Name: high speed sub-ghz spectrometer for brillouin scattering analysis
Uploaded: 2015-12-22T15:00:00
Description: Watch this Scientific Journal Video about High Speed Sub-GHz Spectrometer for Brillouin Scattering Analysis at JoVE.com

This work was supported in part by the National Institutes of Health (P41-EB015903, R21EY023043, K25EB015885), National Science of Foundation (CBET-0853773) and Human Frontier Science Program (Young Investigator Grant).

Note: Brillouin spectral analysis requires a single-longitudinal mode laser (~10 mW at the sample). For aligning purposes, use a strongly attenuated portion of this laser beam (&#60;0.1 mW).
1. Initial Setup of Fiber and the EMCCD (Electron Multiplied Charge Coupled Device) Camera
<ol>
	<li>Identify about 1,600 mm free aligning space for the spectrometer on an optical table.</li>
	<li>Mount the EMCCD camera at the end of the free aligning space.
	<ol>
		<li>Use set screws to attach the camera to ...

<ol>
	<li>Brillouin, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diffusion+de+la+lumiere+et+des+rayonnes+X+par+un+corps+transparent+homogene;+influence+del'agitation+thermique.">Diffusion de la lumiere et des rayonnes X par un corps transparent homogene; influence del'agitation thermique.</a> Ann. Phys. (Paris) . 17, 88-122 (1922).</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=Multistage+VIPA+etalons+for+high-extinction+parallel+Brillouin+spectroscopy.">Multistage VIPA etalons for high-extinction parallel Brillouin spectroscopy.</a> Opt. Exp. 19 (11), 10913-10922 (2011).</li><li>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=Confocal+Brillouin+microscopy+for+three-dimensional+mechanical+imaging.">Confocal Brillouin microscopy for three-dimensional mechanical imaging.</a> Nat. Phot. 2 (1), 39-43 (2008).</li><li>Nichols, A. J., Evans, C. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Video-rate+Scanning+Confocal+Microscopy+and+Microendoscopy.">Video-rate Scanning Confocal Microscopy and Microendoscopy.</a> J. Vis. Exp. (56), e3252 (2011).</li><li>Steelman, Z., Meng, Z., Traverso, A. J., 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=Brillouin+spectroscopy+as+a+new+method+of+screening+for+increased+CSF+total+protein+during+bacterial+meningitis.">Brillouin spectroscopy as a new method of screening for increased CSF total protein during bacterial meningitis.</a> J. Biophoton. 8 (5), 1-7 (2014).</li><li>Koski, K. J., 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=Brillouin+imaging.">Brillouin imaging.</a> Appl. Phys. Lett. 87 (6), 061903 (2005).</li><li>Faris, G. W., Jusinski, L. E., Hickman, A. P. <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+spectroscopy+in+glasses+and+crystals.">High-resolution stimulated Brillouin gain spectroscopy in glasses and crystals.</a> J. Opt. Soc. Am. B. 10 (4), 587-599 (1993).</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., Besner, S., Pineda, R., Kalout, P., 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+Biomechanical+Mapping+of+Normal+and+Keratoconus+Corneas.">In Vivo Biomechanical Mapping of Normal and Keratoconus Corneas.</a> Jama Ophtalmol. , (2015).</li><li>Scarcelli, G., Kim, P., 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+Measurement+of+Age-Related+Stiffening+in+the+Crystalline+Lens+by+Brillouin+Optical+Microscopy."> In Vivo Measurement of Age-Related Stiffening in the Crystalline Lens by Brillouin Optical Microscopy.</a> Biophys. J. 101 (6), 1539-1545 (2011).</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>Meng, Z., Traverso, A. J., Yakovlev, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Background+clean-up+in+Brillouin+microspectroscopy+of+scattering+medium.">Background clean-up in Brillouin microspectroscopy of scattering medium.</a> Opt. Exp. 22 (5), 5410-5415 (2014).</li><li>Reiss, S., Burau, G., Stachs, O., Guthoff, R., Stolz, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spatially+resolved+Brillouin+spectroscopy+to+determine+the+rheological+properties+of+the+eye+lens.">Spatially resolved Brillouin spectroscopy to determine the rheological properties of the eye lens.</a> Biomed. Opt. Exp. 2 (8), 2144-2159 (2011).</li><li>Scarcelli, G., Kling, S., Quijano, E., Pineda, R., Marcos, S., 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=Brillouin+microscopy+of+collagen+crosslinking:+noncontact+depth-dependent+analysis+of+corneal+elastic+modulus.">Brillouin microscopy of collagen crosslinking: noncontact depth-dependent analysis of corneal elastic modulus.</a> Invest. Ophthalmol. Vis. Sci. 54 (2), 1418-1425 (2013).</li></ol>

A key design feature of this spectrometer configuration is that the two stages can be aligned independently. When a VIPA etalon is slid out of the optical path, the remaining lenses of the spectrometer stage form a 1:1 imaging system, so that the spectral pattern from each stage is imaged onto the CCD camera. Therefore, it is straightforward to go back to either one of the stages to improve its performance without affecting the alignment of the other stage. The set of translational stages and degrees of freedom suggested...

Brillouin scattering, first described by Leon Brillouin1 in 1922, is the inelastic scattering of light from the thermal acoustic modes in a solid and from the thermal density fluctuations in a liquid or gas. The spectral shift of the scattered light, usually in the sub GHz-range, provides information about the interaction between the incident light and the acoustic phonons in the sample. As a result, it can provide useful information regarding the viscoelastic properties of the examined material.
In its spontaneous version, Brillouin scattering generally has cross-sections in the order of Raman scattering, resulting in a very weak signal. Additionally, Brillouin frequency shifts are orders of magnitude smaller than Raman shifts. As a consequence, elastically scattered light (from Rayleigh or Mie scattering), stray light, and back-reflections off of the sample can all easily overshadow the Brillouin spectral signature. Hence, a Brillouin spectrometer needs to not only achieve sub-GHz spectral resolution but also high spectral contrast or extinction.
In traditional Brillouin spectrometers these requirements are met by scanning-grating monochromators, optical beating methods, and, most popularly, multiple-pass scanning Fabry-Perot interferometers2. These methods measure each spectral component sequentially. This approach leads to acquisition times for a single Brillouin spectrum ranging from a few minutes to several hours, depending on the instrument and on the sample. The two-stage VIPA spectrometer, built using this protocol, has the ability to collect all of the spectral components within less than a second while providing sufficient extinction (&#62;60 dB) to effectively suppress other spurious signals2.
The integration of the VIPA etalons is the key element of this spectrometer. A VIPA is a solid etalon with three different coating areas: in the front surface, a narrow anti-reflection coating strip allows the light to enter the VIPA, while the rest of the surface features a highly reflective (HR) coating; in the back surface, a partially reflective coating allows a small portion (~5%) of the light to be transmitted. When focused onto the narrow entrance of the slightly tilted VIPA, the light beam gets reflected into sub-components with fixed phase difference within the VIPA2. Interference between the sub components achieves the aspired high spectral dispersion. Aligning two VIPAs sequentially in cross-axis configuration introduces spectral dispersion in orthogonal directions3. The spectral dispersion in orthogonal directions spatially separates the Brillouin peaks from unwanted crosstalk, which makes it possible to pick up only the Brillouin signal. Figure 1 displays a schematic of the two stage VIPA spectrometer. The arrows below the optical elements indicate the degree of freedom in which the translational stages should be oriented.
<img alt="Figure 1" class="jove_content" p="" src="/files/ftp_upload/53468/53468fig1.jpg" /> 
Figure 1. Instrumental setup. An optical fiber delivers the Brillouin scattering into the spectrometer. A cylindrical lens C1 (f=200 mm) focuses the light into the entrance of the first VIPA (VIPA1). Another cylindrical lens C2 (f=200 mm) maps the spectral angular dispersion into a spatial separation in the focal plane of C2. In this plane, a vertical mask is used to select the desired portion of the spectrum. An analogous configuration follows, tilted at 90 degrees. The beam passes through a spherical lens S1 (f=200 mm) and is focused into the entrance slit of the second VIPA (VIPA2). A spherical lens S2 (f=200 mm) creates the two-dimensional spectrally separated pattern in its focal plane, where another horizontal mask is placed. The horizontal mask is imaged onto the EMCCD camera using an achromatic lens pair. <a href="https://www.jove.com/files/ftp_upload/53468/53468fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
An undergraduate student with some optics coursework and basic aligning experience should be able to build and use this two-stage spectrometer. The spectrometer has recently been shown to be compatible with a variety of standard optical probes3,4,5 (e.g., confocal microscope, endoscope, slit-lamp ophthalmoscope). Here, the spectrometer is connected to a confocal microscope. The laser light is aligned into a standard research inverted system microscope after integrating a 90:10 beam splitter. The backscattering light from the sample is coupled into a single mode fiber, making the microscope confocal.

<table border="0" cellpadding="0" cellspacing="0" width="573">
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			<td height="21" style="height:21px;width:216px;">OPTICS:</td>
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			<td height="63" style="height:63px;width:216px;">VIPA (virtual image phase array)</td>
			<td style="width:71px;">LIGH MACHINERY</td>
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			<td height="63" style="height:63px;width:216px;">Bundle of Three 423 Linear Stages with SM-25 Micrometers</td>
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			<td>SM-13</td>
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			<td height="42" style="height:42px;">Adjustable Width Slit</td>
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			<td>SV-0.5</td>
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			<td>DS40-Z</td>
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			<td height="42" style="height:42px;">&#216;1/2&#34; Optical Post, 8-32 Setscrew, 1/4&#34;-20 Tap, L = 2&#34;, 5 Pack</td>
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			<td>AC254-200-A</td>
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			<td height="42" style="height:42px;">SM1 Lens Tube&#8230;length to adjust depend on CCD, we have 3.5 inches</td>
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			<td height="42" style="height:42px;">High Performance Black Masking Tape, 2&#34; x 60 yds. (50 mm x 55 m) Roll</td>
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			<td height="42" style="height:42px;">60&#34; (W) x 3 yds. (L) x 0.005&#34; (T) (1.5 m x 2.7 m x 0.12 mm) Blackout Fabric</td>
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			<td colspan="2" height="21" style="height:21px;">CAMERA,&#160; LASER and MICROSCOPE&#160;</td>
			<td></td>
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			<td height="21" style="height:21px;width:216px;">EMCCD camera</td>
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			<td height="63" style="height:63px;width:216px;">400 mW single mode green laser</td>
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			<td height="42" style="height:42px;width:216px;">Research Inverted System Microscope&#160;</td>
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high speed sub-ghz spectrometer for brillouin scattering analysis

The goal of this protocol is to build a parallel high-extinction and high-resolution optical Brillouin spectrometer. Brillouin spectroscopy is a non-contact measurement method that can be used to obtain direct readouts of viscoelastic material properties. It has been a useful tool in material characterization, structural monitoring and environmental sensing. In the past, Brillouin spectroscopy has usually employed scanning Fabry-Perot etalons to perform spectral analysis. This process requires high illumination power and long acquisition times, making the technique unsuitable for biomedical applications. A recently introduced novel spectrometer overcomes this challenge by employing two VIPAs in a cross-axis configuration. This innovation enables sub-Gigahertz (GHz) resolution spectral analysis with sub-second acquisition time and illumination power within the safety limits of biological tissue. The multiple new applications facilitated by this improvement are currently being explored in biological research and clinical application.

Figure 3 shows representative Brillouin spectra and their fits for different materials. The VIPAs both have a thickness of 5 mm which results in a FSR of approximately 20 GHz. The integration time for these measurements was 100 msec. 100 measurements were taken and averaged. One calibration measurement was taken prior to acquiring the spectra.
<img alt="Figure 3" src="/files/ftp_upload/53468/53468fig3.jpg" /> 
Figure 3. Brillo...

Watch this Scientific Journal Video about High Speed Sub-GHz Spectrometer for Brillouin Scattering Analysis at JoVE.com

High Speed Sub-GHz Spectrometer for Brillouin Scattering Analysis

Here we present a protocol to build a rapid Brillouin spectrometer. Cascading virtually imaged phase array (VIPA) etalons achieve a measurement speed more than 1,000 times faster than traditional scanning Fabry-Perot spectrometers. This improvement provides the means for Brillouin analysis of tissue and biomaterials at low power levels in vivo.

The goal of this protocol is to build a parallel high-extinction and high-resolution optical Brillouin spectrometer. Brillouin spectroscopy is a ...

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