Name: stimulated stokes and antistokes raman scattering in microspherical whispering gallery mode resonators
Uploaded: 2016-04-04T14:00:00
Description: Watch this Scientific Journal Video about Stimulated Stokes and Antistokes Raman Scattering in Microspherical Whispering Gallery Mode Resonators at JoVE.com

Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi
Ente Cassa di Risparmio di Firenze (No. 2014.0770A2202.8861)

1. Fabrication of Ultrahigh Factor of Quality Microspheres
<ol>
	<li>Strip about 1-2 cm of a standard single-mode (SMF) silica fiber off its acrylic coating using an optical stripper.</li>
	<li>Clean the stripped part with acetone and cleave it.</li>
	<li>Introduce the cleaved tip in one arm of a fusion splicer and produce a series of electric arc discharges using the splicer controller. Select &#34;manual operation&#34; from the splicer controller menu, set the values for arc power level and arc duration to 60 and 800...

<ol>
	<li>Kozyreff, G., Dominguez-Juarez, J. L., Martorell, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Non+linear+optics+in+spheres:+from+second+harmonic+scattering+to+quasi-phase+matched+generation+in+whispering+gallery+modes.">Non linear optics in spheres: from second harmonic scattering to quasi-phase matched generation in whispering gallery modes.</a> Laser Photon. Rev. 5 (6), (2011).</li><li>Farnesi, D., Barucci, A., Righini, G. C., Berneschi, S., Soria, S., Nunzi Conti, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+frequency+generation+in+silica+microspheres.">Optical frequency generation in silica microspheres.</a> Phys. Rev. Lett. 112 (9), 093901 (2014).</li><li>Liang, W., 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=Miniature+multioctave+light+source+based+on+a+monolithic+microcavity.">Miniature multioctave light source based on a monolithic microcavity.</a> Optica. 2 (1), 40-47 (2015).</li><li>Maker, A. J., Armani, 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+of+Silica+Ultra+High+Quality+Factor+Microresonators.">Fabrication of Silica Ultra High Quality Factor Microresonators.</a> J. Vis. Exp. (65), e4164 (2012).</li><li>Coillet, A., Henriet, R., Phan Huy, K., Jacquot, M., Furfaro, L., Balakireva, I., 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=Microwave+Photonics+Systems+Based+on+Whispering-gallery-mode+Resonators.">Microwave Photonics Systems Based on Whispering-gallery-mode Resonators.</a> J. Vis. Exp. (78), e50423 (2013).</li><li>Han, K., Kim, K. H., Kim, J., Lee, W., Liu, J., Fan, X., 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=Fabrication+and+Testing+of+Microfluidic+Optomechanical+Oscillators.">Fabrication and Testing of Microfluidic Optomechanical Oscillators.</a> J. Vis. Exp. (87), e51497 (2014).</li><li>Arnold, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microspheres,+Photonic+Atoms,+and+the+Physics+of+Nothing.">Microspheres, Photonic Atoms, and the Physics of Nothing.</a> American Scientist. 89 (5), 414-421 (2001).</li><li>Chiasera, 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=Spherical+whispering+gallery+mode+microresonators.">Spherical whispering gallery mode microresonators.</a> Laser Photon. Rev. 4 (3), 457-482 (2010).</li><li>Helt, L. G., Liscidini, M., Sipe, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+does+it+scale?+Comparing+quantum+and+classical+nonlinear+optical+processes+in+integrated+devices.">How does it scale? Comparing quantum and classical nonlinear optical processes in integrated devices.</a> J. Opt. Soc. Am. B. 29 (8), 2199-2212 (2012).</li><li>Leach, D. H., Chang, R. K., Acker, W. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stimulated+anti-Stokes+Raman+scattering+in+microdroplets.">Stimulated anti-Stokes Raman scattering in microdroplets.</a> Opt. Lett. 17 (6), 387-389 (1992).</li><li>Farnesi, D., Cosi, F., Trono, C., Righini, G. C., Nunzi Conti, G., Soria, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stimulated+Antistokes+Raman+scattering+resonantly+enhanced+in+silica+microspheres.">Stimulated Antistokes Raman scattering resonantly enhanced in silica microspheres.</a> Opt. Lett. 39 (20), 5993-5996 (2014).</li><li>Qian, S. X., Chang, R. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiorder+Stokes+emission+from+micrometer+size+droplets.">Multiorder Stokes emission from micrometer size droplets.</a> Phys. Rev. Lett. 56 (9), 926-929 (1986).</li><li>Lin, H. B., Campillo, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=CW+nonlinear+optics+in+droplet+microcavities+displaying+enhanced+gain.">CW nonlinear optics in droplet microcavities displaying enhanced gain.</a> Phys. Rev. Lett. 73 (18), 2440-2443 (1994).</li><li>Spillane, S. M., Kippenberg, T. J., Vahala, K. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultralow+threshold+Raman+laser+using+a+spherical+dielectric+microcavity.">Ultralow threshold Raman laser using a spherical dielectric microcavity.</a> Nature. 415 (6872), 621-623 (2002).</li><li>Kippenberg, T. J., Spillane, S. M., Vahala, K. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kerr-Nonlinearity+optical+parametrical+oscillation+in+an+ultrahigh+Q+toroid+microcavity.">Kerr-Nonlinearity optical parametrical oscillation in an ultrahigh Q toroid microcavity.</a> Phys. Rev. Lett. 93 (8), 083904 (2004).</li><li>Hill, S. C., Leach, D. H., Chang, R. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Third+order+sum+frequency+generation+in+droplets:+model+with+numerical+results+for+third-harmonic+generation.">Third order sum frequency generation in droplets: model with numerical results for third-harmonic generation.</a> J. Opt. Soc. Am. B. 10 (1), 16-33 (1993).</li><li>Kozyreff, G., Dominguez Juarez, J. L., Martorell, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Whispering+gallery+mode+phase+matching+for+surface+second+order+nonlinear+optical+processes+in+spherical+microresonators.">Whispering gallery mode phase matching for surface second order nonlinear optical processes in spherical microresonators.</a> Phys. Rev. A. 77 (4), 043817 (2008).</li><li>Jouravlev, M. V., Kurizki, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Unified+theory+of+Raman+and+parametric+amplification+in+nonlinear+microspheres.">Unified theory of Raman and parametric amplification in nonlinear microspheres.</a> Phys. Rev. A. 70 (5), 053804 (2004).</li><li>Brenci, M., Calzolai, R., Cosi, F., Nunzi Conti, G., Pelli, S., Righini, G. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microspherical+resonators+for+biophotonic+sensors.">Microspherical resonators for biophotonic sensors.</a> Proc. SPIE. 6158, 61580S (2006).</li><li>Carmon, T., Yang, L., Vahala, K. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamical+thermal+behavior+and+thermal+self-stability+of+microcavities.">Dynamical thermal behavior and thermal self-stability of microcavities.</a> Opt. Express. 12 (20), 4742-4750 (2004).</li><li>Kippenberg, T. J., Spillane, S. M., Min, B., Vahala, K. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Theoretical+and+experimental+study+of+stimulated+and+cascaded+Raman+scattering+in+ultrahigh+Q+optical+microcavities.">Theoretical and experimental study of stimulated and cascaded Raman scattering in ultrahigh Q optical microcavities.</a> J. Sel. Quantum Electron. 10 (5), 1219-1228 (2004).</li><li>Bloembergen, N., Shen, Y. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coupling+between+vibrations+and+light+waves+in+Raman+laser+media.">Coupling between vibrations and light waves in Raman laser media.</a> Phys. Rev. Lett. 12 (18), 504-507 (1964).</li><li>Gorodestky, M. L., Pryamikov, A. D., Ilchenko, V. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rayleigh+scattering+in+high+Q+microspheres.">Rayleigh scattering in high Q microspheres.</a> J. Opt. Soc. Am. B. 17 (6), 1051-1057 (2000).</li><li>Arnold, S., Ramjit, R., Keng, D., Kolchenko, V., Teraoka, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microparticle+photophysics+illuminates+viral+bio-sensing.">Microparticle photophysics illuminates viral bio-sensing.</a> Faraday Discuss. 137, 65-83 (2008).</li><li>Ozdemir, S. K., 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=Highly+sensitive+detection+of+nanoparticle+with+a+self+referenced+and+self-heterodyned+whispering+gallery+Raman+microlaser.">Highly sensitive detection of nanoparticle with a self referenced and self-heterodyned whispering gallery Raman microlaser.</a> Proc. Natl. Acad. Sci USA. 11 (37), E3836-E3844 (2014).</li></ol>

Microspheres are compact and efficient nonlinear oscillators and they are very easy to fabricate and handle. Tapered fibers can be used for coupling and extracting the light in/from the resonator. Resonance contrast up to 95% and Q factors of about 3 x 108 can be obtained.
The main limitation of these fabrication techniques is mass production and integration. Cleanliness of the fibers is critical to both microspheres and tapers, and so is humidity. Both devices must be kept in dry e...

Whispering gallery mode resonators (WGMR) show two unique properties, a long photon lifetime and small mode volume that allow the reduction of the threshold of nonlinear phenomena1-3. Whispering gallery modes are optical modes that are confined at the dielectric air interface by total internal reflection. The small mode volume is due to the high spatial confinement whereas the temporal confinement is related to the quality factor Q of the cavity. WGMR can have different geometries and there are different fabrication techniques suitable for obtaining high Q resonators4-6 Surface tension cavities such as silica microspheres exhibit near atomic scale roughness, which translates in high quality factors. Both types of confinement significantly reduce the threshold for nonlinear effects due to the strong energy buildup inside the WGMR. It also allows continuous wave (CW) nonlinear optics.
WGMR can be described using the quantum numbers n, l, m and their polarization state, in a strong analogy with the hydrogen atom7. The spherical symmetry allows the separation in radial and angular dependencies. The radial solution is given by Bessel functions, the angular ones by the spherical harmonics8.
Silica glass is centrosymmetric and, therefore, second order phenomena related to &#935;(2) interactions are forbidden. At the surface of the microsphere, the inversion of symmetry is broken and &#935;(2) phenomena can be observed1. However, phase matching conditions for second-order frequency generation are more problematic than the equivalent in third order frequency generation, especially because the wavelengths involved are quite different and the role of dispersion can be quite important. The second order interactions are extremely weak. The generated power scales with Q3 whereas for a third order interaction the generated power scales with Q4.9 For that reason, the focus of this work is third order optical non-linear susceptibility &#935;(3) interactions such as Stimulated Raman Scattering (SRS) and Stimulated Antistokes Raman Scattering (SARS), being SARS the less explored interaction10,11. Chang12 and Campillo13 pioneered the studies of nonlinear phenomena using droplets of highly nonlinear materials as WGMR but the pump laser was pulsed instead of CW. Silica microspheres14,10 and microtoroids15 provided more stable and robust platforms compared to the micro-droplets, gaining much of the attention in the last decades. Particularly, silica microspheres are very easy to fabricate and handle.
SRS is a pure gain process that can be easily achieved in silica WGMR14,15, since reaching a threshold is enough. In this case, the high circulating intensity inside the WGMR guarantees Raman lasing, but for parametric oscillations is not sufficient. In these cases, efficient oscillations require phase and mode matching, energy and momentum conservation law and a good spatial overlap of all resonant modes to be fulfilled16-18. This is the case for SARS and FWM in general.

<table border="0" cellpadding="0" cellspacing="0" width="668">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Optical Fiber</td>
			<td style="width:93px;">Corning</td>
			<td style="width:119px;">SMF28</td>
			<td style="width:240px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Fiber coating stripper</td>
			<td style="width:93px;">Thorlabs</td>
			<td style="width:119px;">T06S13</td>
			<td>Available from other vendors as well</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Fiber cleaver</td>
			<td style="width:93px;">Fitel</td>
			<td style="width:119px;">S325A</td>
			<td>Available from other vendors as well</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Fusion splicer</td>
			<td style="width:93px;">Furakawa</td>
			<td style="width:119px;">S177A-1R</td>
			<td>Available from other vendors as well</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Butane and Oxygen Gas</td>
			<td style="width:93px;">n/a</td>
			<td style="width:119px;"></td>
			<td>any vendor</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Microscope tube</td>
			<td style="width:93px;">Navitar</td>
			<td style="width:119px;">Zoom 6000</td>
			<td>Modular Kit</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">CCD camera</td>
			<td style="width:93px;">n/a</td>
			<td style="width:119px;">N/A</td>
			<td>any will fit</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Monitor</td>
			<td style="width:93px;">n/a</td>
			<td style="width:119px;">N/A</td>
			<td>any monitor is valid</td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:216px;">3-Axis Stage</td>
			<td style="width:93px;">PI Instruments, Thorlabs, Melles</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Assorted posts and mounts</td>
			<td style="width:93px;">Thorlabs</td>
			<td style="width:119px;"></td>
			<td>Available from other vendors as well</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Polarization control</td>
			<td style="width:93px;">Thorlabs</td>
			<td style="width:119px;">FPC030</td>
			<td>Available from other vendors as well</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Attenuator</td>
			<td style="width:93px;">Throlabs</td>
			<td style="width:119px;">VOA50</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Photodiode</td>
			<td style="width:93px;">Thorlabs</td>
			<td style="width:119px;">PDA400</td>
			<td>discontinued, replaced by PDA10CS-EC</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Oscilloscope</td>
			<td style="width:93px;">Tektronix</td>
			<td style="width:119px;">DPO7104</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Optical spectrum analyzer</td>
			<td style="width:93px;">Ando</td>
			<td>AQ6317B</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Erbium Doped Fiber Amplifier</td>
			<td style="width:93px;">IPG Photonics</td>
			<td style="width:119px;">EAD-2K-C</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Tunable Laser</td>
			<td style="width:93px;">Yenista</td>
			<td style="width:119px;">TUNICS</td>
			<td></td>
		</tr>
	</tbody>
</table>

stimulated stokes and antistokes raman scattering in microspherical whispering gallery mode resonators

Dielectric microspheres can confine light and sound for a length of time through high quality factor whispering gallery modes (WGM). Glass microspheres can be thought as a store of energy with a huge variety of applications: compact laser sources, highly sensitive biochemical sensors and nonlinear phenomena. A protocol for the fabrication of both the microspheres and coupling system is given. The couplers described here are tapered fibers. Efficient generation of nonlinear phenomena related to third order optical non-linear susceptibility &#935;(3) interactions in triply resonant silica microspheres is presented in this paper. The interactions here reported are: Stimulated Raman Scattering (SRS), and four wave mixing processes comprising Stimulated Anti-stokes Raman Scattering (SARS). A proof of the cavity-enhanced phenomenon is given by the lack of correlation among the pump, signal and idler: a resonant mode has to exist in order to obtain the pair of signal and idler. In the case of hyperparametric oscillations (four wave mixing and stimulated anti-stokes Raman scattering), the modes must fulfill the energy and momentum conservation and, last but not least, have a good spatial overlap.

The Q factors of the microspheres fabricated following the protocol described above are in excess of 108 (Figure 5) for large diameters (&#62;200 &#956;m) and in excess of 106 for small diameters (&#60; 50 &#956;m). Resonance contrast above 95% (close to critical coupling) can be easily observed. For high circulating intensities, the following nonlinear effects in the infrared region can be observed: stimulated Raman scattering (SRS), cascaded SRS<su...

Watch this Scientific Journal Video about Stimulated Stokes and Antistokes Raman Scattering in Microspherical Whispering Gallery Mode Resonators at JoVE.com

Stimulated Stokes and Antistokes Raman Scattering in Microspherical Whispering Gallery Mode Resonators

Efficient generation of nonlinear phenomena related to third order optical non-linear susceptibility &#935;(3) interactions in triply resonant silica microspheres is presented in this paper. The interactions here reported are: Stimulated Raman Scattering (SRS), and four wave mixing processes comprising Stimulated Anti-stokes Raman Scattering (SARS).

Dielectric microspheres can confine light and sound for a length of time through high quality factor whispering gallery modes (WGM). Glass microspheres ...

The overall goal of this procedure is to generate new optical frequencies using silica microspherical whispering-gallery-mode resonators for optical and photonics applications ranging from compact laser sources to biochemical sensing. In whispering gallery-mode microresonators light can be guided with a unique combination of strong spatial confinement and long cavity lifetime. Low losses ensure high quality factors.Such resonators are ideally suited for nonlinear optical interactions. In particular, silica microspheres show a great potential as frequency generators for continuous wave compact, narrow-line width and tunable sources. The interest of using fusion techniques for fabrication of the electric microsphere is based on low scattering losses can be achieved and in consequence very high quality factors.We used homemade taper fiber to couple light into the microspheres. The high coupling efficiency and the high cavity buildup factor can trigger nonlinear Kerr effects with low continuous wave pump power. Demonstrating the taper procedure will be Franco Cosi, a technician from our laboratory.To create a microsphere, first get a length of fiber to work with. Gather the equipment needed to create a microsphere using single-mode silica fiber. This includes the fiber, acetone, an optical coating stripper, and a fiber cleaver.In addition, have ready a fusion splicer. Use the stripper to remove about 1-2 centimeters of the acrylic coating from the end of the fiber. Follow this by cleaning the stripped portion with a clean wipe and acetone.Place the end of the fiber into the fiber cleaver and cleave to isolate the stripped portion. Collect the cleaved fiber from the cleaver. Move the fiber tip to the fusion splicer.There, position the fiber and hold it in place according to the manufacturer's guidelines. Close the cover, check that the arc power and the arc duration are correct, then start the arc. Monitor progress on the display.As the arc melts the glass, the fiber shape will begin to form a sphere due to surface tension. When the sphere begins to take shape, stop the arc and open the cover. Access the fiber in the holder, rotate it by 90 degrees to preserve the spherical shape, then secure the fiber in place again.Close the cover and restart the arc. Performing at least three such 90 degree rotations over five to 10 minutes will produce a microsphere of about 160 micrometers. When removing the microsphere and its fiber stem, be prepared to store it or use it within a day.This t-shaped holder is translation stage-mountable for use with light-coupling experiments. It has a channel down its middle for the microsphere's fiber stem. Place the residual stem end of the microsphere in the channel so the microsphere is unobstructed above the holder.Afix the stem with clear tape. Now, begin to create a tapered fiber to couple light into the microsphere. This will require a device that can slowly pull the fiber ends apart.Start with a length of single-mode silica fiber and identify its midpoint. Use the optical coating stripper to remove about 3-4 centimeters of the coating around this point. Once this is done, slip an alumina cylinder over the stripped portion of the fiber to serve as an oven.Next, use a bare fiber terminator to connect one end of the fiber to a laser capable of operating at 635 nanometers. Connect the other end of the fiber to a power meter. Once the fiber is in place, arrange for an oxygen-butane flame to heat the alumina cylinder to a temperature close to the silica melting point of about 2, 100 degrees Celsius.Start the fiber puller so that it slowly moves the two ends away from one another. With the 635 nanometer laser on, monitor the power transmitted through the fiber with the power meter. Changing values reflect the ongoing tapering.At this point, stop pulling the fiber and stop the flame. Occasionally remove the fiber from the power meter input to project the fiber output onto a beam card to check that a homogeneous circular spot is preserved during the tapering process. Work with fiber after it has been freed from all equipment including the cylinder.Position a glass microscope slide cut to form a U'near the fiber's taper. Next, put the fiber on the slide with taper centered on the U'Keep the fiber taut and apply glue where the fiber and slide overlap to hold the fiber in place. At this point, prepare to couple light into the microsphere with the tapered fiber.To do this, use separate translation stages for the microsphere and the tapered fiber. On a stage with piezoelectric actuators, mount the T-shaped holder with the microsphere so that the microsphere points up. On the other translation stage, mount the glass slide with the fiber oriented perpendicular to the microsphere fiber stem.Use a terminated fiber cable to connect one end of the tapered fiber to a tunable diode laser. Connect the other end to an indium-gallium-arsenide photodiode detector. Now, situate both of the translation stages beneath the microscope tube that will be used for observation of the gap between the microsphere and the taper.The two should be placed so the fiber taper and microsphere are within the travel distance of the translation stages. In addition, place a mirror at 45 degrees with respect to the microscope tube to monitor the vertical position of the taper. Position the microsphere using its translation stage and feedback from the microscope tube.The goal is to have the equator of the microsphere in contact with the taper. Once this is done, turn on the continuous wave laser and monitor the transmission spectrum on an oscilloscope. Tune the laser until Lorentzian-shaped dips due to resonances appear in the spectrum.Measure the resonance line widths and calculate the quality factor. Continue the experiment by exploring coupling efficiency as a function of the gap between the taper and the sphere. Fiber coupling is crucial in order to find good resonance to trigger nonlinear effects.A good resonance is narrow, it is high contrast at low power. Prepare the set-up to realize stimulated Raman scattering. Light from a tunable diode laser operating at 15, 015 nanometers enters the tapered fiber.After the laser, there is an erbium doped fiber amplifier to boost the laser power to achieve nonlinear effect. Next, there is an attenuator and then, an inline fiber polarizer. The light then goes through the taper, which is coupled to a microsphere.After passing the microsphere, there is a 3-decibel-milliwatt splitter. One output of the splitter goes to an optical spectrum analyzer. The other goes to a photodetector connected to an oscilloscope.Tune the laser from high to low frequencies to achieve thermal self-locking. On the oscilloscope, observe a resonance with the thermal drift comparable to the wavelength scan speed. The resonance will broaden when thermal self-locking is achieved.Check the output power transmitted into the optical spectrum analyzer. Manipulate the attenuator to increase the power until the Raman laser line appears. The Raman laser line is detuned from the pump wavelength at about 13.5 terahertz.This is a measurement from 50-micrometer diameter microsphere pumped at about 1, 547 nanometers. On either side of the pump wavelength, there are two four-wave mixing lines about 13 nanometers away. Two stimulated Raman scattering lines are at about 1, 610 and 1, 710 nanometers.Measurements of a 98-nanometer sphere produced similar results. In this case, the pump peak is at 1, 551 nanometers. The stimulated Raman scattering line is centered at 1, 646 nanometers.The stimulated antistokes Raman scattering line is centered at about 1, 452 nanometers. The symmetric lines near the stimulated antistokes line are from degenerated four-wave mixing. A Raman cone is centered at 1, 666 nanometers.This spectrum from a microsphere of 40-micrometer diameter provides evidence of stimulated antistokes enhancement when its frequency is resonant with the cavity mode and phased-matched with the pump and stimulated stokes signal. The pump frequency is 1, 540 nanometers, the stokes line is at 1, 630 nanometers, and the antistokes line is at 1, 460 nanometers. This spectrum from a 65-micrometer microsphere has a stimulated antistokes to stimulated stokes scattering ratio close to one.The pump frequency is centered at 1, 572 nanometers, the stokes line at 1, 640 nanometers, the antistokes line at 1, 490 nanometers. After watching this video, you should have a good understanding of how to fabricate high-Q silica microsphere, how to draw a fiber taper, and how to efficiently couple light into microresonator to study fundamental light-matter interactions. The electrical microspheres are photonic platforms that play an extremely important role in modern optics.They can be exploited for CW nonlinear frequency conversion due to their capability to confine light for long time periods in very small volumes. The microresonator technologies that have been demonstrated may also be effectively exploited for biosensing. Our group is achieving excellent results in this area.

stimulated-stokes-antistokes-raman-scattering-microspherical

Research

JoVE Journal

Engineering

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

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

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

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

Microwave Photonics Systems Based on Whispering-gallery-mode Resonators

Microwave photonics systems rely fundamentally on the interaction between microwave and optical signals. These systems are extremely promising for various areas of technology and applied science, such as aerospace and communication engineering, sensing, metrology, nonlinear photonics, and quantum optics. In this article, we present the principal techniques used in our lab to build microwave photonics systems based on ultra-high Q whispering gallery mode resonators. First detailed in this article is the protocol for resonator polishing, which is based on a grind-and-polish technique close to the ones used to polish optical components such as lenses or telescope mirrors. Then, a white light interferometric profilometer measures surface roughness, which is a key parameter to characterize the quality of the polishing. In order to launch light in the resonator, a tapered silica fiber with diameter in the micrometer range is used. To reach such small diameters, we adopt the "flame-brushing" technique, using simultaneously computer-controlled motors to pull the fiber apart, and a blowtorch to heat the fiber area to be tapered. The resonator and the tapered fiber are later approached to one another to visualize the resonance signal of the whispering gallery modes using a wavelength-scanning laser. By increasing the optical power in the resonator, nonlinear phenomena are triggered until the formation of a Kerr optical frequency comb is observed with a spectrum made of equidistant spectral lines. These Kerr comb spectra have exceptional characteristics that are suitable for several applications in science and technology. We consider the application related to ultra-stable microwave frequency synthesis and demonstrate the generation of a Kerr comb with GHz intermodal frequency.

The customized techniques developed in our lab to build microwave photonics systems based on ultra-high Q whispering gallery mode resonators are presented. The protocols to obtain and characterize these resonators are detailed, and an explanation of some of their applications in microwave photonics is given.

Microwave photonics systems rely fundamentally on the interaction between microwave and optical signals. These systems are extremely promising for various ...

Coherent anti-Stokes Raman Scattering (CARS) Microscopy Visualizes Pharmaceutical Tablets During Dissolution

Traditional pharmaceutical dissolution tests determine the amount of drug dissolved over time by measuring drug content in the dissolution medium. This method provides little direct information about what is happening on the surface of the dissolving tablet. As the tablet surface composition and structure can change during dissolution, it is essential to monitor it during dissolution testing. In this work coherent anti-Stokes Raman scattering microscopy is used to image the surface of tablets during dissolution while UV absorption spectroscopy is simultaneously providing inline analysis of dissolved drug concentration for tablets containing a 50% mixture of theophylline anhydrate and ethyl cellulose. The measurements showed that in situ CARS microscopy is capable of imaging selectively theophylline in the presence of ethyl cellulose. Additionally, the theophylline anhydrate converted to theophylline monohydrate during dissolution, with needle-shaped crystals growing on the tablet surface during dissolution. The conversion of theophylline anhydrate to monohydrate, combined with reduced exposure of the drug to the flowing dissolution medium resulted in decreased dissolution rates. Our results show that in situ CARS microscopy combined with inline UV absorption spectroscopy is capable of monitoring pharmaceutical tablet dissolution and correlating surface changes with changes in dissolution rate.

Coherent anti-Stokes Raman Scattering CARS Microscopy Visualizes Pharmaceutical Tablets During Dissolution

Coherent anti-Stokes Raman scattering (CARS) microscopy is combined with an intrinsic flow-through dissolution setup to allow in situ and real-time visualization of the surface of pharmaceutical tablets undergoing dissolution. Using this custom-built setup, it is possible to correlate CARS videos with drug dissolution profiles recorded using inline UV absorption spectroscopy.

Traditional pharmaceutical dissolution tests determine the amount of drug dissolved over time by measuring drug content in the dissolution medium. This ...

Fabrication and Characterization of Superconducting Resonators

Superconducting microwave resonators are of interest for a wide range of applications, including for their use as microwave kinetic inductance detectors (MKIDs) for the detection of faint astrophysical signatures, as well as for quantum computing applications and materials characterization. In this paper, procedures are presented for the fabrication and characterization of thin-film superconducting microwave resonators. The fabrication methodology allows for the realization of superconducting transmission-line resonators with features on both sides of an atomically smooth single-crystal silicon dielectric. This work describes the procedure for the installation of resonator devices into a cryogenic microwave testbed and for cool-down below the superconducting transition temperature. The set-up of the cryogenic microwave testbed allows one to do careful measurements of the complex microwave transmission of these resonator devices, enabling the extraction of the properties of the superconducting lines and dielectric substrate (e.g., internal quality factors, loss and kinetic inductance fractions), which are important for device design and performance.

Superconducting microwave resonators are of interest for detection of light, quantum computing applications and materials characterization. This work presents a detailed procedure for fabrication and characterization of superconducting microwave resonator scattering parameters.

Superconducting microwave resonators are of interest for a wide range of applications, including for their use as microwave kinetic inductance detectors ...

Fabrication of Nanopillar-Based Split Ring Resonators for Displacement Current Mediated Resonances in Terahertz Metamaterials

Terahertz (THz) split ring resonator (SRR) metamaterials (MMs) has been studied for gas, chemical, and biomolecular sensing applications because the SRR is not affected by environmental characteristics such as the temperature and pressure surrounding the resonator. Electromagnetic radiation in THz frequencies is biocompatible, which is a critical condition especially for the application of the biomolecular sensing. However, the quality factor (Q-factor) and frequency responses of traditional thin-film based split ring resonator (SRR) MMs are very low, which limits their sensitivities and selectivity as sensors. In this work, novel nanopillar-based SRR MMs, utilizing displacement current, are designed to enhance the Q-factor up to 450, which is around 45 times higher than that of traditional thin-film-based MMs. In addition to the enhanced Q-factor, the nanopillar-based MMs induce a larger frequency shifts (17 times compared to the shift obtained by the traditional thin-film based MMs). Because of the significantly enhanced Q-factors and frequency shifts as well as the property of biocompatible radiation, the THz nanopillar-based SRR are ideal MMs for the development of biomolecular sensors with high sensitivity and selectivity without inducing damage or distortion to biomaterials. A novel fabrication process has been demonstrated to build the nanopillar-based SRRs for displacement current mediated THz MMs. A two-step gold (Au) electroplating process and an atomic layer deposition (ALD) process are used to create sub-10 nm scale gaps between Au nanopillars. Since the ALD process is a conformal coating process, a uniform aluminum oxide (Al2O3) layer with nanometer-scale thickness can be achieved. By sequentially electroplating another Au thin film to fill the spaces between Al2O3 and Au, a close-packed Au-Al2O3-Au structure with nano-scale Al2O3 gaps can be fabricated. The size of the nano-gaps can be well defined by precisely controlling the deposition cycles of the ALD process, which has an accuracy of 0.1 nm.

A protocol for the design and fabrication of a novel nanopillar-based split ring resonator (SRR) is presented.

Terahertz (THz) split ring resonator (SRR) metamaterials (MMs) has been studied for gas, chemical, and biomolecular sensing applications because the SRR ...

Scanning Light Scattering Profiler (SLPS) Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light scattering from intraocular lenses (IOLs) using goniophotometer principles. This protocol describes the SLSP platform and how it employs a 360&#176; rotational photodetector sensor that is scanned around an IOL sample while recording the intensity and location of scattered light as it passes through the IOL medium. The SLSP platform can be used to predict, non-clinically, the propensity for current and novel IOL designs and materials to induce light scatter. Non-clinical evaluation of light scattering properties of IOLs can significantly reduce the number of patient complaints related to unwanted glare, glistening, optical defects, poor image quality, and other phenomena associated with the unintended light scattering. Future studies should be conducted to correlate SLSP data with clinical results to help identify which measured light scatter is most problematic for patients that have undergone cataract surgery subsequent to IOL implantation.

Scanning Light Scattering Profiler SLPS Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

This protocol describes the scanning light scattering profiler (SLSP) that enables the full-angle quantitative evaluation of forward and backward scattering of light from intraocular lenses (IOLs) using goniophotometer principles.

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light ...

High-speed Continuous-wave Stimulated Brillouin Scattering Spectrometer for Material Analysis

Recent years have witnessed a significant increase in the use of spontaneous Brillouin spectrometers for non-contact analysis of soft matter, such as aqueous solutions and biomaterials, with fast acquisition times. Here, we discuss the assembly and operation of a Brillouin spectrometer that uses stimulated Brillouin scattering (SBS) to measure stimulated Brillouin gain (SBG) spectra of water and lipid emulsion-based tissue-like samples in transmission mode with &lt;10 MHz spectral-resolution and &lt;35 MHz Brillouin-shift measurement precision at &lt;100 ms. The spectrometer consists of two nearly counter-propagating continuous-wave (CW) narrow-linewidth lasers at 780 nm whose frequency detuning is scanned through the material Brillouin shift. By using an ultra-narrowband hot rubidium-85 vapor notch filter and a phase-sensitive detector, the signal-to-noise-ratio of the SBG signal is significantly enhanced compared to that obtained with existing CW-SBS spectrometers. This improvement enables measurement of SBG spectra with up to 100-fold faster acquisition times, thereby facilitating high spectral-resolution and high-precision Brillouin analysis of soft materials at high speed.

We describe the construction of a rapid continuous-wave-stimulated-Brillouin-scattering (CW-SBS) spectrometer. The spectrometer employs single-frequency diode-lasers and an atomic vapor notch-filter to acquire transmission spectra of turbid/non-turbid samples with high spectral-resolution at speeds up to 100-fold faster than those of existing CW-SBS spectrometers. This improvement enables high-speed Brillouin material analysis.

Recent years have witnessed a significant increase in the use of spontaneous Brillouin spectrometers for non-contact analysis of soft matter, such as ...

Ultrasonic Fatigue Testing in the Tension-Compression Mode

Ultrasonic fatigue testing is one of a few methods which allow investigating fatigue properties in the ultra-high cycle region. The method is based on exposing the specimen to longitudinal vibrations on its resonance frequency close to 20 kHz. With use of this method, it is possible to significantly decrease the time required for the test, when compared to conventional testing devices usually working at frequencies under 200 Hz. It is also used to simulate loading of material during operation in high speed conditions, such as those experienced by components of jet engines or car turbo pumps. It is necessary to operate only in the high and ultra-high cycle region, due to the possibility of extremely high deformation rates, which can have a significant influence on the test results. Specimen shape and dimensions have to be carefully selected and calculated to fulfill the resonance condition of the ultrasonic system; thus, it is not possible to test the full components or specimens of arbitrary shape. Before each test, it is necessary to harmonize the specimen with the frequency of the ultrasonic system to compensate for deviations of the real shape from the ideal one. It is not possible to run a test until a total fracture of the specimen, since the test is automatically terminated after initiation and propagation of the crack to a certain length, when the stiffness of the system changes enough to shift the system out of the resonance frequency. This manuscript describes the process of evaluation of materials' fatigue properties at high-frequency ultrasonic fatigue loading with use of mechanical resonance at a frequency close to 20 kHz. The protocol includes a detailed description of all steps required for a correct test, including specimen design, stress calculation, harmonizing with the resonance frequency, performing the test, and final static fracture.

A protocol for ultrasonic fatigue testing in the high and ultra-high cycle region in axial tension-compression loading mode.

Ultrasonic fatigue testing is one of a few methods which allow investigating fatigue properties in the ultra-high cycle region. The method is based on ...

Scattering And Absorption of Light in Planetary Regoliths

Theoretical, numerical, and experimental methods are presented for multiple scattering of light in macroscopic discrete random media of densely-packed microscopic particles. The theoretical and numerical methods constitute a framework of Radiative Transfer with Reciprocal Transactions (R2T2). The R2T2 framework entails Monte Carlo order-of-scattering tracing of interactions in the frequency space, assuming that the fundamental scatterers and absorbers are wavelength-scale volume elements composed of large numbers of randomly distributed particles. The discrete random media are fully packed with the volume elements. For spherical and nonspherical particles, the interactions within the volume elements are computed exactly using the Superposition T-Matrix Method (STMM) and the Volume Integral Equation Method (VIEM), respectively. For both particle types, the interactions between different volume elements are computed exactly using the STMM. As the tracing takes place within the discrete random media, incoherent electromagnetic fields are utilized, that is, the coherent field of the volume elements is removed from the interactions. The experimental methods are based on acoustic levitation of the samples for non-contact, non-destructive scattering measurements. The levitation entails full ultrasonic control of the sample position and orientation, that is, six degrees of freedom. The light source is a laser-driven white-light source with a monochromator and polarizer. The detector is a mini-photomultiplier tube on a rotating wheel, equipped with polarizers. The R2T2 is validated using measurements for a mm-scale spherical sample of densely-packed spherical silica particles. After validation, the methods are applied to interpret astronomical observations for asteroid (4) Vesta and comet 67P/Churyumov-Gerasimenko (Figure 1) recently visited by the NASA Dawn mission and the ESA Rosetta mission, respectively.

Numerical and experimental methods are presented for multiple scattering of light in discrete random media of densely-packed particles. The methods are utilized to interpret the observations of asteroid (4) Vesta and comet 67P/Churyumov-Gerasimenko.

Theoretical, numerical, and experimental methods are presented for multiple scattering of light in macroscopic discrete random media of densely-packed ...

Implementation of a Nonlinear Microscope Based on Stimulated Raman Scattering

Stimulated Raman scattering (SRS) microscopy uses near-infrared excitation light; therefore, it shares many multi-photon microscopic imaging properties. SRS imaging modality can be obtained using commercial laser-scanning microscopes by equipping with a non-descanned forward detector with proper bandpass filters and lock-in amplifier (LIA) detection scheme. A schematic layout of a typical SRS microscope includes the following: two pulsed laser beams, (i.e., the pump and probe directed in a scanning microscope), which must be overlapped in both space and time at the image plane, then focused by a microscope objective into the sample through two scanning mirrors (SMs), which raster the focal spot across an x-y plane. After interaction with the sample, transmitted output pulses are collected by an upper objective and measured by a forward detection system inserted in an inverted microscope. Pump pulses are removed by a stack of optical filters, whereas the probe pulses that are the result of the SRS process occurring in the focal volume of the specimen are measured by a photodiode (PD). The readout of the PD is demodulated by the LIA to extract the modulation depth. A two-dimensional (2D) image is obtained by synchronizing the forward detection unit with the microscope scanning unit. In this paper, the implementation of an SRS microscope is described and successfully demonstrated, as well as the reporting of label-free images of polystyrene beads with diameters of 3 &#181;m. It is worth noting that SRS microscopes are not commercially available, so in order to take advantage of these characteristics, the homemade construction is the only option. Since SRS microscopy is becoming popular in many fields, it is believed that this careful description of the SRS microscope implementation can be very useful for the scientific community.

In this manuscript, the implementation of a stimulated Raman scattering (SRS) microscope, obtained by the integration of an SRS experimental set-up with a laser scanning microscope, is described. The SRS microscope is based on two femtosecond (fs) laser sources, a Ti-Sapphire (Ti:Sa) and synchronized optical parametric oscillator (OPO).

Stimulated Raman scattering (SRS) microscopy uses near-infrared excitation light; therefore, it shares many multi-photon microscopic imaging properties. ...