Name: high-speed continuous-wave stimulated brillouin scattering spectrometer for material analysis
Uploaded: 2017-09-22T12:30:00
Description: Watch this Scientific Journal Video about High-speed Continuous-wave Stimulated Brillouin Scattering Spectrometer for Material Analysis at JoVE.com

IR is grateful to the Azrieli Foundation for the PhD fellowship award.

Note: Unless stated otherwise, (i) connect all mounts to post holders and tighten the post bases with a clamping fork or mounting base to the optical table, and (ii) use output laser powers of 2 - 10 mW for all alignment procedures.
Note: Turn on all electrical/optoelectronic devices in the setup and allow 30 min of warmup time prior to use.
1. Prepare the Probe Beam Optical Path
<ol>
	<li>Mount and align the fiber collimator of the probe laser.
	...

<ol>
	<li>Koski, K. J., Akhenblit, P., McKiernan, K., Yarger, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Non-invasive+determination+of+the+complete+elastic+moduli+of+spider+silks.">Non-invasive determination of the complete elastic moduli of spider silks.</a> Nat. Mater. 12 (3), 262-267 (2013).</li><li>Palombo, F., Madami, M., Stone, N., Fioretto, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanical+mapping+with+chemical+specificity+by+confocal+Brillouin+and+Raman+microscopy.">Mechanical mapping with chemical specificity by confocal Brillouin and Raman microscopy.</a> Analyst. 139 (4), 729-733 (2014).</li><li>Scarcelli, G., Yun, S. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+Brillouin+optical+microscopy+of+the+human+eye.">In vivo Brillouin optical microscopy of the human eye.</a> Opt. Exp. 20 (8), 9197-9202 (2012).</li><li>Scarcelli, G., 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=Noncontact+three-dimensional+mapping+of+intracellular+hydromechanical+properties+by+Brillouin+microscopy.">Noncontact three-dimensional mapping of intracellular hydromechanical properties by Brillouin microscopy.</a> Nat. Methods. 12 (12), 1132-1134 (2015).</li><li>Traverso, A. J., Thompson, J. V., Steelman, Z. A., Meng, Z., Scully, M. O., Yakovlev, V. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dual+Raman-Brillouin+microscope+for+chemical+and+mechanical+characterization+and+imaging.">Dual Raman-Brillouin microscope for chemical and mechanical characterization and imaging.</a> Anal. Chem. 87 (15), 7519-7523 (2015).</li><li>Antonacci, G., Foreman, M. R., Paterson, C., T&#246;r&#246;k, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spectral+broadening+in+Brillouin+imaging.">Spectral broadening in Brillouin imaging.</a> Appl. Phys. Lett. 103 (22), 221105 (2013).</li><li>Antonacci, G., 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=Quantification+of+plaque+stiffness+by+Brillouin+microscopy+in+experimental+thin+cap+fibroatheroma.">Quantification of plaque stiffness by Brillouin microscopy in experimental thin cap fibroatheroma.</a> J. R. Soc. Interface. 12 (112), 20150483 (2015).</li><li>Grubbs, W. T., MacPhail, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+resolution+stimulated+Brillouin+gain+spectrometer.">High resolution stimulated Brillouin gain spectrometer.</a> Rev. Sci. Instrum. 65 (1), 34-41 (1994).</li><li>Ballmann, C. W., Thompson, J. V., Traverso, A. J., Meng, Z., Scully, M. O., Yakovlev, V. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stimulated+Brillouin+scattering+microscopic+imaging.">Stimulated Brillouin scattering microscopic imaging.</a> Sci Rep. 5, 18139 (2015).</li><li>Remer, I., Bilenca, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Background-free+Brillouin+spectroscopy+in+scattering+media+at+780+nm+via+stimulated+Brillouin+scattering.">Background-free Brillouin spectroscopy in scattering media at 780 nm via stimulated Brillouin scattering.</a> Opt. Lett. 41 (5), 926-929 (2016).</li><li>Remer, I., Bilenca, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-speed+stimulated+Brillouin+scattering+spectroscopy+at+780+nm.">High-speed stimulated Brillouin scattering spectroscopy at 780 nm.</a> APL Photonics. 1 (6), 061301 (2016).</li><li>She, C. Y., Moosm&#252;ller, H., Herring, 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=Coherent+light+scattering+spectroscopy+for+supersonic+flow+measurements.">Coherent light scattering spectroscopy for supersonic flow measurements.</a> Appl. Phys. B-Lasers O. 46 (4), 283-297 (1988).</li><li>Fiore, A., Zhang, j., Peng Shao, ., Yun, S. H., Scarcelli, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-extinction+virtually+imaged+phased+array-based+Brillouin+spectroscopy+of+turbid+biological+media.">High-extinction virtually imaged phased array-based Brillouin spectroscopy of turbid biological media.</a> Appl. Phys. Lett. 108 (20), 203701 (2016).</li></ol>

The system, shown in Figure 1, was designed to be built on an 18&#39;&#39; x 24&#39;&#39; breadboard that can be mounted vertically on an optical table, facilitating placement of watery samples. As a result, it is important to strongly tighten all optical and mechanical elements and ensure that the pump and probe beams are collinear and concentric with the various elements prior to illuminating the sample in off-axis geometry.
Difficulties in observing the stimulated Brillouin...

Spontaneous Brillouin spectroscopy has been established, in recent years, as a valuable approach for the mechanical analysis of soft materials, such as liquids, real tissue, tissue phantoms and biological cells1,2,3,4,5,6,7. In this approach, a single laser illuminates the sample and light that is inelastically scattered from spontaneous thermal acoustic waves in the medium is collected by a spectrometer, providing useful information on the viscoelastic properties of the sample. The spontaneous Brillouin spectrum includes two Brillouin peaks at the acoustic Stokes and anti-Stokes resonances of the material, and a Rayleigh peak at the illuminating laser frequency (due to elastically scattered light). For a Brillouin backscattering geometry, the Brillouin frequencies are shifted by several GHz from the illuminating laser frequency and have spectral width of hundreds of MHz.
While scanning Fabry-Perot spectrometers have been the systems-of-choice for acquiring spontaneous Brillouin spectra in soft matter1,2, recent technological advances in virtually imaged phase array (VIPA) spectrometers have enabled significantly faster (sub-second) Brillouin measurements with adequate spectral-resolution (sub-GHz)3,4,5,6,7. In this protocol, we present the construction of a different, high-speed, high spectral-resolution, accurate Brillouin spectrometer based on the detection of continuous-wave-stimulated-Brillouin-scattering (CW-SBS) light from non-turbid and turbid samples in a nearly back scattering geometry.
In CW-SBS spectroscopy, continuous-wave (CW) pump and probe lasers, slightly detuned in frequency, overlap in a sample to stimulate acoustic waves. When the frequency difference between the pump and probe beams matches a specific acoustic resonance of the material, amplification or deamplification of the probe signal is provided by stimulated Brillouin gain or loss (SBG/SBL) processes, respectively; otherwise, no SBS (de)amplification occurs8,9,10,11. Thus, an SBG (SBL) spectrum can be acquired by scanning the frequency difference between the lasers across the material Brillouin resonances and detecting the increase (decrease), or gain (loss), in the probe intensity due to SBS. Unlike in spontaneous Brillouin scattering, elastic scattering background is inherently absent in SBS, enabling excellent Brillouin contrast in both turbid and non-turbid samples without any need for Rayleigh rejection filters as required in VIPA spectrometers10,11,13.
The main building blocks of a CW-SBS spectrometer are the pump and probe lasers and the stimulated Brillouin gain/loss detector. For high spectral-resolution, high speed CW-SBS spectroscopy, the lasers need to be single-frequency (&#60; 10 MHz linewidth) with sufficiently wide wavelength tunability (20 - 30 GHz) and scanning rate (&#62; 200 GHz/s), long-term frequency stability (&#60;50 MHz/h) and low intensity noise. Furthermore, linearly polarized and diffraction-limited laser beams with powers of few hundreds (tens) of mW on the sample are required for the pump (probe) beam. Finally, the stimulated Brillouin gain/loss detector should be designed to reliably detect weak backward stimulated Brillouin gain/loss (SBG/SBL) levels (10-5 - 10-6) in soft matter. To meet these needs, we selected distributed feedback (DFB) diode lasers coupled to polarization-maintaining fibers along with a stimulated Brillouin gain/loss detector combining an ultra-narrowband atomic vapor notch-filter and a high-frequency single-modulation lock-in amplifier as illustrated in Figure 1. This detection scheme doubles the intensity of the SBG signal while significantly reducing noise in the probe intensity, where the desired SBG signal is embedded11. Note that the role of the atomic vapor notch-filter used in our SBS spectrometer is to significantly reduce the detection of unwanted stray pump reflections rather than to decrease the elastic scattering background as in VIPA spectrometers that detect both spontaneous Rayleigh and Brillouin scattered light. Using the protocol detailed below, a CW-SBS spectrometer can be constructed with the capability of acquiring transmission spectra of water and tissue phantoms with SBG levels as low as 10-6 at &#60;35 MHz Brillouin-shift measurement precision and within 100 ms or less.
<img alt="Figure 1" src="/files/ftp_upload/55527/55527fig1.jpg" /> 
Figure 1: Continuous-wave Stimulated Brillouin Scattering (CW-SBS) Spectrometer. Two continuous-wave pump and probe diode lasers (DL), frequency detuned around the Brillouin shift of the sample, are coupled into polarization-maintaining single-mode fibers with collimators C1 and C2, respectively. The pump-probe frequency difference is measured by detecting the beat frequency between beams peeled from the pump and probe lasers using a set of fiber splitters (FS), a fast photodetector (FPD), and a frequency counter (FC). The S-polarized probe beam (light red), expanded using a Keplerian beam expander (L1 and L2), is right circularly polarized by a quarter-wave plate (&#955;1/4) and focused on the sample (S) by an achromatic lens (L3). For effective SBS interaction and optical isolation, the pump beam (deep red), expanded using a Keplerian beam expander (L5 and L6), is first P-polarized using a half-wave plate &#955;2/4), then transmitted through a polarizing beam splitter (PBS), and is finally left circularly polarized by a quarter-wave plate (&#955;2/4) and focused on the sample with an achromatic lens (L4; same as L3). Note that the pump and probe beams nearly counter-propagate in the sample and that an S-oriented polarizer (P) was used to prevent the P-polarized pump beam (coming out of &#955;1/4) from entering the probe laser. For lock-in detection, the pump beam is sinusoidally modulated at fm with an acousto-optical modulator (AOM). The SBG signal, manifested as intensity variations at frequency fm (see inset), is demodulated with a lock-in amplifier (LIA) following detection by a large-area photodiode (PD). For significant elimination of stray pump reflections in the photodiode, a narrowband Bragg filter (BF) and an atomic notch filter (85RB) around the pump wavelength are used alongside with a light-blocking iris (I). Data is recorded by a data acquisition card (DAQ) connected to a personal computer (PC) for further analysis of the Brillouin spectrum. All folding mirrors (M1-M6) are used to fit the spectrometer on a 18&#39;&#39;&#215;24&#39;&#39; breadboard that is vertically mounted on the optical table for facilitating placement of watery samples. <a href="http://cloudflare.jove.com/files/ftp_upload/55527/55527fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

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	<tbody>
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			<td>Probe diode laser head and controller</td>
			<td>Toptica Photonics</td>
			<td>SYST DL-100-DFB</td>
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			<td>Pump amplified diode laser and controller</td>
			<td>Toptica Photonics</td>
			<td>SYST TA-pro-DFB</td>
			<td>Quantity: 1</td>
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			<td>FC/APC fiber dock</td>
			<td>Toptica Photonics</td>
			<td>FiberDock&#160;</td>
			<td>Quantity: 3</td>
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			<td>High power single mode polarization maintaining FC/APC fiber patchcord</td>
			<td>Toptica Photonics</td>
			<td>OE-000796</td>
			<td>Quantity: 1</td>
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		<tr>
			<td>FC/APC fiber collimation with adjustable collimation optics</td>
			<td>Toptica Photonics</td>
			<td>FiberOut</td>
			<td>Quantity: 1</td>
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			<td>FC/APC fiber fixed collimator</td>
			<td>OZ Optics</td>
			<td>HPUCO-33A-780-P-6.1-AS</td>
			<td>Quantity: 1</td>
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			<td>Single mode polarization maintaining fiber splitter 33:67</td>
			<td>OZ Optics</td>
			<td>FOBS-12P-111-4/125-PPP-780-67/33-40-3A3A3A-3-1</td>
			<td>Quantity: 1</td>
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			<td>Single mode polarization maintaining fiber splitter 50:50</td>
			<td>OZ Optics</td>
			<td>FOBS-12P-111-4/125-PPP-780-50/50-40-3S3A3A-3-1</td>
			<td>Quantity: 1</td>
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			<td>f=25 mm, &#216;1/2&#34; Achromatic Doublet, SM05-Threaded Mount, ARC: 650-1050 nm</td>
			<td>Thorlabs</td>
			<td>AC127-025-B-ML</td>
			<td>Quantity: 1</td>
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			<td>f=30 mm, &#216;1&#34; Achromatic Doublet, SM1-Threaded Mount, ARC: 650-1050 nm</td>
			<td>Thorlabs</td>
			<td>AC254-30-B-ML</td>
			<td>Quantity: 2</td>
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			<td>f=50 mm, &#216;1&#34; Achromatic Doublet, SM1-Threaded Mount, ARC: 650-1050 nm</td>
			<td>Thorlabs</td>
			<td>AC254-50-B-ML</td>
			<td>Quantity: 1</td>
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			<td>f=100 mm, &#216;1&#34; Achromatic Doublet, SM1-Threaded Mount, ARC: 650-1050 nm</td>
			<td>Thorlabs</td>
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AC254-100-B-ML</td>
			<td>Quantity: 1</td>
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			<td>f=200 mm, &#216;1&#34; Achromatic Doublet, SM1-Threaded Mount, ARC: 650-1050 nm</td>
			<td>Thorlabs</td>
			<td>
AC254-200-B-ML</td>
			<td>Quantity: 1</td>
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			<td>&#216;1/2&#34; Broadband Dielectric Mirror, 750-1100 nm</td>
			<td>Thorlabs</td>
			<td>
BB05-E03</td>
			<td>Quantity: 4</td>
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			<td>&#216;1&#34; Broadband Dielectric Mirror, 750-1100 nm</td>
			<td>Thorlabs</td>
			<td>
BB1-E03</td>
			<td>Quantity: 2</td>
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			<td>1&#34; Polarizing beamsplitter cube, 780 nm</td>
			<td>Thorlabs</td>
			<td>
PBS25-780</td>
			<td>Quantity: 1</td>
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		<tr>
			<td>&#216;1&#34; Linear polarizer with N-BK7 protective windows, 600-1100 nm</td>
			<td>Thorlabs</td>
			<td>
LPNIRE100-B</td>
			<td>Quantity: 1</td>
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		<tr>
			<td>Shearing Interferometer with a 1-3 mm Beam Diameter Shear Plate</td>
			<td>Thorlabs</td>
			<td>SI035</td>
			<td>Quantity: 1</td>
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		<tr>
			<td>6-Axis Locking kinematic optic mount</td>
			<td>Thorlabs</td>
			<td>
K6XS</td>
			<td>Quantity: 4</td>
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			<td>Compact five-axis platform</td>
			<td>Thorlabs</td>
			<td>
PY005</td>
			<td>Quantity: 1</td>
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		<tr>
			<td>Pedestal mounting adapter for 5-axis platform</td>
			<td>Thorlabs</td>
			<td>
PY005A2</td>
			<td>Quantity: 1</td>
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			<td>Polaris low drift &#216;1/2&#34; kinematic mirror mount, 3 adjusters</td>
			<td>Thorlabs</td>
			<td>
POLARIS-K05</td>
			<td>Quantity: 4</td>
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			<td>Lens mount for &#216;1&#34; optics</td>
			<td>Thorlabs</td>
			<td>
LMR1</td>
			<td>Quantity: 5</td>
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		<tr>
			<td>Adapter with external SM1 threads and Internal SM05 threads, 0.40&#34; thick</td>
			<td>Thorlabs</td>
			<td>
SM1A6T</td>
			<td>Quantity: 1</td>
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		<tr>
			<td>Rotation mount for &#216;1&#34; optics</td>
			<td>Thorlabs</td>
			<td>
RSP1</td>
			<td>Quantity: 2</td>
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		<tr>
			<td>1&#34; Kinematic prism mount</td>
			<td>Thorlabs</td>
			<td>
KM100PM</td>
			<td>Quantity: 1</td>
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		<tr>
			<td>Graduated ring-activated SM1 iris diaphragm</td>
			<td>Thorlabs</td>
			<td>
SM1D12C</td>
			<td>Quantity: 1</td>
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		<tr>
			<td>Post-mounted iris diaphragm, &#216;12.0 mm max aperture</td>
			<td>Thorlabs</td>
			<td>ID12</td>
			<td>Quantity: 2</td>
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		<tr>
			<td>1/2&#34; translation stage with standard micrometer</td>
			<td>Thorlabs</td>
			<td>MT1</td>
			<td>Quantity: 3</td>
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		<tr>
			<td>&#216;1&#34; Pedestal pillar post, 8-32 taps, L = 1&#34;</td>
			<td>Thorlabs</td>
			<td>RS1P8E</td>
			<td>Quantity: 1</td>
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			<td>&#216;1&#34; Pedestal pillar post, 8-32 taps, L = 1.5&#34;</td>
			<td>Thorlabs</td>
			<td>RS1.5P8E</td>
			<td>Quantity: 2</td>
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		<tr>
			<td>&#216;1&#34; Pedestal pillar post, 8-32 taps, L = 2&#34;</td>
			<td>Thorlabs</td>
			<td>RS2P8E</td>
			<td>Quantity: 4</td>
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		<tr>
			<td>&#216;1&#34; Pedestal pillar post, 8-32 taps, L = 2.5&#34;</td>
			<td>Thorlabs</td>
			<td>RS2.5P8E</td>
			<td>Quantity: 1</td>
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		<tr>
			<td>&#216;1&#34; Pedestal pillar post, 8-32 taps, L = 3&#34;</td>
			<td>Thorlabs</td>
			<td>RS3P8E</td>
			<td>Quantity: 4</td>
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		<tr>
			<td>Short clamping fork</td>
			<td>Thorlabs</td>
			<td>CF125</td>
			<td>Quantity: 12</td>
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		<tr>
			<td>Mounting base</td>
			<td>Thorlabs</td>
			<td>BA1S</td>
			<td>Quantity: 8</td>
		</tr>
		<tr>
			<td>Large V-Clamp with PM4 Clamping Arm, 2.5&#34; Long, Imperial</td>
			<td>Thorlabs</td>
			<td>VC3C</td>
			<td>Quantity: 1</td>
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		<tr>
			<td>&#216;1/2&#34; Post holder, spring-loaded hex-locking thumbscrew, L = 1&#34;</td>
			<td>Thorlabs</td>
			<td>PH1</td>
			<td>Quantity: 2</td>
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		<tr>
			<td>&#216;1/2&#34; Post holder, spring-loaded hex-locking thumbscrew, L = 1.5&#34;</td>
			<td>Thorlabs</td>
			<td>PH1.5</td>
			<td>Quantity: 2</td>
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			<td>&#216;1/2&#34; Post holder, spring-loaded hex-locking thumbscrew, L = 2&#34;</td>
			<td>Thorlabs</td>
			<td>PH2</td>
			<td>Quantity: 6</td>
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		<tr>
			<td>&#216;1/2&#34; Optical post, SS, 8-32 setscrew, 1/4&#34;-20 tap, L = 1&#34;</td>
			<td>Thorlabs</td>
			<td>TR1</td>
			<td>Quantity: 2</td>
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		<tr>
			<td>&#216;1/2&#34; Optical post, SS, 8-32 setscrew, 1/4&#34;-20 tap, L = 1.5&#34;</td>
			<td>Thorlabs</td>
			<td>TR1.5</td>
			<td>Quantity: 2</td>
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		<tr>
			<td>&#216;1/2&#34; Optical post, SS, 8-32 setscrew, 1/4&#34;-20 tap, L = 2&#34;</td>
			<td>Thorlabs</td>
			<td>TR2</td>
			<td>Quantity: 6</td>
		</tr>
		<tr>
			<td>Aluminum breadboard 18&#34; x 24&#34; x 1/2&#34;, 1/4&#34;-20 taps</td>
			<td>Thorlabs</td>
			<td>MB1824</td>
			<td>Quantity: 1</td>
		</tr>
		<tr>
			<td>12&#34; Vertical bracket for breadboards, 1/4&#34;-20 holes, 1 piece</td>
			<td>Thorlabs</td>
			<td>VB01</td>
			<td>Quantity: 2</td>
		</tr>
		<tr>
			<td>Si photodiode, 40 ns Rise time, 400 - 1100 nm, 10 mm x 10 mm active area</td>
			<td>Thorlabs</td>
			<td>
FDS1010</td>
			<td>Quantity: 1</td>
		</tr>
		<tr>
			<td>Waveplate, zero order, 1/4 wave 780nm</td>
			<td>Tower Optics</td>
			<td>Z-17.5-A-.250-B-780</td>
			<td>Quantity: 2</td>
		</tr>
		<tr>
			<td>Waveplate, zero order, 1/2 wave 780nm</td>
			<td>Tower Optics</td>
			<td>Z-17.5-A-.500-B-780</td>
			<td>Quantity: 1</td>
		</tr>
		<tr>
			<td>Fiber coupled ultra high speed photodetector</td>
			<td>Newport</td>
			<td>1434</td>
			<td>Quantity: 1</td>
		</tr>
		<tr>
			<td>Gimbal optical miror mount</td>
			<td>Newport</td>
			<td>U100-G2H ULTIMA</td>
			<td>Quantity: 3</td>
		</tr>
		<tr>
			<td>linear stage with 25 mm travel range</td>
			<td>Newport</td>
			<td>&#160;M-423&#160;</td>
			<td>Quantity: 1</td>
		</tr>
		<tr>
			<td>Lockable differential micrometer, 25 mm coarse, 0.2 mm fine,11 lb. load</td>
			<td>Newport</td>
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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.

Figures 2b and 3b display typical point SBG spectra of distilled water and lipid-emulsion tissue phantom samples (with 2.25 scattering events and an attenuation coefficient of 45 cm-1) measured within 10 ms and 100 ms, respectively. For comparison, we measured the SBG spectra in 10 s as shown in Figures 2a and 3a. In these measurements, the rubidium-85 vapor cell was heated to 90 &#176;C for attenuating stray p...

Watch this Scientific Journal Video about High-speed Continuous-wave Stimulated Brillouin Scattering Spectrometer for Material Analysis at JoVE.com

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

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 ...

The goal of this experiment is to construct and operate a continuous-wave stimulated Brillouin scattering spectrometer to acquire transmission stimulated Brillouin spectra of turbid and non-turbid samples with high spectro resolution and speed. This method can advance the use of Brillouin spectroscopy and imaging for investigating the mechanics of biomaterials such as cells and tissue. The main advantage of this technique is that it can provide rapid acquisition of Brillouin spectra of turbid and non-turbid matter.To begin the experiment, verify that the components of the CW-SBS spectrometer are securely mounted on an optical board. Check that the custom data acquisition software is receiving data from the microwave frequency counter, the lock-in amplifier, the pump and probe laser controllers, and the function generator. Then fill with distilled water a sample chamber made of two 25 millimeter diameter 0.17 millimeter thick glass cover slips and 500 micrometer thick polytetrafluoroethylene tape.Mount a chamber holder on a three-axis motorized translation stage. Secure the water sample in the chamber holder. Translate the sample to the common focus point of the probe and pump focusing lenses.Then adjust the current knob of the tapered amplifier pump laser controller until the pump laser power is above 250 milliwatts. Set the lock-in amplifier time constant to one second, the low-pass filter to 24 decibels per octave, and the sensitivity to one millivolt RMS. Set the phase shift between the amplifier reference and signal inputs to zero.While monitoring the stray pump reflections on channel one, slowly adjust the pump laser current until the observed reflections are at a minimum. Then set the rubidium vapor cell heating assembly power supply to 17 volts DC.Once the rubidium cell stabilizes at 90 degrees Celsius, place the power meter before the probe laser focusing lens. Slowly adjust the probe laser current until the measured power is over 10 milliwatts.Next, move the power meter behind the rubidium cell. Adjust the probe laser temperature until the measured power is at a minimum. Then adjust the probe laser current until the measured power stabilizes above 10 milliwatts.Alter the probe laser current to set the frequency detuning between the pump and probe lasers to approximately the Brillouin shift of the sample. Set the lock-in amplifier sensitivity to 100 microvolts RMS and set the phase shift back to zero. Then carefully turn the pitch and yaw screws of the pump beam folding mirror kinematic mount and transfer the pump focusing lens along the optical axis of the system to optimize the crossing efficiency of the pump and probe lasers.Block the probe beam and note the levels of the stray pump laser reflections while monitoring channel one of the lock-in amplifier. It is critical to properly reject pump stray reflections from the chamber and sample. If needed, slightly close the iris placed in front of the rubidium cell and slightly increase the cross angle between the pump and probe laser to improve the rejection levels.Unblock the probe beam and continue adjusting the pump laser mirror and focusing lens until the stimulated Brillouin gain signal is at a maximum above two microvolts RMS and the stray pump reflections are at a constant minimum. Once the system has been optimized for the sample, create a calibration curve from a plot of probed modulation current versus pump-probe frequency detuning. Set the lock-in amplifier time constant to greater than or equal to 100 microseconds.Set the function generator connected to the laser controller current modulation input to channel one. Select a triangle waveform, set the amplitude to a peak to peak voltage of 150 millivolts, and set the frequency to 50 Hertz. Set the data acquisition unit sampling rate to less than or equal to 100, 000 samples per second per channel.Using the custom data acquisition software, record the SBG and probe laser modulation current signals for at least 10 milliseconds. Import the acquired data into computational software. Use the calibration curve to convert the measured probe laser modulation current values to the pump-probe frequency detuning values.Subtract the average noise floor. Plot the SBG measurements against the pump-probe frequency detuning values to generate the SBG spectrum. Fit the spectrum with a Lorentzian curve using the amplitude, frequency position, and full width at half of the highest point of the spectrum as initial values.Calculate the Brillouin shift and the line width from the frequency positions of the maximum and the full width at half maximum of the Lorentzian fit respectively. Use values from repeated Lorentzian fitted spectra to generate a corresponding histogram. SBG spectra of distilled water and lipid emulsion tissue phantom samples were generated using this method with a spatial resolution of approximately eight micrometers.The water samples were acquired in 10 seconds and 10 milliseconds and the lipid samples were acquired in 10 seconds and 100 milliseconds. The mean Brillouin shifts determined from the rapidly acquired spectra were 5.08 gigahertz for water and 5.11 gigahertz for the tissue phantom. These values were consistent with those calculated from the spectra recorded over 10 seconds and with literature values.200 successive measurements were performed on each sample and the standard deviations of the distributions of estimated Brillouin shifts were evaluated. The standard deviations were 8.5 megahertz and 33 megahertz for the water and tissue samples respectively. After watching this video, you should have a good understanding of how to assemble and operate a stimulated Brillouin scattering spectrometer to rapidly measure stimulated Brillouin gained spectra of water and tissue-like samples in transmission mode.

high-speed-continuous-wave-stimulated-brillouin-scattering

Research

JoVE Journal

Engineering

Measuring Spatially- and Directionally-varying Light Scattering from Biological Material

Light interacts with an organism's integument on a variety of spatial scales. For example in an iridescent bird: nano-scale structures produce color; the milli-scale structure of barbs and barbules largely determines the directional pattern of reflected light; and through the macro-scale spatial structure of overlapping, curved feathers, these directional effects create the visual texture. Milli-scale and macro-scale effects determine where on the organism's body, and from what viewpoints and under what illumination, the iridescent colors are seen. Thus, the highly directional flash of brilliant color from the iridescent throat of a hummingbird is inadequately explained by its nano-scale structure alone and questions remain. From a given observation point, which milli-scale elements of the feather are oriented to reflect strongly? Do some species produce broader "windows" for observation of iridescence than others? These and similar questions may be asked about any organisms that have evolved a particular surface appearance for signaling, camouflage, or other reasons.
In order to study the directional patterns of light scattering from feathers, and their relationship to the bird's milli-scale morphology, we developed a protocol for measuring light scattered from biological materials using many high-resolution photographs taken with varying illumination and viewing directions. Since we measure scattered light as a function of direction, we can observe the characteristic features in the directional distribution of light scattered from that particular feather, and because barbs and barbules are resolved in our images, we can clearly attribute the directional features to these different milli-scale structures. Keeping the specimen intact preserves the gross-scale scattering behavior seen in nature. The method described here presents a generalized protocol for analyzing spatially- and directionally-varying light scattering from complex biological materials at multiple structural scales.

We present a non-destructive method for sampling spatial variation in the direction of light scattered from structurally complex materials. By keeping the material intact, we preserve gross-scale scattering behavior, while concurrently capturing fine-scale directional contributions with high-resolution imaging. Results are visualized in software at biologically-relevant positions and scales.

Light interacts with an organism's integument on a variety of spatial scales. For example in an iridescent bird: nano-scale structures produce color; the ...

High-resolution, High-speed, Three-dimensional Video Imaging with Digital Fringe Projection Techniques

Digital fringe projection (DFP) techniques provide dense 3D measurements of dynamically changing surfaces.&#160;Like the human eyes and brain, DFP uses triangulation between matching points in two views of the same scene at different angles to compute depth.&#160;However, unlike a stereo-based method, DFP uses a digital video projector to replace one of the cameras1. The projector rapidly projects a known sinusoidal pattern onto the subject, and the surface of the subject distorts these patterns in the camera&#8217;s field of view. Three distorted patterns (fringe images) from the camera can be used to compute the depth using triangulation.
Unlike other 3D measurement methods, DFP techniques lead to systems that tend to be faster, lower in equipment cost, more flexible, and easier to develop.&#160;DFP systems can also achieve the same measurement resolution as the camera.&#160;For this reason, DFP and other digital structured light techniques have recently been the focus of intense research (as summarized in1-5). Taking advantage of DFP, the graphics processing unit, and optimized algorithms, we have developed a system capable of 30&#160;Hz 3D video data acquisition, reconstruction, and display for over 300,000 measurement points per frame6,7.&#160;Binary defocusing DFP methods can achieve even greater speeds8.
Diverse applications can benefit from DFP techniques. Our collaborators have used our systems for facial function analysis9, facial animation10, cardiac mechanics studies11, and fluid surface measurements, but many other potential applications exist.&#160;This video will teach the fundamentals of DFP techniques and illustrate the design and operation of a binary defocusing DFP system.

This video describes the fundamentals of digital fringe projection techniques, which provide dense 3D measurements of dynamically changing surfaces.&#160;It also demonstrates the design and operation of a high-speed binary defocusing system based on these techniques.

Digital fringe projection (DFP) techniques provide dense 3D measurements of dynamically changing surfaces.&#160;Like the human eyes and brain, DFP uses ...

High-speed Particle Image Velocimetry Near Surfaces

Multi-dimensional and transient flows play a key role in many areas of science, engineering, and health sciences but are often not well understood. The complex nature of these flows may be studied using particle image velocimetry (PIV), a laser-based imaging technique for optically accessible flows. Though many forms of PIV exist that extend the technique beyond the original planar two-component velocity measurement capabilities, the basic PIV system consists of a light source (laser), a camera, tracer particles, and analysis algorithms. The imaging and recording parameters, the light source, and the algorithms are adjusted to optimize the recording for the flow of interest and obtain valid velocity data. 
Common PIV investigations measure two-component velocities in a plane at a few frames per second. However, recent developments in instrumentation have facilitated high-frame rate (&gt; 1 kHz) measurements capable of resolving transient flows with high temporal resolution. Therefore, high-frame rate measurements have enabled investigations on the evolution of the structure and dynamics of highly transient flows. These investigations play a critical role in understanding the fundamental physics of complex flows.
A detailed description for performing high-resolution, high-speed planar PIV to study a transient flow near the surface of a flat plate is presented here. Details for adjusting the parameter constraints such as image and recording properties, the laser sheet properties, and processing algorithms to adapt PIV for any flow of interest are included.

A procedure for studying transient flows near boundaries using high-resolution, high-speed particle image velocimetry (PIV) is described here. PIV is a non-intrusive measurement technique applicable to any optically accessible flow by optimizing several parameter constraints such as the image and recording properties, the laser sheet properties, and analysis algorithms.

Multi-dimensional and transient flows play a key role in many areas of science, engineering, and health sciences but are often not well understood. The ...

Measuring Material Microstructure Under Flow Using 1-2 Plane Flow-Small Angle Neutron Scattering

A new small-angle neutron scattering (SANS) sample environment optimized for studying the microstructure of complex fluids under simple shear flow is presented. The SANS shear cell consists of a concentric cylinder Couette geometry that is sealed and rotating about a horizontal axis so that the vorticity direction of the flow field is aligned with the neutron beam enabling scattering from the 1-2 plane of shear (velocity-velocity gradient, respectively). This approach is an advance over previous shear cell sample environments as there is a strong coupling between the bulk rheology and microstructural features in the 1-2 plane of shear. Flow-instabilities, such as shear banding, can also be studied by spatially resolved measurements. This is accomplished in this sample environment by using a narrow aperture for the neutron beam and scanning along the velocity gradient direction. Time resolved experiments, such as flow start-ups and large amplitude oscillatory shear flow are also possible by synchronization of the shear motion and time-resolved detection of scattered neutrons. Representative results using the methods outlined here demonstrate the useful nature of spatial resolution for measuring the microstructure of a wormlike micelle solution that exhibits shear banding, a phenomenon that can only be investigated by resolving the structure along the velocity gradient direction. Finally, potential improvements to the current design are discussed along with suggestions for supplementary experiments as motivation for future experiments on a broad range of complex fluids in a variety of shear motions.

A shear cell is developed for small-angle neutron scattering measurements in the velocity-velocity gradient plane of shear and is used to characterize complex fluids. Spatially resolved measurements in the velocity gradient direction are possible for studying shear-banding materials. Applications include investigations of colloidal dispersions, polymer solutions, and self-assembled structures.

A new small-angle neutron scattering (SANS) sample environment optimized for studying the microstructure of complex fluids under simple shear flow is ...

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

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

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

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

Visualization of High Speed Liquid Jet Impaction on a Moving Surface

Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds between 0 and 25 m/sec) and a spinning disk device (for examining surface speeds between 15 and 100 m/sec). The air cannon linear traverse is a pneumatic energy-powered system that is designed to accelerate a metal rail surface mounted on top of a wooden projectile. A pressurized cylinder fitted with a solenoid valve rapidly releases pressurized air into the barrel, forcing the projectile down the cannon barrel. The projectile travels beneath a spray nozzle, which impinges a liquid jet onto its metal upper surface, and the projectile then hits a stopping mechanism. A camera records the jet impingement, and a pressure transducer records the spray nozzle backpressure. The spinning disk set-up consists of a steel disk that reaches speeds of 500 to 3,000 rpm via a variable frequency drive (VFD) motor. A spray system similar to that of the air cannon generates a liquid jet that impinges onto the spinning disc, and cameras placed at several optical access points record the jet impingement. Video recordings of jet impingement processes are recorded and examined to determine whether the outcome of impingement is splash, splatter, or deposition. The apparatuses are the first that involve the high speed impingement of low-Reynolds-number liquid jets on high speed moving surfaces. In addition to its rail industry applications, the described technique may be used for technical and industrial purposes such as steelmaking and may be relevant to high-speed 3D printing.

Two experimental devices for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device and a spinning disk device. The apparatuses are used to determine optimal approaches to the application of liquid friction modifier (LFM) onto rail tracks for top-of-rail friction control.

Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds ...

Experimental Methods for Investigation of Shape Memory Based Elastocaloric Cooling Processes and Model Validation

Shape Memory Alloys (SMA) using elastocaloric cooling processes have the potential to be an environmentally friendly alternative to the conventional vapor compression based cooling process. Nickel-Titanium (Ni-Ti) based alloy systems, especially, show large elastocaloric effects. Furthermore, exhibit large latent heats which is a necessary material property for the development of an efficient solid-state based cooling process. A scientific test rig has been designed to investigate these processes and the elastocaloric effects in SMAs. The realized test rig enables independent control of an SMA&#39;s mechanical loading and unloading cycles, as well as conductive heat transfer between SMA cooling elements and a heat source/sink. The test rig is equipped with a comprehensive monitoring system capable of synchronized measurements of mechanical and thermal parameters. In addition to determining the process-dependent mechanical work, the system also enables measurement of thermal caloric aspects of the elastocaloric cooling effect through use of a high-performance infrared camera. This combination is of particular interest, because it allows illustrations of localization and rate effects &#8212; both important for efficient heat transfer from the medium to be cooled.
The work presented describes an experimental method to identify elastocaloric material properties in different materials and sample geometries. Furthermore, the test rig is used to investigate different cooling process variations. The introduced analysis methods enable a differentiated consideration of material, process and related boundary condition influences on the process efficiency. The comparison of the experimental data with the simulation results (of a thermomechanically coupled finite element model) allows for better understanding of the underlying physics of the elastocaloric effect. In addition, the experimental results, as well as the findings based on the simulation results, are used to improve the material properties.

Experimental methods for investigation of solid state cooling processes and characterization of elastocaloric material properties of Shape Memory Alloys (SMA) are presented. A custom-built test rig has been designed for controlling and comprehensive monitoring of elastocaloric cooling processes. Furthermore, it provides a validation platform for thermomechanically coupled modeling approaches.

Shape Memory Alloys (SMA) using elastocaloric cooling processes have the potential to be an environmentally friendly alternative to the conventional vapor ...

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.

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 ...

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 ...

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. ...