e.g., using single particle optical sensing techniques) to ensure the tail end of the distribution is adequately rogue particle-free9,20.</li>
</ol>
2. Preparation of Workpiece (Etching and Blocking)
Before polishing, chemically etch the as-received fine ground workpiece to reduce the amount of material removal needed to remove the sub-surface grinding damage21. Then, block the workpiece (if the aspect ratio (i.e., length/thickness) is &#62;10) using a novel pitch button blocking (PBB) technique to prevent the workpiece from bending during blocking and polishing22.
<ol>
	<li>Etch the fine ground workpiece (specifically a 265 x 265 x 8 mm3 fused silica glass flat) in a tank filled with HF:NH4F (6:1 buffered oxide etch (BOE) 3x diluted with DI water) for 6 hr removing 10 &#181;m of glass from surface of workpiece. CAUTION! BOE is extremely hazardous; wear appropriate personal protective equipment (PPE) . Remove workpiece from etch tank and aggressively rinse the workpiece with DI water and allow the workpiece to air dry vertically.</li>
	<li>Inspect the workpiece for deep damage during the grinding process using a bright light inspection in a dark room. If no deep damage is found, proceed to the next step, else send workpiece back for re-grinding.</li>
	<li>Heat up blocking pitch in a glue gun to ~95 &#186;C and place droplets (also called buttons) of pitch (~0.06 g) onto the face of the blocking plate in a 9 x 9 array (81 buttons with 26 mm spacing). For different size workpieces, refer to design rules for the ideal number, size, and spacings of pitch button22. Place the blocking plate with the applied buttons face up in a pre-heated oven at 70 &#186;C.</li>
	<li>Apply tape to the face of the workpiece that is not to be polished. Avoid generating air bubbles or excessively stretching the tape.</li>
	<li>Place the workpiece with tape side face down onto buttons on the blocking plate in the oven. Cover the workpiece-button-block to minimize convective flow. After 1.5 hr, set oven to cool 10 &#186;C/hr to room temperature. After cooling, the pitch thickness on the blocked workpiece should be ~1 mm.</li>
</ol>
3. Convergent Polishing
<ol>
	<li>Turn on humidity system in environmental chamber of CISR polisher to prevent slurry from drying during polishing and to minimize rogue particles scratching the workpiece.</li>
	<li>Install and mount the specifically designed and prepared septum into polisher. Install PBB workpiece into CISR polisher and lower boom to hold the workpiece.</li>
	<li>Polish workpiece on CISR for 4 hr at a matched lap and workpiece rotation rate of 25 rpm with a radial stroke of ~75 mm and with a slurry flow from filtration system of 1 gal/min. 
	NOTE: The blocking plate also serves as the loading weight on the workpiece corresponding to 0.6 psi applied pressure.</li>
	<li>Turn off lap and workpiece rotation and slurry flow. Remove PBB workpiece from CISR polisher and submerse it into DI water filled bath. Wipe workpiece surface with cleanroom cloth while submerged. Remove PBB workpiece from bath and spray rinse with DI water.</li>
	<li>Deblock workpiece by inserting a shim at workpiece-block interface. Remove tape from workpiece surface. Aggressively rinse workpiece with DI water and air dry.</li>
	<li>PBB the opposing face of the workpiece as described in Section 2. Then repeat polishing procedure as described in Section 3.</li>
</ol>
4. Metrology and Inspection
<ol>
	<li>Measure reflected wavefront (i.e., surface figure) of both sides of workpiece as well as transmitted wavefront using an interferometer.</li>
	<li>Mount workpiece on bright light inspection station and measure the scratch/dig properties using optical fabrication standard methods. A short BOE etch of the workpiece, as described in step 2.1, can be used to expose hidden scratches for workpieces used in high fluence laser applications. For measurement of fine scratches or roughness on the workpiece, standard optical microscopy or white light interferometry may be used.</li>
	<li>Store completed workpiece in a container minimizing contact with face of the workpiece.</li>
</ol>

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	<li>Anderson, D., Burge, J., Thompson, B., Malacara, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ch+28.+Handbook+of+optical+engineering.">Ch 28. Handbook of optical engineering.</a> Optical fabrication. , (2001).</li><li>Karow, 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> Fabrication Methods for Precision Optics. , (1993).</li><li>Brown, N. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+short+course+in+optical+fabrication+technology.">A short course in optical fabrication technology.</a> , (1981).</li><li>Cook, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemical+processes+in+glass+polishing.">Chemical processes in glass polishing.</a> J. Non-Crystal. Solids. 120, 152-171 (1990).</li><li>Preston, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Structure+of+Abraded+Glass+Surfaces.">The Structure of Abraded Glass Surfaces.</a> Trans. Opt. Soc. 23 (3), 141-14 (1922).</li><li>Suratwala, T., Feit, M., Steele, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Toward+Deterministic+Material+Removal+and+Surface+Figure+During+Fused+Silica+Pad+Polishing.">Toward Deterministic Material Removal and Surface Figure During Fused Silica Pad Polishing.</a> J. Am. Ceram. Soc. 93 (5), 1326-1340 (2010).</li><li>Suratwala, T., Steele, R., Feit, M., Desjardin, R., Mason, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Convergent+Pad+Polishing+of+amorphous+fused+silica.">Convergent Pad Polishing of amorphous fused silica.</a> International Journal of Applied Glass Science. 3 (1), 14-28 (2012).</li><li>Suratwala, T., Feit, M., Steele, R., Wong, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+Temperature+and+Material+Deposit+on+Material+Removal+Uniformity+during+Optical+Pad+Polishing.">Influence of Temperature and Material Deposit on Material Removal Uniformity during Optical Pad Polishing.</a> J. Am. Ceram. 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Tribology Int. 33, 723-730 (2000).</li><li>Luo, J., Dornfeld, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+Abrasive+Size+Distribution+in+Chemical+Mechanical+Planarization:+Modeling+and+Verification.">Effects of Abrasive Size Distribution in Chemical Mechanical Planarization: Modeling and Verification.</a> IEEE T. Semicond. M. 16 (3), 469-476 (2003).</li><li>Luo, J., Dornfeld, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Material+Removal+Mechanism+in+Chemical+Mechanical+Polishing:+Theory+and+Modeling.">Material Removal Mechanism in Chemical Mechanical Polishing: Theory and Modeling.</a> IEEE T. Semiconduct. 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The authors have nothing to disclose.

As discussed in the Introduction, successful implementation of Convergent Polishing with respect to surface figure involves eliminating or minimizing all the phenomena that influence spatial material non-uniformity except that of workpiece-lap mismatch due to workpiece shape. If any one of these phenomena is not appropriately mitigated, either through process control or through appropriate engineering of the polisher, then the desired convergence point cannot be achieved or maintained; hence essentially every mitigation ...

The major steps in a typical optical fabrication process include shaping, grinding, full aperture polishing, and sometimes small tool polishing1-3. With increasing demand for high quality optical components for imaging and laser systems, there have been significant advancements in optical fabrication over the last several decades. For example, precision, deterministic material removal is now possible during the shaping and grinding processes with advancements in Computer Numerical Controlled (CNC) glass shaping machines. Similarly, small tool polishing technologies (e.g., computer controlled optical surfacing (CCOS), ion figuring, and magneto-rheological finishing (MRF)) have led to deterministic material removal and surface figure control, thus strongly impacting the optical fabrication industry. However, the intermediate step of the finishing process, full aperture polishing, still lacks high determinism, typically requiring skilled opticians to carry out multiple, often long, iterative cycles with multiple process changes to achieve to the desired surface figure1-3.
The large number of polishing methods, process variables, and the complex chemical and mechanical interactions between the workpiece, lap and slurry3-4 have made it challenging to transform optical polishing from an &#8216;art&#8217; to a science. To achieve deterministic full aperture polishing, the material removal rate must be well understood. Historically, material removal rate has been described by the widely used Preston equation5
<img alt="Equation 1" fo:content-width="1in" fo:src="/files/ftp_upload/51965/51965eqn1.jpg" src="/files/ftp_upload/51965/51965eqn1.jpg" width="100px" />&#160;(1)
where dh/dt is the average thickness removal rate, kp is the Preston constant, &#963;o is the applied pressure, and Vr is the average relative velocity between the workpiece and the lap. Figure 1 schematically depicts the physical concepts that influence material removal rate as described the Preston Equation, including spatial and temporal variations in velocity and pressure, differences between the applied pressure and the pressure distribution that the workpiece experiences, and friction effects6-8. In particular, the actual pressure distribution experienced by the workpiece is governed by a number of phenomena (described in detail elsewhere6-8) which strongly affect resulting surface figure of the workpiece. Also, in the Preston Equation, the microscopic and molecular level effects are largely folded into the macroscopic Preston constant (kp), which influences the overall material removal rate, micro-roughness, and even scratching on the workpiece. Various studies have expanded Preston&#8217;s model to account for microscopic slurry particle-pad-workpiece interactions to explain material removal rate and microroughness9-16.
To achieve deterministic control of surface figure during full aperture polishing, each of the phenomena described above needs to be understood, quantified and then controlled. The strategy behind Convergent Polishing is to eliminate or minimize the undesirable causes of non-uniform material removal, either through engineered polisher design or by process control, such that removal is driven only by the workpiece-lap mismatch due to workpiece shape7,17-18. Figure 2 illustrates how workpiece shape can lead to convergence based on the workpiece-lap mismatch concept. Consider a flat lap and a hypothetical workpiece of complex shape shown at the top left. The interface height mismatch (referred to as the gap, &#916;hoL) influences the interface pressure distribution (&#963;) as:
<img alt="Equation 2" fo:content-width="1in" fo:src="/files/ftp_upload/51965/51965eqn2.jpg" src="/files/ftp_upload/51965/51965eqn2.jpg" width="100px" />&#160;(2)
where h&#773; is a constant describing the rate at which the pressure declines with an increase in gap &#916;hoL6. In this example, the workpiece has the highest local pressure in the center (see bottom left of Figure 2), and hence this location will observe the highest initial material removal rate during polishing. As material is removed, the pressure differential across the workpiece will decrease due to a decrease in the workpiece-lap mismatch, and the workpiece will converge to the shape of the lap. At convergence, the workpiece pressure distribution, and hence material removal, will be uniform across the workpiece (see right side of Figure 2). This example is illustrated for a flat lap, however, the same concept applies for a spherical lap (either concave or convex). Again, this convergence process only works if all the other phenomena affecting spatial material non-uniformity have been eliminated. The specific procedural and engineering mitigations implemented in the Convergent Polishing protocol are described in the Discussion.
The protocol described in the following study is the Convergent Polishing process specifically for a 26.5 cm square fused silica glass workpiece starting from a fine ground surface. In 8 hours of polishing (4 hours/surface), this workpiece can achieve a polished flatness of ~&#955;/2 with very high surface quality (i.e., low scratch density).

<table border="0" cellpadding="0" cellspacing="0" width="634">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Name of Material/Equipment</td>
			<td style="width:245px;">Company</td>
			<td style="width:139px;">Catalog Number</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">MHN 50 mil Polyurethane Pad&#160;</td>
			<td>Eminess Technologies</td>
			<td>PF-MHN15A050L-56</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Cerium oxide polishing slurry</td>
			<td>Universal Photonics</td>
			<td>HASTILITE PO</td>
		</tr>
		<tr height="21">
			<td dir="LTR" height="21" style="height:21px;width:251px;">Septum Glass (waterjet cut)</td>
			<td dir="LTR" style="width:245px;">Borofloat ; Schott&#160;</td>
			<td dir="LTR" style="width:139px;">NA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Diamond conditioner</td>
			<td>Morgan Advanced Ceramics&#160;</td>
			<td>CMP-25035-SFT</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ultrasonic Cleaner</td>
			<td>Advanced Sonics Processing System</td>
			<td>URC4</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Purification Optima Filter cartridge</td>
			<td>3M</td>
			<td>CMP560P10FC</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Blocking Pitch</td>
			<td>Universal Photonics</td>
			<td>BP1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Blocking Tape</td>
			<td>3M</td>
			<td>#4712</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Cleanroom Cloth</td>
			<td>ITW Texwipe</td>
			<td>AlphaWipe TX1013</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Single Particle Optical Sensing</td>
			<td>Paritcle Sizing Systems</td>
			<td>Accusizer 780 AD</td>
		</tr>
	</tbody>
</table>

convergent polishing: a simple, rapid, full aperture polishing process of high quality optical flats &amp; spheres

Convergent Polishing is a novel polishing system and method for finishing flat and spherical glass optics in which a workpiece, independent of its initial shape (i.e., surface figure), will converge to final surface figure with excellent surface quality under a fixed, unchanging set of polishing parameters in a single polishing iteration. In contrast, conventional full aperture polishing methods require multiple, often long, iterative cycles involving polishing, metrology and process changes to achieve the desired surface figure. The Convergent Polishing process is based on the concept of workpiece-lap height mismatch resulting in pressure differential that decreases with removal and results in the workpiece converging to the shape of the lap. The successful implementation of the Convergent Polishing process is a result of the combination of a number of technologies to remove all sources of non-uniform spatial material removal (except for workpiece-lap mismatch) for surface figure convergence and to reduce the number of rogue particles in the system for low scratch densities and low roughness. The Convergent Polishing process has been demonstrated for the fabrication of both flats and spheres of various shapes, sizes, and aspect ratios on various glass materials. The practical impact is that high quality optical components can be fabricated more rapidly, more repeatedly, with less metrology, and with less labor, resulting in lower unit costs. In this study, the Convergent Polishing protocol is specifically described for fabricating 26.5 cm square fused silica flats from a fine ground surface to a polished ~&#955;/2 surface figure after polishing 4 hr per surface on a 81 cm diameter polisher.

The Convergent Polishing protocol described above allows a ground fused silica workpiece (in this case a 26.5 cm square) to be polished, in a single iteration of 4 hr per surface, to a peak-to-valley flatness of ~&#955;/2 (~330 nm) for low aspect ratio workpieces and ~1&#955; (~633 nm) for high aspect ratio workpieces (see Figure 3). Again, this process repeatedly converges workpieces to the same final surface figure without requiring changes to polishing parameters and is independent of the initial surf...

Watch this Scientific Journal Video about Convergent Polishing: A Simple, Rapid, Full Aperture Polishing Process of High Quality Optical Flats & Spheres at JoVE.com

Convergent Polishing: A Simple, Rapid, Full Aperture Polishing Process of High Quality Optical Flats &amp; Spheres

A novel optical polishing process, called &#8220;Convergent Polishing&#8221;, which enables faster, lower cost polishing, is described. Unlike conventional polishing processes, Convergent Polishing allows a glass workpiece to be polished in a single iteration and with high surface quality to its final surface figure without requiring changes to polishing parameters.

Convergent Polishing is a novel polishing system and method for finishing flat and spherical glass optics in which a workpiece, independent of its initial ...

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11.0K Views.  Lawrence Livermore National Laboratory. A novel optical polishing process, called “Convergent Polishing”, which enables faster, lower cost polishing, is described. Unlike conventional polishing processes, Convergent Polishing allows a glass workpiece to be polished in a single iteration and with high surface quality to its final surface figure without requiring changes to polishing parameters.

Video: Convergent Polishing: A Simple, Rapid, Full Aperture Polishing Process of High Quality Optical Flats & Spheres

Fabrication of Silica Ultra High Quality Factor Microresonators

Whispering gallery resonant cavities confine light in circular orbits at their periphery.1-2 The photon storage lifetime in the cavity, quantified by the quality factor (Q) of the cavity, can be in excess of 500ns for cavities with Q factors above 100 million. As a result of their low material losses, silica microcavities have demonstrated some of the longest photon lifetimes to date1-2. Since a portion of the circulating light extends outside the resonator, these devices can also be used to probe the surroundings. This interaction has enabled numerous experiments in biology, such as single molecule biodetection and antibody-antigen kinetics, as well as discoveries in other fields, such as development of ultra-low-threshold microlasers, characterization of thin films, and cavity quantum electrodynamics studies.3-7
The two primary silica resonant cavity geometries are the microsphere and the microtoroid. Both devices rely on a carbon dioxide laser reflow step to achieve their ultra-high-Q factors (Q&gt;100 million).1-2,8-9 However, there are several notable differences between the two structures. Silica microspheres are free-standing, supported by a single optical fiber, whereas silica microtoroids can be fabricated on a silicon wafer in large arrays using a combination of lithography and etching steps. These differences influence which device is optimal for a given experiment.
Here, we present detailed fabrication protocols for both types of resonant cavities. While the fabrication of microsphere resonant cavities is fairly straightforward, the fabrication of microtoroid resonant cavities requires additional specialized equipment and facilities (cleanroom). Therefore, this additional requirement may also influence which device is selected for a given experiment.
Introduction
An optical resonator efficiently confines light at specific wavelengths, known as the resonant wavelengths of the device. 1-2 The common figure of merit for these optical resonators is the quality factor or Q. This term describes the photon lifetime (&tau;o) within the resonator, which is directly related to the resonator's optical losses. Therefore, an optical resonator with a high Q factor has low optical losses, long photon lifetimes, and very low photon decay rates (1/&tau;o). As a result of the long photon lifetimes, it is possible to build-up extremely large circulating optical field intensities in these devices. This very unique property has allowed these devices to be used as laser sources and integrated biosensors.10
A unique sub-class of resonators is the whispering gallery mode optical microcavity. In these devices, the light is confined in circular orbits at the periphery. Therefore, the field is not completely confined within the device, but evanesces into the environment. Whispering gallery mode optical cavities have demonstrated some of the highest quality factors of any optical resonant cavity to date.9,11 Therefore, these devices are used throughout science and engineering, including in fundamental physics studies and in telecommunications as well as in biodetection experiments. 3-7,12
Optical microcavities can be fabricated from a wide range of materials and in a wide variety of geometries. A few examples include silica and silicon microtoroids, silicon, silicon nitride, and silica microdisks, micropillars, and silica and polymer microrings.13-17 The range in quality factor (Q) varies as dramatically as the geometry. Although both geometry and high Q are important considerations in any field, in many applications, there is far greater leverage in boosting device performance through Q enhancement. Among the numerous options detailed previously, the silica microsphere and the silica microtoroid resonator have achieved some of the highest Q factors to date.1,9 Additionally, as a result of the extremely low optical loss of silica from the visible through the near-IR, both microspheres and microtoroids are able to maintain their Q factors over a wide range of testing wavelengths.18 Finally, because silica is inherently biocompatible, it is routinely used in biodetection experiments.
In addition to high material absorption, there are several other potential loss mechanisms, including surface roughness, radiation loss, and contamination loss.2 Through an optimization of the device size, it is possible to eliminate radiation losses, which arise from poor optical field confinement within the device. Similarly, by storing a device in an appropriately clean environment, contamination of the surface can be minimized. Therefore, in addition to material loss, surface scattering is the primary loss mechanism of concern.2,8
In silica devices, surface scattering is minimized by using a laser reflow technique, which melts the silica through surface tension induced reflow. While spherical optical resonators have been studied for many years, it is only with recent advances in fabrication technologies that researchers been able to fabricate high quality silica optical toroidal microresonators (Q&gt;100 million) on a silicon substrate, thus paving the way for integration with microfluidics.1
The present series of protocols details how to fabricate both silica microsphere and microtoroid resonant cavities. While silica microsphere resonant cavities are well-established, microtoroid resonant cavities were only recently invented.1 As many of the fundamental methods used to fabricate the microsphere are also used in the more complex microtoroid fabrication procedure, by including both in a single protocol it will enable researchers to more easily trouble-shoot their experiments.

We describe the use of a carbon dioxide laser reflow technique to fabricate silica resonant cavities, including free-standing microspheres and on-chip microtoroids. The reflow method removes surface imperfections, allowing long photon lifetimes within both devices. The resulting devices have ultra high quality factors, enabling applications ranging from telecommunications to biodetection.

Whispering gallery resonant cavities confine light in circular orbits at their periphery.1-2 The photon storage lifetime in the cavity, quantified by the ...

Process of Making Three-dimensional Microstructures using Vaporization of a Sacrificial Component

Vascular structures in natural systems are able to provide high mass transport through high surface areas and optimized structure. Few synthetic material fabrication techniques are able to mimic the complexity of these structures while maintaining scalability. The Vaporization of a Sacrificial Component (VaSC) process is able to do so. This process uses sacrificial fibers as a template to form hollow, cylindrical microchannels embedded within a matrix. Tin (II) oxalate (SnOx) is embedded within poly(lactic) acid (PLA) fibers which facilitates the use of this process. The SnOx catalyzes the depolymerization of the PLA fibers at lower temperatures. The lactic acid monomers are gaseous at these temperatures and can be removed from the embedded matrix at temperatures that do not damage the matrix. Here we show a method for aligning these fibers using micromachined plates and a tensioning device to create complex patterns of three-dimensionally arrayed microchannels. The process allows the exploration of virtually any arrangement of fiber topologies and structures.

The Vaporization of a Sacrificial Component (VaSC) process is used to fabricate microvascular structures. This procedure uses sacrificial poly(lactic) acid fibers to form hollow microchannels with precise 3D geometric positioning provided by laser micromachined guide plates.

Vascular structures in natural systems are able to provide high mass transport through high surface areas and optimized structure. Few synthetic material ...

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

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

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

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

The Generation of Higher-order Laguerre-Gauss Optical Beams for High-precision Interferometry

Thermal noise in high-reflectivity mirrors is a major impediment for several types of high-precision interferometric experiments that aim to reach the standard quantum limit or to cool mechanical systems to their quantum ground state. This is for example the case of future gravitational wave observatories, whose sensitivity to gravitational wave signals is expected to be limited in the most sensitive frequency band, by atomic vibration of their mirror masses. One promising approach being pursued to overcome this limitation is to employ higher-order Laguerre-Gauss (LG) optical beams in place of the conventionally used fundamental mode. Owing to their more homogeneous light intensity distribution these beams average more effectively over the thermally driven fluctuations of the mirror surface, which in turn reduces the uncertainty in the mirror position sensed by the laser light.
We demonstrate a promising method to generate higher-order LG beams by shaping a fundamental Gaussian beam with the help of diffractive optical elements. We show that with conventional sensing and control techniques that are known for stabilizing fundamental laser beams, higher-order LG modes can be purified and stabilized just as well at a comparably high level. A set of diagnostic tools allows us to control and tailor the properties of generated LG beams. This enabled us to produce an LG beam with the highest purity reported to date. The demonstrated compatibility of higher-order LG modes with standard interferometry techniques and with the use of standard spherical optics makes them an ideal candidate for application in a future generation of high-precision interferometry.

Large laser-interferometers are being constructed to create a new type of astronomy based on gravitational waves. Their sensitivities, as for many other high-precision experiments, are approaching fundamental noise limits such as the atomic vibration of their components. We are pioneering technologies to overcome these limits using novel laser beam shapes.

Thermal noise in high-reflectivity mirrors is a major impediment for several  types of high-precision interferometric experiments that aim to reach the  ...

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 ...

Adsorption Device Based on a Langatate Crystal Microbalance for High Temperature High Pressure Gas Adsorption in Zeolite H-ZSM-5

We present a high-temperature and high-pressure gas adsorption measurement device based on a high-frequency oscillating microbalance (5 MHz langatate crystal microbalance, LCM) and its use for gas adsorption measurements in zeolite H-ZSM-5. Prior to the adsorption measurements, zeolite H-ZSM-5 crystals were synthesized on the gold electrode in the center of the LCM, without covering the connection points of the gold electrodes to the oscillator, by the steam-assisted crystallization (SAC) method, so that the zeolite crystals remain attached to the oscillating microbalance while keeping good electroconductivity of the LCM during the adsorption measurements. Compared to a conventional quartz crystal microbalance (QCM) which is limited to temperatures below 80 &#176;C, the LCM can realize the adsorption measurements in principle at temperatures as high as 200-300 &#176;C (i.e., at or close to the reaction temperature of the target application of one-stage DME synthesis from the synthesis gas), owing to the absence of crystalline-phase transitions up to its melting point (1,470 &#176;C). The system was applied to investigate the adsorption of CO2, H2O, methanol and dimethyl ether (DME), each in the gas phase, on zeolite H-ZSM-5 in the temperature and pressure range of 50-150 &#176;C and 0-18 bar, respectively. The results showed that the adsorption isotherms of these gases in H-ZSM-5 can be well fitted by Langmuir-type adsorption isotherms. Furthermore, the determined adsorption parameters, i.e., adsorption capacities, adsorption enthalpies, and adsorption entropies, compare well to literature data. In this work, the results for CO2 are shown as an example.

A protocol for high-temperature and high-pressure gas adsorption measurements on zeolite H-ZSM-5 using an adsorption measurement device based on a langatate crystal microbalance is presented. Prior to the adsorption measurements, the synthesis of zeolite H-ZSM-5 on the langatate crystal microbalance sensor by the steam-assisted crystallization (SAC) method is demonstrated.

We present a high-temperature and high-pressure gas adsorption measurement device based on a high-frequency oscillating microbalance (5 MHz langatate ...

Challenges in Rheological Characterization of Highly Concentrated Suspensions &#8212; A Case Study for Screen-printing Silver Pastes

A comprehensive rheological characterization of highly concentrated suspensions or pastes is mandatory for a targeted product development meeting the manifold requirements during processing and application of such complex fluids. In this investigation, measuring protocols for a conclusive assessment of different process relevant rheological parameters have been evaluated. This includes the determination of yield stress, viscosity, wall slip velocity, structural recovery after large deformation and elongation at break as well as tensile force during filament stretching.
The importance of concomitant video recordings during parallel-plate rotational rheometry for a significant determination of rheological quantities is demonstrated. The deformation profile and flow field at the sample edge can be determined using appropriate markers. Thus, measurement parameter settings and plate roughness values can be identified for which yield stress and viscosity measurements are possible. Slip velocity can be measured directly and measuring conditions at which plug flow, shear banding or sample spillover occur can be identified clearly. 
Video recordings further confirm that the change in shear moduli observed during three stage oscillatory shear tests with small deformation amplitude in stage I and III but large oscillation amplitude in stage II can be directly attributed to structural break down and recovery. For the pastes investigated here, the degree of irreversible, shear-induced structural change increases with increasing deformation amplitude in stage II until a saturation is reached at deformations corresponding to the crossover of G' and G'', but the irreversible damage is independent of the duration of large amplitude shear. 
A capillary breakup elongational rheometer and a tensile tester have been used to characterize deformation and breakup behavior of highly filled pastes in uniaxial elongation. Significant differences were observed in all experiments described above for two commercial screen-printing silver pastes used for front side metallization of Si-solar cells.

Challenges in Rheological Characterization of Highly Concentrated Suspensions &amp;#8212; A Case Study for Screen-printing Silver Pastes

A protocol for a robust and application relevant rheological characterization of highly concentrated suspensions is presented. Silver pastes used for screen-printing application in solar cell production are employed as model systems.

A comprehensive rheological characterization of highly concentrated suspensions or pastes is mandatory for a targeted product development meeting the ...

Method for Recording Broadband High Resolution Emission Spectra of Laboratory Lightning Arcs

Lightning is one of the most common and destructive forces in nature and has long been studied using spectroscopic techniques, first with traditional camera film methods and then digital camera technology, from which several important characteristics have been derived. However, such work has always been limited due to the inherently random and non-repeatable nature of natural lightning events in the field. Recent developments in lightning test facilities now allow the reproducible generation of lightning arcs within controlled laboratory environments, providing a test bed for the development of new sensors and diagnostic techniques to understand lightning mechanisms better. One such technique is a spectroscopic system using digital camera technology capable of identifying the chemical elements with which the lightning arc interacts, with these data then being used to derive further characteristics. In this paper, the spectroscopic system is used to obtain the emission spectrum from a 100 kA peak, 100 &#181;s duration lightning arc generated across a pair of hemispherical tungsten electrodes separated by a small air gap. To maintain a spectral resolution of less than 1 nm, several individual spectra were recorded across discrete wavelength ranges, averaged, stitched, and corrected to produce a final composite spectrum in the 450 nm (blue light) to 890 nm (near infrared light) range. Characteristic peaks within the data were then compared to an established publicly available database to identify the chemical element interactions. This method is readily applicable to a variety of other light emitting events, such as fast electrical discharges, partial discharges, and sparking in electrical equipment, apparatus, and systems.

Emission spectroscopy techniques have traditionally been used to analyze inherently random lightning arcs occurring in nature. In this paper, a method developed to obtain the emission spectroscopy from reproducible lightning arcs generated within a laboratory environment is described.

Lightning is one of the most common and destructive forces in nature and has long been studied using spectroscopic techniques, first with traditional ...

Atomic Layer Deposition of Vanadium Dioxide and a Temperature-dependent Optical Model

Vanadium dioxide is a material that has a reversible metal-insulator phase change near 68 &#176;C. To grow VO2 on a wide variety of substrates, with wafer-scale uniformity and angstrom level control of thickness, the method of atomic-layer deposition was chosen. This ALD process enables high-quality, low-temperature (&#8804;150 &#176;C) growth of ultrathin films (100-1000 &#197;) of VO2. For this demonstration, the VO2 films were grown on sapphire substrates. This low temperature growth technique produces mostly amorphous VO2 films. A subsequent anneal in an ultra-high vacuum chamber with a pressure of 7x10-4 Pa of ultra-high purity (99.999%) oxygen produced oriented, polycrystalline VO2 films. The crystallinity, phase, and strain of the VO2 were determined by Raman spectroscopy and X-ray diffraction, while the stoichiometry and impurity levels were determined by X-ray photoelectron spectroscopy, and finally the morphology was determined by atomic force microscopy. These data demonstrate the high-quality of the films grown by this technique. A model was created to fit to the data for VO2 in its metallic and insulating phases in the near infrared spectral region. The permittivity and refractive index of the ALD VO2 agreed well with the other fabrication methods in its insulating phase, but showed a difference in its metallic state. Finally, the analysis of the films&#39; optical properties enabled the creation of a wavelength- and temperature-dependent model of the complex optical refractive index for developing VO2 as a tunable refractive index material.

Thin films (100-1000 &#197;) of vanadium dioxide (VO2) were created by atomic-layer deposition (ALD) on sapphire substrates. Following this, the optical properties were characterized through the metal-insulator transition of VO2. From the measured optical properties, a model was created to describe the tunable refractive index of VO2.

Vanadium dioxide is a material that has a reversible metal-insulator phase change near 68 &#176;C. To grow VO2 on a wide variety of substrates, with ...

Predicting Catalyst Extrudate Breakage Based on the Modulus of Rupture

The mechanical strength of extruded catalysts and their natural or forced breakage by either collision against a surface or by a compressive load in a fixed bed are important phenomena in catalyst technology. The mechanical strength of the catalyst is measured here by its bending strength or flexural strength. This technique is relatively new from the perspective of applying it to commercial catalysts of typical sizes used in the industry. Catalyst breakage by collision against a surface is measured after a fall of the extrudates through the ambient air in a vertical pipe. Quantifying the impact force is done theoretically by applying Newton's second law. Measurement of catalyst breakage due to stress in a fixed bed is done following the standard procedure of the bulk crush strength test. Novel here is the focus on measuring the reduction in the length to diameter ratio of the extrudates as a function of the stress.

Here we present a protocol to measure the modulus of rupture of an extruded catalyst and the breakage of said catalyst extrudates by collision against a surface or by compression in a fixed bed.

The mechanical strength of extruded catalysts and their natural or forced breakage by either collision against a surface or by a compressive load in a ...