The authors would like to thank G. Shambat, C. Phillips, K. Aghaei for invaluable discussions, F. Afshinmanesh for SEM images, T. Marvdashti for experimental support, and M.F. Churbanov and G.E. Snopatin from the Institute of Chemistry of High-Purity Substances and V.G. Plotnichenko and E.M. Dianov from the Fiber Optics Research Center of the Russian Academy of Sciences for providing the As2S3 fiber. We also are grateful for support from the Office of Naval Research, NASA, the Air Force Office of Scientific Research, Agilent, and the Joint Technologies Office.

1. Tapering Setup Fabrication (See Assembled Setup in Figure 1)
<ol>
	<li>Secure the motorized linear stages on the breadboard (roughly centered) so that the stages are in contact and will translate towards and away from one another</li>
	<li>Prepare and place the fiber mounts
	<ol>
		<li>Attach two optical posts to the motorized linear stage plates (one each) using the holes closest to each other.</li>
		<li>Attach the bare optical fiber mounts to the tops of the posts. Make sure that the v-grooves for the fiber are aligned. (Note: The height of the bare optical fiber mounts will roughly be the beam height of the system. Choose the future post and pedestal heights accordingly.)</li>
	</ol>
	</li>
	<li>Prepare and place the input and output coupling elements
	<ol>
		<li>Attach the linear translation stages to the motorized linear stages (one for the input and one for the output side) with the adapter plates.</li>
		<li>Place the AR coated ZnSe input coupling lens (mounted in an optical mount with x and y translation on a pedestal) on the input translation stage. Choose a focal length that gives optimal coupling from the pump source to the core of the fiber. Make sure the center of the lens is at the same height as the v-grooves of the fiber clamps.</li>
		<li>Place the uncoated ZnSe output coupling lens (mounted in an optical mount with x and y translation on a pedestal) on the output translation stage. Make sure the center of the lens is at the same height as the v-groove.</li>
	</ol>
	</li>
	<li>Prepare and place the heating element (as shown in Figure 2)
	<ol>
		<li>Machine the aluminum block to desired dimensions (~6 mm x 25.4 mm x 17.5 mm) with holes for the fiber (with a slit for inserting and removing the fiber) and for monitoring the fiber temperature, holes for the cartridge heaters, and 8/32 tapped holes on top and bottom for mounting and securing the cartridge heaters.</li>
		<li>Insert the cartridge heaters to the proper holes of the aluminum block and secure them with 8/32 set screws.</li>
		<li>Attach a ceramic post to the top 8/32 set screw for thermal isolation.</li>
		<li>Attach an optical post to the ceramic post and use a right angle post clamp with an additional optical post to secure the heater to the XYZ linear stage.</li>
		<li>Secure the XYZ linear stage to the breadboard so that the hole for the As2S3 fiber in the aluminum heater can be centered with the v-grooves of the fiber clamps.</li>
		<li>Translate the aluminum heater with the XYZ linear stage so that the heater is no longer near the bare optical fiber clamps, allowing the fiber to be secured without obstruction.</li>
	</ol>
	</li>
</ol>
2. Chalcogenide Fiber Preparation
<ol>
	<li>Soak a desired length of the jacketed As2S3 fiber (must be longer than 8.5 cm-the length of jacketed fiber needed for each fiber taper) in acetone for about 10 min or until the jacket becomes soft. (Use the appropriate solvent for the jacket if using a different fiber).</li>
	<li>Gently remove the softened jacket with a KimWipe, removing a section no longer than 5 cm at a time.</li>
	<li>Clean the bare fiber with isopropanol on a KimWipe.</li>
	<li>Use the beavertail cleaver to cleave one end of the As2S3 fiber. Image the discarded fiber tip to inspect cleave quality.</li>
	<li>Measure and break at least a 6.35-cm length piece of the fiber. This fiber length must be ~2 cm longer than the length needed for the fiber to barely stick out of the fiber clamps.</li>
	<li>Use the beavertail cleaver to cleave the second end of the fiber. Image the discarded fiber tip to inspect cleave quality. Avoid contact with the first cleaved end of fiber.</li>
	<li>Place the fiber in the fiber clamps of the tapering setup. Avoid touching the center of the fiber (where the fiber will be heated).</li>
</ol>
3. In-situ Fiber Tapering Procedure
<ol>
	<li>Couple the mid-IR pump source to the fundamental mode of the fiber with the AR coated ZnSe lens (f = 12.7 mm). Use the uncoated ZnSe lens (f = 20 mm) to image the output facet of the fiber with the Pyrocam to ensure the power is mostly in the fundamental mode. Make sure that the pump beam is propagating along the axis of the fiber. If it is not, the coupling will change once the motorized stages begin to move.</li>
	<li>
	<ol>
		<li>Place a chopper in front of the pump source. (This step is needed for AC coupled detectors).</li>
		<li>Couple the output of the fiber through the monochromator and to the InSb detector using the uncoated CaF2 lenses (f = 20 mm) before and after the monochromator.</li>
		<li>Rotate the grating of the monochromator to allow the long wavelength side of the spectrum to pass through the monochromator until the transmitted signal is barely above the noise floor (at ~3.9 &mu;m). Instead of filtering with the monochromator (steps 3.2.2 and 3.2.3), an appropriate optical filter can be used to measure the power in detectable wavelengths longer than the longest measureable wavelength content of the pump.</li>
	</ol>
	</li>
	<li>Translate the aluminum heater until the fiber slips through the slit and is centered in the aluminum heater's fiber hole.</li>
	<li>Place the RTD sensor level with one of the cartridge heaters. Gently press the RTD sensor against the aluminum heater so that it is fully in contact with the block as shown in Figure 2. If the RTD is not in contact with the heater correctly (or not in a repeatable fashion), the temperature of the block will be unknown and cause the fiber to break during tapering. Make sure that the signal to the monochromator has not decreased.
	<ol>
		<li>A small RTD can be placed inside the other hole of the heater block to monitor the temperature in the hole. (Optional)</li>
	</ol>
	</li>
	<li>Use the digital microscope to image the fiber in the heater block to allow for monitoring of the fiber during the tapering process. (Optional)</li>
	<li>Cover the setup with a box (with holes for the input and output beams) to reduce airflow and allow for stable tapering temperature.</li>
	<li>With the RTD and cartridge heaters connected, turn on the temperature controller. Set the temperature to ~200 &deg;C, where the fiber begins to soften (the exact temperature will depend on the dimensions of the heater, the environment temperature, and air flow around the fiber).</li>
	<li>Once the temperature is stable around the set point, start the Labview program that translates the motorized stages away from one another at ~10 &mu;m/sec in each direction.</li>
	<li>Monitor the signal of the InSb detector, which is the spectral measurement signal. Once the detector signal reaches its maximum value (be careful not to saturate the detector), stop the motorized stages and turn off the cartridge heaters (temperature controller).</li>
	<li>Wait for ~10 min for the fiber to solidify (the detector signal will decrease a little during this process, most likely due to the temperature dependence of the refractive index or thermal contraction).</li>
	<li>Translate the heater block along the fiber towards a fiber clamp where the fiber is untapered. Then translate the heater block away from the fiber using the slit in the heater block to allow the fiber to pass.</li>
	<li>Characterize the SCG through spectral measurements with the monochromator. An InAs filter may be needed to accurately measure the long wavelength portion of the spectrum.</li>
	<li>Remove the fiber if desired.</li>
</ol>

<ol>
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A., Hollberg, L., Mbele, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+fingerprinting+with+the+resolved+modes+of+a+femtosecond+laser+frequency+comb.">Molecular fingerprinting with the resolved modes of a femtosecond laser frequency comb.</a> Nature. 445, 627-630 (2007).</li><li>Thorpe, M. J., Balslev-Clausen, D., Kirchner, M. S., Ye, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cavity-enhanced+optical+frequency+comb+spectroscopy:+application+to+human+breath+analysis.">Cavity-enhanced optical frequency comb spectroscopy: application to human breath analysis.</a> Optics Express. 16, 2387-2397 (2008).</li><li>Sears, C. M. S., Colby, E., England, R. J., Ischebeck, R., McGuinness, C., Nelson, J., Noble, R., Siemann, R. H., Spencer, J., Walz, D., Plettner, T., Byer, R. 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J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tapered+photonic+crystal+fibers.">Tapered photonic crystal fibers.</a> Optics Express. 12, 776-784 (2004).</li><li>Ozeki, T., Kawasaki, B. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+directional+coupler+using+tapered+sections+in+multimode+fibers.">Optical directional coupler using tapered sections in multimode fibers.</a> Applied Physics Letters. 28, 528-529 (1976).</li><li>Yataki, M. S., Payne, D. N., Varnahm, M. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=All-fibre+wavelength+filters+using+concatenated+fused-taper+couplers.">All-fibre wavelength filters using concatenated fused-taper couplers.</a> Electronic Letters. 21, 248-249 (1985).</li><li>Chandalia, J. K., Eggleton, B. J., Windeler, R. S., Kosinski, S. G., Liu, X., Xu, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adiabatic+coupling+in+tapered+air-silica+microstructured+optical+fiber.">Adiabatic coupling in tapered air-silica microstructured optical fiber.</a> IEEE Photonics Technology Letters. 13, 52-54 (2001).</li><li>Mora, J., D&#237;ez, A., Fonjallaz Andr&#233;z, P. Y., Popov, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tunable+dispersion+compensator+based+on+a+fiber+Bragg+grating+written+in+a+tapered+fiber.">Tunable dispersion compensator based on a fiber Bragg grating written in a tapered fiber.</a> IEEE Photonics Technology Letters. 16, 2631-2633 (2004).</li><li>Rusu, M., Herda, R., Kivist&#246;, S., Okhotnikov, O. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fiber+taper+for+dispersion+management+in+a+mode-locked+ytterbium+fiber+laser.">Fiber taper for dispersion management in a mode-locked ytterbium fiber laser.</a> Optics Letters. 31, 2257-2259 (2006).</li><li>Alfanao, R. R., Shapiro, S. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Emission+in+the+region+4000+to+7000+A+via+four-photon+coupling+in+glass.">Emission in the region 4000 to 7000 A via four-photon coupling in glass.</a> Physical Review Letters. 24, 584-587 (1970).</li><li>Eggleton, B. J., Luther-Davies, B., Richardson, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chalcogenide+photonics.">Chalcogenide photonics.</a> Nature Photonics. 5, 141148 (2011).</li><li>Snopatin, G. E., Shiryaev, V. S., Plotnichenko, V. G., Dianov, E. M., Churbanov, M. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-purity+chalcogenide+glasses+for+fiber+optics.">High-purity chalcogenide glasses for fiber optics.</a> Inorganic Materials. 45, 1439-1460 (2009).</li><li>Harbold, J. M., Ilday, F. O., Wise, F. W., Sanghera, J. S., Nguyen, V. Q., Shaw, L. B., Aggarwal, I. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+nonlinear+As-S-Se+glasses+for+all-optical+switching.">Highly nonlinear As-S-Se glasses for all-optical switching.</a> Optics Letters. 27, 119-121 (2002).</li><li>Hudson, D. D., Dekker, S. A., Magi, E. C., Judge, A. C., Jackson, S. D., Li, E., Sanghera, J. S., Shaw, L. B., Aggarwal, I. D., Eggleton, B. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Octave+spanning+supercontinuum+in+an+As2S3+taper+using+ultralow+pump+pulse+energy.">Octave spanning supercontinuum in an As2S3 taper using ultralow pump pulse energy.</a> Optics Letters. 36, 1122-1124 (2011).</li><li>Domachuk, P., Wolchover, N. A., Cronin-Golomb, M., Wang, A., George, A. K., Cordeiro, C. M. B., Knight, J. C., Omenetto, F. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Over+4000+nm+bandwidth+of+mid-IR+supercontinuum+generation+in+sub-centimeter+segments+ofhighly+nonlinear+tellurite+PCFs.">Over 4000 nm bandwidth of mid-IR supercontinuum generation in sub-centimeter segments ofhighly nonlinear tellurite PCFs.</a> Optics Express. 6, 7161-7168 (2008).</li><li>Hu, J., Menyuk, C. R., Shaw, L. B., Sanghera, J. S., Aggarwal, I. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Maximizing+the+bandwidth+of+supercontinuum+generation+in+As2Se3+chalcogenide+fibers.">Maximizing the bandwidth of supercontinuum generation in As2Se3 chalcogenide fibers.</a> Optics Express. 18, 6722-6739 (2010).</li><li>El-Amraoui, M., Fatome, J., Jules, J. C., Kibler, B., Gadret, G., Fortier, C., Smektala, F., Skripatchev, I., Polacchini, C. F., Messaddeq, Y., Troles, J., Brilland, L., Szpulak, M., Renversez, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strong+infrared+spectral+broadening+inlow-loss+As-S+chalcogenide+suspended+core+microstructured+optical+fibers.">Strong infrared spectral broadening inlow-loss As-S chalcogenide suspended core microstructured optical fibers.</a> Optics Express. 18, 4547-4556 (2010).</li><li>Marandi, A., Leindecker, N., Byer, R. L., Vodopyanov, K. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coherence+properties+of+a+broadband+femtosecond+mid-IR+optical+parametric+oscillator+operating+at+degeneracy.">Coherence properties of a broadband femtosecond mid-IR optical parametric oscillator operating at degeneracy.</a> Optics Express. 20, 7255-7262 (2012).</li><li>Dudley, J. 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A United States provisional patent has been filed protecting the technology disclosed in this article.

We have demonstrated a novel fiber tapering procedure and verified its validity by performing SCG in the mid-IR. To the best of our knowledge, the alternative method for this application is based on determining the fiber pulling length required to create a tapered fiber diameter that adds enough waveguide dispersion to optimize SCG in the fiber taper through calculation; however, since the pulling length needed to maximize the spectral broadening for a specific length of fiber varies for each experiment, this calc...

After being first produced in the visible wavelength range1,7 SCG sources have shifted towards the mid-IR, largely driven by applications in spectroscopy.3, 4 Chalcogenide fibers, which include sulfides, selenides, and tellurides, have been a popular material for the mid-IR due to their low propagation loss and high nonlinearity,18 less than 100 dB/km19 and ~200 times that of silica for As2S3,20 respectively. However, the zero GVD wavelength of most chalcogenides is located in the mid-IR, beyond the center wavelength of the majority of available ultrafast pump sources, making SCG challenging in a bulk material or a standard single mode chalcogenide fiber. Waveguide dispersion can be used to modify the zero GVD point for SCG.7 Methods for introducing strong waveguide dispersion include fiber tapering,8, 21 using microstructured fibers,22-24 or even a combination of the two.10 By shifting the zero GVD wavelength below the pump wavelength, the pump will experience anomalous dispersion in the fiber. In the anomalous dispersion regime, soliton formation occurs through balancing the nonlinear chirp caused by self phase modulation and the linear chirp caused by GVD. For a femtosecond pump source, spectral broadening is usually dominated by soliton fission or pulse breaking, which occurs after an initial temporal compression as the pulse propagates along the fiber.7 In the case of fiber tapering, calculating the total GVD-including both material and waveguide dispersion-can provide an approximation of the final taper diameter needed to produce a significantly broadened spectrum. Due to SCG's strong dependence on GVD and fluctuations between experimental trials, including changes to the fiber length before the tapered region and coupling of the pump to the fiber, the calculated approximation is not sufficient for achieving an optimized taper in a single trial. Spectral monitoring allows for these variations in experimental setup to be observed and accounted for in in-situ tapering.
Moreover, generating an efficient supercontinuum (SC) in a short tapered fiber reduces the amount of nonlinear noise amplification preserving the coherence of the SCG and the frequency comb properties of the pump source.25-27 Proper dispersion management, and therefore the necessity of in-situ tapering, becomes even more critical when the fiber length is short, as the SCG tolerance scales with length.
The in-situ tapering setup begins with the pump source, which is the subharmonic of a mode-locked Er-doped fiber laser,9 coupled into the core of the As2S3 fiber that will be tapered. The output of the fiber is then coupled to a device that characterizes the spectral profile. In the experiment, a InSb detector after a monochromator with ~20 nm of resolution is used to monitor a portion of the output spectrum where there is initially a very low signal from the pump source (at ~3.9 &mu;m) so that the fiber may be monitored while tapering. When the fiber is tapered and the spectrum broadens, the spectral measurement signal increases as the dispersion is optimized for the individual experiment. By monitoring the spectrum during the tapering procedure, tapering can be stopped at the moment when the spectral broadening has been maximized. In-situ tapering allows for optimized dispersion management for efficient SCG in a single fiber taper. Tapering with a static, narrow heat zone produces a short fiber taper waist,28 which allows for low-noise SCG. Together, in-situ static tapering can enable coherent, low-noise, octave-spanning SCG in the mid-IR.

<table border="1">
		<tbody>
		 <tr>
			<td>Name of Equipment</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		 </tr>
		 <tr>
			<td>Motorized Linear Stages</td>
			<td>Newport</td>
			<td>MFA-PPD</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Motorized Stage Controller</td>
			<td>Newport</td>
			<td>ESP301</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Aluminum Block</td>
			<td>Any vendor.</td>
			<td></td>
			<td>Dimensions will vary depending on desired taper length.</td>
		 </tr>
		 <tr>
			<td>RTD Sensor</td>
			<td>Omega</td>
			<td>1PT100GX1510</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Cartridge Heaters</td>
			<td>Omega</td>
			<td>CSS-01115/120V</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Temperature Controller</td>
			<td>Omega</td>
			<td>CSC32</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Input Coupling Linear Translation Stage</td>
			<td>CVI</td>
			<td>07TXS224</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Output Coupling Linear Translation Stage</td>
			<td>Newport</td>
			<td>422-1S</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>XYZ Linear Translation Stage</td>
			<td>Newport</td>
			<td>461</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Assorted posts, optics mounts, bases, and forks</td>
			<td>Any vendor.</td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>Optical Breadboard</td>
			<td>Thorlabs</td>
			<td>MB12</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Input Coupling ZnSe Lens</td>
			<td>Thorlabs</td>
			<td>AL72512-E</td>
			<td>Available from other vendors. Input coupling focal length depends on pump source and fiber mode field diameter.</td>
		 </tr>
		 <tr>
			<td>Output Coupling ZnSe Lens</td>
			<td>Edmund Optics</td>
			<td>NT62-961</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Box</td>
			<td>Any type will do.</td>
			<td></td>
			<td>Must be large enough to allow stage movement. Needs apertures for input and output coupling of light.</td>
		 </tr>
		 <tr>
			<td>Ceramic Optical Post</td>
			<td>Any vendor.</td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>Digital Microscope</td>
			<td>Any vendor.</td>
			<td></td>
			<td>Optional.</td>
		 </tr>
		 <tr>
			<td>Table Clamps</td>
			<td>Thorlabs</td>
			<td>CL5</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Bare Fiber clamps</td>
			<td>Thorlabs</td>
			<td>HFF003</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
		 <td></td>
		 <td></td>
		 <td></td>
		 <td>Table 1. Tapering Setup Materials.</td>
	 </tr>
		 <tr>
			<td>As2S3 Optical Fiber</td>
			<td>Fiber Optics Research Center of the Russian Academy of Sciences</td>
			<td></td>
			<td>Available from other vendors, such as CorActive. </td>
		 </tr>
		 <tr>
			<td>Beavertail Cleaver</td>
			<td>Fiber Network Tools</td>
			<td>S-315</td>
			<td>Available from other vendors. Hand cleaving or polishing fiber tips can also produce high quality fiber tips.</td>
		 </tr>
		 <tr>
			<td>KimWipes</td>
			<td>Kimberly-Clark Professional</td>
			<td>34120</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Acetone, Isopropanol</td>
			<td>Any vendor.</td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
		 <td></td>
		 <td></td>
		 <td></td>
		 <td>Table 2. Materials for Chalcogenide Fiber Preparation.</td>
	 </tr>
		 <tr>
			<td>Pyrocam</td>
			<td>Ophir Photonics</td>
			<td>Pyrocam III Series</td>
			<td>Any camera with sensitivity at pump wavelength will work.</td>
		 </tr>
		 <tr>
			<td>Monochromator</td>
			<td>Photon Technology International</td>
			<td></td>
			<td>A 100 line/mm grating was used. Any spectral measurement device will work (e.g. longpass filter). </td>
		 </tr>
		 <tr>
			<td>CaF2 Lenses</td>
			<td>Thorlabs</td>
			<td>LB5922</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>InAs Filter</td>
			<td>Any vendor.</td>
			<td></td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Amplified InSb Detector</td>
			<td>Hamamatsu</td>
			<td>P4631-03</td>
			<td>Available from other vendors.</td>
		 </tr>
		 <tr>
			<td>Computer</td>
			<td>Any vendor.</td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>DAQ</td>
			<td>National Instruments</td>
			<td>USB X Series</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Labview software for motorized stages</td>
			<td>National Instruments</td>
			<td></td>
			<td>Optional. Custom program.</td>
		 </tr>
		 <tr>
			<td>Labview software for collecting detector data</td>
			<td>National Instruments</td>
			<td></td>
			<td>Optional. Custom program.</td>
		 </tr>
		 <tr>
			<td>Assorted posts, optics mounts, bases, and forks</td>
			<td></td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>1" Gold mirrors</td>
			<td>Any vendor.</td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>Chopper and controller</td>
			<td>Any vendor.</td>
			<td>SRS Model SR540</td>
			<td>Optional. Depends on detector being used.</td>
		 </tr>
		 <tr>
		 <td></td>
		 <td></td>
		 <td></td>
		 <td>Table 3. Materials for In-situ Tapering Procedure.</td>
	 </tr>
		</tbody>
 </table>

in-situ tapering of chalcogenide fiber for mid-infrared supercontinuum generation

Supercontinuum generation (SCG) in a tapered chalcogenide fiber is desirable for broadening mid-infrared (or mid-IR, roughly the 2-20 &mu;m wavelength range) frequency combs1, 2 for applications such as molecular fingerprinting, 3 trace gas detection, 4 laser-driven particle acceleration, 5 and x-ray production via high harmonic generation. 6 Achieving efficient SCG in a tapered optical fiber requires precise control of the group velocity dispersion (GVD) and the temporal properties of the optical pulses at the beginning of the fiber, 7 which depend strongly on the geometry of the taper. 8 Due to variations in the tapering setup and procedure for successive SCG experiments-such as fiber length, tapering environment temperature, or power coupled into the fiber, in-situ spectral monitoring of the SCG is necessary to optimize the output spectrum for a single experiment.
	In-situ fiber tapering for SCG consists of coupling the pump source through the fiber to be tapered to a spectral measurement device. The fiber is then tapered while the spectral measurement signal is observed in real-time. When the signal reaches its peak, the tapering is stopped. The in-situ tapering procedure allows for generation of a stable, octave-spanning, mid-IR frequency comb from the sub harmonic of a commercially available near-IR frequency comb. 9 This method lowers cost due to the reduction in time and materials required to fabricate an optimal taper with a waist length of only 2 mm.
	The in-situ tapering technique can be extended to optimizing microstructured optical fiber (MOF) for SCG10 or tuning of the passband of MOFs, 11 optimizing tapered fiber pairs for fused fiber couplers12 and wavelength division multiplexers (WDMs), 13 or modifying dispersion compensation for compression or stretching of optical pulses.14-16

After successful completion of the in-situ tapering procedure, the pump spectrum broadened to cover from 2.2 to 5 &mu;m (at ~40 dB below the peak), as seen in Figure 3. The pump pulse energy in the As2S3 fiber was ~250 pJ with an initial pulse length under 100 fsec. The short length of the tapered waist, ~2.1 mm, allows for generation of a broadband, coherent SC. This preserves the frequency comb properties of the pump source. More information about the frequency comb and o...

Watch this Scientific Journal Video about In-situ Tapering of Chalcogenide Fiber for Mid-infrared Supercontinuum Generation at JoVE.com

In-situ Tapering of Chalcogenide Fiber for Mid-infrared Supercontinuum Generation

We describe a method for in-situ tapering of As2S3 fibers to achieve efficient mid-infrared supercontinuum generation. By tapering while monitoring the supercontinuum&#x2019;s spectrum, the spectral width can be maximized for a fiber taper. In-situ fiber tapering can be applied to optimize the performance of other fiber-based devices.

In-situ Tapering of Chalcogenide Fiber for Mid-infrared Supercontinuum Generation

Supercontinuum  generation (SCG) in a tapered chalcogenide fiber is desirable for broadening mid-infrared  (or mid-IR, roughly the 2-20 &mu;m wavelength ...

in-situ-tapering-chalcogenide-fiber-for-mid-infrared-supercontinuum

Research

JoVE Journal

Engineering

12.2K Views.  Stanford University. We describe a method for in-situ tapering of As2S3 fibers to achieve efficient mid-infrared supercontinuum generation. By tapering while monitoring the supercontinuum’s spectrum, the spectral width can be maximized for a fiber taper. In-situ fiber tapering can be applied to optimize the performance of other fiber-based devices.

Video: In-situ Tapering of Chalcogenide Fiber for Mid-infrared Supercontinuum Generation

In Situ Neutron Powder Diffraction Using Custom-made Lithium-ion Batteries

Li-ion batteries are widely used in portable electronic devices and are considered as promising candidates for higher-energy applications such as electric vehicles.1,2 However, many challenges, such as energy density and battery lifetimes, need to be overcome before this particular battery technology can be widely implemented in such applications.3 This research is challenging, and we outline a method to address these challenges using in situ NPD to probe the crystal structure of electrodes undergoing electrochemical cycling (charge/discharge) in a battery. NPD data help determine the underlying structural mechanism responsible for a range of electrode properties, and this information can direct the development of better electrodes and batteries.
We briefly review six types of battery designs custom-made for NPD experiments and detail the method to construct the &#8216;roll-over&#8217; cell that we have successfully used on the high-intensity NPD instrument, WOMBAT, at the Australian Nuclear Science and Technology Organisation (ANSTO). The design considerations and materials used for cell construction are discussed in conjunction with aspects of the actual in situ NPD experiment and initial directions are presented on how to analyze such complex in situ data.

In Situ Neutron Powder Diffraction Using Custom-made Lithium-ion Batteries

We describe the design and construction of an electrochemical cell for the examination of electrode materials using in situ neutron powder diffraction (NPD). We briefly comment on alternate in situ NPD cell designs and discuss methods for the analysis of the corresponding in situ NPD data produced using this cell.

Li-ion batteries are widely used in portable electronic devices and are considered as promising candidates for higher-energy applications such as electric ...

Fiber Optic Distributed Sensors for High-resolution Temperature Field Mapping

The reliability of computational fluid dynamics (CFD) codes is checked by comparing simulations with experimental data. A typical data set consists chiefly of velocity and temperature readings, both ideally having high spatial and temporal resolution to facilitate rigorous code validation. While high resolution velocity data is readily obtained through optical measurement techniques such as particle image velocimetry, it has proven difficult to obtain temperature data with similar resolution. Traditional sensors such as thermocouples cannot fill this role, but the recent development of distributed sensing based on Rayleigh scattering and swept-wave interferometry offers resolution suitable for CFD code validation work. Thousands of temperature measurements can be generated along a single thin optical fiber at hundreds of Hertz. Sensors function over large temperature ranges and within opaque fluids where optical techniques are unsuitable. But this type of sensor is sensitive to strain and humidity as well as temperature and so accuracy is affected by handling, vibration, and shifts in relative humidity. Such behavior is quite unlike traditional sensors and so unconventional installation and operating procedures are necessary to ensure accurate measurements. This paper demonstrates implementation of a Rayleigh scattering-type distributed temperature sensor in a thermal mixing experiment involving two air jets at 25 and 45 &#176;C. We present criteria to guide selection of optical fiber for the sensor and describe installation setup for a jet mixing experiment. We illustrate sensor baselining, which links readings to an absolute temperature standard, and discuss practical issues such as errors due to flow-induced vibration. This material can aid those interested in temperature measurements having high data density and bandwidth for fluid dynamics experiments and similar applications. We highlight pitfalls specific to these sensors for consideration in experiment design and operation.

We demonstrate use of a fiber optic distributed sensor for mapping the temperature field of mixing air jets. The Rayleigh scattering-based sensor generates thousands of data points along a single fiber to provide exceptional spatial resolution that is unattainable with traditional sensors such as thermocouples.

The reliability of computational fluid dynamics (CFD) codes is checked by comparing simulations with experimental data. A typical data set consists ...

Electrospray Deposition of Uniform Thickness Ge23Sb7S70 and As40S60 Chalcogenide Glass Films

Solution-based electrospray film deposition, which is compatible with continuous, roll-to-roll processing, is applied to chalcogenide glasses. Two chalcogenide compositions are demonstrated: Ge23Sb7S70 and As40S60, which have both been studied extensively for planar mid-infrared (mid-IR) microphotonic devices. In this approach, uniform thickness films are fabricated through the use of computer numerical controlled (CNC) motion. Chalcogenide glass (ChG) is written over the substrate by a single nozzle along a serpentine path. Films were subjected to a series of heat treatments between 100 &#176;C and 200 &#176;C under vacuum to drive off residual solvent and densify the films. Based on transmission Fourier transform infrared (FTIR) spectroscopy and surface roughness measurements, both compositions were found to be suitable for the fabrication of planar devices operating in the mid-IR region. Residual solvent removal was found to be much quicker for the As40S60 film as compared to Ge23Sb7S70. Based on the advantages of electrospray, direct printing of a gradient refractive index (GRIN) mid-IR transparent coating is envisioned, given the difference in refractive index of the two compositions in this study.

Electrospray Deposition of Uniform Thickness Ge23Sb7S70 and As40S60 Chalcogenide Glass Films

A method of uniform thickness solution-derived chalcogenide glass film deposition is demonstrated using computer numerical controlled motion of a single-nozzle electrospray.

Solution-based electrospray film deposition, which is compatible with continuous, roll-to-roll processing, is applied to chalcogenide glasses. Two ...

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia (YSZ) Scaffolds by In Situ Carbon Templating Xerogels

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) scaffolds with tunable specific surface areas up to 80 m2&#183;g-1. An aqueous solution of a zirconium salt, yttrium salt, and glucose is mixed with propylene oxide (PO) to form a gel. The gel is dried under ambient conditions to form a xerogel. The xerogel is pressed into pellets and then sintered in an argon atmosphere. During sintering, a YSZ ceramic phase forms and the organic components decompose, leaving behind amorphous carbon. The carbon formed in situ serves as a hard template, preserving a high surface area YSZ nanomorphology at sintering temperature. The carbon is subsequently removed by oxidation in air at low temperature, resulting in a porous, nanostructured YSZ scaffold. The concentration of the carbon template and the final scaffold surface area can be systematically tuned by varying the glucose concentration in the gel synthesis. The carbon template concentration was quantified using thermogravimetric analysis (TGA), the surface area and pore size distribution was determined by physical adsorption measurements, and the morphology was characterized using scanning electron microscopy (SEM). Phase purity and crystallite size was determined using X-ray diffraction (XRD). This fabrication approach provides a novel, flexible platform for realizing unprecedented scaffold surface areas and nanomorphologies for ceramic-based electrochemical energy conversion applications, e.g. solid oxide fuel cell (SOFC) electrodes.

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia YSZ Scaffolds by In Situ Carbon Templating Xerogels

A protocol for fabricating porous, nanostructured yttria-stabilized-zirconia (YSZ) scaffolds at temperatures between 1,000 &#176;C and 1,400 &#176;C is presented.

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) ...

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and forging. Adoption of this technique is proceeding despite disagreement concerning the underlying mechanism responsible for EAD. The experimental procedure described herein enables a more explicit study compared to previous EAD research by removing thermal effects, which are responsible for disagreement in interpreting previous EAD results. Furthermore, as the procedure described here enables EAD observation in situ and in real time in a transmission electron microscope (TEM), it is superior to existing post-mortem methods that observe EAD effects post-test. Test samples consist of a single crystal copper (SCC) foil having a free-standing tensile test section of nanoscale thickness, fabricated using a combination of laser and ion beam milling. The SCC is mounted to an etched silicon base that provides mechanical support and electrical isolation while serving as a heat sink. Using this geometry, even at high current density (~3,500 A/mm2), the test section experiences a negligible temperature increase (&#60;0.02 &#176;C), thus eliminating Joule heating effects. Monitoring material deformation and identifying the corresponding changes to microstructures, e.g. dislocations, are accomplished by acquiring and analyzing a series of TEM images. Our sample preparation and in situ experiment procedures are robust and versatile as they can be readily utilized to test materials with different microstructures, e.g., single and polycrystalline copper.

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Isolating electrical and thermal effects on electrically assisted deformation (EAD) is very difficult using macroscopic samples. Metallic sample micro- and nanostructures together with a custom test procedure have been developed to evaluate the impact of applied current on the formation without joule heating and evolution of dislocations on these samples.

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and ...

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of lithium-ion (Li-ion) batteries. However, a number of setbacks prevent their integration into commercial devices. The main limiting factor is due to nanoscale phenomena occurring at the electrode/electrolyte interfaces, ultimately leading to degradation of battery operation. These key problems are highly challenging to observe and characterize as these batteries contain multiple buried interfaces. One approach for direct observation of interfacial phenomena in thin film batteries is through the fabrication of electrochemically active nanobatteries by a focused ion beam (FIB). As such, a reliable technique to fabricate nanobatteries was developed and demonstrated in recent work. Herein, a detailed protocol with a step-by-step process is presented to enable the reproduction of this nanobattery fabrication process. In particular, this technique was applied to a thin film battery consisting of LiCoO2/LiPON/a-Si, and has further been previously demonstrated by in situ cycling within a transmission electron microscope.

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

A protocol for the fabrication of electrochemically active LiPON-based solid-state lithium-ion nanobatteries using a focused ion beam is presented.

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of ...

Installation Method to Enhance Quality Control for Fiber Reinforced Polymer Spike Anchors

Fiber reinforced polymer (FRP) anchors are a promising way to enhance the performance of externally-bonded FRPs applied to existing structures, as they can delay or even prevent debonding failure. However, a major concern faced by designers is the premature failure of the anchors due to stress concentration. Poor installation quality and preparation of the clearance holes can result in stress concentration that provokes this premature failure. This paper deals with an installation method that aims to reduce the impact of the stress concentration and to provide a proper quality control of the preparation of the drill hole. The method involves three parts: the drilling and cleaning of the holes, the smoothing of the hole edges with a customized drill bit, and the installation of the anchor itself, including the impregnation of the anchor dowel and its insertion. Anchor fans (the free length of the spikes) are then bonded to the external FRP reinforcement. For the end anchorage, and in the case of reinforcements with multiple plies, it is recommended that the anchor fan be inserted between two plies to assist the stress-transfer mechanism. 
The proposed procedure is complemented with a design approach for spike anchors, based on an extensive database. It is proposed that the design follow a number of steps, namely: selection of the anchor diameter and subsequent tensile strength of the connector (that is to say, the anchor before fanning out the free end), evaluation of the reduction in the tensile strength due to bending, provision of enough embedment to prevent slippage failure, and consideration of the number and spacing of anchors for a given reinforcement. In this sense, it should be noted that further research is needed in order to obtain a general expression for the contribution of spike anchors to overall bond strength of FRP reinforcements.

This manuscript presents a method for controlling the quality of installation for spike anchors designed to delay delamination of externally bonded fiber reinforced polymers. The protocol includes the preparation of the drill hole and the insertion process. The most influential parameters on the efficiency of the anchors are discussed.

Fiber reinforced polymer (FRP) anchors are a promising way to enhance the performance of externally-bonded FRPs applied to existing structures, as they ...

Three-Dimensional Ultrasonic Needle Tip Tracking with a Fiber-Optic Ultrasound Receiver

Ultrasound is frequently used for guiding minimally invasive procedures, but visualizing medical devices is often challenging with this imaging modality. When visualization is lost, the medical device can cause trauma to critical tissue structures. Here, a method to track the needle tip during ultrasound image-guided procedures is presented. This method involves the use of a fiber-optic ultrasound receiver that is affixed within the cannula of a medical needle to communicate ultrasonically with the external ultrasound probe. This custom probe comprises a central transducer element array and side element arrays. In addition to conventional two-dimensional (2D) B-mode ultrasound imaging provided by the central array, three-dimensional (3D) needle tip tracking is provided by the side arrays. For B-mode ultrasound imaging, a standard transmit-receive sequence with electronic beamforming is performed. For ultrasonic tracking, Golay-coded ultrasound transmissions from the 4 side arrays are received by the hydrophone sensor, and subsequently the received signals are decoded to identify the needle tip&#39;s spatial location with respect to the ultrasound imaging probe. As a preliminary validation of this method, insertions of the needle/hydrophone pair were performed in clinically realistic contexts. This novel ultrasound imaging/tracking method is compatible with current clinical workflow, and it provides reliable device tracking during in-plane and out-of-plane needle insertions.

Accurate and efficient visualization of invasive medical devices is extremely important in many ultrasound-guided minimally invasive procedures. Here, a method for localizing the spatial position of a needle tip relative to the ultrasound imaging probe is presented.

Ultrasound is frequently used for guiding minimally invasive procedures, but visualizing medical devices is often challenging with this imaging modality. ...

Experimental Procedure for Laboratory Studies of In Situ Burning : Flammability and Burning Efficiency of Crude Oil

A new method for the simultaneous study of the flammability and burning efficiency of fresh and weathered crude oil through two experimental laboratory setups is presented. The experiments are easily repeatable compared to operational scale experiments (pool diameter &#8805;2 m), while still featuring quite realistic in situ burning conditions of crude oil on water. Experimental conditions include a flowing water sub-layer that cools the oil slick and an external heat flux (up to 50 kW/m2) that simulates the higher heat feedback to the fuel surface in operational scale crude oil pool fires. These conditions enable a controlled laboratory study of the burning efficiency of crude oil pool fires that are equivalent to operational scale experiments. The method also provides quantitative data on the requirements for igniting crude oils in terms of the critical heat flux, ignition delay time as a function of the incident heat flux, the surface temperature upon ignition, and the thermal inertia. This type of data can be used to determine the required strength and duration of an ignition source to ignite a certain type of fresh or weathered crude oil. The main limitation of the method is that the cooling effect of the flowing water sub-layer on the burning crude oil as a function of the external heat flux has not been fully quantified. Experimental results clearly showed that the flowing water sub-layer does improve how representative this setup is of in situ burning conditions, but to what extent this representation is accurate is currently uncertain. The method nevertheless features the most realistic in situ burning laboratory conditions currently available for simultaneously studying the flammability and burning efficiency of crude oil on water.

Experimental Procedure for Laboratory Studies of In Situ Burning : Flammability and Burning Efficiency of Crude Oil

Here, we present a protocol to simultaneously study the flammability and burning efficiency of fresh and weathered crude oil under conditions that simulate in situ burning operations on the sea.

A new method for the simultaneous study of the flammability and burning efficiency of fresh and weathered crude oil through two experimental laboratory ...

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.

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 ...