Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 15 de 15
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Opt Express ; 24(7): 7456-76, 2016 Apr 04.
Artigo em Inglês | MEDLINE | ID: mdl-27137036

RESUMO

This work presents a detailed analysis of the morphology of femtosecond laser-induced changes in bulk lithium niobate (LiNbO3) - one of the most common host materials in photonics - using second-harmonic generation microscopy and scanning electron microscopy. It is shown that focused linearly polarized near-infrared pulses can produce two or three distinct axially separated regions of modified material, depending on whether the pulse propagation is along or perpendicular to the optical axis. When laser writing in LiNbO3 is conducted in multi-shot irradiation mode and the focused light intensity is kept near the bulk damage threshold, periodic planar nanostructures aligned perpendicular to the laser polarization are produced inside the focal volume. These results provide a new perspective to laser writing in crystalline materials, including the fabrication of passive and active waveguides, photonic crystals, and optical data storage devices.

2.
Opt Express ; 23(9): 12444-53, 2015 May 04.
Artigo em Inglês | MEDLINE | ID: mdl-25969330

RESUMO

We demonstrate that an annulus of light whose polarization is linear at each point, but the plane of polarization gradually rotates by π radians can be used to generate Bessel-Poincaré beams. In any transverse plane this beam exhibits concentric rings of polarization singularities in the form of L-lines, where the polarization is purely linear. Although the L-lines are invisible in terms of light intensity variations, we present a simple way to visualize them as dark rings around a sharp peak of intensity in the beam center. To do this we use a segmented polarizer whose transmission axes are oriented differently in each segment. The radius of the first L-line is always smaller than the radius of the central disk of the zero-order Bessel beam that would be produced if the annulus were homogeneously polarized and had no phase circulation along it.

3.
Opt Express ; 21(22): 26335-40, 2013 Nov 04.
Artigo em Inglês | MEDLINE | ID: mdl-24216856

RESUMO

We employ conical refraction of light in a biaxial crystal to create an optical bottle for photophoretic trapping and manipulation of particles in gaseous media. We show that by only varying the polarization state of the input light beam the optical bottle can be opened and closed in order to load and unload particles in a highly controllable manner.

4.
Opt Lett ; 33(12): 1312-4, 2008 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-18552942

RESUMO

Circularly polarized (CP) femtosecond laser light focused into fused silica produces a permanent recording of optical helicity. Material modification is in the form of highly ordered submicrometer chiral structures whose handedness follows the handedness of the CP light. The evolution of the ordered structures from chaotic modification is described.

5.
Opt Lett ; 32(19): 2888-90, 2007 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-17909607

RESUMO

Tightly focused, linearly polarized, femtosecond laser radiation can produce highly birefringent nanograting structures inside fused silica glass. Here we report that when the polarization direction of the femtosecond light is changed, old nanogratings are erased and simultaneously replaced with new ones whose orientation is solely determined by the polarization of the rewrite beam. We also show that these volume nanogratings can be rewritten 1000 times with little degradation in their quality.

6.
Opt Lett ; 32(11): 1459-61, 2007 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-17546154

RESUMO

We demonstrate that within a restricted optical pulse duration-pulse energy parameter space tightly focused femtosecond laser radiation can be used to fabricate porous capillaries in bulk fused silica glass by simply moving the laser focus through the material. We show that the rate of penetration of liquids into the porous capillaries can be controlled by the laser polarization, which determines their morphology. The fluid propagation is measured using the form birefringence of nanocrack/nanovoid structures produced inside the capillaries. We also demonstrate the nanofiltration capabilities of the capillaries by separating the relatively small molecules of Rhodamine 6G dye from their solvent.

7.
Phys Rev Lett ; 96(5): 057404, 2006 Feb 10.
Artigo em Inglês | MEDLINE | ID: mdl-16486984

RESUMO

Linearly polarized femtosecond light pulses, focused inside fused silica to an intensity that leads to multiphoton ionization, produce arrayed planes of modified material having their normal parallel to the laser polarization. The planes are < or = 10 nm thick and are spaced at approximately lambda/2 in the medium for free space wavelengths of both 800 and 400 nm. By slowly scanning the sample under a fixed laser focus, order is maintained over macroscopic distances for all angles between the polarization and scan direction. With the laser polarization parallel to the scan direction we produce long-range Bragg-like gratings. We discuss how local field enhancement influences dielectric ionization, describe how this leads to nanoplane growth, why the planes are arrayed, and how long-range order is maintained.

8.
Phys Rev Lett ; 97(25): 253001, 2006 Dec 22.
Artigo em Inglês | MEDLINE | ID: mdl-17280346

RESUMO

We demonstrate a shot-to-shot reduction in the threshold laser intensity for ionization of bulk glasses illuminated by intense femtosecond pulses. For SiO2 the threshold change serves as positive feedback reenforcing the process that produced it. This constitutes a memory in nonlinear ionization of the material. The threshold change saturates with the number of pulses incident at a given spot. Irrespective of the pulse energy, the magnitude of the saturated threshold change is constant (approximately 20%). However, the number of shots required to reach saturation does depend on the pulse energy. Recognition of a memory in ionization is vital to understand multishot optical or electrical breakdown phenomena in dielectrics.

9.
Opt Lett ; 30(14): 1867-9, 2005 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-16092372

RESUMO

We fabricate microchannels in fused silica by femtosecond laser irradiation followed by etching in diluted hydrofluoric acid. We show a dramatic dependence of the etch rate on the laser polarization, spanning 2 orders of magnitude. We establish the existence of an energy-per-pulse threshold at which etching of the laser-modified zones becomes highly polarization selective. The enhanced selective etching is due to long-range, periodic, polarization-dependent nanostructures formed in the laser-modified material.

10.
Opt Lett ; 29(12): 1312-4, 2004 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-15233419

RESUMO

We identify two states of stress induced in waveguides fabricated by femtosecond lasers in fused silica and show how they can be relieved by annealing. In-plane stress and stress concentration are revealed through birefringence and loss measurements. Another kind of laser-induced stress appears in the form of swelling of the glass surface when waveguides are written near the surface and is a manifestation of confined rapid material quenching. By annealing the sample we reduce the losses by approximately 30% (at 633 nm) and decrease the birefringence by a factor of 4 in fused silica.

11.
Opt Express ; 12(5): 916-28, 2004 Mar 08.
Artigo em Inglês | MEDLINE | ID: mdl-19474902

RESUMO

Low power cw laser radiation at lambda=1.32microm was coupled into a chemically etched,metalized Near-Field Scanning Optical Microscopy (NSOM) fiber probe to generate a stable microbubble in water as well as in other fluids.The microbubble,which was attached to the end face of the fiber probe,was used to trap, manipulate and mix micron sized glass,latex and fluorescent particles as well as biological material.

12.
Opt Lett ; 28(12): 1043-5, 2003 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-12836773

RESUMO

A femtosecond laser beam focused inside fused silica and other glasses can modify the refractive index of the glass. Chemical etching and atomic-force microscope studies show that the modified region can have a sharp-tipped cone-shaped structure with a tip diameter as small as 100 nm. Placing the structure near the bottom surface of a silica glass sample and applying a selective chemical etch to the bottom surface produces clean, circular, submicrometer-diameter holes. Holes spaced as close to one another as 1.4 microm are demonstrated.

13.
J Microsc ; 211(Pt 1): 37-47, 2003 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-12839549

RESUMO

Bent near-field optical probes for biological applications have been fabricated using a combination of a two-step chemical etching method and focused ion beam milling to create a well-defined aperture. The transmission efficiencies have been evaluated as a function of laser wavelength (lambda) and aperture size (D) for both large and small core fibres. The probe transmission behaviour follows a (D/lambda)3 relationship. The double-etched probes are compared to pulled probes fabricated from highly GeO2-doped dispersion compensating fibre and a standard single-mode optical fibre. The transmission efficiencies of both types of pulled probes are approximately two orders of magnitude lower than double-etched probes with similar aperture sizes. To demonstrate the utility of the various probes, their imaging performance has been evaluated for samples of polymer beads and phase-separated phospholipid monolayers of dipalmitoylphosphatidylcholine or cholesterol/phosphatidylcholine/sphingomyelin mixtures. Both pulled and double-etched probes are suitable for fluorescence imaging of polymer spheres. However, pulled probes are rapidly damaged at the higher input laser intensities required for fluorescence imaging of monolayer samples doped with < 1% of a fluorescent dye-labelled lipid. The images obtained with the double-etched probes show excellent spatial resolution and signal/noise, illustrating the potential of such probes for imaging of biological samples.


Assuntos
Microscopia de Fluorescência/instrumentação , Microscopia de Varredura por Sonda/instrumentação , Microscopia de Força Atômica , Microscopia Eletrônica de Varredura , Microscopia de Fluorescência/métodos , Microesferas , Fosfolipídeos/química , Polímeros/química , Espectrometria de Fluorescência
14.
Opt Express ; 11(7): 775-81, 2003 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-19461790

RESUMO

The combination of selective chemical etching and atomic force microscopy has been used for the first time to make ultra-high spatial resolution (20 nm) index of refraction profiles of femtosecond laser modified structures in silica glass.

15.
Opt Express ; 11(21): 2775-82, 2003 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-19471393

RESUMO

A single optical fiber probe has been used to trap a solid 2 ìm diameter glass bead in 3-D in water. Optical confinement in 2-D was produced by the annular light distribution emerging from a selectively chemically etched, tapered, hollow tipped metalized fiber probe. Confinement of the bead in 3-D was achieved by balancing an electrostatic force of attraction towards the tip and the optical scattering force pushing the particle away from the tip.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...