Showing papers on "Bessel beam published in 1999"

An experiment to study a “nondiffracting” light beam

Abstract: We present a simple experiment by which a student can generate and study a zeroth-order Bessel beam. Such beams are often termed nondiffracting (propagation invariant) as they have a central maximum that can propagate for extended distances without experiencing appreciable spreading.

Noncollinear second-harmonic generation in periodically poled KTiOPO4 excited by the Bessel beam.

Abstract: Frequency doubling in periodically poled KTiOPO(4) excited by the Bessel-like distribution of the fundamental radiation has been investigated. Theoretical analysis and experiments show that the use of noncollinear geometry provides new possibilities for engineering nonlinear interactions in periodically poled crystals. We demonstrate conversion of the ring-shaped fundamental mode to the axial second-harmonic beam with 30% efficiency for 220-muJ Q -switched Nd:YAG pulses.

Generation of Bessel light beams under the conditions of internal conical refraction

Abstract: A new optical effect involving transformation of the order of a Bessel beam from the zeroth to the first during propagation of light in a biaxial crystal was investigated theoretically and experimentally. The beam transformation occurs during propagation of circularly polarised light along the optical axes of the crystal under the conditions of internal conical refraction. It is shown that there is a possibility of the total transformation of the input-field energy into a first-order Bessel beam when the length of the crystal or the cone angle of the incident beam are selected appropriately.

Analysis of Gaussian beam and Bessel beam driven laser accelerators.

Abstract: This paper presents a comparison of Gaussian and Bessel beam driven laser accelerators. The emphasis is on the vacuum beat wave accelerator (VBWA), employing two laser beams of differing wavelengths to impart a net acceleration to particles. Generation of Bessel beams by means of circular slits, holographic optical elements, and axicons is outlined and the image space fields are determined by making use of Huygens{close_quote} principle. Bessel beams{emdash}like Gaussian beams{emdash}experience a Guoy phase shift in the vicinity of a focal region, resulting in a phase velocity that exceeds {ital c}, the speed of light {ital in vacuo}. In the VBWA, by appropriate choice of parameters, the Guoy phases of the laser beams cancel out and the beat wave phase velocity equals {ital c}. The particle energy gain and beam quality are determined by making use of an analytical model as well as simulations. The analytical model{emdash}including the {bold v}{times}{bold B} interaction{emdash}predicts that for equal laser powers Gaussian and Bessel beams lead to identical energy gains. However, three-dimensional, finite-emittance simulations, allowing for detuning, transverse displacements, and including all the electromagnetic field components, show that the energy gain of a Gaussian beam driven VBWA exceeds that of a Bessel beam driven VBWAmore » by a factor of 2{endash}3. The particle beam emerging from the interaction is azimuthally symmetric and collimated, with a relatively small angular divergence. A table summarizing the ratios of final energies, acceleration lengths, and gradients for a number of acceleration mechanisms is given. {copyright} {ital 1999} {ital The American Physical Society}« less

Generation of Bessel Beam from Equiamplitude-Driven Annular Transducer Array Consisting of a Few Elements

Abstract: We present a method for generating a nondiffraction beam using an annular transducer array. In this method, each element is driven with equiamplitude and with an antiphase from its neighboring elements. Theoretical and experimental analyses of an array of this type have been carried out, and the feasibility of this method is confirmed. The beam from a continuous wave is shown using radiated pressure magnitude distributions and it is shown that there exist most suitable values of the width and number of elements. When the array is driven by a burst signal, the beam propagates as a plane wave which has an amplitude corresponding to the zeroth-order Bessel function of the first kind, J0. Since this beam is realized by an annular array consisting of a few elements, it suggests the possibility of a transducer of this form developing into a source which generates nondiffraction beams.

Conical wave packets: their propagation speed and their longitudinal fields

Abstract: We establish the distinction between free-space Bessel beams (the so-called `diffraction-free beams') and the guided modes of circular cylindrical geometry whose radial profiles take the form of Bessel functions. We explain why these two types of optical beams have different dispersion relations. A free-space Bessel beam can be produced by illuminating a mask with a single transparent ring placed at the focus of a lens; such a beam has group and phase velocities that are equal and larger than c, the speed of light in vacuo. We examine the propagation of polychromatic Bessel beams that can be produced when short pulses are illuminating a mask with one transmission ring; spectral modulation, temporal breakup and loss of fringe visibility can take place under such circumstances. Polychromatic Bessel beams are shown to constitute wave packets whose spatio-temporal field distributions are invariant upon propagation in vacuo; these wave packets have the shape of a double cone, and are sometimes called `X-pulses'. We present experimental evidence of loss of fringe visibility when very short pulses are used to generate such conical wave packets. The coherent superposition of multiple monochromatic Bessel beams can lead to a self-imaging phenomenon along the propagation axis when the spatial frequencies of the Bessel beams in the radial direction are properly selected. We specify the conditions for temporal self-imaging when a polychromatic single Bessel beam propagates in a dispersive medium. Spatio-temporal self-imaging is also possible when multiple polychromatic Bessel beams are propagated in a dispersive medium. We also examine the longitudinal fields associated to Bessel beams and conical wavepackets, and evaluate their suitability for partial acceleration.

Nonlinear propagation of Bessel–Gauss ultrasonic beams

Abstract: We investigate theoretically the properties of the fundamental and second harmonic components of the Bessel beam with a finite aperture, the Bessel–Gauss beam, whose transverse profile is given by the product of Bessel and Gaussian functions. The analysis is based on the linearized and quasilinear solutions of the Khokhlov–Zabolotskaya–Kuznetsov nonlinear wave equation. The analytical and approximate expressions are derived for the fundamental and the second harmonic generation in this beam. It is thereby demonstrated that under certain circumstances, the second harmonic in the Bessel–Gauss beam is nearly radially nondiffracting, and that the beamwidth is approximately one-half of that of the fundamental. This result is an extension to the previous work on the nonlinearity of the Bessel beam, where the infinite extent of the beam has been assumed.

Generation of periodic inhomogeneities in optical breakdown by a Bessel laser beam

Abstract: A model of the appearance of periodic structures in the plasma channel of an extended laser spark is considered. It is shown that sideways delivery of the heating radiation by a Bessel beam to the breakdown region and expansion of the heated plasma result in inhomogeneous refraction and, consequently, give rise to structures with a longitudinal period ~λ/γ2 (λ is the radiation wavelength and γ is the angle of inclination of the beam to the axis). This model is used to account for the results of experiments demonstrating that such structures are not observed in the case of a low-density gas (at pressures of 0.05 bar or less) and short (~0.1 ns) heating pulses.

A generalized modal impulse response and Fourier transform approach to investigate acoustic transient Bessel beams and Bessel bullets

Abstract: A generalized modal space–time impulse response and Fourier transform approach is developed to investigate the general properties of transient Bessel beam (TBB) fields which are generated using planar circular apertures. The approach is based on a modal decomposition of the aperture source distributions which are required to generate the space–time TBB fields. Numerical results are presented to illustrate the general space–time properties of the modal impulse responses and the modal source functions. The on-axis far field for the finite aperture is shown to be simply related to the lowest order term in the modal expansion. The space–time properties of the acoustic field for a particular type of band-limited TBB field which is designated as an acoustic Bessel bullet (BB) are then investigated. Some numerical results are presented to illustrate the space–time properties of acoustic BB fields generated from an infinite aperture. Analogous on-axis harmonic results from a finite aperture are presented. These latter results clearly indicate that the higher-order modes exhibit spatial rates of decay which are greater than the inverse range decay for the lowest order mode.

Spatial and spectral properties of stimulated Rayleigh-wing scattering pumped with a Bessel beam: role of four-photon parametric processes

Abstract: Stimulated Rayleigh-wing scattering is studied here in various liquids excited with a Bessel beam that allows a complete spatial separation between the transmitted exciting light and the scattered light. The results show that a large Stokes spectral band displaying substructures is obtained in the absence of self-focusing, cross-focusing, self-phase modulation, and cross-phase modulation. An interpretation is proposed based on the role of cascade Stokes–anti-Stokes coupled scattering processes.

Dynamics of periodic structures in an extended laser spark

Abstract: The time scans of the intrinsic and scattered heating radiations of plasma foci, arising in the spark channel of the optical gas breakdown in a Bessel beam, were investigated. The experiments were carried out in argon at atmospheric pressure by using the heating radiation from a powerful nanosecond neodymium laser. The influence of independent preionisation and of the presence of aerosol particles was studied separately. The results indicate the appearance of bright foci against the background of the initially almost homogeneous plasma. The location of the foci in the longitudinal direction and the dynamics of the emitted radiation by them make it possible to assign the observed inhomogeneities to two quasi-periodic structures with periods differing almost by an order of magnitude. The above structures result from the operation of various mechanisms of the formation of inhomogeneities. (interaction of laser radiation with matter. laser plasma)

Spatial distortions of a Bessel beam in a Kerr-type medium

Abstract: We report on the observation of far field spatial distortions of a Bessel beam after passing through a Kerr liquid. A co-axial ring structure has been observed to occur at some threshold power. It consists of two closely spaced ( 1 . 5-3 . 5 mrad)sharp rings of comparable intensity and a diffuse inner ring of smaller intensity separated by 8-9 mrad. Evolution of the farfield pattern with moving the sample along the propagation path of the Bessel beam shows strong dependence of beam distortions upon the position of the sample. The phenomenon is supposed to be due to nonlinearly induced phase aberrations resulting in the distortion of angular spectrum.Keywords: Bessel beam, beam distortion, nonlinear propagation, optical Kerr effect, nonlinear refraction Introduction About a decade ago Durnin and co-workers"2 proposed the possibility of producing nondiffracting light beams whichhave a transverse intensity distribution proportional to the square of zeroth-order Bessel function of the first kind j0 .

Second harmonic generation with Bessel fundamental beam

Abstract: . Theoretical treatment of nonlinear. three-wave interaction and second harmonic generation (SHG) of Bessel fundamentalbeams in case of collinear phase matching is reported. The expressions of power and conversion efficiency of SHG ofBessel fundamental beams are found. We also demonstrate operation of SHG pumped by a Nd:YAG Bessel beam using}W*P nonlinear crystal. It is shown that the output of SHG of Bessel beam has a transverse profile and its conversionefficiency is higher than that of the Gaussian beam.Keywords: Second harmonic generation, Bessel pump beam, KDP nonlinear crystal. 1. INTRODUCTION During the past few years the properties of nondiffrating (Bessel) light beams have been under extensive consideration. 1 2.3 especially in the field of nonlinear optics. There are few studies published such as Nonlinear Optics of Bessel beams . Optical parametric oscillator pumped by a Bessel beam . which have given interesting results. The properties of Besselbeam J(.) are 6 . Planar wavefronts (nonuniform intensity distributions in the transverse plane).

Atom guiding along "non-diffracting" light beams

Abstract: Summary form only given. Recent advances in cold atom physics have seen the emergence of the area of atom guiding along hollow core optical fibres and also along light beams. Both employ the optical dipole force which for suitably tuned light can restrict the atoms to the dark hollow region of the fibre or the light beam. In this work, we discuss and analyse a novel scheme of channelling cold atoms into a high-order Bessel beam (via a high-order Laguerre-Gaussian beam) and demonstrate an efficient method of producing such beams.

Efficient generation of Bessel beams

Abstract: Andrzej Kolodziejczyk**, and Javier Morales**Unjversjdad Nacional de Colombi Ssede MedellIn, Physics Department, A.A. 3840 MedellIn, Colombia** Institute ofPhysics, Warsaw University ofTechnology, Koszykowa75, 00-662 Warsaw, Poland# on leave from: Institute ofApplied Optics, Kamionkowska 18, 03-805 Warsaw, PolandABSTRACTA novel and efficient method for Bessel beams generation is proposed. It relies on using a toroidal zoneplate as an element forming the ring focus and subsequent Fourier transforming of the ring focus into theBessel beam. The proposed solution, thanks to focusing of all illuminating wave into the ring focus allowsto achieve greater efficiency than earlier solutions. Moreover it enables to generate higher order Besselbeams by adding a linear angular phase term to the transmittance of the zone plate. The proposed methodis confirmed by numerical simulations.Key words: Bessel beams, zone plates, diffractive optical elements.The concept of the Bessel beam was introduced for the first time by Durnin in 1987 [1]. In the general case as theBessel beam it is understood a free-space solution of the wave equation which is separable for transversal and perpendicularco-ordinates and possesses a well defined central peak. In the simplest (and paraxial) case it is given by: