Differential ellipsometric surface plasmon resonance sensors with liquid crystal polarization modulators

Copyright © 2004 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 85 (2004) and may be found at http://link.aip.org/link/?APPLAB/85/3017/1Differential ellipsometric interrogation of surface plasmon (SP) resonances is a technique that gives ultrahigh sensitivity to refractive index changes, and it may provide the basis for chemical and biological sensors. In this study, a liquid crystal polarization modulator has been developed to provide such a differential technique. A refractive index sensitivity of 2×10–7 refractive index units is demonstrated, which is at least as sensitive as more established SP sensing techniques. The use of a liquid crystal modulator allows for low-voltage signal modulation and also feedback locking to zero. Possibly more important, it leads to pixelization for array sensing and for potential imaging

Dispersion of surface plasmon polaritons on short-pitch metal gratings

Ian R. Hooper and J. Roy Sambles, Physical Review B, Vol. 65, article 165432 (2002). "Copyright © 2002 by the American Physical Society."The dispersion of surface plasmon polaritons (SPPs) has been calculated for short-pitch metal gratings for various depths. For gratings with depths greater than their pitch very flat SPP bands are formed in the zero-order region of the spectrum which may be resonantly excited with radiation polarized with its electric field in the plane of incidence of the radiation, which also contains the grating vector. The dispersion curves of these modes evolve as deformations of the familiar shallow grating dispersion curve due to the opening of very large band gaps, and interactions of the SPP bands with both the light line and other SPP bands. Also presented are the dispersion curves for the equivalent modes excited by radiation having its plane of incidence perpendicular to the grating vector, but polarized with its electric field parallel to this grating vector. The full dispersion curve of these SPP bands for all orientations of the grating relative to the plane of incidence is also presented

Slow waves caused by cuts perpendicular to a single subwavelength slit in metal

Copyright © 2007 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. This is the published version of an article published in New Journal of Physics Vol. 9, article 1. DOI: 10.1088/1367-2630/9/1/001Resonant transmission of microwaves through a subwavelength slit in a thick metal plate, into which subwavelength cuts have been made, is explored. Two orientations of the cuts, parallel and perpendicular to the long axis of the slit, are examined. The results show that the slits act as though filled with a medium with anisotropic effective relative permeability which at low mode numbers has the two values ~(1, 9.1), increasing to ~(1, 14.4) for higher mode numbers

Coupled surface plasmon polaritons on thin metal slabs corrugated on both surfaces

Ian R. Hooper and J. Roy Sambles, Physical Review B, Vol. 70, article 045421 (2004). "Copyright © 2004 by the American Physical Society."A modelling study of the effect of coupled surface plasmon polaritons (SPPs) on the optical response of a thin metal film corrugated on both surfaces is presented. Initially the case of conformally corrugated metal films (the corrugations on each surface are identical and in phase with each other) is considered. Sinusoidal structures, and those having an additional first harmonic, 2kg (where kg is the grating vector) component, are investigated. This 2kg component opens up significant band gaps in the SPP dispersion curves, and also causes anticrossing behavior between the long range SPPs and short range SPPs. It is shown that this anticrossing, and the band gap, have a common explanation. Following this, nonconformally corrugated films are examined, and strongly enhanced resonant transmission is shown to occur, which can be almost independent of the in-plane wave vector. The results presented show that, though the enhanced transmission through hole arrays which has provoked extensive recent investigation is of great interest from a physics viewpoint, other structures which exhibit enhanced transmission may provide more benefits, including higher transmission, for some applications

Observation of backflow in the switch-on dynamics of a hybrid aligned nematic

Copyright © 2004 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 84 (2004) and may be found at http://link.aip.org/link/?APPLAB/84/46/1The optical convergent-beam technique is used to measure, in 0.3 ms steps, the response of the director in a 4.6-µm-thick ZLI-2293 filled hybrid aligned nematic cell when a 10 kHz, 7 Vrms ac voltage is applied to the cell. The total time taken for the reorientation process is 2.4 ms, with backflow observed during the first 1.5 ms after the application of the voltage. The measured director profiles show excellent agreement with theoretical profiles produced from the Leslie–Eriksen–Parodi theory using typical values for the viscosity coefficients. Fluid velocity profiles within the cell are also modeled

Backflow in the relaxation of a hybrid aligned nematic cell

Copyright © 2003 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 82 (2003) and may be found at http://link.aip.org/link/?APPLAB/82/3156/1The optical convergent-beam technique has been used to measure the changing director profile in a 4.6 µm ZLI-2293 filled hybrid aligned nematic cell when a 7 Vrms ac voltage was removed. The relaxation process has been recorded in 0.3 ms time steps allowing the detailed director backflow occurring in the initial 9 ms of the reorientation process to be quantified. The measured tilt profiles over the 60 ms total relaxation period were compared to model tilt profiles produced using the Leslie–Eriksen–Parodi theory, and excellent agreement was found. Further analysis shows that the backflow is dominated by the viscosity coefficient η1 and the overall relaxation is governed by the coefficient γ1

Sensing using differential surface plasmon ellipsometry

Copyright © 2004 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Applied Physics 96 (2004) and may be found at http://link.aip.org/link/?JAPIAU/96/3004/1In this work a differential ellipsometric method utilizing surface plasmons (SPs) for monitoring refractive index changes, which could be used in chemical and biological sensors, is presented. The method is based upon determining the azimuth of elliptically polarized light reflected from a Kretschmann SP system, resulting from linearly polarized light containing both p and s components incident upon it. The sensitivity of this azimuth to the refractive index of a dielectric on the nonprism side of the metal film is demonstrated both experimentally and theoretically. The smallest refractive index change which is resolvable is of the order of 10–7 refractive index units, although it is believed that this could be improved upon were it not for experimental constraints due to atmospheric changes and vibrations. The method requires the Kretschmann configuration to be oriented at a fixed angle, and the SP to be excited at a fixed wavelength. With no moving parts this method would be particularly robust from an application point of view

Remarkable Zeroth-Order Resonant Transmission of Microwaves through a Single Subwavelength Metal Slit

James R. Suckling, J. Roy Sambles, and Christopher R. Lawrence, Physical Review Letters, Vol. 95, article 187407 (2005). "Copyright © 2005 by the American Physical Society."A slit in a thick metal plate that is extremely subwavelength will not transmit microwaves polarized parallel to it. It is shown here that cuts perpendicular to the slit allow parallel polarized radiation to resonantly transmit. Furthermore, a zero-order mode may be excited within the slit, the frequency of which, to first order, is independent of the plate depth. Remarkably, for this novel type of resonance, the field in the slit oscillates with a constant phase and little amplitude variation throughout the plate depth, while the resonant wavelength tends to infinity as the slit width approaches zero

Resonant transmission of microwaves through a hexagonal array of holes in a thin metal layer

Copyright © 2007 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. This is the published version of an article published in New Journal of Physics Vol. 9, article 101. DOI: 10.1088/1367-2630/9/4/101Resonant transmission of microwaves through a hexagonal array of holes in a very thin aluminium layer is studied. The array of holes, with diameter much less than the incident wavelength, leads to a strong transmission peak at a frequency just lower than the diffraction limit of the array. The results are well-modelled using a finite element package. The effect of metal depth on transmission intensity and the maximum efficiency of the hole array is also explored. Further experimental data are presented for the transmission of microwaves as a function of angle of incidence. It is shown that strong transmission occurs at frequencies just lower than the diffraction edges of the array. Incidentally, it is also shown that less than 0.01% of normally incident microwave radiation is transmitted through a continuous metal layer of thickness only 40% of the skin depth

Voltage dependent director of a homeotropic negative liquid crystal cell

Copyright © 2008 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 93 (2008) and may be found at http://link.aip.org/link/?APPLAB/93/031909/1Thin layers of obliquely (60° to normal) thermally evaporated SiOx lead to homeotropic alignment of a nematic liquid crystal (LC) having negative dielectric anisotropy. Under application of an ac voltage the director, as characterized by the fully leaky waveguide technique, is found to realign with a voltage controlled tilt along the evaporation direction. This behavior is in complete contrast with that of a LC having positive dielectric anisotropy and may have important implications for modern LC display technology