This research was supported by the Chinese University of Hong Kong through the Direct Grants 4053077 and 4441179, RGC Competitive Earmarked Research Grants, 402812 and 14304314, and Area of Excellence AoE/P-02/12.

1. Setup of Interference Lithography
NOTE: Interference lithography is used to fabricate the periodic arrays12. The schematic setup, as is shown in Figure 1, is built up as follows:
<ol>
	<li>Focus the 325 nm laser from a HeCd multimode laser to a 13X UV objective lens and pass it through a 50 &#956;m pinhole based spatial filter for mode cleaning.</li>
	<li>Place two 2.5 cm diameter irises 30 cm apart to further filter the central region of the diverging light. After the second iris, the beam diameter equals 2.5 cm and increases very slowly with distance, which is &#60; 3 cm at 1 m distance from the second iris. The light is assumed to be nearly collimated. 
	NOTE: The output from second iris should be uniform when checked by naked eyes.</li>
	<li>Steer the collimated beam to a Lloyd&#39;s mirror interferometer. The Lloyd&#39;s setup contains a prism-based sample holder and a 5.04 cm mirror positioned perpendicular to it. The direct and reflected illuminations together create a stable standing wave along the sample surface for patterning. The prism acts as an antireflection device. 
	NOTE: The period P of the standing wave can be written as: <img alt="Equation 9" src="/files/ftp_upload/56735/56735eq9.jpg" />, where &#955; = 325 nm and &#945; is the incident angle with respect to sample normal, as is shown in Figure 1. The incident angle can be tuned by rotating the Lloyd&#39;s setup.</li>
</ol>
2. Periodic Array Preparation
NOTE: The sample is prepared under the standard procedure suggested by the manufacturer. All the procedures are performed at room temperature.
<ol>
	<li>Use a 1 cm2 glass substrate. Clean the glass with methanol and acetone for 10 min each in an ultrasonic bath and then pre-bake it on a hot plate at 200 &#176;C for 1 h to remove dirt.</li>
	<li>Spin-coat the glass substrate with a 5 nm thick adhesion layer and a 100 nm thick negative SU-8 photoresist with a two-speed spin-coater.
	<ol>
		<li>Dilute the SU-8 photoresist with Gamma-Butyrolactone in a ratio of 1:5 (v/v) so that the thickness can be controlled close to 100 nm after spin-coating.</li>
		<li>Dispense 3-5 drops (0.2 mL) of adhesion solution on the glass substrate and spin at 600 rpm for 10 s and 3600 rpm for 1 min, consecutively.</li>
		<li>Repeat step 2.2.2 with 5-7 (0.3 mL) drops of diluted SU-8 from step 2.2.1 at the same speed. 
		NOTE: The adhesion layer improves the adhesion between the glass substrate and the photoresist so that the photoresist would not peel off during developing. The thickness of the SU-8 layer is controlled by the concentration and the speed of spin-coater.</li>
	</ol>
	</li>
	<li>Prebake the sample on 65 &#176;C and 95 &#176;C hotplates for 1 min each. Ovens are not recommended here.</li>
	<li>Transfer the sample to the prism in the interferometer. Add a drop of refractive index matching oil (n=1.45) to attach the sample on the prism. Place it as close to the mirror as possible. 
	NOTE: The sample is attached on prism surface due to the surface tension of the oil. The refractive index of oil is chosen to be the same as prism and glass substrate to eliminate back reflection from the interference.</li>
	<li>For a two-dimensional square lattice, expose the sample twice with the same exposure time but orthogonal directions; that is, expose the sample and then rotate it by 90&#176; for the second exposure. When the photoresist is exposed to a 325 nm light, it crosslinks and cannot be dissolved by the SU-8 developer. 
	NOTE: The diameter D of the array can be controlled by adjusting the exposure time.</li>
	<li>Hard bake the sample at 65 &#176;C and 95 &#176;C for 2 min to prevent film cracking.</li>
	<li>Immerse the whole sample in developer for 2 min with continuous agitation to dissolve the unexposed area.</li>
	<li>Immerse the sample in isopropyl alcohol for 1 min to rinse the residuals and then dry it with compressed air. A nanohole array is then produced.</li>
</ol>
3. Gold Film Deposition and Light Emitter Coating
<ol>
	<li>Attach the sample to the sample holder of the radio-frequency magnetron sputtering deposition system with double-sided tape for Au film deposition.</li>
	<li>Pump down the chamber to a 2x10-6 Torr base pressure using a turbomolecular pump and then back fill it with 6x10-3 Torr ultra-high purity Ar gas.</li>
	<li>Use a 5 cm diameter 99.9% Au target and place a shutter between the sample and the target. Use low power (50 W) to reduce the deposition rate as well as the surface roughness. With the shutter closed, pre-sputter the target for 10 min to remove dirt.</li>
	<li>Open the shutter to process deposition at room temperature for 20 min. A film thickness of 100 nm is routinely deposited to ensure that the plasmonic system is optically thick with no transmission.</li>
	<li>Once the sample is ready, spin-coat the light emitting materials such as organic dyes or quantum dots on the metal surface to form a thin layer of dielectrics.
	<ol>
		<li>For the styryl 8 dye used in the reference9, dissolve 20 &#181;g of styryl 8 and 500 &#181;g of polyvinyl alcohol polymer&#160;(PVA) in 5 mL of methanol.</li>
		<li>Dispense 3-5 drops (0.2 mL) of dye solution on the sample and spin at 600 rpm for 10 s and 3600 rpm for 1 min consecutively. The thickness is estimated to be 80 nm. 
		NOTE: Water soluble or insoluble polymer can be used as anchoring material depending on the type of emitting material. However, the polymer should be non-emissive so that it would not interfere with the photoluminescence measurements. Polyvinyl alcohol polymer (PVA)&#160;is recommended for dissolving water-soluble dyes such as rhodamine 6G and styryl 8.</li>
	</ol>
	</li>
</ol>
4. Reflectivity Measurements for Determining the SPP Decay Rates
NOTE: The polarization- and angle-resolved reflectivity spectroscopy setup is shown in Figure 2. It consists of a goniometer with three rotation stages for independently changing the sample orientation (stage 1) and detection angle (stage 2) as well as the sample azimuthal angle (stage 3).
<ol>
	<li>Use a broadband white light from a quartz lamp as the light source. First couple it to a multimode fiber bundle and then collimate it by a pair of collinear face-to-face objective lenses (5X and 60X). Illuminate the light beam on the sample at different incident angles by changing sample orientation. Place a pair of incident polarizer and detection analyzer before and after the sample for polarization-dependent measurements. 
	NOTE: The face to face objectives act as a lens system that collimates and expands the white light source from the multimode fiber.</li>
	<li>Use a multimode fiber to collect the specular reflection from the sample, which is connected to a spectrometer and a CCD detector for spectroscopy.</li>
	<li>Align the setup carefully to ensure both the sample orientation stage and detection rotation stages are concentric, i.e., their rotation axes are collinear.</li>
	<li>Calibrate the setup with a flat Au film. Measure the reflection spectra at different incident angles and compare them with the theoretical reflection spectra calculated by Fresnel equations using a known Au dielectric function. The two sets of data should be consistent with less than 5% of error.</li>
	<li>Once the setup is ready, measure the linearly polarized, p or s, reflection spectra of the sample at different incident angles. The step size of the incident angle is 0.5&#176; and the wavelength resolution is 0.66 nm. To collect the spectra under multiple incident angles, a control program is written for automation including the mechanical motion, shutter control, data acquisition, background subtraction, etc. 
	NOTE: This step is done computationally. The program is available upon request. Please send an email to the corresponding author for the source code if needed.</li>
	<li>Contour plot the reflectivity vs. wavelength and incident angle to obtain the dispersion relation of the plasmonic system for mode identification and decay rate determination. 
	NOTE: The sample azimuthal angle is to locate the position in the Brillouin zone. For example, for square lattice sample, rotate the sample azimuthally so that one of its periods is parallel with the incident plane and this defines the &#915;-X direction. Rotate the sample by 45&#176; to define the &#915;-M direction.</li>
	<li>If the incident polarized is set at 45&#176; with respect to the incident plane and the analyzer is at -45&#176;, measure the orthogonal, or cross-polarized, reflectivity mapping.</li>
	<li>Extract the p-polarized and orthogonal reflection spectra and fit them by using CMT9,12,13, as described in the Discussion to determine the decay rates of SPPs.</li>
</ol>
5. Photoluminescence Measurements for Determining the Emission Power Ratio
Note: The angle- and polarization-resolved photoluminescence setup is shown in Figure 3.
<ol>
	<li>Replace the broadband light source with 514&#160;nm argon ion or 633 nm HeNe laser. Use a laser line filter with a full width half maximum (FWHM) less than 5 nm to clean the laser spectrally and place a half-wave plate to control the polarization state of the laser beam. The goniometer and the detection unit remain unchanged. Place a notch filter before the detection unit to remove the laser line, which buries the luminescence. 
	NOTE: The wavelength of the laser depends on the type of emitting materials. Higher photon energy is required to excite the material with shorter emission wavelength.</li>
	<li>To measure the emission power ratio for Eq. (2) &#38; (3), conduct two types of measurements: the detection and incident scans. The interplay between the incident and detection scans assist in determining <img alt="Equation 10" src="/files/ftp_upload/56735/56735eq10.jpg" />, <img alt="Equation 11" src="/files/ftp_upload/56735/56735eq11.jpg" />, <img alt="Equation 12" src="/files/ftp_upload/56735/56735eq12.jpg" />, and <img alt="Equation 13" src="/files/ftp_upload/56735/56735eq13.jpg" />.</li>
	<li>For the incident scan, vary the incident angle continuously but fix the detection angle with respect to the sample normal. 
	NOTE: This step is done computationally. This configuration selectively excites the incoming SPPs, which are incident angle dependent, while monitoring the variation of the emission under the chosen detection angle. In other words, the emission increases when the incident angle fulfills the phase matching equation in Eq. (1).
	<ol>
		<li>Contour plot the photoluminescence spectra against wavelength and the incident angle for the incident scan mapping. Measure the mappings for different detection angles but the relative intensities are found the same. Therefore, the incident scan probes the effect of the incoming SPPs on the emission or simply the excitation enhancement, which allows us to measure <img alt="Equation 10" src="/files/ftp_upload/56735/56735eq10.jpg" /> and <img alt="Equation 11" src="/files/ftp_upload/56735/56735eq11.jpg" />.</li>
	</ol>
	</li>
	<li>For the detection scan, fix the incident angle with respect to the sample normal but vary the detection angle. 
	NOTE: This step is done computationally.
	<ol>
		<li>Similarly, contour plot the photoluminescence spectra with wavelength and detection angle yields the detection scan mapping. As the SPP emission arises from the radiation damping of SPPs, the emission is strongly detection angle dependent. Therefore, under constant excitation, the emission increases when the detection angle fulfills Eq. (1). This configuration probes the emission enhancement and allows us to determine <img alt="Equation 12" src="/files/ftp_upload/56735/56735eq12.jpg" /> for different &#945;th order as long as it has well-defined detection angle dependence.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Okamoto, 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=Surface-plasmon-enhanced+light+emitters+based+on+InGaN+quantum+wells.">Surface-plasmon-enhanced light emitters based on InGaN quantum wells.</a> Nature Materials. 3 (9), 601-605 (2004).</li><li>Akselrod, G. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Leveraging+Nanocavity+Harmonics+for+Control+of+Optical+Processes+in+2D+Semiconductors.">Leveraging Nanocavity Harmonics for Control of Optical Processes in 2D Semiconductors.</a> Nano Letters. 15 (5), 3578-3584 (2015).</li><li>Gontijo, 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=Coupling+of+InGaN+quantum-well+photoluminescence+to+silver+surface+plasmons.">Coupling of InGaN quantum-well photoluminescence to silver surface plasmons.</a> Physical Review B. 60 (16), 11564 (1999).</li><li>Huang, K. C. Y., 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=Antenna+electrodes+for+controlling+electroluminescence.">Antenna electrodes for controlling electroluminescence.</a> Nature Communications. 3, 1005 (2012).</li><li>Atwater, H. A., Polman, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plasmonics+for+improved+photovoltaic+devices.">Plasmonics for improved photovoltaic devices.</a> Nature Materials. 9 (3), 205-213 (2010).</li><li>Anker, J. N., 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=Biosensing+with+plasmonic+nanosensors.">Biosensing with plasmonic nanosensors.</a> Nature Materials. 7 (6), 442-453 (2008).</li><li>Chen, Y., 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=Excitation+enhancement+of+CdSe+quantum+dots+by+single+metal+nanoparticles.">Excitation enhancement of CdSe quantum dots by single metal nanoparticles.</a> Applied Physics Letters. 93 (5), 053106 (2008).</li><li>Birowosuto, M. D., Skipetrov, S. E., Vos, W. L., Mosk, 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=Observation+of+Spatial+Fluctuations+of+the+Local+Density+of+States+in+Random+Photonic+Media.">Observation of Spatial Fluctuations of the Local Density of States in Random Photonic Media.</a> Physical Review Letters. 105 (1), 013904 (2010).</li><li>Cao, Z. L., Ong, H. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+coupling+rate+of+light+emitter+to+surface+plasmon+polaritons+supported+on+nanohole+array.">Determination of coupling rate of light emitter to surface plasmon polaritons supported on nanohole array.</a> Applied Physics Letters. 102 (24), 241109 (2013).</li><li>Lin, M., Cao, Z. L., Ong, H. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+the+excitation+rate+of+quantum+dots+mediated+by+momentum-resolved+Bloch-like+surface+plasmon+polaritons.">Determination of the excitation rate of quantum dots mediated by momentum-resolved Bloch-like surface plasmon polaritons.</a> Optics Express. 25 (6), 6029-6103 (2017).</li><li>Nikolaev, I. S., Lodahl, P., Driel, A. F. V., Koenderink, A. F., Vos, W. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strongly+nonexponential+time-resolved+fluorescence+of+quantum-dot+ensembles+in+three-dimensional+photonic+crystals.">Strongly nonexponential time-resolved fluorescence of quantum-dot ensembles in three-dimensional photonic crystals.</a> Physical Review B. 75 (11), 115302 (2007).</li><li>Cao, Z. L., Lo, H. Y., Ong, H. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+absorption+and+radiative+decay+rates+of+surface+plasmon+polaritons+from+nanohole+array.">Determination of absorption and radiative decay rates of surface plasmon polaritons from nanohole array.</a> Optics Letters. 37 (24), 5166-5168 (2012).</li><li>Haus, H. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Waves and Fields in Optoelectronics. , (1984).</li></ol>

The authors declare that they have no competing financial interests.

In this protocol, there are several critical steps. First, mechanical stability is crucial in sample preparation. The standing wave generated by Lloyd&#39;s setup is sensitive to the phase difference between two illumination beams. Therefore, any vibration during the exposure time will degrade the uniformity and edge sharpness of the nanohole. It is highly recommended to operate in a vibration-free environment, e.g., an optical table with vibration isolation supports. In addition, high power laser is also desired to minimize vibration as it reduces exposure time accordingly. Second, the pinhole in step 1.1 must be chosen properly. The hole size should be small enough to perform mode cleaning on one side and still large enough to transmit sufficient power for exposure on the other side. We recommend a 50 &#956;m pinhole and 13X objective for the HeCd multimode laser. Third, it is noted that the Lorentzian line shape of orthogonal reflectivity is valid only when rp&#8776; rs, where rp and rs are non-resonant reflectivity for p- and s-polarized illumination12. However, for a nanohole array with glancing incident angle or some anisotropic metamaterials, the difference between rp and rs cannot be neglected and the resulting reflectivity yields <img alt="Equation 23" src="/files/ftp_upload/56735/56735eq23.jpg" />, giving rise to Fano lineshape.
In summary, this protocol describes a method to determine the excitation and coupling rates between the light emitters and SPPs from 2D metallic periodic arrays. The rate is measured by angle- and polarization-resolved reflectivity and photoluminescence spectroscopy, both of which are frequency domain techniques. Compared with conventional time-resolved techniques, this method not only differentiates the excitation and decay processes of SPMF, which are not considered in most fluorescence enhancement studies, but also determines the coupling rates of light emitters to different SPP modes. As time-resolved techniques only measure the total lifetime of a light emitter and are unable to identify the contributions from different resonant modes, our method would certainly add value to this field especially when light emitters are being placed in a complex resonance system. For a periodic plasmonic system, <img alt="Equation 24" src="/files/ftp_upload/56735/56735eq24.jpg" /> mode has a well-defined decay direction whereas direct emission is assumed to be isotropic. Their differences in emission direction give rise to the mode identification. As directional emission is a universal behavior in nanomaterials, such differentiation can be easily extended to other resonant systems like metamaterials and photonic crystals. We anticipate this technique to be an enabling technology for studying fluorescence enhancement between light emitters and resonant cavities.

Surface plasmon mediated fluorescence (SPMF) has received considerable attention recently1,2,3,4,5,6. When light emitters are placed in close proximity to a plasmonic system, energy can be transferred between the emitters and surface plasmon polaritons (SPPs). In general, the strong plasmonic fields can strongly enhance the excitation of the emitters2. At the same time, the emission rate is also increased because of the large density-of-states created by SPPs, yielding the well-known Purcell effect3. These two processes work hand in hand in producing the SPMF. As SPMF has stimulated numerous applications in solid-state lighting1,4, energy harvesting5, and bio-detection6, it is currently under intensive investigation. In particular, the knowledge of the energy transfer rates from the SPPs to the emitters and vice versa, i.e., the excitation and coupling rates, is of great importance. However, the excitation and emission processes are usually entangled together, study on this aspect is still lacking. For example, most of the studies only determine the excitation efficiency ratio, which simply compares the emission with and without SPPs7. The exact measurement of the excitation rate is still missing. On the other hand, conventional time-resolved techniques such as fluorescence lifetime spectroscopy are routinely used for studying the dynamics of the emission process, but they are unable to separate the coupling rate from the total decay rate8. Here, we describe how one can determine them by combining the rate equation model and the temporal coupled mode theory9,10. Remarkably, we find that the excitation and coupling rates can be expressed in terms of measurable quantities, which can be accessed by performing angle- and polarization-resolved reflectivity and photoluminescence spectroscopy. We will first outline the formulation and then describe the instrumentation in detail. This approach is entirely frequency domain based and it does not require any time-resolved accessories such as ultra-fast lasers and time-correlated single-photon counters, which are expensive and sometimes difficult to implement8,11. We anticipate this technique to be an enabling technology for determining the excitation and coupling rates between light emitters and resonant cavities.
The SPMF in periodic systems is briefed here. For a periodic plasmonic system where Bloch-like SPPs can be generated, other than direct excitation and emission, which are characterized by the excitation efficiency&#160;&#951; and spontaneous emission rate &#915;r, the emitters can be excited by incoming SPPs and decay via outgoing SPPs. In other words, under resonance excitation, incoming SPPs are generated to create strong plasmonic fields that energize the emitters. Once the emitters are excited, energy from them can be transferred to outgoing SPPs, which subsequently radiatively dissipate to far-field, giving rise to enhanced emission. They define SPMF. For simple two-level emitters, the excitation refers to the increased transition of electrons from the ground to the excited states whereas the emission defines the decay of electrons back to the ground states, accompanied by photon emission at wavelengths defined by the energy difference between the excited and ground states. The excitation and emission conditions for the SPMF are required to fulfill the well-known phase matching equation to excite the incoming and outgoing SPPs9
<img alt="Equation 1" src="/files/ftp_upload/56735/56735eq1.jpg" /> (1)
where &#949;a and &#949;m are the dielectric constants of the dielectrics and the metal,&#160;&#952; and&#160;&#966; are the incident and azimuthal angles, P is the period of the array,&#160;&#955; is the excitation or emission wavelength, and m and n are the integers specifying the order of SPPs. For excitation, the in-plane wavevector of the laser beam will be Bragg scattered to momentum match with the incoming SPPs and the &#952; and&#160;&#966; together define the specified incident configuration for exciting the SPPs to enhance the electronic absorption at the excitation wavelength &#955;ex. Likewise, for the emission, the outgoing SPPs will be reversely Bragg scattered to match with the light line and the angles now represent the possible emission channels at the emission wavelength &#955;em. However, it is noted that as the emitters can couple their energy to vectorial propagating SPPs with <img alt="Equation 2" src="/files/ftp_upload/56735/56735eq2.jpg" /> that has the same magnitude <img alt="Equation 3" src="/files/ftp_upload/56735/56735eq3.jpg" /> but different directions, the SPPs can decay via various combination of (m,n) to far-field following Eq. (1).
By using the rate equation model and temporal coupled mode theory (CMT), we find that the excitation rate &#915;ex, i.e., the energy transfer rate from SPPs to emitters, can be expressed as9,12,13
<img alt="Equation 4" src="/files/ftp_upload/56735/56735eq4.jpg" /> (2)
where &#951; is the aforementioned direct excitation rate in the absence of the incoming SPPs, &#915;tot is the total decay rate of the incoming SPPs&#160;<img alt="Equation 5" src="/files/ftp_upload/56735/56735eq5.jpg" /> in which &#915;abs and &#915;rad are the Ohmic absorption and radiative decay rates of SPPs, and&#160;<img alt="Equation 6" src="/files/ftp_upload/56735/56735eq6.jpg" /> is the photoluminescence power ratio with and without the incoming SPPs. On the other hand, the coupling rate &#915;c, i.e., the energy transfer rate from emitters to SPPs, can be written as:
<img alt="Equation 7" src="/files/ftp_upload/56735/56735eq7.jpg" /> (3)
where &#915;r is the direct emission rate, <img alt="Equation 8" src="/files/ftp_upload/56735/56735eq8.jpg" /> is the photoluminescence power ratio between the &#945;th SPP mediated decay and direct ports, and &#915;rad&#945; and &#915;tot are the radiative decay rates for the &#945;th port and the total decay rates. We will see that while all the SPP decay rates can be measured by reflectivity spectroscopy, the emission power ratio can be determined by photoluminescence spectroscopy. Details of the formulations can be found in reference9,10.

<table><tbody><tr><td>SU-8</td><td>MicroChem</td><td>SU-8 2000.5</td><td></td></tr><tr><td>Adhesion solution</td><td>MicroChem</td><td>Omnicoat</td><td></td></tr><tr><td>SU-8 Thinner (Gamma-Butyrolactone)</td><td>MicroChem</td><td>SU-8 2000 Thinner</td><td></td></tr><tr><td>SU-8 Developer</td><td>MicroChem</td><td>SU-8 Developer</td><td></td></tr><tr><td>Spin Coater</td><td>Chemat Technology</td><td>KW-4A</td><td></td></tr><tr><td>HeCd laser</td><td>KIMMON KOHA CO., LTd</td><td>IK3552R-G</td><td></td></tr><tr><td>Shutter</td><td>Thorlabs</td><td>SH05</td><td></td></tr><tr><td>Objective for sample preparation</td><td>Newport</td><td>U-13X</td><td></td></tr><tr><td>Pinhole</td><td>Newport</td><td>PNH-50</td><td></td></tr><tr><td>Iris</td><td>Newport</td><td>M-DI47.50</td><td></td></tr><tr><td>Prism</td><td>Thorlabs</td><td>PS611</td><td></td></tr><tr><td>Rotation stage for sample preparation</td><td>Newport</td><td>481-A</td><td></td></tr><tr><td>Supttering Deposition System</td><td>Homemade</td><td></td><td></td></tr><tr><td>Rotation Stage 1</td><td>Newport</td><td>URM80ACC</td><td></td></tr><tr><td>Rotation Stage 2</td><td>Newport</td><td>RV120PP</td><td></td></tr><tr><td>Rotation Stage 3</td><td>Newport</td><td>SR50PP</td><td></td></tr><tr><td>Detection arm</td><td>Homemade</td><td></td><td></td></tr><tr><td>Quartz lamp</td><td>Newport</td><td>66884</td><td></td></tr><tr><td>Fiber Bundle</td><td>Newport</td><td>77578</td><td></td></tr><tr><td>Objective for measurement</td><td>Newport</td><td>M-5X &amp;amp; M-60X</td><td></td></tr><tr><td>Polarizer &amp;amp; Analyzer</td><td>Thorlabs</td><td>GT15</td><td></td></tr><tr><td>Multimode Fiber</td><td>Thorlabs</td><td>BFL105LS02</td><td></td></tr><tr><td>Spectrometer</td><td>Newport</td><td>MS260i</td><td></td></tr><tr><td>CCD</td><td>Andor</td><td>DV420-OE</td><td></td></tr><tr><td>514nm Argon Ion Laser</td><td>Spectra-Physics</td><td>177-G01</td><td></td></tr><tr><td>633nm HeNe Laser</td><td>Newport</td><td>R-32413</td><td></td></tr><tr><td>CdSeTe quantum dot</td><td>Thermo Fisher Scientific</td><td>q21061mp</td><td></td></tr><tr><td>Polyvinyl alcohol polymer (PVA)</td><td>SIGMA-ALDRICH</td><td>363073</td><td></td></tr><tr><td>Control program</td><td>National Instruments</td><td>LabVIEW</td><td></td></tr></tbody></table>

determination of the excitation and coupling rates between light emitters and surface plasmon polaritons

We have developed a unique method to measure the excitation and coupling rates between the light emitters and surface plasmon polaritons (SPPs) arising from metallic periodic arrays without involving time-resolved techniques. We have formulated the rates by quantities that can be measured by simple optical measurements. The instrumentation based on angle- and polarization-resolved reflectivity and photoluminescence spectroscopy will be described in detail here. Our approach is intriguing due to its simplicity, which requires routine optics and several mechanical stages, and thus is highly affordable to most of the research laboratories.

An example of an Au periodic array is given in the inset of Figure 4a8. The plane view SEM image shows that the sample is a 2D square lattice circular hole array with a period of 510 nm, a hole depth of 280 nm, and a hole diameter of 140 nm. The p-polarized reflectivity mapping taken along the &#915;-X direction is shown in Figure 4a. The dash line is calculated by the phase matching equation Eq. (1) indicating that (m = -1, n = 0) SPPs are excited.
When the polarizer and analyzer are set at orthogonal positions, the corresponding reflectivity mapping is shown in Figure 4b. We see that the mapping is almost identical to the linear polarized mapping except the background now becomes zero as the non-resonant reflection is removed by the analyzer. In addition, the reflectivity profiles are changed from dips to peaks as only the SPP radiation damping remains after the removal of the background.
In fact, the dispersion relation is a good tool for studying SPMF. Assuming the laser excitation wavelength is 700 nm, incoming SPPs will be generated at a 19&#176; incident angle and they will interact with the emitters if their absorption band matches. On the other hand, SPP emission will be detected at a 23&#176; incident angle if the emission occurs at 730 nm. Therefore, the SPP resonances allow us to excite the incoming SPPs for excitation enhancement and to locate the outgoing SPPs for emission enhancement.
We spin coat CdSeTe quantum dots doped PVA polymer on the array10. Figure 5a &#38; 5b display the p-polarized and orthogonal reflectivity mapping taken along the along the &#915;-X direction, showing the (-1,0). Figure 5c &#38; 5d shows the corresponding photoluminescence incident and detection scan mappings taken at the detection and incident angles of 0&#176; and 0&#176;, respectively. The laser wavelength &#955;ex is 633 nm. In fact, consistent with the reflectivity mapping, we see that strong emission occurs at an incident angle of 18.5&#176; where the incoming (-1,0) SPPs are excited. On the other hand, from the detection scan, the strong resemblance between the reflectivity and the photoluminescence verifies that the emissions are enhanced when the outgoing SPPs are excited.
The determination of the excitation and coupling rates requires the SPP decay rates and photoluminescence power ratios10. To determine the decay rates at 633 nm along the &#915;-X direction, the p-polarized and orthogonal reflectivity spectra extracted from Figure 5a &#38; 5b are shown in Figure 6a. The p-polarized spectrum shows a Fano-like profile that can be described as <img alt="Equation 14" src="/files/ftp_upload/56735/56735eq14.jpg" />, where rp is the nonresonant reflectivity and &#969;SPP is the resonant photon energy, whereas the orthogonal counterpart follows <img alt="Equation 15" src="/files/ftp_upload/56735/56735eq15.jpg" />, exhibiting a Lorentzian lineshape12. They are then best fitted and the total and radiative decay rates, &#915;tot and &#915;rad, are 95.08 and 27.15 meV (with h).
On the other hand, the photoluminescence power ratio is obtained as follows. From the incident scan in Figure 5c, the emission profile at the emission wavelength &#955;em = 690 nm, where the direct emission locates, is extracted in Figure 6b. The power ratio <img alt="Equation 16" src="/files/ftp_upload/56735/56735eq16.jpg" />, which is defined as the direct emission with and without the incoming SPPs, simply is the intensity at 18.5&#176; divided by the flat background (6.896). <img alt="Equation 17" src="/files/ftp_upload/56735/56735eq17.jpg" /> is then determined to be 574.04 meV.
On the other hand, the coupling rate is emission wavelength dependent. The emission wavelength at 690 nm is chosen as an example. The total and radiative decay rates, &#915;tot and &#915;rad, are 60.06 and 17.12 meV (with h), respectively. The detection scan profile is extracted from Figure 5d and displayed in Figure 6c. The power ratio <img alt="Equation 18" src="/files/ftp_upload/56735/56735eq18.jpg" /> is defined as the (-1,0) SPP emission divided by the half-space direct emission assuming that the sample has no transmission. Since the detector covers a solid angle &#916;&#937;~ &#960;3/7202 sr, for a Lambertian surface, <img alt="Equation 19" src="/files/ftp_upload/56735/56735eq19.jpg" />, where b follows the background in Figure 6c as <img alt="Equation 20" src="/files/ftp_upload/56735/56735eq20.jpg" />. On the other hand, the <img alt="Equation 21" src="/files/ftp_upload/56735/56735eq21.jpg" /> is given as the peak profile divided by &#916;&#937;. As a result, <img alt="Equation 22" src="/files/ftp_upload/56735/56735eq22.jpg" /> is found to be 0.805.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56735/56735fig1.jpg" /> 
Figure 1. Schematic of interference lithography. A 325 nm laser light focused through a spatial filter and then is illuminated on a Lloyd&#39;s mirror interferometer where the sample is located. The standing wave forms along the sample surface for exposure. Inset: schematics of the top and side view of the sample completed in section 2. <a href="/files/ftp_upload/56735/56735fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56735/56735fig2.jpg" /> 
Figure 2. Polarization- and angle-resolved reflectivity spectroscopy. (a) Schematics of polarization- and angle-resolved reflectivity spectroscopy. Three rotation stages are used for constructing the goniometer. A multimode fiber coupled spectrometer and CCD detector is used for detection. A broadband white light source is used for reflectivity measurements. (b) Real-life image of the major part (black dash box in (a)) of the polarization- and angle-resolved reflectivity spectroscopy. <a href="/files/ftp_upload/56735/56735fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56735/56735fig3.jpg" /> 
Figure 3. Schematics of polarization- and angle-resolved photoluminescence spectroscopy. A 514 or 633 nm laser is used for photoluminescence. <a href="/files/ftp_upload/56735/56735fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/56735/56735fig4.jpg" /> 
Figure 4. Reflectivity mappings and deduced decay rates. (a) The p-polarized reflectivity mapping of an Au array taken along the &#915;-X direction. The dash line is calculated by using the phase matching equation, showing (-1,0) SPPs are excited at different wavelengths. Inset: the plane-view SEM image of the array. (b) The corresponding orthogonal reflectivity mapping showing that the background is nulled and the reflectivity dips now become peaks. (c) The plot of &#915;tot and &#915;rad as a function of wavelength. The results are reproduced from reference9. <a href="/files/ftp_upload/56735/56735fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/56735/56735fig5.jpg" /> 
Figure 5. The reflectivity, incident and detection scan mappings of an array coated with CdSeTe quantum dots taken along the &#915;-X direction. The (a) p-polarized and (b) orthogonal reflectivity mappings and the corresponding photoluminescence (c) incident and (d) detection scan mappings taken at detection and incident angle = 0&#176; and 0&#176;, respectively. The laser wavelength &#955;ex is 633 nm. The results are reproduced from reference10. <a href="/files/ftp_upload/56735/56735fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/56735/56735fig6.jpg" /> 
Figure 6. Representative reflectivity, incident and detection scan profile. (a) The p-polarized and orthogonal reflectivity spectra together with the best fits for determining &#915;tot and &#915;rad at 633 nm. (b) The extracted (b) incident and (c) detection scan profiles. The results are reproduced from reference10. <a href="/files/ftp_upload/56735/56735fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Determination of the Excitation and Coupling Rates Between Light Emitters and Surface Plasmon Polaritons at JoVE.com

Determination of the Excitation and Coupling Rates Between Light Emitters and Surface Plasmon Polaritons

This protocol describes the instrumentation for determining the excitation and coupling rates between light emitters and Bloch-like surface plasmon polaritons arising from periodic arrays.

We have developed a unique method to measure the excitation and coupling rates between the light emitters and surface plasmon polaritons (SPPs) arising ...

determination-excitation-coupling-rates-between-light-emitters

Nanyang Technological University

Research

JoVE Journal

Engineering

6.7K Views.  Sun Yat-sen University. Dit protocol beschrijft de instrumentatie voor de bepaling van de excitatie en koppeling tussen licht vervuilers en Bloch-achtige oppervlakte plasmon polaritons die voortvloeien uit periodieke matrices.

Video: Determination of the Excitation and Coupling Rates Between Light Emitters and Surface Plasmon Polaritons

Design, Fabrication, and Experimental Characterization of Plasmonic Photoconductive Terahertz Emitters

In this video article we present a detailed demonstration of a highly efficient method for generating terahertz waves. Our technique is based on photoconduction, which has been one of the most commonly used techniques for terahertz generation 1-8. Terahertz generation in a photoconductive emitter is achieved by pumping an ultrafast photoconductor with a pulsed or heterodyned laser illumination. The induced photocurrent, which follows the envelope of the pump laser, is routed to a terahertz radiating antenna connected to the photoconductor contact electrodes to generate terahertz radiation. Although the quantum efficiency of a photoconductive emitter can theoretically reach 100%, the relatively long transport path lengths of photo-generated carriers to the contact electrodes of conventional photoconductors have severely limited their quantum efficiency. Additionally, the carrier screening effect and thermal breakdown strictly limit the maximum output power of conventional photoconductive terahertz sources. To address the quantum efficiency limitations of conventional photoconductive terahertz emitters, we have developed a new photoconductive emitter concept which incorporates a plasmonic contact electrode configuration to offer high quantum-efficiency and ultrafast operation simultaneously. By using nano-scale plasmonic contact electrodes, we significantly reduce the average photo-generated carrier transport path to photoconductor contact electrodes compared to conventional photoconductors 9. Our method also allows increasing photoconductor active area without a considerable increase in the capacitive loading to the antenna, boosting the maximum terahertz radiation power by preventing the carrier screening effect and thermal breakdown at high optical pump powers. By incorporating plasmonic contact electrodes, we demonstrate enhancing the optical-to-terahertz power conversion efficiency of a conventional photoconductive terahertz emitter by a factor of 50 10.

We describe methods for the design, fabrication, and experimental characterization of plasmonic photoconductive emitters, which offer two orders of magnitude higher terahertz power levels compared to conventional photoconductive emitters.

In this video article we present a detailed demonstration of a highly efficient method for generating terahertz waves. Our technique is based on ...

Evaluating Plasmonic Transport in Current-carrying Silver Nanowires

Plasmonics is an emerging technology capable of simultaneously transporting a plasmonic signal and an electronic signal on the same information support1,2,3. In this context, metal nanowires are especially desirable for realizing dense routing networks4. A prerequisite to operate such shared nanowire-based platform relies on our ability to electrically contact individual metal nanowires and efficiently excite surface plasmon polaritons5 in this information support. In this article, we describe a protocol to bring electrical terminals to chemically-synthesized silver nanowires6 randomly distributed on a glass substrate7. The positions of the nanowire ends with respect to predefined landmarks are precisely located using standard optical transmission microscopy before encapsulation in an electron-sensitive resist. Trenches representing the electrode layout are subsequently designed by electron-beam lithography. Metal electrodes are then fabricated by thermally evaporating a Cr/Au layer followed by a chemical lift-off. The contacted silver nanowires are finally transferred to a leakage radiation microscope for surface plasmon excitation and characterization8,9. Surface plasmons are launched in the nanowires by focusing a near infrared laser beam on a diffraction-limited spot overlapping one nanowire extremity5,9. For sufficiently large nanowires, the surface plasmon mode leaks into the glass substrate9,10. This leakage radiation is readily detected, imaged, and analyzed in the different conjugate planes in leakage radiation microscopy9,11. The electrical terminals do not affect the plasmon propagation. However, a current-induced morphological deterioration of the nanowire drastically degrades the flow of surface plasmons. The combination of surface plasmon leakage radiation microscopy with a simultaneous analysis of the nanowire electrical transport characteristics reveals the intrinsic limitations of such plasmonic circuitry.

Silver nanowires can simultaneously transport electrons and optical information in the form of surface plasmons. A procedure is described here to realize such a shared circuitry and the limitations at propagating both information carriers are evaluated.

Plasmonics is an emerging technology capable of simultaneously transporting a plasmonic signal and an electronic signal on the same information ...

Synthesis, Characterization, and Functionalization of Hybrid Au/CdS and Au/ZnS Core/Shell Nanoparticles

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large extinction coefficients which can be tuned across the visible spectrum. Research into the plasmonic enhancement of optical transitions has become popular, due to the possibility of altering and in some cases improving photo-absorption or emission properties of nearby chromophores such as molecular dyes or quantum dots. The electric field of the plasmon can couple with the excitation dipole of a chromophore, perturbing the electronic states involved in the transition and leading to increased absorption and emission rates. These enhancements can also be negated at close distances by energy transfer mechanism, making the spatial arrangement of the two species critical. Ultimately, enhancement of light harvesting efficiency in plasmonic solar cells could lead to thinner and, therefore, lower cost devices. The development of hybrid core/shell particles could offer a solution to this issue. The addition of a dielectric spacer between a gold nanoparticles and a chromophore is the proposed method to control the exciton plasmon coupling strength and thereby balance losses with the plasmonic gains. A detailed procedure for the coating of gold nanoparticles with CdS and ZnS semiconductor shells is presented. The nanoparticles show high uniformity with size control in both the core gold particles and shell species allowing for a more accurate investigation into the plasmonic enhancement of external chromophores.

The synthesis of uniform gold nanoparticles coated with semiconductor shells of CdS or ZnS is performed. The semiconductor coating is conducted by first depositing a silver sulfide shell and exchanging the silver cations for zinc or cadmium cations.

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large ...

Chemistry

Measurement of Scattering Nonlinearities from a Single Plasmonic Nanoparticle

Plasmonics, which are based on the collective oscillation of electrons due to light excitation, involve strongly enhanced local electric fields and thus have potential applications in nonlinear optics, which requires extraordinary optical intensity. One of the most studied nonlinearities in plasmonics is nonlinear absorption, including saturation and reverse saturation behaviors. Although scattering and absorption in nanoparticles are closely correlated by the Mie theory, there has been no report of nonlinearities in plasmonic scattering until very recently. 
Last year, not only saturation, but also reverse saturation of scattering in an isolated plasmonic particle was demonstrated for the first time. The results showed that saturable scattering exhibits clear wavelength dependence, which seems to be directly linked to the localized surface plasmon resonance (LSPR). Combined with the intensity-dependent measurements, the results suggest the possibility of a common mechanism underlying the nonlinear behaviors of scattering and absorption. These nonlinearities of scattering from a single gold nanosphere (GNS) are widely applicable, including in super-resolution microscopy and optical switches. 
In this paper, it is described in detail how to measure nonlinearity of scattering in a single GNP and how to employ the super-resolution technique to enhance the optical imaging resolution based on saturable scattering. This discovery features the first super-resolution microscopy based on nonlinear scattering, which is a novel non-bleaching contrast method that can achieve a resolution as low as l/8 and will potentially be useful in biomedicine and material studies.

Saturable and reverse saturable scattering were discovered in isolated plasmonic particles and adopted as a novel non-bleaching contrast method in super-resolution microscopy. Here the experimental procedures of detecting and extracting nonlinear scattering are explained in detail, as well as how to enhance resolution with the aid of saturated excitation microscopy.

Plasmonics, which are based on the collective oscillation of electrons due to light excitation, involve strongly enhanced local electric fields and thus ...

Colloidal Synthesis of Nanopatch Antennas for Applications in Plasmonics and Nanophotonics

We present a method for colloidal synthesis of silver nanocubes and the use of these in combination with a smooth gold film, to fabricate plasmonic nanoscale patch antennas. This includes a detailed procedure for the fabrication of thin films with a well-controlled thickness over macroscopic areas using layer-by-layer deposition of polyelectrolyte polymers, namely poly(allylamine) hydrochloride (PAH) and polystyrene sulfonate (PSS). These polyelectrolyte spacer layers serve as a dielectric gap in between silver nanocubes and a gold film. By controlling the size of the nanocubes or the gap thickness, the plasmon resonance can be tuned from about 500 nm to 700 nm. Next, we demonstrate how to incorporate organic sulfo-cyanine5 carboxylic acid (Cy5) dye molecules into the dielectric polymer gap region of the nanopatch antennas. Finally, we show greatly enhanced fluorescence of the Cy5 dyes by spectrally matching the plasmon resonance with the excitation energy and the Cy5 absorption peak. The method presented here enables the fabrication of plasmonic nanopatch antennas with well-controlled dimensions utilizing colloidal synthesis and a layer-by-layer dip-coating process with the potential for low cost and large-scale production. These nanopatch antennas hold great promise for practical applications, for example in sensing, ultrafast optoelectronic devices and for high-efficiency photodetectors.

A protocol for the colloidal synthesis of silver nanocubes and fabrication of plasmonic nanoscale patch antennas with sub-10 nm gaps is presented.

We present a method for colloidal synthesis of silver nanocubes and the use of these in combination with a smooth gold film, to fabricate plasmonic ...

Measurement of Quantum Interference in a Silicon Ring Resonator Photon Source

Silicon photonic chips have the potential to realize complex integrated quantum information processing circuits, including photon sources, qubit manipulation, and integrated single-photon detectors. Here, we present the key aspects of preparing and testing a silicon photonic quantum chip with an integrated photon source and two-photon interferometer. The most important aspect of an integrated quantum circuit is minimizing loss so that all of the generated photons are detected with the highest possible fidelity. Here, we describe how to perform low-loss edge coupling by using an ultra-high numerical aperture fiber to closely match the mode of the silicon waveguides. By using an optimized fusion splicing recipe, the UHNA fiber is seamlessly interfaced with a standard single-mode fiber. This low-loss coupling allows the measurement of high-fidelity photon production in an integrated silicon ring resonator and the subsequent two-photon interference of the produced photons in a closely integrated Mach-Zehnder interferometer. This paper describes the essential procedures for the preparation and characterization of high-performance and scalable silicon quantum photonic circuits.

Silicon photonic chips have the potential to realize complex integrated quantum systems. Presented here is a method for preparing and testing a silicon photonic chip for quantum measurements.

Silicon photonic chips have the potential to realize complex integrated quantum information processing circuits, including photon sources, qubit ...

Performing Spectroscopy on Plasmonic Nanoparticles with Transmission-Based Nomarski-Type Differential Interference Contrast Microscopy

Differential interference contrast (DIC) microscopy is a powerful imaging tool that is most commonly employed for imaging microscale objects using visible-range light. The purpose of this protocol is to detail a proven method for preparing plasmonic nanoparticle samples and performing single particle spectroscopy on them with DIC microscopy. Several important steps must be followed carefully in order to perform repeatable spectroscopy experiments. First, landmarks can be etched into the sample substrate, which aids in locating the sample surface and in tracking the region of interest during experiments. Next, the substrate must be properly cleaned of debris and contaminants that can otherwise hinder or obscure examination of the sample. Once a sample is properly prepared, the optical path of the microscope must be aligned, using Kohler Illumination. With a standard Nomarski style DIC microscope, rotation of the sample may be necessary, particularly when the plasmonic nanoparticles exhibit orientation-dependent optical properties. Because DIC microscopy has two inherent orthogonal polarization fields, the wavelength-dependent DIC contrast pattern reveals the orientation of rod-shaped plasmonic nanoparticles. Finally, data acquisition and data analyses must be carefully performed. It is common to represent DIC-based spectroscopy data as a contrast value, but it is also possible to present it as intensity data. In this demonstration of DIC for single particle spectroscopy, the focus is on spherical and rod-shaped gold nanoparticles.

The goal of this protocol is to detail a proven approach for the preparation of plasmonic nanoparticle samples and for performing single particle spectroscopy on them with differential interference contrast (DIC) microscopy.

Differential interference contrast (DIC) microscopy is a powerful imaging tool that is most commonly employed for imaging microscale objects using ...

Spectral and Angle-Resolved Magneto-Optical Characterization of Photonic Nanostructures

Photonic crystals are periodic nanostructures that can support a variety of confined electromagnetic modes. Such confined modes are usually accompanied by local enhancement of electric field intensity that strengthens light-matter interactions, enabling applications such as surface-enhanced Raman scattering (SERS) and surface plasmon enhanced sensing. In the presence of magneto-optically active materials, the local field enhancement gives rise to anomalous magneto-optical activity. Typically, the confined modes of a given photonic crystal depend strongly on the wavelength and incidence angle of the incident electromagnetic radiation. Thus, spectral and angular-resolved measurements are needed to fully identify them as well as to establish their relationship with the magneto-optical activity of the crystal. In this article, we describe how to use a Fourier-plane (back focal plane) microscope to characterize magneto-optically active samples. As a model system, here we use a plasmonic grating built out of magneto-optically active Au/Co/Au multilayer. In the experiments, we apply a magnetic field on the grating in situ and measure its reciprocal space response, obtaining the magneto-optical response of the grating over a range of wavelengths and incident angles. This information enables us to build a complete map of the plasmonic band structure of the grating and the angle and wavelength dependent magneto-optical activity. These two images allow us to pinpoint the effect that the plasmon resonances have on the magneto-optical response of the grating. The relatively small magnitude of magneto-optical effects requires a careful treatment of the acquired optical signals. To this end, an image processing protocol for obtaining magneto-optical response from the acquired raw data is laid out.

Photonic band structure enables understanding how confined electromagnetic modes propagate within a photonic crystal. In photonic crystals that incorporate magnetic elements, such confined and resonant optical modes are accompanied by enhanced and modified magneto-optical activity. We describe a measurement procedure to extract the magneto-optical band structure by Fourier space microscopy.

Photonic crystals are periodic nanostructures that can support a variety of confined electromagnetic modes. Such confined modes are usually accompanied by ...

Optical Trapping of Plasmonic Nanoparticles for In Situ Surface-Enhanced Raman Spectroscopy Characterizations

Surface-enhanced Raman spectroscopy (SERS) enables the ultrasensitive detection of analyte molecules in various applications due to the enhanced electric field of metallic nanostructures. Salt-induced silver nanoparticle aggregation is the most popular method for generating SERS-active substrates; however, it is limited by poor reproducibility, stability, and biocompatibility. The present protocol integrates optical manipulation and SERS detection to develop an efficient analytical platform to address this. A 1064 nm trapping laser and a 532 nm Raman probe laser are combined in a microscope to assemble silver nanoparticles, which generate plasmonic hotspots for in situ SERS measurements in aqueous environments. Without aggregating agents, this dynamic plasmonic silver nanoparticle assembly enables an approximately 50-fold enhancement of the analyte molecule signal. Moreover, it provides spatial and temporal control to form the SERS-active assembly in as low as 0.05 nM analyte-coated silver nanoparticle solution, which minimizes the potential perturbation for in vivo analysis. Hence, this optical trapping-integrated SERS platform holds great potential for efficient, reproducible, and stable molecular analyses in liquids, especially in aqueous physiological environments.

Optical Trapping of Plasmonic Nanoparticles for In Situ Surface-Enhanced Raman Spectroscopy Characterizations

The present protocol describes a convenient approach to integrating optical trapping and surface-enhanced Raman spectroscopy (SERS) to manipulate plasmonic nanoparticles for sensitive molecular detection. Without aggregating agents, the trapping laser assembles plasmonic nanoparticles to enhance the SERS signals of target analytes for in situ spectroscopic measurements.

Surface-enhanced Raman spectroscopy (SERS) enables the ultrasensitive detection of analyte molecules in various applications due to the enhanced electric ...

Bioengineering

Localized Surface Plasmon Resonance Imaging to Detect Protein Secretions from a Single Cell

Source: Raghu, D. et al., <a href="https://app-jove-com.remotexs.ntu.edu.sg/v/53120">A Label-free Technique for the Spatio-temporal Imaging of Single Cell Secretions.</a> J. Vis. Exp.&#160;(2015)
This video demonstrates localized surface plasmon resonance imaging to detect protein secretions from a single cell. Using a microfluidic setup and a peptide-bound plasmonic nanostructure chip, changes in reflected light intensity at the resonance angle reveal interactions with secreted proteins from a single cell.

Determination of the Excitation and Coupling Rates Between Light Emitters and Surface Plasmon Polaritons

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