Search results for " Optics"
showing 10 items of 5880 documents
Artificially inscribed defects in opal photonic crystals
2005
Opals are three-dimensional photonic crystals, self-assembled from dielectric spherical beads into a face-centered cubic lattice. By introducing intentional defects in the crystal lattice, one modifies features such as spontaneous emission and the directionality of diffracted light. We here present a method for the artificial introduction of a lattice of such intentional defects in self-assembled poly(methyl methacrylate) (PMMA) photonic crystals by means of electron beam lithography. The inscribed defects are of the size of an individual bead, providing a broad spectral range between adjacent resonance peaks. This opens for devices with single line transmission in the photonic band gap, as…
Dispersion-compensated Lau-like processor
2004
We present a diffractive lens-based optical assembly with which to achieve high-contrast Lau-like interferential fringes with totally incoherent illumination.
Spatial soliton formation in photonic crystal fibers
2003
We demonstrate the existence of spatial soliton solutions in photonic crystal fibers (PCF's). These guided localized nonlinear waves appear as a result of the balance between the linear and nonlinear diffraction properties of the inhomogeneous photonic crystal cladding. The spatial soliton is realized self-consistently as the fundamental mode of the effective fiber defined simultaneously by the PCF linear and the self-induced nonlinear refractive indices. It is also shown that the photonic crystal cladding is able to stabilize these solutions, which would be unstable otherwise if the medium was entirely homogeneous.
Super-resolved imaging with randomly distributed, time- and size-varied particles
2009
In this paper we present a super-resolved approach aimed at overcoming the diffraction limit in imaging systems. It is based on place randomly and time-varied particles having different sizes on the top of the sample. By considering particle sizes smaller than the object's minimum detail that an imaging system can resolve, it is possible to recover a high resolution image from a set of low resolution images while before capturing each image we produce a randomly modified distribution of the particles by vibrating the sample. The simulation process as well as experimental results validates the proposed approach that includes effectively decreasing the F number of the imaging system while bei…
Degree of coherence: a lensless measuring technique.
2009
We present a technique for measuring the degree of coherence that is based on the self-imaging phenomenon. The technique is lensless, has multiplexing capabilities, and can work with high light throughput. Experimental verifications are given.
Investigating the performance of reconstruction methods used in structured illumination microscopy as a function of the illumination pattern's modula…
2016
Surpassing the resolution of optical microscopy defined by the Abbe diffraction limit, while simultaneously achieving optical sectioning, is a challenging problem particularly for live cell imaging of thick samples. Among a few developing techniques, structured illumination microscopy (SIM) addresses this challenge by imposing higher frequency information into the observable frequency band confined by the optical transfer function (OTF) of a conventional microscope either doubling the spatial resolution or filling the missing cone based on the spatial frequency of the pattern when the patterned illumination is two-dimensional. Standard reconstruction methods for SIM decompose the low and hi…
The use of simulation methods to obtain the structure and conformation of 10-cyano-9,9′-bianthryl by electron diffraction and high-resolution imaging
1995
Abstract Experimental electron diffraction patterns and high-resolution images were used to determine the space group and unit cell dimensions of 10-cyano-9,9′-bianthryl. Subsequently the molecular conformation was calculated by semi-empirical quantum-mechanical methods. The molecule was then placed with the appropriate symmetry into the unit cell and the conformational as well as the packing energy deduced by an iterative procedure until good agreement was obtained between experiment and theory.
Anomalous pressure dependence of the Lamb-Mössbauerf-factor in the spin crossover system [Fe(2-pic-ND2)3]Cl2·EtOD
1987
The pressure dependence of the Lamb-Mossbauer factor of the spin crossover compound [Fe(2-pic-ND2)3]Cl2·EtOD(2-pic-ND2=2-picolylamine, deuterated at the−NH2 group) has been measured at pressures up to 1500 bar and at three temperatures (115.7, 146.7, 185.6 K) around the transition temperatureT t=135 K. The temperature dependence of the unit cell volume has been determined by X-ray diffraction. In the transition region (T=146.7 K), the pressure dependence of thef-factor shows an anomalous increase as compared to the dependence below and above the transition. The behaviour off(p, T), its anomaly and absolute value, can be consistently explained within a theoretical model which treats the comp…
Fractal-structured multifocal intraocular lens
2017
[EN] In this work, we present a new concept of IOL design inspired by the demonstrated properties of reduced chromatic aberration and extended depth of focus of Fractal zone plates. A detailed description of a proof of concept IOL is provided. The result was numerically characterized, and fabricated by lathe turning. The prototype was tested in vitro using dedicated optical system and software. The theoretical Point Spread Function along the optical axis, computed for several wavelengths, showed that for each wavelength, the IOL produces two main foci surrounded by numerous secondary foci that partially overlap each other for different wavelengths. The result is that both, the near focus an…
Fractal zone plates with variable lacunarity.
2009
Fractal zone plates (FZPs), i.e., zone plates with fractal structure, have been recently introduced in optics. These zone plates are distinguished by the fractal focusing structure they provide along the optical axis. In this paper we study the effects on this axial response of an important descriptor of fractals: the lacunarity. It is shown that this parameter drastically affects the profile of the irradiance response along the optical axis. In spite of this fact, the axial behavior always has the self-similarity characteristics of the FZP itself.