Showing papers on "Bessel beam published in 1991"

Comparison of the propagation characteristics of Bessel, Bessel–Gauss, and Gaussian beams diffracted by a circular aperture

Abstract: We use the scalar Kirchhoff–Huygens diffraction integral to obtain analytic expressions for both axial and transverse intensity distributions, assuming normal incidence on a circular aperture for four types of incident field: (1) plane wave, (2) Bessel beam, (3) Gaussian beam, and (4) Bessel–Gauss beam. We use the Fresnel approximation to obtain the axial intensity as a function of distance from the aperture. We consider both Fresnel and Fraunhofer diffraction for the case of the transverse intensity distributions. For the axial case, we find that the Bessel–Gauss beam performs worse than the Bessel beam, in terms both of the magnitude of intensity and of its ability to extend a distance from the aperture. In the transverse case, we find that the Bessel–Gauss beam performance in terms of remaining nearly diffraction free over a given distance is highly dependent on the relationship among the aperture radius, the beam waist parameter, and the transverse wave number.

Simple laser accelerator: Optics and particle dynamics

Abstract: When a laser is focused it develops a longitudinal component. This could be used to develop a laser particle accelerator. A lens waveguide array is discussed, and it is shown that such a system could generate high-energy particle beams. The possibility of using a ``diffraction-free'' Bessel beam is discussed, and a possible configuration is suggested. To accelerate electrons from one to a few MeV seems possible using a well-focused, 1-J, 1-ps laser pulse. This would provide a simple proof-of-principle experiment. In order to accelerate heavier particles, such as protons, the injected particle beam would have to be ultrarelativistic such as that produced by the superconducting supercollider.

Pulse-echo imaging using a nondiffracting beam transducer.

Abstract: Conventional ultrasonic transducers generate beams that diffract as they travel. This phenomenon causes images produced in B-mode to be degraded in the far-field of the transducers. Focused transducers are used to improve image quality. Unfortunately, focused transducers have short depth of field. Although multiple pulse transmissions focused at several depths are used to increase the effective depth of field, imaging frame rate is reduced dramatically leading to blurred images of moving objects such as the heart. We present a family of transducers that produce nondiffracting beams of large depth of field. Therefore, uniformly high resolution throughout the imaging area can be obtained without sacrificing the imaging frame rate. In addition, the nondiffracting property of these beams makes the correction for beam diffraction negligible in tissue characterization. This paper reports the results of computer simulations as well as in vitro and in vivo pulse-echo imaging experiments with a nondiffracting transducer. Images are compared to those obtained by conventional focused Gaussian shaded beam transducers and a commercial ACUSON 128 B-scanner. The new transducer has much longer depth of field with higher sidelobes than conventional transducers of the same aperture. Sidelobes can be reduced using the new transducer to transmit and the dynamically focused transducer to receive.

Diffraction-free beam generation using refracting systems

Abstract: An optical refracting system has been designed to transform an input Gaussian laser beam into a diffraction-free Bessel beam. The optical systems characteristics are optimized for ease of fabrication.

Bessel beams propagation through axisymmetric optical systems

Abstract: Analytical expression for the field generated by a Bessel beam through any axisymmetric optical system that can be described by an ABCD ray-transfer matrix is given. Solution is obtained, in the paraxial approximation, by integration of the generalized Huygens-Fresnel diffraction integral. Free space propagation and beam expanders are discussed as particular cases.

Review of Nondiffracting Bessel Beams

Abstract: The theory of nondiffracting beam propagation and experimental evidence for nearly-nondiffractive Bessel beam propagation are reviewed. The experimental results are reinterpreted using simple optics formulas, which show that the observed propagation distances are characteristic of the optical systems used to generate the beams and do not depend upon the initial beam profiles. A set of simple experiments are described which support this interpretation. It is concluded that nondiffracting Bessel beam propagation has not yet been experimentally demonstrated.

Bessel beam generating optical device

Abstract: PURPOSE: To provide a Bessel beam generation device which can change a generation position in the direction of the optical axis CONSTITUTION: This optical device consists of an optical means which consists of a 1st concentric interference fringe hologram 2 and a 2nd hologram 3 and converts an incident laser beam 1 into an annular light beam and a 3rd hologram 4 which is irradiated with the annular light beam 1; and at least one of the 1st and 2nd holograms is shift in the optical axis direction to change the Bessel beam generation position in the optical axis direction COPYRIGHT: (C)1993,JPO&Japio

Holographic Bessel beam amplification

Abstract: The generation of a diffraction‐free Bessel beam from a beam that is originally Gaussian is accompanied by substantial power loss. We employed the technique of holographic intensity amplification to enhance the conversion from a Gaussian beam to a Bessel beam with conversion efficiency approaching 50%. In addition the maximum propagation distance was extended.

Bessel beam generation: theory and application proposal

Abstract: A new method of Bessel beam generation by means of generation of special mode of electromagnetic field in confocal resonator with annular active medium is proposed. The estimations of sizes of " diffraction-free" zone are presented. A proposal is made to apply Bessel beam to accelerate a beam of charged particles