Color filters based upon nano-structured metals have garnered significant interest in recent years, having been positioned as alternatives to the organic dye-based filters which provide color selectivity in image sensors, as non-fading 'printing' technologies for producing images with nanometer pixel resolution, and as ultra-high-resolution, small foot-print optical storage and encoding solutions. Here, we demonstrate a plasmonic filter set with polarizationswitchable color properties, based upon arrays of asymmetric cross-shaped nano-apertures in an aluminum thin-film. Acting as individual color-emitting nano-pixels, the plasmonic cavityapertures have dual-color selectivity, transmitting one of two visible colors, controlled by the polarization of the white light incident on the rear of the pixel and tuned by varying the critical dimensions of the geometry and periodicity of the array. This structural approach to switchable optical filtering enables a single nano-aperture to encode two information states within the same physical nano-aperture; an attribute we use here to create micro image displays containing duality in their optical information states.

Plasmonic color filtering has provided a range of new techniques for "printing" images at resolutions beyond the diffraction-limit, significantly improving upon what can be achieved using traditional, dye-based filtering methods. Here, a new approach to high-density data encoding is demonstrated using full color, dual-state plasmonic nanopixels, doubling the amount of information that can be stored in a unit-area. This technique is used to encode two data sets into a single set of pixels for the first time, generating vivid, near-full sRGB (standard Red Green Blue color space)color images and codes with polarization-switchable information states. Using a standard optical microscope, the smallest "unit" that can be read relates to 2 × 2 nanopixels (370 nm × 370 nm). As a result, dual-state nanopixels may prove significant for long-term, high-resolution optical image encoding, and counterfeit-prevention measures. over their microscale, dye-based counterparts. Chief among these are their subwavelength dimensions (leading to ultradense, ultrathin pixel arrays), and their long-term environmental stability (they do not degrade or fade over time due to radiation exposure). As a result, plasmonic filters have been positioned as new technological solutions for subwavelength color printing, [1,4,[7][8][9]12] anticounterfeiting measures, [19,20] and RGB splitting for image sensors; [2,17,21,22] thus representing one of the most promising, technologically relevant areas of current plasmonic research activity. Here, we explore a new application of polarizationcontrolled plasmonic filters: dual output, full-color optical image encoding. Recent developments in the engineering and manipulation of materials on the nanoscale have given rise to a number of new techniques with the potential for physically encoding data and images into optically readable volumes and surfaces. [23,24] Using semiconductor quantum dots, [25][26][27] graphene, [28] and various super-resolution lithography techniques, [29][30][31][32][33][34] researchers are demonstrating novel 2D and 3D techniques that may enable the next generation of optical storage and encoding technologies. Plasmonic particles and filters have also seen applications in these research areas, with the aforementioned image encoding examples having been joined by demonstrations of their use in optical data storage. [23,24,[35][36][37] Here, we show a new utilization of image encoding using polarization multiplexed plasmonic filters, where, unlike previous studies that employed color or position switching in fixed images, [14,38] we show that two arbitrary, full-color images can be encoded into a single array of pixels. Our individual pixels are comprised of asymmetric cross-shaped nanoapertures in a thin film of aluminum. Each aperture is engineered to exhibit two independent plasmonic resonances which can be tuned across the sRGB (standard Red Green Blue) color-space (a single pixel can be encoded with any two arbitrary colors). We go on to show that by using the smallest visible unit ...

Surface enhanced resonance Raman spectroscopy (SERRS) is a powerful molecular sensing tool that can be applied to a number of applications in the field of molecular diagnostics. We demonstrate that by using electron beam lithography to manipulate the nanoscale geometry of Ag split-ring resonators we can tune their optical properties such that they exhibit two independently addressable high frequency plasmon resonance modes for SERRS. This tailored multimodal, polarization dependent activity enables the split rings to act as discriminating sensors, with each resonance tuned for a particular sensing purpose. The structures are used as multiwavelength, multianalyte DNA SERRS sensors, with each resonance tuned to both the absorption wavelength of a differently colored Raman reporter molecule and its corresponding laser excitation wavelength. The ability of each resonance to independently sense small concentrations of a single DNA type from within a mixed population is demonstrated. Also shown is the effect of the split ring's dichroic response on the SERRS signal and the sensor's limit of detection of each resonance mode (switching its sensory reaction "on" and "off" depending on the orientation of the exciting light).

Electron beam lithography was used to fabricate gold crescent shaped split-ring resonators with 30nm minimum feature size. By varying the crescent’s arc length over a range of nanometer-scale dimensions the authors demonstrate the tuneability of visible resonances within such structures. Results, which correlate closely with those predicted using finite-difference time-domain modeling, open the way for these devices to be used in near-field biological sensing.

The photofragmentation of the nitrotoluene isomers in the gas phase is studied in the wavelength region 210-270 nm using a pulsed UV laser in conjunction with a time-of-flight mass spectrometer. Laser-induced mass spectra are analysed and compared with those produced by the electron impact technique. The generation of the observed fragment ions is explained by invoking different fragmentation pathways followed by these molecules. Observed differences in the mass spectra of the ortho-meta-, and para-nitrotoluene isomers and in the wavelength dependence of the NO fragment released from these molecules are discussed as a possible way of providing a laser-based method for their identification.Recently, it has been shown by Kosmidis et al.' that the mass spectrum from the multiphoton ionization and dissociation of nitrobenzene, using UV laser light, can be explained by both the dissociation ionization (DIdissociation followed by ionization) and the ionization dissociation (ID-ionization followed by dissociation) decomposition mechanisms. For these two fragmentation routes, different dissociation pathways have been proposed.Due to the similarities which exist between nitrobenzene and the nitrotoluene isomers it is believed that many common characteristics could appear in their photodissociation processes. Thus, while the knowledge of the photochemistry of nitrobenzene is essential for understanding that of the nitrotoluene isomers, it is expected that the latter could contribute to the understanding of the entire group of nitro-explosive compounds which includes dinitrotoluene and trinitrotoluene. Moreover, this knowledge is a prerequisite for the sensitive and selective photodetection of these materials.The photodecomposition of the nitrobenzene molecule has been extensively studied using laser light, but the case is different for the nitrotoluenes. Although the fragmentation of their molecular ions has been well by other techniques, little work has been presented for molecular fragmentation using lasers.'"'' These laser studies do not, however, cover all the isomers and have mainly been carried out using a small number of discrete wavelengths.In this paper, the UV-laser-induced dissociation of ortho-, meta-and para-nitrotoluene in the gas phase is presented in the wavelength range 210-270 nm. The electron impact (EI) mass spectra of these molecules have also been recorded for reasons of completeness, and are compared with the laser-induced mass spectra.The study is carried out in this wavelength range for two reasons. Firstly, there is the possibility to study the molecular fragmentation with respect to the ionization thresholds. For aromatic molecules, it has been proposed that the extensive fragmentation observed after a

Understanding and controlling plasmon resonances from metallic nanoscale structures have been the focus of much attention recently, with applications including local surface plasmon resonance sensing, surface enhanced Raman spectroscopy, and negative refractive index materials. In this letter the authors demonstrate the fabrication of uniform arrays of split rings from gold and show that such structures are capable of supporting multiple plasmon resonances. The authors show that up to five plasmon resonances can be identified and use finite difference time domain modeling and absorption spectroscopy to fully characterize and identify each resonance. The implications of higher order surface plasmon resonances for sensing are discussed

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