Search results for "Physics::Optics"
showing 10 items of 1958 documents
Ultracompact x-ray dosimeter based on scintillators coupled to a nano-optical antenna
2017
International audience; We show that nano-optical antennas are capable of controlling the luminescence induced by the absorption of x rays into matter. The x-ray-excited luminescence from a tiny scintillation cluster coupled to a horn nano-optical antenna is highly directed and determined by the antenna’s geometrical parameters. Directionality is sufficiently high to efficiently outcouple the x-ray-excited luminescence to a narrow single-mode optical fiber, thus enabling ultracompact fiber-integrated x-ray sensors. Our nano-optically driven approach offers the possibility of x-ray profiling and dosimetry in ultra-confined environments, opening up new avenues in the fields of x-ray imaging, …
Ultrafast diffraction of tightly focused waves with spatiotemporal stabilization
2008
Experimental studies of ultrafast beam shaping have come about from the need to compensate diffraction-induced dispersive effects in femtosecond laser beams. From a theoretical point of view, chromatic matching of diffracted spherical waves in the vicinity of the geometrical focus is attained by applying conveniently dispersive boundary conditions in the far-field zone, a subject thoroughly analyzed in the paraxial regime. For applications demanding high spatial resolution, however, high-numerical-aperture microscope objectives may be employed instead and would lead to nonparaxiality of the focal wavefields. These circumstances have motivated our investigation. Concretely we report on prere…
Superresolved imaging based on wavelength multiplexing of projected unknown speckle patterns
2015
We propose a method for resolution enhancement of a diffraction limited optical system based on the capture of a set of low resolution images. These images are obtained after projection of an ensemble of unknown speckle patterns on top of the high resolution object that is to be imaged. Each speckle pattern is generated by the same thin (and unknown) diffuser, but illuminated with a slightly different wavelength. From the ensemble of low resolution images, we obtain a system of equations that can be solved in an iterative manner that enables reconstruction of the high resolution object. As a result, we also achieve the projected high resolution speckle patterns used for the encoding.
Three-dimensional point spread function and generalized amplitude transfer function of near-field flat lenses.
2010
We derive a nonsingular, polarization-dependent, 3D impulse response that provides unambiguously the wave field scattered by a negative-refractive-index layered lens and distributed in its image volume. By means of a 3D Fourier transform, we introduce the generalized amplitude transfer function in order to gain a deep insight into the resolution power of the optical element. In the near-field regime, fine details containing some depth information may be transmitted through the lens. We show that metamaterials with moderate absorption are appropriate for subwavelength resolution keeping a limited degree of depth discrimination.
Left-handed metamaterial coatings for subwavelength-resolution imaging
2012
We report on a procedure to improve the resolution of far-field imaging by using a neighboring high-index medium that is coated with a left-handed metamaterial. The resulting plot can also exhibit an enhanced transmission by considering proper conditions to retract backscattering. Based on negative refraction, geometrical aberrations are considered in detail since they may cause a great impact in this sort of diffraction-unlimited imaging by reducing its resolution power. We employ a standard aberration analysis to refine the asymmetric configuration of metamaterial superlenses. We demonstrate that low-order centrosymmetric aberrations can be fully corrected for a given object plane. For su…
Nonlinear polarization effects in optical fibers: polarization attraction and modulation instability [Invited]
2014
We review polarization stabilization techniques based on the polarization attraction effect in low-birefringence fibers. Polarization attraction or pulling may be based on cross-polarization modulation, on parametric amplification, and on Raman or Brillouin scattering. We also review methods for laser frequency conversion based on polarization modulation instabilities in low- and high-birefringence fibers, and photonic crystal fibers. Polarization instabilities in nonlinear fibers may also be exploited for sensing applications.
Magneto-optical linear dichroism in threshold photoemission electron microscopy of polycrystalline Fe films.
2000
Magnetic linear dichroism in threshold photoemission has been exploited to obtain magnetic contrast in a photoemission electron microscope using a mercury arc lamp. The dichroism at threshold can be described similar to the magneto-optical Kerr effect in the region of visible light. The asymmetry of electron intensity observed for a 100 nm polycrystalline Fe film on silicon is A=(0.37+/-0.05)%. The asymmetry occurs for the geometry of the transverse Kerr effect. For unpolarized light the asymmetry was about half the value observed for linearly polarized light. Threshold photoemission microscopy has a large potential for high resolution magnetic domain imaging with fast data acquisition.
Linear infrared dichroism by a double modulation technique
1991
In the first part of this paper an experimental setup using Fourier-transform infrared spectroscopy (FTIR) in combination with a photoelastic modulator (PEM) for linear dichroism measurements is described. The second part shows the influence of PEM-amplitude and scan-velocity on the sensitivity of the instrument. The third part deals with the fringe-problem in the baselines of absorbance spectra and its influence on the determination of the linear dichroic ratio.
Vibrational and rotational collisional relaxation in CO2–Ar and CO2–He mixtures studied by stimulated Raman-infrared double resonance
1999
0021-9606; The collisional relaxation among vibrational levels of the Fermi dyad of CO2 mixed with Ar and He (10% CO2, 90% rare gas) has been studied at room temperature with a double resonance experiment. Stimulated Raman effect from the ground state achieved the pumping process with a Nd:YAG laser and a pulse amplified dye laser. After pumping the v(1) or 2v(2)(Sigma(+)g) level, a cw CO2 laser was used to probe either the depopulation rates of the pumped levels (vibrationally or rotationally resolved) or the energy transfer rates to neighboring states. The vibrational energy relaxation has been studied from experimental depopulation of v(1) and population of 2v(2) levels through a five-le…
Step-along power vector method for astigmatic wavefront propagation
2013
Purpose To propose both a new algebraic solution and a graphical monitoring method for astigmatic wavefront propagation in the framework provided by power vectors. Methods The generalised propagation equation describing the propagation of astigmatic wavefronts from one plane to another is adapted to the power vectors formalism using a novel algorithm based on a step-along method. The step-along procedure is directly applied to the tuple of power vectors [M, J0, J45] representing an arbitrary astigmatic wavefront and it permits the calculation of the tuple of power vectors [M′, J′0, J′45] after a given propagation distance. This is achieved mathematically first by temporarily rotating the as…