Showing papers on "Bessel beam published in 1997"

Demonstration of the Bessel-X pulse propagating with strong lateral and longitudinal localization in a dispersive medium.

Abstract: We report experiments on ultrashort pulses that maintain their strong lateral and longitudinal localization in a bulk linear highly dispersive medium. The diameter of the central peak and the temporal width of the field autocorrelation function of the pulses were 20 µm and 210 fs, respectively, and the spatiotemporal structure was preserved in the course of 7-cm propagation in the sample. The pulses were obtained with a computer hologram designed for generating the Bessel beam and can be applied in femtosecond laser optics.

Laser-driven acceleration with bessel beams

Abstract: The possibility of enhancing the energy gain in laser-driven accelerators by using Bessel laser beams is examined. A formalism based on Huygens' principle is developed to describe the diffraction of finite power (bounded) Bessel beams. An analytical expression for the maximum propagation distance is derived and found to be in excellent agreement with numerical calculations. Scaling laws are derived for the propagation length, acceleration gradient, and energy gain in various accelerators. Assuming that the energy gain is limited only by diffraction (i.e., in the absence of phase velocity slippage), a comparison is made between Gaussian and Bessel beam drivers. For equal beam powers, the energy gain can be increased by a factor of ${\mathrm{N}}^{1\mathrm{/}2}$ by utilizing a Bessel beam with N lobes, provided that the acceleration gradient is linearly proportional to the laser field. This is the case in the inverse free electron laser and the inverse Cherenkov accelerators. If the acceleration gradient is proportional to the square of the laser field (e.g., the laser wakefield, plasma beat wave, and vacuum beat wave accelerators), the energy gain is comparable with either beam profile.

Properties of Bessel beams generated by periodic gratings of circular symmetry

Abstract: We show that the transmission of a periodic grating with circular symmetry can be composed of the sum of the transmissions of positive and negative axicons of different orders. The properties of the light beams generated by the gratings can be understood from the well-known properties of the light beam of an axicon, which is approximately a Bessel beam of zeroth order. The method is applied to a circular binary phase grating, which is investigated both theoretically and experimentally in the spatial domain and the Fourier domain. A simple and accurate method for determining the focal length of a lens with use of Bessel light beams is presented.

Axial intensity of apertured Bessel beams

Abstract: We give a simple interpretation of a recently noted phenomenon, namely, the resemblance between the axial intensity of an apertured Bessel beam and the squared profile of the windowing function. We also discuss how this effect can be used to control the axial behavior of the beam, and we present examples for the case of a flattened Gaussian profile as aperturing function.

Optical parametric oscillator pumped by a Bessel beam

Abstract: We demonstrate operation of a KTP optical parametric oscillator (OPO) pumped by a Bessel beam for the first time to our knowledge. It is shown that the output of the OPO has a transverse profile, which is consistent with noncollinear phase-matching relations defined by a conical pump. The central spot and ring related to the pair of signal and idler beams were generated in the OPO. By adjusting the OPO cavity mirrors, we easily selected the lowest-order mode as well as the higher-order transverse modes in the central spot. Bessel beam pumping was shown to be useful, providing tubular beam coupling into OPO cavity modes. The OPO threshold pump energy was ~100 muJ in a 6-ns pulse.

Truncation of a two-dimensional nondiffracting cos beam

Abstract: The cosine (cos) beam is the two-dimensional counterpart of the three-dimensional nondiffracting beam, the Bessel beam. The propagation behavior of the truncated cos beam is similar to that of the truncated Bessel beam. The propagation of the apertured cos beams is studied. The pseudonondiffracting beam proposed recently by Rosen [Opt. Lett.20, 423 (1995)] can be obtained by the proper truncation of the cos beam. The temporal nondispersive pulse can be treated in a similar way, owing to the space–time analogy.

Bessel beam generating method and optical scanning device using the same

Abstract: PROBLEM TO BE SOLVED: To generate a Bessel beam with large depth of focus by making a laser beam incident on a diffraction optical element consisting of a binary optical element having optical performance nearly equivalent to that of a conic prism. SOLUTION: The diffraction optical element 1 as a Bessel beam generating means includes the projection surface of the binary optical element, having the optical performance nearly equivalent to that of a comic prism, as a diffraction surface 1a. The incident laser beam L is made incident almost in the state of a plane wave (nearly parallel luminous flux) on the diffraction optical element. The Bessel beam BB has an intensity distribution which is alsmot in proportion to the square of a 0-degree Bessel function of 1st class. This incident laser beam L is coherent laser light and made incident on the diffraction optical element 1 almost in the state of the plane wave. Then a laser beam projected from the diffraction optical element 1 forms a comic wave and generates a Bessel beam BB in an area wherein laser beams projected from both the sides of the optical axis interfere with each other. COPYRIGHT: (C)1998,JPO

Generation of Nearly Diffraction-Free Beams Using a New Optical System

Abstract: A new optical system which can efficiently generate the nearly diffraction-free beams is proposed and its characteristics are investigated by numerical analysis. This optical system consists of a new optical element called a DCC (double-concave-cone) lens and an objective lens with a large numerical aperture, and can generate the Bessel beam and also the Bessel-Gauss beam. The maximum propagation distance of nearly diffraction-free beams generated by the system agrees with its theoretical value for the Bessel beam.

Directional narrowing of the diffractive pattern through a combination of spherical and spiral optical elements within a single aperture

Abstract: The intensity pattern produced by the zero-order Bessel beam can be squeezed along certain directions if it interferes with the Bessel beam of a higher order. The concept of directional narrowing can be extended onto the zone plates by the division of the aperture into a set of concentric annuli; within some of the apertures the phase function of the spherical optical element is substituted or supplemented by the spiral optical element. The proposed approach is verified by the numerical simulation of the interference of Bessel beams, linear axicons, and spherical zone plates of zero order and second order.

Solid state laser and pumping method therefor

Abstract: PROBLEM TO BE SOLVED: To obtain an edge pumping system solid state laser in which both high output and high quality are realized. SOLUTION: A parallel pumping light 1 is converted through a Bessel beam optical system 10 into a Bessel beam which is then directed to the solid state laser medium 40 in an edge pumping system solid state laser. The Bessel beam can have a longer depth of focus for fixed beam diameter and when the oscillation mode region of solid state laser medium 40 is confined in a pumping region determined by the depth of focus and the beam diameter, both high output and high quality can be realized.

Raman conversion of femtosecond laser pulses via Bessel beam pump geometry

Abstract: waist and curvature in the transverse xly-plane in dependence on the propagation coordinate z. Thus, in ansatz (1) the space-time coupling is explicitly taken into account. The complex function I$( z, -q) describes the temporal pulse shape. Note that by use of the Gaussian ansatz (1) a generalized time-dependent ABCDmatrix formalism for the beam parameters can be established analogous to Ref. 2. This dramatically reduces the huge numerical expense of directly three-dimensional modeling as done in Ref. 3 and enables the investigation of an sufficiently extended set of laser parameters to determine the ultimate limitations to the pulse duration in KLM lasers. The temporal pulse shape transformation by the solid-state gain medium is governed by the equation

Optical element for laser beam generation and bar code reader using the same

Abstract: PROBLEM TO BE SOLVED: To read the bar code with minimum line width over wide range by expressing a curved line, which expresses the ridge line of a cross section including an optical axis while being rotationally symmetrical to the optical axis, as a non-linear function which can not be differentiated on the optical axis, increasing the inclination at the part of the ridge line closer to the optical axis and providing an optical element having a little inclination of the ridge line away from the optical axis. SOLUTION: The curved line of ridge lines D' and D" of the cross section cut by a plane including an optical axis 4 while being rotationally symmetrical to the optical axis 4 uses an optical element 3 for laser beam generation in the form expressed by the non-linear function which can not be differentiated on the optical axis 4. The light to be made incident to this optical element 3 for laser beam generation is divided to the optical axis 3, two light flux C' and C" emitted from the element 3 is mutually interferred and light intensity is gradually attenuated. Therefore, this element 3 generates the long focus laser beam similar to a Bessel beam. Besides, the inclination of ridge lines D' and D" of the element 3 closer to the optical axis 4 is increased but the inclination away from the optical axis 4 is decreased and a condensed light spot diameter is reduced.

Optical Measurements Using Bessel Beams

Abstract: The characterization of optical beams generally involves interferometric instrumentation where, most often, a reference arm must be stabilized to a fraction of a wavelength. The classical methods of interferometry are well suited for the testing of optical components in clean, vibration-free laboratories. However it happens frequently that optical beams are used for sensing surface deformations in various industries; it turns out that, in most industrial environments, conditions are adverse to interferometric measurements. In this paper we describe an optical technique that provides a direct reading of the curvature of an optical wavefront without the requirement of interferometric stabilility. The physical principle behind the technique is the phase sensitivity of the interference pattern produced by copropagating Bessel beams. The technique is robust against vibrations since it does not involve any reference arm; however it yields global information about optical beams, and not pointlike information as do most interferometric instruments. The technique is also appropriate to the measurement of the nonlinear properties of optical materials. We recall that, in recent years, the optical characterization of various types of nonlinear materials has become a subject of growing importance due to the needs of photonic technology.