Showing papers on "Bessel beam published in 2010"

Microscopy with self-reconstructing beams

Abstract: A prototype microscope built with self-reconstructing Bessel beams is shown to be able to reduce scattering artifacts as well as increase image quality and penetration depth in three-dimensional inhomogeneous opaque media.

Airy–Bessel wave packets as versatile linear light bullets

Abstract: The generation of spatiotemporal optical wave packets that are resistant to both dispersion and diffraction are attractive for bioimaging applications and plasma physics. By combining Bessel beams in the transverse plane with temporal Airy pulses, scientists now report the first observation of a class of versatile three-dimensional linear light ‘bullets’.

Angular momenta and spin-orbit interaction of nonparaxial light in free space

Abstract: We give an exact self-consistent operator description of the spin and orbital angular momenta, position, and spin-orbit interactions of nonparaxial light in free space. Both quantum-operator formalism and classical energy-flow approach are presented. We apply the general theory to symmetric and asymmetric Bessel beams exhibiting spin- and orbital-dependent intensity profiles. The exact wave solutions are clearly interpreted in terms of the Berry phases, quantization of caustics, and Hall effects of light, which can be readily observedexperimentally.

High aspect ratio taper-free microchannel fabrication using femtosecond Bessel beams

Abstract: We present a systematic study of femtosecond laser microchannel machining in glass using nondiffracting Bessel beams. In particular, our results identify a source and focusing parameter working window where high aspect ratio taper-free microchannels can be reproducibly produced without sample translation. With appropriate source parameters, we machine channels of 2 microm diameter and with aspect ratios up to 40. We propose the filamentation stability of the Bessel beam propagation as the critical factor underlying the controlled and reproducible results that have been obtained.

Light beats the spread: ``non-diffracting'' beams

Abstract: “Non-diffracting” beams do not spread as they propagate. This property is useful in many areas. Here, the theory, generation, properties, and applications of various “non-diffracting” beams, including the Bessel beam, Mathieu beam, and Airy beam is reviewed. Applications include imaging, micromanipulation, nonlinear optics, and optical transfection.

Analytical partial wave expansion of vector Bessel beam and its application to optical binding

Abstract: Explicit partial wave coefficients are derived for nondiffractive vector Bessel beam of arbitrary order and polarization. Calculations based on the analytical partial wave expansion yield results that agree well with recent numerical calculations and experiments on optical binding. We have also investigated how one can tailor the interparticle interaction by overlaying different coatings. It is found that the Ag and low dielectric coating can increase the number of equilibrium positions, whereas the antireflection coating reduces it.

Characterization of a refractive logarithmic axicon.

Abstract: We show that it is feasible to design and manufacture a refractive logarithmic axicon that generates a quasi-diffraction-free/Bessel beam with nearly constant beam size and intensity over a predetermined range. The novel optical element was characterized with both coherent and incoherent light, and good correspondence with the predicted behavior of the intensity distribution and spot size was found. The energy flow was also found to be nearly constant over most of the designed range. Logarithmic axicons may find applications in situations where large depth of field and uniform axial intensity/energy distributions are important.

Diffraction-free beams in thin films.

Abstract: The propagation and transmission of Bessel beams through nano-layered structures has been discussed recently. Within this framework we recognize the formation of unguided diffraction-free waves with the spot size approaching and occasionally surpassing the limit of a wavelength when a Bessel beam of any order n is launched onto a thin material slab with grazing incidence. On the basis of the plane-wave representation of cylindrical waves, a simple model is introduced providing an exact description of the transverse pattern of this type of diffraction-suppressed localized wave. Potential applications in surface science are put forward for consideration.

Realization of curved Bessel beams: propagation around obstructions

Abstract: We present an experimental realization of spiraling and snaking zero-order Bessel beams; light modes designed to deviate from straight-line propagation. We show that these modes can be generated with a tunable lateral deviation, amplitude and axial periodicity using a dynamic adaptive optical element, namely a spatial light modulator. We demonstrate that such beams can elude obstructions placed on the optical axis. We discuss their applications for micromanipulation and within lab-on-a-chip systems.

Goos-Haenchen and Imbert-Fedorov shifts of a nondiffracting Bessel beam

Abstract: Goos-Haenchen and Imbert-Fedorov shifts are diffractive corrections to geometrical optics that have been extensively studied for a Gaussian beam that is reflected or transmitted by a dielectric interface. Propagating in free space before and after reflection or transmission, such a Gaussian beam spreads due to diffraction. We address here the question how the Goos-Haenchen and Imbert-Fedorov shifts behave for a ``nondiffracting'' Bessel beam.

Bessel–like beams with z–dependent cone angles

Abstract: The conventional means of generating Bessel–Gauss beams by axicons in the laboratory results in the distinct disadvantage of an abrupt change in intensity at the boundary of the non–diffracting region. We outline theoretically and then demonstrate experimentally a concept for the creation of Bessel–like beams that have a z–dependent cone angle, thereby allowing for a far greater quasi non–diffracting propagation region.

Ionization-induced conversion of ultrashort Bessel beam to terahertz pulse.

Abstract: We examine the conical terahertz emission from the superluminous ionization front created in air by an axicon-focused femtosecond laser pulse. We develop the theoretical model that explains the experimental results and predicts new possibilities to control terahertz pulse parameters.

Scattering of an unpolarized Bessel beam by spheres

Abstract: The scattering process of an unpolarized Bessel beam through spherical scatterers is investigated. We derive the analytical solutions of scattered fields of x- and y-polarized Bessel beams using a sphere, after which the dimensionless scattering function for an unpolarized Bessel beam is obtained. The dimensionless scattering function is applicable to spherical scatterers of any size on the beam axis or near it. Through numerical simulations, we demonstrate that extreme points exist in the direction or neighboring direction of the conical angle for spherical scatterers on the beam axis, whereas the existence of extreme points depends on the ratio between the spherical scatterers size and central spot size of the Bessel beam.

Gouy phase shift in nondiffracting Bessel beams.

Abstract: The results of a theoretical and experimental investigation of the Gouy effect in Bessel beams are presented. We point out that the peculiar feature of the Bessel beams of being nondiffracting is related to the accumulation of an extra axial phase shift (i.e., the Gouy phase shift) linearly dependent on the propagation distance. The constant spatial rate of variation of the Gouy phase shift is independent of the order of the Bessel beam, while it is a growing function of the transverse component of the angular spectrum wave-vectors, originated by the transverse confinement of the beam. A free-space Mach-Zehnder interferometer has been set-up for measuring the transverse intensity distribution of the interference between holographically-produced finite-aperture Bessel beams of order from zero up to three and a reference Gaussian beam, at a wavelength of 633 nm. The interference patterns have been registered for different propagation distances and show a spatial periodicity, in agreement with the expected period due to the linear increase of the Gouy phase shift of the realized Bessel beams.

Generation and control of the spiraling zero-order Bessel beam.

Abstract: We report on the generation of a spiraling zero order Bessel beam by means of conventional axicon and the phase hologram. Obtained results are in a fairly good agreement with the theoretical predictions.

Modeling the sharp focus of a radially polarized laser mode using a conical and a binary microaxicon

Abstract: Based on the radial finite-difference time domain method we numerically show that the illumination of a conical glass microaxicon of base radius 7 μm and height 6 μm (numerical aperture NA=0.6) by a radially polarized annular R-TEM01 laser mode of wavelength λ=1 μm produces, 20 nm apart from the cone apex, a sharp focus of transverse diameter FWHM=0.30λ and longitudinal (axial) width FWHMz=0.08λ. The focal spot area at half-maximum intensity is HMA=0.071λ2. For comparison the focus diameter reported here is 1.7 times smaller than the diameter of the minimal diffraction spot (Airy disk, NA=1) of FWHM=0.51λ, with its area being 2.87 times smaller than that of the Airy disk HMA=0.204λ2. Also it is smaller than the diameter of a focal spot formed by a lens with NA=0.6 in an immersion medium n=1.5, FWHM=0.51λ/n NA=0.55λ, smaller than the diffraction limit in the medium (n=1.5, NA=1) FWHM=0.51λ/n=0.33λ and smaller than the focusing limit for the Bessel beam (NA=1)FWHM=0.36λ.

Bessel beam transformation by anisotropic crystals

Abstract: Transformation of Bessel beams by biaxial and uniaxial crystals is investigated experimentally and theoretically. Experimental observations show beam symmetry changing and formation of complex intensity patterns, depending on the orientation of the crystal. These patterns can appear as a regular system of peak intensities. Results of numerical calculations support the experimental findings.

Generation of J(0) Bessel beams with controlled spatial coherence features.

Abstract: An alternative method to generate J0 Bessel beams with controlled spatial partial coherence properties is introduced. Far field diffraction from a discrete number of source points on an annular region is calculated. The average for different diffracted fields produced at several rotation angles is numerically calculated and experimentally detected. Theoretical and experimental results show that for this particular case, the J0 Bessel beam is a limit when the number of points tends towards infinity and the associated complex degree of coherence is also a function of the number of points.

Ultrafast Bessel beams for high aspect ratio taper free micromachining of glass

Abstract: Although ultrafast lasers have demonstrated much success in structuring and ablating dielectrics on the micrometer scale and below, high aspect ratio structuring remains a challenge. Specifically, microfluidics or lab-on-chip DNA sequencing systems require high aspect ratio sub-10 μm wide channels with no taper. Micro-dicing also requires machining with vertical walls. Backside water assisted ultrafast laser processing with Gaussian beams allows the production of high aspect ratio microchannels but requires sub-micron sample positioning and precise control of translation velocity. In this context, we propose a new approach based on Bessel beams that exhibit a focal range exceeding the Rayleigh range by over one order of magnitude. An SLM-based setup allows us to produce a Bessel beam with central core diameter of 1.5 μm FWHM extending over a longitudinal range of 150 μm. A working window in the parameter space has been identified that allows the reliable production of high aspect ratio taper-free microchannels without sample translation. We report a systematic investigation of the damage morphology dependence on focusing geometry and energy per pulse.

Bessel-Gaussian beam phase fluctuations in randomly inhomogeneous media

Abstract: Bessel-Gaussian beam phase fluctuations in randomly inhomogeneous media are studied. The results of calculations by the method of smooth perturbations of the variance of phase fluctuations of the above type of beams in the turbulent atmosphere are presented. The effect of the relative weakening of Bessel-Gaussian beam phase fluctuations in comparison with the case of a plane wave is revealed. A weak dependence of the phase fluctuation variance on the parameters of the Gaussian beam factor is observed. Gaussian beam phase fluctuations are spatially inhomogeneous: the ratio of the variances of the beam phase fluctuations at an out-of-optical-axis point to those at its optical axis is minimum in the Bessel beam maxima and maximum in the minima.

Generation of J0 Bessel Beams with controlled spatial coherence features

Abstract: An alternative method to generate J0 Bessel beams with controlled spatial partial coherence properties is introduced. Far field diffraction from a discrete number of source points on an annular region is calculated. The average for different diffracted fields produced at several rotation angles is numerically calculated and experimentally detected. Theoretical and experimental results show that for this particular case, J0 Bessel beam is a limit when the number of points tends towards infinity and the associated complex degree of coherence is also a function of the number of points.

Propagation properties of Bessel and Bessel–Gaussian beams in a fractional Fourier transform optical system

Abstract: The properties of Bessel–Gaussian beams (BGBs) and Bessel beams (BBs) propagating through a fractional Fourier transform (FRT) optical system have been investigated. The analytical transformation formulae for BBs and BGBs propagation through a FRT optical system are derived based on definition of the FRT in the cylindrical coordinate system. By using the derived formula, numerical examples are illustrated.

Diffraction-free propagation of subwavelength light beams in layered media

Abstract: Self-collimation of tightly localized laser beams demonstrated in periodic media relies on a perfect-matched rephasing of the Fourier constituents of the wavefield induced by a plane isofrequency curve. An alternate way paved for the achievement of such a phase matching condition developed a suitable spatial filtering in order to select those frequencies experiencing the same phase velocity projected over a given orientation. In principle this procedure is valid for complex structured metamaterials. However, a great majority of studies have focused on free-space propagation leading to the well-known Bessel beams. This paper is devoted to the analysis of this sort of nondiffracting beams traveling in one-dimensional metallic-dielectric photonic crystals. Specifically we present a family of localized radiation modes in multilayered periodic media, where in-phase superposition of p-polarized waves leads to radiative confinement around the beam axis. Excitation of surface plasmon polaritons yields an enhanced localization normally to the interfaces. Subwavelength beam widths along an infinitely long distance might potentially be obtained.

Study of non-diffracting light beams from broad-stripe edge-emitting semiconductor lasers

Abstract: Broad-stripe edge-emitting semiconductor lasers have been used to obtain propagation-invariant (nondiffracting) light beams with powers and diameters of the central ray acceptable for optical manipulation and tweezing. The results of investigations of the propagation of Bessel beams generated from broad-stripe lasers with spectrally selective resonator show that the spatial homogeneity of emission plays a much greater role than the temporal coherence in the formation of Bessel beams. The main factors limiting the length of non-diffracting beam propagation (without distortion of the central ray) are the astigmatism and multimode character of laser radiation.

Transformation of high-order Bessel vortices in one-dimensional photonic crystals

Abstract: Based on the matrix method, a theory of propagation of vector Bessel light beams (BLBs) in a one-dimensional photonic crystal (1DPC) is developed. The transmission through a 1DPC (with and without a defect impurity—a layer of a uniaxial crystal) has been calculated and analyzed. Based on this, a method of highly effective generation of Bessel vortices has been proposed. The conditions for the highly effective transformation of an incident (m−1)-order Bessel beam into a transmitted through 1DPC Bessel beam of (m+1) order are derived. The influence of parameters of the structure (refractive indices and thicknesses of the 1DPC component) and cone angle of the incident BLB on the process of this transformation is analyzed.

Large focal depth of THz imaging system based on quasi-Bessel beams

Abstract: THz imaging technology will be potentially used in structure's defects detection, package inspection, on line product quality control, security screening or other nondestructive testing fields. But due to its long wavelength, it is difficult to obtain high spatial resolution and large focal depth simultaneously for conventional imaging systems. In this paper, diffraction free quasi-Bessel beams are used in THz imaging system to enhance the focal depth with high spatial resolution. PE conical lenses were designed and fabricated to generate quasi Bessel beams. Numeric simulations demonstrated that with suitable parameters of the conical lens, the diffraction free propagation distance and effective focal depth of the imaging system are easily reached up to 165mm, 100mm, respectively. A THz imaging system based on quasi-Bessel beams was established, and results were in good agreement with simulations. Furthermore, the inner defects built-in artificially in phenolic foam samples with diameter of 0.4mm were figured out successfully.