Search results for "WAVELENGTH"
showing 10 items of 741 documents
Designing the properties of dispersion-flattened photonic crystal fibers
2001
We present a systematic study of group-velocity-dispersion properties in photonic crystal fibers (PCF's). This analysis includes a thorough description of the dependence of the fiber geometrical dispersion on the structural parameters of a PCF. The interplay between material dispersion and geometrical dispersion allows us to established a well-defined procedure to design specific predetermined dispersion profiles. We focus on flattened, or even ultraflattened, dispersion behaviors both in the telecommunication window (around 1.55 microm) and in the Ti-Za laser wavelength range (around 0.8 microm}. We show the different possibilities of obtaining normal, anomalous, and zero dispersion curves…
Guiding properties of a photonic quasi-crystal fiber based on the thue-morse sequence
2015
We present a novel microstructured optical fiber having a quasi-periodic distribution of air holes based on the Thue–Morse sequence. The transverse section of these fibers is basically a two-dimensional photonic quasi-crystal that can also provide complete photonic bandgaps without being a perfect periodic structure. Like in the conventional photonic crystal fibers, if the quasi-periodicity is broken by decreasing the size of some air holes or by introducing an extra air hole, the modified holes become defects that localize and guide light along the fiber. The guidance is attributed to the inhibition of transverse radiation produced by the photonic quasi-crystal cladding. Dispersion curves …
Thermally induced emission of light from a metallic diffraction grating, mediated by surface plasmons
1999
The angular emission of light of wavelength 710 and 810 nm from a gold diffraction grating was studied at about 700°C. A peak in the emission was found for defined angles. This contribution is purely TM-polarised and is attributed to thermally excited surface plasmons, coupled to light waves by the diffraction grating.
Surface plasmon polariton propagation across a gentle silver step
2001
Abstract Surface plasmon polaritons (SPPs) are excited with light of wavelength λ1=632.8 nm on or near a gentle Ag/Ag step structure using focused beam, prism coupling and detected using a bare, sharpened fibre tip. The tip–sample separation is controlled by means of an evanescent optical field at wavelength λ2=543.5 nm in a photon scanning tunnelling microscope (PSTM). The SPP propagation properties are first characterised on both the thin and thick sections of the Ag film structure either side of the step, both macroscopically, using attenuated total reflection, and microscopically from the PSTM images; the two techniques yield very good agreement. It is found that the SPP propagation len…
Spatial and spectral properties of small area THz generation for sub-wavelength microscopy
2010
A highly localized THz source is a promising candidate for sub-wavelength microscopy, due to its superior radiation power throughput with respect to others near-field techniques. Here, we report on the spatial and the spectral near-field properties of our highly localized THz source.
Broadband asymmetric transmission of THz radiation through double metallic gratings
2013
We analyse numerically and experimentally the asymmetric transmission through sub-wavelength double metallic gratings. The possibility of achieving a broadband unidirectional transmission of THz waves through the grating is confirmed. The proposed gratings allow for efficient one-way transmission in the wavelength range from 2.5 to 3.5 mm.
Wavelength multiplexed hydrogen sensor based on palladium-coated fibre-taper and Bragg grating
2004
A novel configuration of a wavelength multiplexed hydrogen sensor based on a palladium-coated tapered fibre and a fibre Bragg grating is presented. This scheme allows cascading several sensors along a single fibre, which increases the capability of implementing multipoint sensor networks for volumetric detection. Moreover, in this configuration the light interacts twice with the palladium layer, thus enhancing the sensitivity of the sensor.
Real-space imaging and motion analysis in sheared colloidal crystals
2007
Microscopic imaging of single particles is a powerful tool to investigate the local structure of colloidal suspensions. For single-particle identification with high-resolution microscopy the resolution power is limited by refraction to roughly the wavelength of light. In this case the depth of sharpness is on a scale of less than this limit. For this reason the simultaneous observation of particles in two or more layers of a colloidal crystal seems to be impossible. We report a method with which we can image more than one particle layer in dilute colloidal suspensions with preserved resolution. The analysis of the images obtained, in particular for the investigation of crystal layer motion …
Opto-thermally controlled beam steering in nonlinear all-dielectric metastructures
2021
Reconfigurable metasurfaces have recently gained a lot of attention in applications such as adaptive meta-lenses, hyperspectral imaging and optical modulation. This kind of metastructure can be obtained by an external control signal, enabling us to dynamically manipulate the electromagnetic radiation. Here, we theoretically propose an AlGaAs device to control the second harmonic generation (SHG) emission at nanoscale upon optimized optical heating. The asymmetric shape of the used meta-atom is selected to guarantee a predominant second harmonic (SH) emission towards the normal direction. The proposed structure is concurrently excited by a pump beam at a fundamental wavelength of 1540 nm and…
Phase defect inspection of multilayer masks for 13.5 nm optical lithography using PEEM in a standing wave mode
2007
We report on recent developments of an "at wavelength" full-field imaging technique for defect inspection of multilayer mask blanks for extreme ultraviolet lithography (EUVL). Our approach uses photoemission electron microscopy (PEEM) in a near normal incidence mode at 13.5 nut wavelength to image the photoemission induced by the EUV wave field on the multilayer blank surface. We analyze buried defects on Mo/Si multilayer samples down to a lateral size of 50 nm and report on first, results obtained from a six inches mask blank prototype as prerequisite for industrial usage. (c) 2007 Elsevier B.V. All rights reserved.