The addition of a dielectric layer on a slab configuration is frequently utilized in various electromagnetic devices in order to give them certain desired operational characteristics. In this work, we consider a grounded dielectric film-slab, which is externally excited by a normally-incident Gaussian beam. On top of the film-slab, we use an additional suitably selected single isotropic superstrate layer in order to increase the field concentration inside the slab and hence achieve optimal power transfer from the external source to the internal region. We define a quantity of interest, called “enhancement factor,” expressing the increase of the field concentration in the film-slab when the superstrate is present compared to the case that it is absent. It is shown that large enhancement factor values may be achieved by choosing properly the permittivity, the permeability, and the thickness of the superstrate. In particular, it is demonstrated that the field in the film-slab is significantly enhanced when the slab is composed by an ？-near-zero (ENZ) or low-index metamaterial. 1. Introduction Increased field intensity in a localized area is required in a variety of applications from simple traditional implementations to complex state-of-the-art experiments. Indicatively, a resonance plasmon mode, characterized by a substantial local electric field enhancement, has been reported to be formed between a gold nanorod and an infinite slab in infrared range [1]. In addition, the optical trapping force on a spherical dielectric particle for an arbitrarily positioned focused beam has been demonstrated in [2], by using the generalized vector diffraction theory. Moreover, when considering a simple, analytically solvable cylindrical configuration, it has been shown that optical vortices appear which can be used to stably trap particles of particular sizes and index contrasts with the background [3]. Field enhancement of incident near-infrared light has been also investigated in [4], by using the exhibited surface plasmon polariton from erbium ions in a golden film. On the other hand, layered, dielectric slab configurations are commonly used in electromagnetic (EM) devices since they possess certain functional advantages such as conformability and ease of fabrication. In particular, dielectric layers, with carefully selected physical and geometrical parameters, are extensively employed to lend particular beneficial characteristics to the considered devices. In [5], a multi-layered dielectric coating has been used in semiconductor laser diode optical amplifiers to
References
[1]
Y. J. Zheng, H. Liu, S. M. Wang et al., “Selective optical trapping based on strong plasmonic coupling between gold nanorods and slab,” Applied Physics Letters, vol. 98, no. 8, Article ID 083117, 2011.
[2]
A. A. R. Neves, A. Fontes, L. Y. De Pozzo et al., “Electromagnetic forces for an arbitrary optical trapping of a spherical dielectric,” Optics Express, vol. 14, no. 26, pp. 13101–13106, 2006.
[3]
T. M. Grzegorczyk and J. A. Kong, “Analytical prediction of stable optical trapping in optical vortices created by three TE or TM plane waves,” Optics Express, vol. 15, no. 13, pp. 8010–8020, 2007.
[4]
E. Verhagen, L. Kuipers, and A. Polman, “Field enhancement in metallic subwavelength aperture arrays probed by erbium upconversion luminescence,” Optics Express, vol. 17, no. 17, pp. 14586–14598, 2009.
[5]
C. Vassallo, “Theory and practical calculation of antireflection coatings on semiconductor laser diode optical amplifiers,” IEE Proceedings, vol. 137, no. 4, pp. 193–202, 1990.
[6]
C. A. Valagiannopoulos, “High selectivity and controllability of a parallel-plate component with a filled rectangular ridge,” Progress In Electromagnetics Research, vol. 119, pp. 497–511, 2011.
[7]
J.-H. Choe, Q. H. Park, and H. Jeon, “Effect of metallic slab cladding on photonic crystal band structures,” Journal of the Korean Physical Society, vol. 53, no. 5, pp. 2591–2595, 2008.
[8]
A. Alù, D. Rainwater, and A. Kerkhoff, “Plasmonic cloaking of cylinders: finite length, oblique illumination and cross-polarization coupling,” New Journal of Physics, vol. 12, Article ID 103028, 2010.
[9]
C. A. Valagiannopoulos and N. L. Tsitsas, “Integral equation analysis of a low-profile receiving planar microstrip antenna with a cloaking superstrate,” Radio Science, vol. 47, Article ID RS2022, 2012.
[10]
C. A. Valagiannopoulos, “Electromagnetic scattering of the field of a metamaterial slab antenna by an arbitrarily positioned cluster of metallic cylinders,” Progress in Electromagnetics Research, vol. 114, pp. 51–66, 2011.
[11]
F. Yang, A. Aminian, and Y. Rahmat-Samii, “A novel surface-wave antenna design using a thin periodically loaded ground plane,” Microwave and Optical Technology Letters, vol. 47, no. 3, pp. 240–245, 2005.
[12]
G. D. Landry and T. A. Maldonado, “Gaussian beam transmission and reflection from a general anisotropic multilayer structure,” Applied Optics, vol. 35, no. 30, pp. 5870–5879, 1996.
[13]
E. E. Kriezis, P. K. Pandelakis, and A. G. Papagiannakis, “Diffraction of a Gaussian beam from a periodic planar screen,” Journal of the Optical Society of America A, vol. 11, no. 2, pp. 630–636, 1994.
[14]
J. Yang, L.-W. Li, K. Yasumoto, and C. H. Liang, “Two-dimensional scattering of a gaussian beam by a periodic array of circular cylinders,” IEEE Transactions on Geoscience and Remote Sensing, vol. 43, no. 2, pp. 280–285, 2005.
[15]
P. H. Bolivar, M. Brucherseifer, J. G. Rivas et al., “Measurement of the dielectric constant and loss tangent of high dielectric-constant materials at terahertz frequencies,” IEEE Transactions on Microwave Theory and Techniques, vol. 51, no. 4, pp. 1062–1066, 2003.
[16]
A. Alù, A. Salandrino, and N. Engheta, “Negative effective permeability and left-handed materials at optical frequencies,” Optics Express, vol. 14, no. 4, pp. 1557–1567, 2006.
[17]
B. García-Cámara, F. Moreno, F. González, J. M. Saiz, and G. Videen, “Light scattering resonances in small particles with electric and magnetic propertie,” Journal of the Optical Society of America A, vol. 25, no. 2, pp. 327–334, 2008.
[18]
P.-Y. Chen, M. Farhat, and A. Alù, “Bistable and self-tunable negative-index metamaterial at optical frequencies,” Physical Review Letters, vol. 106, no. 10, Article ID 105503, 2011.
[19]
M. Silveirinha and N. Engheta, “Tunneling of electromagnetic energy through subwavelength channels and bends using ε-near-zero materials,” Physical Review Letters, vol. 97, no. 15, Article ID 157403, 2006.
[20]
A. Alù, M. G. Silveirinha, A. Salandrino, and N. Engheta, “Epsilon-near-zero metamaterials and electromagnetic sources: Tailoring the radiation phase pattern,” Physical Review B, vol. 75, no. 15, Article ID 155410, 2007.
[21]
G. Lovat, P. Burghignoli, F. Capolino, D. R. Jackson, and D. R. Wilton, “Analysis of directive radiation from a line source in a metamaterial slab with low permittivity,” IEEE Transactions on Antennas and Propagation, vol. 54, no. 3, pp. 1017–1030, 2006.
[22]
C. A. Valagiannopoulos, “Effect of cylindrical scatterer with arbitrary curvature on the features of a metamaterial slab antenna,” Progress in Electromagnetics Research, vol. 71, pp. 59–83, 2007.
