By applying the Maxwell Garnett model to gold nanoparticles in water we deduce a value of Im i (3) ϭ 1.1 ϫ 10 Ϫ7 esu for the imaginary part of the cubic susceptibility for gold corresponding to a Fermi smearing mechanism. We also demonstrate a sign reversal in the nonlinear absorption for gold particles in 1, 1Ј, 3, 3, 3Ј, 3Ј-hexamethylindotricarbocyanine iodide. Although the imaginary part of (3) is positive for each component by itself, remarkably the imaginary part of (3) is negative for the colloid as a whole. We show that the nonlinearity of the host must be considered and that the sign reversal in (3) is a result of the fact that at the surface plasmon resonance the local field factor has an imaginary component that arises from a phase shift between the applied field and the local field inside the particle.

Terahertz digital off-axis holography is demonstrated using a Mach-Zehnder interferometer with a highly coherent, frequency tunable, continuous wave terahertz source emitting around 0.7 THz and a single, spatially-scanned Schottky diode detector. The reconstruction of amplitude and phase objects is performed digitally using the angular spectrum method in conjunction with Fourier space filtering to reduce noise from the twin image and DC term. Phase unwrapping is achieved using the dual wavelength method, which offers an automated approach to overcome the 2π phase ambiguity. Potential applications for nondestructive test and evaluation of visually opaque dielectric and composite objects are discussed.

Since the early works on diffraction of chafJ there has been no mathematical modelization available for a real physical solution. This work presents one and gives a rigorous exploitation of the polarization behavior. One can find here a general model which can take into account all the phenomena appearing in a cloud of dipoles: the polarimetric effects, the mask, and the coupling influences. This development is new and can be generalized for clouds of spheres, discs, cylinders, or other simple shapes [ l , 21. 0 199. T John

Methods for spectrally controlling light absorption in optoelectronic devices have attracted considerable attention in recent years. It is now well known that a Fabry-Perot nanocavity comprising thin semiconductor and metal films can be used to absorb light at selected wavelengths. The absorption wavelength is controlled by tailoring the thickness of the nanocavity and also by nanostructure patterning. However, the realization of dynamically tuning the absorption wavelength without changing the structural geometry remains a great challenge in optoelectronic device development. Here it is shown how an ultrathin n-type doped indium antimonide integrated into a subwavelengththick optical nanocavity can result in an electrically tunable perfect light absorber in the visible and near infrared range. These absorbers require simple thin-film fabrication processes and are cost effective for large-area devices without resorting to sophisticated nanopatterning techniques. In the visible range, a 40 nm spectral shift can be attained by applying a reasonable bias voltage to effect the color change. It is also shown that these electrically tunable absorbers may be used as optical modulators in the infrared. The predicted (up to) 95.3% change in reflectance, transforming the device from perfectly absorbing to highly reflective, should make this technology attractive to the telecommunication (switching) industry.Thin-film light absorbers have recently received considerable attention due to their straightforward fabrication, low cost, and wide range of potential applications, however they have been restricted to the near infrared range or they are not tunable, or they are not perfect absorbers. Tunable perfect light absorbers functioning in the visible range as discussed in this paper comprise a Fabry-Perot nanocavity made of thin metal and semiconductor films that absorb light completely over selected wavelength ranges in the visible and infrared. The fundamental absorption wavelength is determined by the thickness of the nanocavity and tunability is bias voltage controlled. This newest generation of perfect light absorbers would have many interdisciplinary applications in chemical and biological sensing 1-7 , solar energy harvesting 8-11 , photodetectors 12,13 , gas sensors 14 , structural color printing [15][16][17][18] , and color filters [19][20][21][22][23][24][25][26] . However, if the absorption could be controlled in real time, then multiple new applications can be envisioned such as high speed, high resolution, high grey scale displays, smart windows, and a variety of telecommunication devices to compete with those currently available. To ascertain the possibilities, a theoretical investigation into ultrathin spectrally selective perfect light absorption in a nanocavity structure made of an epsilon-near-zero (ENZ) material (as the active layer) is summarized here. The metal/ENZ/dielectric/metal structure is modeled as a nanocavity, allowing the enhancement of light absorption at the resonant wavelength to be explored....