Bessel beam

About: Bessel beam is a research topic. Over the lifetime, 1946 publications have been published within this topic receiving 42264 citations.

Laser Nonlinear Propagation In Gases: The Properties And Applications

Abstract: When an intense femtosecond laser pulse propagates in a gas, it undergoes filamentation, a spectacular process where the pulse spatial, spectral and temporal characteristics change considerably. A thin short-lived plasma column is formed in the wake of the propagating pulse. My PhD work has been dedicated to the further understanding of the filamentation process. In a first part, I compare the properties of a usual filament with those of a filament formed by a femtosecond laser pulse with a Bessel beam profile. Using a laser pulse of same intensity and duration, I show that a Bessel beam can form a longer and more uniform plasma column in air, but that the plasma density is significantly lower. In a second part, I show that it is possible to increase considerably the lifetime of the plasma column, using a dual femtosecond/nanosecond laser pulse technique. To obtain an increased lifetime over a significant segment of a plasma column, I rely on the properties of Bessel beams in the nonlinear regime developed in the first chapter. In a third part, I study the dynamics of free electrons that are produced in the filamentation process. To do this, I have developed a specially designed current probe. Experiments reveal a very rich behaviour. The longitudinal displacements of electrons in the plasma column depend sensitively on the nature of the gas and its pressure as well as on the laser polarization of the laser. I propose a model to explain this behaviour. The direction of electron flow results from the competition between pure laser forces and a Coulomb wake field force. In the last chapter, I study filamentation in a Helium gas. This required improving the laser characteristics in order to reach the necessary power for filamentation. Improved characteristics have been achieved by implementing a planar compression stage which shortened the laser pulse from 50 fs to 10 fs without appreciable energy loss. The first experimental evidence for filamentation in He is presented at the end of the thesis. Agreement is found with a numerical simulation.

Generating and analyzing non-diffracting vector vortex beams

Abstract: We experimentally generate non-diffracting vector vortex beams by using a Spatial Light Modulator (SLM) and an azimuthal birefringent plate (q-plate). The SLM generates scalar Bessel beams and the q-plate converts them to vector vortex beams. Both single order Bessel beam and superposition cases are studied. The polarization and the azimuthal modes of the generated beams are analyzed. The results of modal decompositions on polarization components are in good agreement with theory. We demonstrate that the generated beams have cylindrical polarization and carry polarization dependent Orbital Angular Momentum (OAM).

High-aspect ratio damage and modification in transparent materials by tailored focusing of femtosecond lasers

Abstract: We discuss studies of laser damage inside various transparent materials (glasses, polymers, sapphire, diamond) caused by femtosecond lasers at 515, 800, and 1030 nm, with nJ to mJ pulse energies, single-shot to 2 MHz repetition rates, single and 10 ns burst-mode pulses, chirped pulses, and linear, circular, and radial beam polarizations. Experiments have created high-aspect damage features and voids using aberration-controlled focusing, axicon-formed Bessel beams with <1 μm diameter central lobes extending hundreds of microns through the materials, and tightly focused lines (~1 μm × <100 μm). Mechanisms include self-focusing, filamentation, and material expansion/compaction and expulsion.

Dielectric Metalens for Superoscillatory Focusing Based on High-Order Angular Bessel Function

Abstract: The phenomenon of optical superoscillation provides an unprecedented way to solve the problem of optical far-field label-free super-resolution imaging. Numerous optical devices that enable superoscillatory focusing were developed based on scalar and vector diffraction theories in the past several years. However, these reported devices are designed according to the half-wave zone method in spatial coordinates. In this paper, we propose a dielectric metalens for superoscillatory focusing based on the diffraction of angular Bessel functional phase modulated vector field, under the inspiration of the tightly autofocusing property of a radially polarized high-order Bessel beam. Based on this kind of metalens with a numerical aperture (NA) of 0.9, the linearly polarized light is converted into a radially polarized one and then focus into a superoscillating focal spot with the size of 0.32λ/NA. This angular spectrum modulation theory involved in this paper provides a different way of designing superoscillatory devices.

Trapping of dielectric microparticles on iron-doped lithium niobate crystal by optical Bessel beam-induced space-charge field

Abstract: We report the trapping of dielectric micro-particles of CaCO3 via dielectrophoretic forces on the surface of Fe doped LiNbO3 (LN:Fe) crystal with recorded volume holographic grating which provides quasi-periodic space-charge electric field distribution on the crystal surface. The non-diffracting Bessel beam approach was used for optical induction of holographic grating by 20÷40 mW power Bessel beam at 532 nm wavelength in photorefractive Y-cut LN:Fe crystal providing the Bessel lattice periodicity of ~40 m and hologram size on the crystal surface of 4 mm. This approach provides the induction of high contrast 2D periodic distribution of electric field on the crystal surface and high quality 2D patterning of microparticles. The particles are trapped on the crystal surface in the areas of refractive index maxima of the Bessel lattice. The physical model was developed to explain the experimental results. The photovoltaic approach of trapping and manipulation of micro- and nanoparticles is promising for applications in photonics, integrated optics and biotechnology.