The authors would like to acknowledge the Union College Faculty Research Fund, Student Research Grant program, and the summer undergraduate research program for financial support of the project. The authors would also like to acknowledge Joana Santos for the design of the three-piece mold, Chris Avanessian for SEM imaging, Ronald Tocci for etching onto the curved aerogel surface, and Dr. Ioannis Michaloudis for inspiration and initial work on the etching project as well as for providing the Kouros image and cylindrical aerogel.

<ol>
	<li>Aegerter, M. A., Leventis, N., Koebel, M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Aerogels Handbook. , (2011).</li><li>Pierre, A. C., Pajonk, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemistry+of+aerogels+and+their+applications.">Chemistry of aerogels and their applications.</a> Chemical Reviews. 102 (11), 4243-4266 (2002).</li><li>Zinzi, M., 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=Optical+and+visual+experimental+characterization+of+a+glazing+system+with+monolithic+silica+aerogel.">Optical and visual experimental characterization of a glazing system with monolithic silica aerogel.</a> Solar Energy. 183, 30-39 (2019).</li><li>Bhuiya, M. M. H., 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=Preparation+of+monolithic+silica+aerogel+for+fenestration+applications:+scaling+up,+reducing+cycle+time,+and+improving+performance.">Preparation of monolithic silica aerogel for fenestration applications: scaling up, reducing cycle time, and improving performance.</a> Industrial &amp; Engineering Chemistry Research. 55 (25), 6971-6981 (2016).</li><li>Jelle, B. P., 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=Fenestration+of+today+and+tomorrow:+A+state-of-the-art+review+and+future+research+opportunities.">Fenestration of today and tomorrow: A state-of-the-art review and future research opportunities.</a> Solar Energy Materials and Solar Cells. 96, 1-28 (2012).</li><li>Michalous, I., Carroll, M. K., Kupiec, S., Cook, K., Anderson, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Facile+method+for+surface+etching+of+silica+aerogel+monoliths.">Facile method for surface etching of silica aerogel monoliths.</a> Journal of Sol-Gel Science and Technology. 87 (1), 22-26 (2018).</li><li>Stanec, A. M., Anderson, A. M., Avanessian, C., Carroll, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+and+characterization+of+etched+silica+aerogels.">Analysis and characterization of etched silica aerogels.</a> Journal of Sol-Gel Science and Technology. 94, 406-415 (2020).</li><li>Sun, J., Longtin, J. P., Norris, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrafast+laser+micromachining+of+silica+aerogels.">Ultrafast laser micromachining of silica aerogels.</a> Journal of Non-Crystalline Solids. 281 (1-3), 39-47 (2001).</li><li>Bian, Q., 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=Micromachining+of+polyurea+aerogel+using+femtosecond+laser+pulses.">Micromachining of polyurea aerogel using femtosecond laser pulses.</a> Journal of Non-Crystalline Solids. 357 (1), 186-193 (2011).</li><li>Yalizay, B., 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=Versatile+liquid-core+optofluidic+waveguides+fabricated+in+hydrophobic+silica+aerogels+by+femtosecond-laser+ablation.">Versatile liquid-core optofluidic waveguides fabricated in hydrophobic silica aerogels by femtosecond-laser ablation.</a> Optical Materials. 47, 478-483 (2015).</li><li>Vainos, N. A., Karoutsos, V., Mills, B., Eason, R. W., Prassas, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isotropic+contractive+scaling+of+laser+written+microstructures+in+vitrified+aerogels.">Isotropic contractive scaling of laser written microstructures in vitrified aerogels.</a> Optical Materials Express. 6 (12), 3814-3825 (2016).</li><li>Plata, D. L., 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=Aerogel-platform+optical+sensors+for+oxygen+gas.">Aerogel-platform optical sensors for oxygen gas.</a> Journal of Non- Crystalline Solids. 350, 326-335 (2004).</li><li>Carroll, M. K., Anderson, A. M., Aegerter, M., Leventis, N., Koebel, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aerogels+as+platforms+for+chemical+sensors.">Aerogels as platforms for chemical sensors.</a> Aerogels Handbook. Advances in Sol-Gel Derived Materials and Technologies. , (2011).</li><li>Bockhorst, M., Heinloth, K., Pajonk, G. M., Begag, R., Elaloui, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescent+dye+doped+aerogels+for+the+enhancement+of+Cerenkov+light+detection.">Fluorescent dye doped aerogels for the enhancement of Cerenkov light detection.</a> Journal of Non-Crystalline Solids. 186, 388-394 (1995).</li><li>Carroll, M. K., Anderson, A. M., Gorka, C. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparing+silica+aerogel+monoliths+via+a+rapid+supercritical+extraction+method.">Preparing silica aerogel monoliths via a rapid supercritical extraction method.</a> Journal of Visualized Experiments: JoVE. (84), e51421 (2014).</li><li>Gauthier, B. M., Bakrania, S. D., Anderson, A. M., Carroll, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+fast+supercritical+extraction+technique+for+aerogel+fabrication.">A fast supercritical extraction technique for aerogel fabrication.</a> Journal of Non-Crystalline Solids. 350, 238-243 (2004).</li><li>Gauthier, B. M., Anderson, A. M., Bakrania, S. D., Mahony, M. K., Bucinell, R. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Method+and+device+for+fabricating+aerogels+and+aerogel+monoliths+obtained+thereby.">Method and device for fabricating aerogels and aerogel monoliths obtained thereby.</a> U.S. Patent. , (2011).</li><li>Gauthier, B. M., Anderson, A. M., Bakrania, S. D., Mahony, M. K., Bucinell, R. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Method+and+device+for+fabricating+aerogels+and+aerogel+monoliths+obtained+thereby.">Method and device for fabricating aerogels and aerogel monoliths obtained thereby.</a> U.S. Patent. , (2008).</li><li>Estok, S. K., Hughes, T. A., Carroll, M. K., Anderson, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+and+characterization+of+TEOS-based+silica+aerogels+prepared+using+rapid+supercritical+extraction.">Fabrication and characterization of TEOS-based silica aerogels prepared using rapid supercritical extraction.</a> Journal of Sol-gel Science and Technology. 70 (3), 371-377 (2014).</li><li>Roth, T. B., Anderson, A. M., Carroll, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+a+rapid+supercritical+extraction+aerogel+fabrication+process:+Prediction+of+thermodynamic+conditions+during+processing.">Analysis of a rapid supercritical extraction aerogel fabrication process: Prediction of thermodynamic conditions during processing.</a> Journal of Non-Crystalline Solids. 354 (31), 3685-3693 (2008).</li><li>Bouck, R. M., Anderson, A. M., Prasad, C., Hagerman, M. E., Carroll, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cobalt-alumina+sol+gels:+Effects+of+heat+treatment+on+structure+and+catalytic+ability.">Cobalt-alumina sol gels: Effects of heat treatment on structure and catalytic ability.</a> Journal of Non-Crystalline Solids. 453, 94-102 (2016).</li><li>Dunn, N. J. H., Carroll, M. K., Anderson, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+alumina+and+nickel-alumina+aerogels+prepared+via+rapid+supercritical+extraction.">Characterization of alumina and nickel-alumina aerogels prepared via rapid supercritical extraction.</a> Polymer Preprints. 52 (1), 250-251 (2011).</li><li>Tobin, Z. M., 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=Preparation+and+characterization+of+copper-containing+alumina+and+silica+aerogels+for+catalytic+applications.">Preparation and characterization of copper-containing alumina and silica aerogels for catalytic applications.</a> Journal of Sol-gel Science and Technology. 84 (3), 432-445 (2017).</li><li>Tsou, P., Brownlee, D. E., Glesias, R., Grigoropoulos, C. P., Weschler, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cutting+silica+aerogel+for+particle+extraction.">Cutting silica aerogel for particle extraction.</a> Lunar and Planetary Science XXXVI. Part 19. , (2005).</li><li>Ishii, H. A., 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=Rapid+extraction+of+dust+impact+tracks+from+silica+aerogel+by+ultrasonic+microblades.">Rapid extraction of dust impact tracks from silica aerogel by ultrasonic microblades.</a> Meteoritics &amp; Planetary Science. 40 (11), 1741-1747 (2005).</li><li>Ishii, H. A., Bradley, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Macroscopic+subdivision+of+silica+aerogel+collectors+for+sample+return+missions.">Macroscopic subdivision of silica aerogel collectors for sample return missions.</a> Meteoritics &amp; Planetary Science. 41 (2), 233-236 (2006).</li></ol>

The authors have nothing to disclose.

This protocol demonstrates how laser etching and the inclusion of dyes can be employed to prepare aesthetically pleasing aerogel materials.
Making large (10 cm x 11 cm x 1.5 cm) aerogel monoliths requires proper mold preparation through sanding, cleaning, and grease application to prevent the aerogel from sticking to the mold and major cracks from forming. The parts of the mold in direct contact with the precursor solution/soon to be formed aerogel are the most critical. Reducing the surface r...

Silica aerogel is a nanoporous, high surface area, acoustically insulating material with low thermal conductivity that can be used in a range of applications from collecting space dust to building insulation material1,2. When manufactured in monolithic form, silica aerogels are translucent and can be used to make highly insulating windows3,4,5.
Recently, we have demonstrated that it is possible to alter the appearance of a silica aerogel by etching onto or cutting through the surface using a laser engraving system6,7 without causing bulk structural damage to the aerogel. This could be useful for making aesthetic enhancements, printing inventory information and machining aerogel monoliths into various forms. Femtosecond lasers have been shown to work for crude &#34;micro-machining&#34; of aerogels8,9,10,11; however, the current protocol demonstrates the ability to alter the surface of aerogels with a simple laser engraving system. As a result, this protocol is broadly applicable to the artistic and technical communities.
It is also possible to incorporate dyes into the aerogel chemical precursor mixture and thereby make dye-doped aerogels with a range of hues. This method has been used to fabricate chemical sensors12,13, to enhance Cerenkov detection14, and for purely aesthetic reasons. Here, we demonstrate the use of dyes and laser etching to prepare aesthetically pleasing aerogels.
In the section that follows, we describe procedures for making large silica aerogel monoliths, altering the monolith preparation procedure to incorporate dyes, etching text, patterns and images onto the surface of an aerogel monolith, and cutting shapes from large dyed monoliths to be assembled into mosaics.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>2000 grit sandpaper</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>50W Laser Engraver</td>
			<td>Epilog Laser</td>
			<td></td>
			<td>Any laser cutter is suitable</td>
		</tr>
		<tr>
			<td>Acetone</td>
			<td>Fisher Scientific www.fishersci.com</td>
			<td>A18-20</td>
			<td>Certified ACS Reagent Grade&#160;</td>
		</tr>
		<tr>
			<td>Ammonium Hydroxide (aqueous ammonia)</td>
			<td>Fisher Scientific www.fishersci.com</td>
			<td>A669S212</td>
			<td>Certified ACS Plus, about 14.8N, 28.0-20.0 w/w%</td>
		</tr>
		<tr>
			<td>Beakers</td>
			<td>Purchased from Fisher Scientific</td>
			<td></td>
			<td>Any glass beaker is suitable.</td>
		</tr>
		<tr>
			<td>Deionized Water</td>
			<td>On tap in house</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Digital balance</td>
			<td>OHaus Explorer Pro</td>
			<td></td>
			<td>Any digital balance is suitable.</td>
		</tr>
		<tr>
			<td>Disposable cleaning wipes</td>
			<td>Fisher Scientific www.fishersci.com</td>
			<td>06-666</td>
			<td>KimWipe</td>
		</tr>
		<tr>
			<td>Drawing Software</td>
			<td>CorelDraw Graphics Suite</td>
			<td></td>
			<td>CorelDraw</td>
		</tr>
		<tr>
			<td>Flexible Graphite Sheet</td>
			<td>Phelps Industrial Products</td>
			<td>7500.062.3</td>
			<td>1/16&#34; thick</td>
		</tr>
		<tr>
			<td>Fluorescein</td>
			<td>Sigma Aldrich www.sigmaaldrich.com</td>
			<td>F2456</td>
			<td>Dye content ~95%</td>
		</tr>
		<tr>
			<td>Foam paint brush&#160;</td>
			<td>Various&#160;</td>
			<td></td>
			<td>1-2 cm size</td>
		</tr>
		<tr>
			<td>High Vacuum Grease</td>
			<td>Dow Corning</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Hydraulic Hot Press</td>
			<td>Tetrahedron www.tetrahedronassociates.com</td>
			<td>MTP-14</td>
			<td>Any hot press with temperature and force control will work. Needs maximum temperature of ~550 F and maximum force of 24 tons.</td>
		</tr>
		<tr>
			<td>Laser Engraver</td>
			<td>Epilogue Laser</td>
			<td>Helix - 24</td>
			<td>50 W</td>
		</tr>
		<tr>
			<td>Methanol (MeOH)</td>
			<td>Fisher Scientific www.fishersci.com</td>
			<td>A412-20</td>
			<td>Certified ACS Reagent Grade, &#8805;99.8%</td>
		</tr>
		<tr>
			<td>Mold</td>
			<td>Fabricated in House</td>
			<td></td>
			<td>Fabricate from cold-rolled steel or stainless steel.</td>
		</tr>
		<tr>
			<td>Paraffin Film</td>
			<td>Fisher Scientific www.fishersci.com</td>
			<td>S37441</td>
			<td>Parafilm M Laboratory Film</td>
		</tr>
		<tr>
			<td>Rhodamine-6G 
			Rhodamine-6g 
			FlouresceinRhodamine-6g</td>
			<td>Sigma Aldrich www.sigmaaldrich.com</td>
			<td>20,132-4</td>
			<td>Dye content ~95%</td>
		</tr>
		<tr>
			<td>Rhodamine-B 
			Rhodamine-6g 
			FlouresceinRhodamine-6g</td>
			<td>Sigma Aldrich www.sigmaaldrich.com</td>
			<td>R-953</td>
			<td>Dye content ~80%</td>
		</tr>
		<tr>
			<td>Soap to clean mold</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Stainless Steel Foil</td>
			<td>Various</td>
			<td></td>
			<td>.0005&#34; thick, 304 Stainless Steel</td>
		</tr>
		<tr>
			<td>Tetramethylorthosilicate (TMOS)</td>
			<td>Sigma Aldrich www.sigmaaldrich.com</td>
			<td>218472-500G</td>
			<td>98% purity, CAS 681-84-5</td>
		</tr>
		<tr>
			<td>Ultrasonic Cleaner</td>
			<td>FisherScientific FS6</td>
			<td>153356</td>
			<td>Any sonicator is suitable.</td>
		</tr>
		<tr>
			<td>Vacuum Exhaust system</td>
			<td>Purex</td>
			<td>800i</td>
			<td>Any exhaust system is suitable.</td>
		</tr>
		<tr>
			<td>Variable micropipettor, 100-1000 &#181;L</td>
			<td>Manufactured by Eppendorf, purchased from Fisher Scientific www.fishersci.com</td>
			<td>S304665</td>
			<td>Any 100-1000 &#181;L pipettor is suitable.</td>
		</tr>
	</tbody>
</table>

aesthetically enhanced silica aerogel via incorporation of laser etching and dyes

A procedure for aesthetically enhancing silica aerogel monoliths by laser etching and incorporation of dyes is described in this manuscript. Using a rapid supercritical extraction method, large silica aerogel monolith (10 cm x 11 cm x 1.5 cm) can be fabricated in about 10 h. Dyes incorporated into the precursor mixture result in yellow-, pink- and orange-tinged aerogels. Text, patterns, and images can be etched onto the surface (or surfaces) of the aerogel monolith without damaging the bulk structure. The laser engraver can be used to cut shapes from the aerogel and form colorful mosaics.

This protocol can be employed to prepare a wide variety of aesthetically pleasing aerogel monoliths for applications including, but not limited to, art and sustainable building design. Inclusion in the precursor mixture of the small amounts of dye employed here is only observed to impact the color of the resulting aerogel monolith; changes in other optical or structural properties are not observed.
Figure 8<...

Watch this Scientific Journal Video about Aesthetically Enhanced Silica Aerogel Via Incorporation of Laser Etching and Dyes at JoVE.com

Aesthetically Enhanced Silica Aerogel Via Incorporation of Laser Etching and Dyes

This protocol describes a method for etching text, patterns, and images onto the surface of silica aerogel monoliths in native and dyed form and assembling the aerogels into mosaic designs.

A procedure for aesthetically enhancing silica aerogel monoliths by laser etching and incorporation of dyes is described in this manuscript. Using a rapid ...

aesthetically-enhanced-silica-aerogel-via-incorporation-laser-etching

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JoVE Journal

Engineering

2.8K Views.  Union College. This protocol describes a method for etching text, patterns, and images onto the surface of silica aerogel monoliths in native and dyed form and assembling the aerogels into mosaic designs.

Video: Aesthetically Enhanced Silica Aerogel Via Incorporation of Laser Etching and Dyes

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 ...

Spatial Separation of Molecular Conformers and Clusters

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

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

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

Scalable Nanohelices for Predictive Studies and Enhanced 3D Visualization

Spring-like materials are ubiquitous in nature and of interest in nanotechnology for energy harvesting, hydrogen storage, and biological sensing applications.&#160; For predictive simulations, it has become increasingly important to be able to model the structure of nanohelices accurately.&#160; To study the effect of local structure on the properties of these complex geometries one must develop realistic models.&#160; To date, software packages are rather limited in creating atomistic helical models.&#160; This work focuses on producing atomistic models of silica glass (SiO2) nanoribbons and nanosprings for molecular dynamics (MD) simulations. Using an MD model of &#8220;bulk&#8221; silica glass, two computational procedures to precisely create the shape of nanoribbons and nanosprings are presented.&#160; The first method employs the AWK programming language and open-source software to effectively carve various shapes of silica nanoribbons from the initial bulk model, using desired dimensions and parametric equations to define a helix.&#160; With this method, accurate atomistic silica nanoribbons can be generated for a range of pitch values and dimensions.&#160; The second method involves a more robust code which allows flexibility in modeling nanohelical structures.&#160; This approach utilizes a C++ code particularly written to implement pre-screening methods as well as the mathematical equations for a helix, resulting in greater precision and efficiency when creating nanospring models.&#160; Using these codes, well-defined and scalable nanoribbons and nanosprings suited for atomistic simulations can be effectively created.&#160; An added value in both open-source codes is that they can be adapted to reproduce different helical structures, independent of material.&#160; In addition, a MATLAB graphical user interface (GUI) is used to enhance learning through visualization and interaction for a general user with the atomistic helical structures.&#160; One application of these methods is the recent study of nanohelices via MD simulations for mechanical energy harvesting purposes.

Accurate modeling of nanohelical structures is important for predictive simulation studies leading to novel nanotechnology applications.&#160; Currently, software packages and codes are limited in creating atomistic helical models.&#160; We present two procedures designed to create atomistic nanohelical models for simulations, and a graphical interface to enhance research through visualization.

Spring-like materials are ubiquitous in nature and of interest in nanotechnology for energy harvesting, hydrogen storage, and biological sensing ...

Characterizing Far-infrared Laser Emissions and the Measurement of Their Frequencies

The generation and subsequent measurement of far-infrared radiation has found numerous applications in high-resolution spectroscopy, radio astronomy, and Terahertz imaging. For about 45 years, the generation of coherent, far-infrared radiation has been accomplished using the optically pumped molecular laser. Once far-infrared laser radiation is detected, the frequencies of these laser emissions are measured using a three-laser heterodyne technique. With this technique, the unknown frequency from the optically pumped molecular laser is mixed with the difference frequency between two stabilized, infrared reference frequencies. These reference frequencies are generated by independent carbon dioxide lasers, each stabilized using the fluorescence signal from an external, low pressure reference cell. The resulting beat between the known and unknown laser frequencies is monitored by a metal-insulator-metal point contact diode detector whose output is observed on a spectrum analyzer. The beat frequency between these laser emissions is subsequently measured and combined with the known reference frequencies to extrapolate the unknown far-infrared laser frequency. The resulting one-sigma fractional uncertainty for laser frequencies measured with this technique is &#177; 5 parts in 107. Accurately determining the frequency of far-infrared laser emissions is critical as they are often used as a reference for other measurements, as in the high-resolution spectroscopic investigations of free radicals using laser magnetic resonance. As part of this investigation, difluoromethane, CH2F2, was used as the far-infrared laser medium. In all, eight far-infrared laser frequencies were measured for the first time with frequencies ranging from 0.359 to 1.273 THz. Three of these laser emissions were discovered during this investigation and are reported with their optimal operating pressure, polarization with respect to the CO2 pump laser, and strength.

We describe the generation of far-infrared radiation using an optically pumped molecular laser along with the measurement of their frequencies with heterodyne techniques. The experimental system and techniques are demonstrated using difluoromethane (CH2F2) as the laser medium whose results include three new laser emissions and eight measured laser frequencies.

The generation and subsequent measurement of far-infrared radiation has found numerous applications in high-resolution spectroscopy, radio astronomy, and ...

Compact Lens-less Digital Holographic Microscope for MEMS Inspection and Characterization

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and automotive. However, effective inspection and characterization metrology systems are needed to ensure the functional reliability of MEMS. This study presents a system based on digital holography as a tool for MEMS metrology. Digital holography has gained increasing attention in the past 20 years. With the fast development and decreasing cost of sensor arrays, resolution of such systems has increased broadening potential applications. Thus, it has attracted attention from both research and industry sides as a potential reliable tool for industrial metrology. Indeed, by recording the interference pattern between an object beam (which contains sample height information) and a reference beam on a CCD camera, one can retrieve the quantitative phase information of an object. However, most of digital holographic systems are bulky and thus not easy to implement on industry production lines. The novelty of the system presented is that it is lens-less and thus very compact. In this study, it is shown that the Compact Digital Holographic Microscope (CDHM) can be used to evaluate several characteristics typically consider as criteria in MEMS inspections. The surface profiles of MEMS in both static and dynamic conditions are presented. Comparison with AFM is investigated to validate the accuracy of the CDHM.

We present a compact reflection digital holographic system (CDHM) for inspection and characterization of MEMS devices. A lens-less design using a diverging input wave providing natural geometrical magnification is demonstrated. Both static and dynamic studies are presented.

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and ...

Automation of Mode Locking in a Nonlinear Polarization Rotation Fiber Laser through Output Polarization Measurements

When a laser is mode-locked, it emits a train of ultra-short pulses at a repetition rate determined by the laser cavity length. This article outlines a new and inexpensive procedure to force mode locking in a pre-adjusted nonlinear polarization rotation fiber laser. This procedure is based on the detection of a sudden change in the output polarization state when mode locking occurs. This change is used to command the alignment of the intra-cavity polarization controller in order to find mode-locking conditions. More specifically, the value of the first Stokes parameter varies when the angle of the polarization controller is swept and, moreover, it undergoes an abrupt variation when the laser enters the mode-locked state. Monitoring this abrupt variation provides a practical easy-to-detect signal that can be used to command the alignment of the polarization controller and drive the laser towards mode locking. This monitoring is achieved by feeding a small portion of the signal to a polarization analyzer measuring the first Stokes parameter. A sudden change in the read out of this parameter from the analyzer will occur when the laser enters the mode-locked state. At this moment, the required angle of the polarization controller is kept fixed. The alignment is completed. This procedure provides an alternate way to existing automating procedures that use equipment such as an optical spectrum analyzer, an RF spectrum analyzer, a photodiode connected to an electronic pulse-counter or a nonlinear detecting scheme based on two-photon absorption or second harmonic generation. It is suitable for lasers mode locked by nonlinear polarization rotation. It is relatively easy to implement, it requires inexpensive means, especially at a wavelength of 1550 nm, and it lowers the production and operation costs incurred in comparison to the above-mentioned techniques.

A protocol to detect and automate mode locking in a pre-adjusted nonlinear polarization rotation fiber laser is presented. The detection of a sudden change in the output polarization state when mode locking occurs is used to command the alignment of an intra-cavity polarization controller in order to find mode-locking conditions.

When a laser is mode-locked, it emits a train of ultra-short pulses at a repetition rate determined by the laser cavity length. This article outlines a ...

Laser-induced Forward Transfer of Ag Nanopaste

Over the past decade, there has been much development of non-lithographic methods1-3 for printing metallic inks or other functional materials. Many of these processes such as inkjet3 and laser-induced forward transfer (LIFT)4 have become increasingly popular as interest in printable electronics and maskless patterning has grown. These additive manufacturing processes are inexpensive, environmentally friendly, and well suited for rapid prototyping, when compared to more traditional semiconductor processing techniques. While most direct-write processes are confined to two-dimensional structures and cannot handle materials with high viscosity (particularly inkjet), LIFT can transcend both constraints if performed properly. Congruent transfer of three dimensional pixels (called voxels), also referred to as laser decal transfer (LDT)5-9, has recently been demonstrated with the LIFT technique using highly viscous Ag nanopastes to fabricate freestanding interconnects, complex voxel shapes, and high-aspect-ratio structures. In this paper, we demonstrate a simple yet versatile process for fabricating a variety of micro- and macroscale Ag structures. Structures include simple shapes for patterning electrical contacts, bridging and cantilever structures, high-aspect-ratio structures, and single-shot, large area transfers using a commercial digital micromirror device (DMD) chip.

We demonstrate the use of the Laser-induced forward transfer technique (LIFT) for the printing of high-viscosity Ag paste. This technique offers a simple, low temperature, robust process for non-lithographically printing microscale 2D and 3D structures.

Over the past decade, there has been much development of non-lithographic methods1-3 for printing metallic inks or other functional materials. Many of ...

Electrochemical Etching and Characterization of Sharp Field Emission Points for Electron Impact Ionization

A new variation of the drop-off method for fabricating field emission points by electrochemically etching tungsten rods in a NaOH solution is described. The results of studies in which the etching current and the molarity of the NaOH solution used in the etching process were varied are presented. The investigation of the geometry of the tips, by imaging them with a scanning electron microscope, and by operating them in field emission mode is also described. The field emission tips produced are intended to be used as an electron beam source for ion production via electron impact ionization of background gas or vapor in Penning trap mass spectrometry applications.

A method for electrochemically etching field emission tips is presented. Etching parameters are characterized and the operation of the tips in field emission mode is investigated.

A new variation of the drop-off method for fabricating field emission points by electrochemically etching tungsten rods in a NaOH solution is described. ...

The Evolution of Silica Nanoparticle-polyester Coatings on Surfaces Exposed to Sunlight

Corrosion of metallic surfaces is prevalent in the environment and is of great concern in many areas, including the military, transport, aviation, building and food industries, amongst others. Polyester and coatings containing both polyester and silica nanoparticles (SiO2NPs) have been widely used to protect steel substrata from corrosion. In this study, we utilized X-ray photoelectron spectroscopy, attenuated total reflection infrared micro-spectroscopy, water contact angle measurements, optical profiling and atomic force microscopy to provide an insight into how exposure to sunlight can cause changes in the micro- and nanoscale integrity of the coatings. No significant change in surface micro-topography was detected using optical profilometry, however, statistically significant nanoscale changes to the surface were detected using atomic force microscopy. Analysis of the X-ray photoelectron spectroscopy and attenuated total reflection infrared micro-spectroscopy data revealed that degradation of the ester groups had occurred through exposure to ultraviolet light to form COO&#903;, -H2C&#903;, -O&#903;, -CO&#903; radicals. During the degradation process, CO and CO2 were also produced.

Two types of surfaces, polyester-coated steel and polyester coated with a layer of silica nanoparticles, were studied. Both surfaces were exposed to sunlight, which was found to cause substantial changes in the chemistry and nanoscale topography of the surface.

Corrosion of metallic surfaces is prevalent in the environment and is of great concern in many areas, including the military, transport, aviation, ...

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.