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Virtual Journal for Biomedical Optics

Virtual Journal for Biomedical Optics

| EXPLORING THE INTERFACE OF LIGHT AND BIOMEDICINE

  • Editors: Andrew Dunn and Anthony Durkin
  • Vol. 7, Iss. 7 — Jun. 25, 2012
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Imaging slit-coupled surface plasmon polaritons using conventional optical microscopy

R. Mehfuz, F. A. Chowdhury, and K. J. Chau  »View Author Affiliations


Optics Express, Vol. 20, Issue 10, pp. 10526-10537 (2012)
http://dx.doi.org/10.1364/OE.20.010526


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Abstract

We develop a technique that now enables surface plasmon polaritons (SPPs) coupled by nano-patterned slits in a metal film to be detected using conventional optical microscopy with standard objective lenses. The crux of this method is an ultra-thin polymer layer on the metal surface, whose thickness can be varied over a nanoscale range to enable controllable tuning of the SPP momentum. At an optimal layer thickness for which the SPP momentum matches the momentum of light emerging from the slit, the SPP coupling efficiency is enhanced about six times relative to that without the layer. The enhanced efficiency results in distinctive and bright plasmonic signatures near the slit visible by naked eye under an optical microscope. We demonstrate how this capability can be used for parallel measurement through a simple experiment in which the SPP propagation distance is extracted from a single microscope image of an illuminated array of nano-patterned slits on a metal surface. We also use optical microscopy to image the focal region of a plasmonic lens and obtain results consistent with a previously-reported results using near-field optical microscopy. Measurement of SPPs near a nano-slit using conventional and widely-available optical microscopy is an important step towards making nano-plasmonic device technology highly accessible and easy-to-use.

© 2012 OSA

An alternative method to realize a plasmonic chip is to pattern a metal surface with nano-scale surface defects, such as holes, slits, or grooves [13

13. K. Lee and Q. Park, “Coupling of surface plasmon polaritons and light in metallic nanoslits,” Phys. Rev. Lett. 95, 103902 (2005). [CrossRef] [PubMed]

16

16. P. Lalanne, J. Hugonin, and J. Rodier, “Theory of surface plasmon generation at nanoslit apertures,” Phys. Rev. Lett. 95, 263902 (2005). [CrossRef]

]. Scattering from a defect provides a boost to the momentum of incident light, enabling a small portion of the scattered light to couple into SPPs localized near the defect site. Coupling using nano-patterned surfaces enables extreme miniaturization not possible using discrete optical elements and opens up the possibility for plasmonic lab-on-a-chip applications. Specialized techniques, such as leakage radiation microscopy [17

17. H. Ditlbacher, J. Krenn, A. Hohenau, A. Leitner, and F. Aussenegg, “Efficiency of local light-plasmon coupling,” Appl. Phys. Lett. 83, 3665–3667 (2003). [CrossRef]

20

20. L. Grave de Peralta, “Study of interference between surface plasmon polaritons by leakage radiation microscopy,” J. Opt. Soc. Am. B 27, 1513–1517 (2010). [CrossRef]

] and near-field optical microscopy [21

21. F. Baida, D. van Labeke, A. Bouhelier, T. Huser, and D. Pohl, “Propagation and diffraction of locally excited surface plasmons,” J. Opt. Soc. Am. A 18, 1552–1561 (2001). [CrossRef]

,22

22. F. López-Tejeira, S. Rodrigo, L. Marín-Moreno, F. García-Vidal, E. Devaux, T. Ebbesen, J. Krenn, I. Radko, S. Bozhevolnyi, M. González, J. Weeber, and A. Dereux, “Efficient unidirectional nanoslit couplers for surface plasmons,” Nat. Phys. 3, 324–328 (2007). [CrossRef]

], have been developed in the past decade to measure SPPs localized near defect sites. Leakage radiation microscopy works by providing a pathway for SPPs to radiate from a metal surface, which is commonly achieved by surrounding one side of a thin metal film with a dielectric of higher refractive index than on the other side. SPPs radiated in a characteristic emission cone away from the metal surface are then captured by an oil-immersion optical microscope and identified by distinctive features in the Fourier plane of the microscope image. Near-field optical microscopy, on the other hand, uses a nano-scale tip to locally sample the SPP fields and generates a SPP image by rastering the tip over a region near the defect site. Both methods, although well-accepted, have yet to achieve widespread use due in part to their operational complexity and, for the case of near-field optical microscopy, high cost.

In this work, we develop a method to directly image SPPs near a slit in a metal film by simple transmission optical microscopy using a standard objective lens. We use a common plasmonic chip configuration consisting of a single slit in an optically-opaque metal film, flanked by two parallel grooves on the top surface of the metal film. The slit is illuminated from below using polarized visible-light, and the top of the slit is viewed under an optical microscope. The key component of our implementation is an ultra-thin polymer layer on the metal film coating the slit and grooves. Variation of the thickness of the polymer layer enables controllable adjustment of the SPP momentum [23

23. R. Mehfuz, M. Maqsood, and K. Chau, “Enhancing the efficiency of slit-coupling to surface-plasmon-polaritons via dispersion engineering,” Opt. Express 18, 18206–18216 (2010). [CrossRef] [PubMed]

], a concept that has been theoretically discussed in Ref. [9

9. T. Homgaard and S. Bozhevolnyi, “Theoretical analysis of dielectric-loaded surface plasmon-polariton waveguides,” Phys. Rev. B 75, 245405 (2007). [CrossRef]

] and experimentally applied to enable selective SPP coupling via the Kretschmann configuration in Refs. [7

7. A. Hohenau, J. Krenn, A. Stepanov, A. Drezet, H. Ditlbacher, B. Steinberger, A. Leitner, and F. Aussenegg, “Dielectric optical elements for surface plasmons,” Opt. Lett. 30, 893–895 (2005). [CrossRef] [PubMed]

,8

8. B. Steinberger, A. Hohenau, H. Ditlbacher, A. Stepanov, A. Drezet, F. Aussenegg, A. Leitner, and J. Krenn, “Dielectric stripes on gold as surface plasmon waveguides,” Appl. Phys. Lett. 88, 094104 (2006). [CrossRef]

], but has yet to be applied to facilitate slit-coupling to SPPs. We show here that when the SPP momentum matches the momentum of light transmitted through the slit, the resulting SPP coupling efficiency is about six times that without the layer. Due to momentum matching conferred by the polymer layer, signatures of SPPs near the slit are directly visible by inspection under an optical microscope and appear as distinct, tell-tale bright spots at the groove locations adjacent to the slit. Direct visualization of SPPs near slits enables parallel SPP measurement by imaging arrays of nano-patterned features. We show how this can be useful by extracting the SPP propagation length from a single microscope image of an array of slit and grooves in which the spacing between the slit and grooves is variable. It is also shown that a focussed SPP beam emitted from a curved array of sub-wavelength holes, previously characterized using more-complex near-field optical microscopy, can now be imaged using optical microscopy. We believe that the simplification of slit-coupled SPP detection is an important initial step towards making nano-plasmonic technology highly accessible, commercially viable, and easy-to-use.

Fig. 1 (a) Re[kSPP] corresponding to SPP modes propagating along a silver metal surface coated with a dielectric layer of refractive index n = 1.5 and surrounded by air, for various layer thickness values, along with the nk0 line. Complex kSPP values are calculated by solving the dispersion relation of a semi-infinite three-layer silver-glass-air waveguide, where the permittivity of silver εm is fitted to experimental data [27]. The circles highlight, for a given dielectric layer thickness, the frequency at which the momentum matching condition Re[kSPP] = nk0 is satisfied. It should be noted that the momentum matching condition is an approximation and provides only a first-order procedure to estimate the optimal dielectric layer thickness. (b) Schematic of the experimental set-up. Polarized light from a He-Ne laser (λ0 = 632.8nm) illuminates the sample and the far-field transmission image is captured by an optical microscope (Zeiss Axio Imager) using a 100× objective lens with a numerical aperture of 0.90 in air ambient and recorded using a Si CCD camera.

We implement our plasmonic chip by sequentially evaporating a 5-nm-thick chromium adhesion layer and then a 300-nm-thick, optically-opaque silver layer onto a glass substrate. Using a FEI Dual Beam Strata-235 focused ion beam tool, we mill a series of slits having a fixed length of 3μm and widths ranging between 100nm ≤ w ≤ 300nm, where the lower bound is set by the milling resolution of the focused ion beam tool and the upper bound is set by the restriction that the dielectric-filled slit sustain only the lowest order mode (which was confirmed by performing FDTD simulations of plane-wave, normal incidence illumination of the slit having a variable width and then visually corroborating that the simulated field structure in the slit was consistent with that of the lowest order mode). Each slit is flanked by two parallel grooves placed 1μm on both sides from the edges of the slit. The grooves have a depth of ≃ 100nm, a width of ≃ 200nm, and a length of 2μm. We create 6 identical sets of slits and grooves, each on its own separate glass substrate. Five of the substrates are spin-coated with a layer of PMMA (n = 1.49), with layer thicknesses varying from 60nm to 140nm in increments of 20nm. The remaining substrate is left uncoated and serves as an experimental control. The optical response of a chip is characterized by illuminating the bottom of the chip with polarized laser light at a wavelength λ0 = 632.8nm and viewing the top of the structure under an optical microscope (Zeiss Axio Imager) with a 100× objective lens, as shown in Fig. 1(b). At the chosen visible wavelength, the experimental range of dielectric layer thickness values is expected to yield a range of SPP momentum values that spans the momentum of light in the dielectric. We examine the structure under illumination with light that is either x-polarized (electric field perpendicular to the slit axis) or y-polarized (electric field along the slit axis). It has been established that a slit illuminated with y-polarized light produces negligible SPP coupling, whereas a slit illuminated with x-polarized light produces a SPP beam emanating from the slit perpendicular to the slit axis [15

15. H. Kihm, K. Lee, D. Kim, J. Kang, and Q. Park, “Control of surface plasmon generation efficiency by slit-width tuning,” Appl. Phys. Lett. 92, 051115 (2008). [CrossRef]

, 22

22. F. López-Tejeira, S. Rodrigo, L. Marín-Moreno, F. García-Vidal, E. Devaux, T. Ebbesen, J. Krenn, I. Radko, S. Bozhevolnyi, M. González, J. Weeber, and A. Dereux, “Efficient unidirectional nanoslit couplers for surface plasmons,” Nat. Phys. 3, 324–328 (2007). [CrossRef]

]. The experiment is designed so that SPPs scattered by the grooves produce a bright spot in the resulting microscope image at the groove location. Due to placement of the grooves on the transmission side of the optically-opaque metal film, the grooves should be visible only when they are illuminated by SPPs propagating along the metal surface and are otherwise invisible.

One of the immediate challenges of measuring SPPs coupled from a slit using transmission-mode optical microscopy is the isolation of weak SPP signatures from light diffracted through the slit. In the absence of the polymer layer, the microscope image of the slit region [Fig. 2(a)] under x-polarized illumination is dominated by a diffraction pattern from the slit consisting of a bright main lobe centered on the slit with subsidiary lobes spanning several microns to the side of the slit. Any light scattered from the groove locations is disguised by the side lobes of the diffraction pattern, precluding unambiguous identification of SPPs by direct observation. The overwhelming diffraction from the slit can be mitigated by adding a polymer layer, which is predicted to better match the momentum of SPPs with the momentum of light and enhance SPP coupling efficiency. With the addition of a 80-nm-thick polymer layer, the microscope image of the slit region [Fig. 2(b)] now reveals distinctive SPP signatures as bright spots at the groove locations. The bright spots have an intensity comparable to that of the main lobe of the diffraction pattern from the slit, indicating that a significant portion of the light in the slit couples into SPPs. The momentum matching conferred by the polymer layer is highly sensitive to the layer thickness. As the polymer layer thickness increases to 120nm, the intensity of the bright spots at the groove locations reduces and it again is difficult to distinguish the diffraction pattern from SPP signatures at the groove locations [Fig. 2(c)]. Comparative microscope images under y-polarized illumination show similar diffraction patterns, albeit without any SPP signatures at the groove location, regardless of the presence of the polymer layer or its thickness.

Fig. 2 Representative microscope images of the slit and grooves for (a) an uncoated sample, (b) a coated sample with PMMA layer thickness d = 80nm, and (c) a coated sample with PMMA layer thickness d = 120nm. The width of the slits is w = 150nm. The left column shows scanning electron microscope (SEM) images, and the middle and right columns show optical microscope images under x-polarized and y-polarized illumination, respectively. The color of the optical microscope images has been modified for clarity, but the images are otherwise unprocessed.

Fig. 3 Experiment to distinguish diffraction from a slit and SPP scattering from adjacent grooves. (a) SEM image of a representative sample consisting of two identical slits of width w = 150nm, one of which is flanked by grooves. The sample is coated with a PMMA layer of thickness d = 80nm. Optical microscope image of the sample under (b) x-polarized illumination and (c) y-polarized illumination. We apply a subtraction procedure to images (b) and (c) in which the region R2 is subtracted from R1. The resulting subtracted image derived from (b) show bright spots at the groove location indicative of SPP scattering. These bright spots are absent in the subtracted image derived from (c), suggesting the absence of SPPs.

We use the brightness of different portions of the microscope image of the slit and grooves to measure the SPP coupling efficiency. The brightness of the slit is proportional to the amount of light that diffracts and radiates from the slit exit. The brightness of the grooves is proportional to the amount of light that has converted into SPPs at the slit exit and radiates upon striking the grooves. We define the quantities Ig,L and Ig,R as the integrated intensity over a region encompassing the left and right grooves, respectively, the quantities Ing,L and Ing,R as the integrated intensity over a region spaced s = 1μm to the left and right of slit 2, respectively, and the quantity Is as the integrated intensity over a region encompassing exit side of slit 2. The SPP coupling efficiency is now defined as
η=Ig,L+Ig,RIng,LIng,RIs+Ig,L+Ig,RIng,LIng,R×100%
(1)
where the numerator describes the intensity contributions to the image due to SPP scattering from the grooves and the denominator describes the intensity contributions to the image due to both SPP scattering from the grooves and diffraction from the slit. Physically, the efficiency as defined in Eq. (1) describes, to a good approximation, the fraction of light at the slit exit that couples into SPPs. For the representative case depicted in Fig. 3 where w = 150nm and d = 80nm, an efficiency of η = 52 ± 6% is measured, considerably higher than the efficiency value (20%) previously reported for nano-slits [26

26. B. Wang, L. Aigouy, E. Bourhis, J. Gierak, J. Hugonin, and P. Lalanne, “Efficient generation of surface plasmon by single-nanoslit illumination under highly oblique incidence,” Appl. Phys. Lett. 94, 011114 (2009). [CrossRef]

], which do not use the dielectric coating technique described here.

Performing similar coupling efficiency measurements as a function of the polymer layer thickness yields the efficiency curve shown in Fig. 4(a). The coupling efficiency has a sharp peak at a layer thickness of 80nm, nearly six times higher than the efficiency without the layer. The measurements are compared with numerical two-dimensional FDTD simulations of x-polarized illumination (at λ0 = 632.8 nm) of a slit in a metal film for discrete d values ranging from 0 to 200 nm. We extract η from the simulations by directly measuring the SPP intensity at the metal surface and light intensity radiated from the slit. Similar to the experimentally-measured efficiency, the FDTD-calculated efficiency peaks at a layer thickness of 80nm. Two observations suggest that the enhanced coupling is due to momentum matching. First, the experimental and simulated efficiency plots both peak at a d value that agrees, within a factor of 2, to the d value predicted to satisfy Re[kSPP] ≃ nk0 using the simplistic design procedure described in Fig. 1(a), which assumed a momentum of light in the slit describable by nk0. Second, the experimental and simulated efficiency plots both drop-off for d values slightly off the optimal value. The drop-off in the simulated η for d > 80nm is not as sharp as that observed in the experiments. We attribute this discrepancy to surface roughness present in the experiment but absent in the simulations. Due to the tighter confinement of SPPs near the surface for increasing d [which can be inferred from the dispersion diagrams in Fig. 1(a)], losses due to surface roughness should be more pronounced for thicker polymer layers and is evident in the efficiency plots. Over the range from 150nm ≤ w ≤ 300nm, we observe good agreement between the experimentally-measured and FDTD-calculated SPP coupling efficiencies as a function of the slit width [Fig. 4(b)]. Over this slit width range (which corresponds to a normalized range of 0.24 ≤ w/λ0 ≤ 0.47), similar reductions in the SPP coupling efficiency as a function of slit width were theoretically predicted in Ref. [16

16. P. Lalanne, J. Hugonin, and J. Rodier, “Theory of surface plasmon generation at nanoslit apertures,” Phys. Rev. Lett. 95, 263902 (2005). [CrossRef]

] using a semi-analytical model of geometrical diffraction from a slit in an infinitely thick Au medium followed by SPP launching on an adjacent flat Au surface. It should be noted that the error in the experimentally-measured SPP coupling efficiency for the thinnest slit width w = 100nm is larger due to weak transmission through the slit.

Fig. 4 (a) SPP coupling efficiency, η, as a function of the PMMA layer thickness, for a fixed slit width of w = 150nm. η is measured using two methods. In the first method, labeled “expt-1”, η is calculated by using Ing,L and Ing,R derived from the image of the slit and grooves under y-polarized illumination and then using Eq. (1) (red circles). In the second method, labeled “expt-2”, η is calculated by using Ing,L and Ing,R derived from the image of the slit with no grooves under x-polarized illumination and then using Eq. (1) (magenta diamond). We calculate η from two-dimensional FDTD simulations modeling x-polarized plane-wave illumination of a coated slit for various d values (blue squares). We also calculate, for the optimal case of d = 80nm, the SPP coupling efficiency when a 20-nm-deep dimple is present in the dielectric layer above the slit (cyan square), which emulates possible non-planarity of the polymer layer due to conforming to the slit walls. (b) shows the SPP coupling efficiency measured using the method “expt-1” (red circles) and calculated using FDTD simulation (blue squares) as a function of the slit width. The error bars in (a) and (b) correspond to the variance of five independent measurements.

Fig. 5 Parallel SPP measurement from a nano-patterned array illuminated by x-polarized visible light and viewed under an optical microscope. (a) SEM image of an array of identical w = 150nm slits where the groove spacing from the slits is varied from s = 1μm to s = 8μm in 1μm increments. The array is coated with a PMMA layer of thickness d = 80nm. (b) shows the corresponding microscope image of the array. (c) depicts profiles of the image intensity along horizontal lines intersecting the slit and grooves for various slit-groove separation values. (c) The integrated SPP intensity normalized to the integrated intensity of the slit as a function of the slit-groove separation (red circles), where the blue line corresponds to an exponential fit.

Massively-parallel SPP measurements can potentially be performed by imaging large two-dimensional arrays, composed of hundreds or thousands of slit-groove structures, under a conventional microscope. The maximum number of slit-groove structures that can be accommodated using this technique is dependent on the field-of-view of the microscope, the length of the slits, and the minimum separation distance between slits, which must be greater than the SPP decay constant to ensure minimal cross-talk. For example, a microscope with a 100μm field-of-view could image approximately 250 slits, assuming a slit length of 2μm and a separation distance between slits of 20μm, chosen to accommodate a SPP decay constant of 10μm.

Fig. 6 Measurement of a focussed SPP beam emitted from a curved array of sub-wavelength holes using optical microscopy. (a) SEM image of three plasmonic lenses consists of a curved array of holes, with different groove patterns milled adjacent to the lenses. The lenses consist of 17 holes, each of diameter ≃ 200nm, milled into a semi-circle of radius 5μm. Optical microscope image of the three lenses under (b) x-polarized illumination and (c) y-polarized illumination.

An added benefit of incorporating a thin polymer layer on a plasmonic chip is passivation of the metal surface, which is especially important for reactive metals like silver. We have observed that the SPP coupling efficiencies of the coated plasmonic chips have remained stable for at least several months and show no visible signs of tarnishing or deterioration.

In conclusion, we have develop a simple method to image SPPs coupled from slits and scattered by grooves using optical microscopy with conventional objective lenses. This method of detection is possible due to an ultra-thin polymer layer on the metal surface, whose thickness can be varied, with precision on the order of 10nm, to controllable tune the SPP momentum. When a thickness is selected which yields momentum matching, the SPP coupling efficiency is enhanced by nearly six times relative to that without the layer. The high coupling efficiency results in SPP signatures that are visible under inspection by an optical microscope and appear as distinctive bright spots located at the groove locations. This method can be used to perform parallel SPP measurement, which we have demonstrated using a linear array of slits and grooves, and can be extended for massively-parallel SPP measurement using larger two-dimensional arrays accommodating the entire microscope field-of-view. A SPP lensing experiment previously performed using near-field optical microscopy has also been re-visited here using optical microscopy. We believe that the development of a simple method to detect SPPs near slits using standard optical microscopy represents an important step towards reducing the technological requirements and operational complexity of nano-scale plasmonic devices.

Acknowledgments

This work was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant 366136 and the University of British Columbia (UBC) Okanagan Internal Research Grant Dispersion Engineering of Nano-Scale Photonic Structures for Light Steering. We thank M. W. Maqsood for helpful discussions and providing the dispersion curve data. We also thank J. F. Holzman and T. Johnson for careful review of the manuscript.

References and links

1.

B. Liedberg, C. Nylander, and I. Lunström, “Surface plasmon resonance for gas detection and biosensing,” Sens. Actuators 4, 299–304 (1983). [CrossRef]

2.

X. Hoa, A. Kirk, and M. Tabrizian, “Towards integrated and sensitive surface plasmon resonance biosensors: A review of recent progress,” Biosens. Bioelectron. 23, 151–160 (2007). [CrossRef] [PubMed]

3.

C. Loo, A. Lowery, N. Halas, J. West, and R. Drezek, “Innumotargeted nanoshells for integrated cancer imaging and therapy,” Nano Lett. 5, 709–711 (2005). [CrossRef] [PubMed]

4.

T. Okamoto, I. Yamaguchi, and T. Kobayashi, “Local plasmon sensor with gold colloid monolayers deposited upon glass substrates,” Opt. Lett. 25, 372–374 (2000). [CrossRef]

5.

E. Kretschmann, “The angular dependence and the polarisation of light emitted by surface plasmons on metals due to roughness,” Opt. Commun. 5, 331–336 (1972). [CrossRef]

6.

B. Vohnsen and S. Bozhevolnyi, “Coupling of surface-plasmon polaritons to directional far-field radiation by an individual surface protrusion,” Appl. Opt. 40, 6081–6085 (2001). [CrossRef]

7.

A. Hohenau, J. Krenn, A. Stepanov, A. Drezet, H. Ditlbacher, B. Steinberger, A. Leitner, and F. Aussenegg, “Dielectric optical elements for surface plasmons,” Opt. Lett. 30, 893–895 (2005). [CrossRef] [PubMed]

8.

B. Steinberger, A. Hohenau, H. Ditlbacher, A. Stepanov, A. Drezet, F. Aussenegg, A. Leitner, and J. Krenn, “Dielectric stripes on gold as surface plasmon waveguides,” Appl. Phys. Lett. 88, 094104 (2006). [CrossRef]

9.

T. Homgaard and S. Bozhevolnyi, “Theoretical analysis of dielectric-loaded surface plasmon-polariton waveguides,” Phys. Rev. B 75, 245405 (2007). [CrossRef]

10.

B. Rothenhausler and W. Knoll, “Surface-plasmon microscopy,” Nature 40, 615–617 (1988).

11.

I. Smolyaninov, C. Davis, J. Elliott, and A. Zayats, “Resolution enhancement of a surface immersion microscope near the plasmon resonance,” Opt. Lett. 40, 381–384 (2005).

12.

Biacore: Sensor Surface Handbook (General Electric Company, 2005).

13.

K. Lee and Q. Park, “Coupling of surface plasmon polaritons and light in metallic nanoslits,” Phys. Rev. Lett. 95, 103902 (2005). [CrossRef] [PubMed]

14.

L. Yin, V. Vlasko-Vlasov, J. Pearson, J. Hiller, J. Hua, U. Welp, D. Brown, and C. Kimball, “Subwavelength focusing and guiding of surface plasmons,” Nano Lett. 5, 1399–1402 (2005). [CrossRef] [PubMed]

15.

H. Kihm, K. Lee, D. Kim, J. Kang, and Q. Park, “Control of surface plasmon generation efficiency by slit-width tuning,” Appl. Phys. Lett. 92, 051115 (2008). [CrossRef]

16.

P. Lalanne, J. Hugonin, and J. Rodier, “Theory of surface plasmon generation at nanoslit apertures,” Phys. Rev. Lett. 95, 263902 (2005). [CrossRef]

17.

H. Ditlbacher, J. Krenn, A. Hohenau, A. Leitner, and F. Aussenegg, “Efficiency of local light-plasmon coupling,” Appl. Phys. Lett. 83, 3665–3667 (2003). [CrossRef]

18.

A. Baudrion, F. de León-Perez, O. Mahboub, A. Hohenau, H. Ditlbacher, F. García-Vidal, J. Dintinger, T. Ebbesen, L. Martín-Moreno, and J. Krenn, “Coupling efficiency of light to surface plasmon polariton for single sub-wavelength holes in a gold film,” Opt. Express 16, 3420–3429 (2008). [CrossRef] [PubMed]

19.

J. Laluet, A. Drezet, C. Genet, and T. Ebbesen, “Generation of surface plasmons at single subwavelength slits: from slit to ridge plasmon,” New J. Phys. 10, 105014 (2008). [CrossRef]

20.

L. Grave de Peralta, “Study of interference between surface plasmon polaritons by leakage radiation microscopy,” J. Opt. Soc. Am. B 27, 1513–1517 (2010). [CrossRef]

21.

F. Baida, D. van Labeke, A. Bouhelier, T. Huser, and D. Pohl, “Propagation and diffraction of locally excited surface plasmons,” J. Opt. Soc. Am. A 18, 1552–1561 (2001). [CrossRef]

22.

F. López-Tejeira, S. Rodrigo, L. Marín-Moreno, F. García-Vidal, E. Devaux, T. Ebbesen, J. Krenn, I. Radko, S. Bozhevolnyi, M. González, J. Weeber, and A. Dereux, “Efficient unidirectional nanoslit couplers for surface plasmons,” Nat. Phys. 3, 324–328 (2007). [CrossRef]

23.

R. Mehfuz, M. Maqsood, and K. Chau, “Enhancing the efficiency of slit-coupling to surface-plasmon-polaritons via dispersion engineering,” Opt. Express 18, 18206–18216 (2010). [CrossRef] [PubMed]

24.

The restriction that the slit sustain only the lowest order mode simplifies the analysis of SPP coupling. Making the slit larger such that it allows higher order modes would then require considerations of possible diffraction-assisted SPP coupling, which was studied in Ref. [25].

25.

M. Maqsood, R. Mehfuz, and K. Chau, “High-throughput diffraction-assisted surface-plasmon-polariton coupling by a super-wavelength slit,” Opt. Express 18, 21669–21677 (2010). [CrossRef] [PubMed]

26.

B. Wang, L. Aigouy, E. Bourhis, J. Gierak, J. Hugonin, and P. Lalanne, “Efficient generation of surface plasmon by single-nanoslit illumination under highly oblique incidence,” Appl. Phys. Lett. 94, 011114 (2009). [CrossRef]

27.

P. Johnson and R. Christy, “Optical constants of the noble metals,” Phys. Rev. B 6, 4370–4379 (1972). [CrossRef]

OCIS Codes
(050.1220) Diffraction and gratings : Apertures
(240.6680) Optics at surfaces : Surface plasmons
(350.4600) Other areas of optics : Optical engineering

ToC Category:
Optics at Surfaces

History
Original Manuscript: February 21, 2012
Revised Manuscript: April 7, 2012
Manuscript Accepted: April 13, 2012
Published: April 23, 2012

Virtual Issues
Vol. 7, Iss. 7 Virtual Journal for Biomedical Optics

Citation
R. Mehfuz, F. A. Chowdhury, and K. J. Chau, "Imaging slit-coupled surface plasmon polaritons using conventional optical microscopy," Opt. Express 20, 10526-10537 (2012)
http://www.opticsinfobase.org/vjbo/abstract.cfm?URI=oe-20-10-10526


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References

  1. B. Liedberg, C. Nylander, and I. Lunström, “Surface plasmon resonance for gas detection and biosensing,” Sens. Actuators4, 299–304 (1983). [CrossRef]
  2. X. Hoa, A. Kirk, and M. Tabrizian, “Towards integrated and sensitive surface plasmon resonance biosensors: A review of recent progress,” Biosens. Bioelectron.23, 151–160 (2007). [CrossRef] [PubMed]
  3. C. Loo, A. Lowery, N. Halas, J. West, and R. Drezek, “Innumotargeted nanoshells for integrated cancer imaging and therapy,” Nano Lett.5, 709–711 (2005). [CrossRef] [PubMed]
  4. T. Okamoto, I. Yamaguchi, and T. Kobayashi, “Local plasmon sensor with gold colloid monolayers deposited upon glass substrates,” Opt. Lett.25, 372–374 (2000). [CrossRef]
  5. E. Kretschmann, “The angular dependence and the polarisation of light emitted by surface plasmons on metals due to roughness,” Opt. Commun.5, 331–336 (1972). [CrossRef]
  6. B. Vohnsen and S. Bozhevolnyi, “Coupling of surface-plasmon polaritons to directional far-field radiation by an individual surface protrusion,” Appl. Opt.40, 6081–6085 (2001). [CrossRef]
  7. A. Hohenau, J. Krenn, A. Stepanov, A. Drezet, H. Ditlbacher, B. Steinberger, A. Leitner, and F. Aussenegg, “Dielectric optical elements for surface plasmons,” Opt. Lett.30, 893–895 (2005). [CrossRef] [PubMed]
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