Showing papers on "Bessel beam published in 2011"

Rapid three-dimensional isotropic imaging of living cells using Bessel beam plane illumination

Abstract: A key challenge when imaging living cells is how to noninvasively extract the most spatiotemporal information possible. Unlike popular wide-field and confocal methods, plane-illumination microscopy limits excitation to the information-rich vicinity of the focal plane, providing effective optical sectioning and high speed while minimizing out-of-focus background and premature photobleaching. Here we used scanned Bessel beams in conjunction with structured illumination and/or two-photon excitation to create thinner light sheets (<0.5 μm) better suited to three-dimensional (3D) subcellular imaging. As demonstrated by imaging the dynamics of mitochondria, filopodia, membrane ruffles, intracellular vesicles and mitotic chromosomes in live cells, the microscope currently offers 3D isotropic resolution down to ∼0.3 μm, speeds up to nearly 200 image planes per second and the ability to noninvasively acquire hundreds of 3D data volumes from single living cells encompassing tens of thousands of image frames.

Single Gradientless Light Beam Drags Particles as Tractor Beams

Abstract: Usually a light beam pushes a particle when the photons act upon it. We investigate the optical forces by nonparaxial gradientless beams and find that the forces can drag suitable particles all the way towards the light source. The major criterion of realizing the backward dragging force is the strong nonparaxiality of the light beam, which contributes to the pulling force owing to momentum conservation. The nonparaxiality of the Bessel beam can be manipulated to possess a dragging force along both the radial longitudinal directions, i.e., a "tractor beam" with stable trajectories is achieved.

Fourier-space generation of abruptly autofocusing beams and optical bottle beams

Abstract: We demonstrate analytically and experimentally that a circular abruptly autofocusing (AAF) Airy beam can be generated by Fourier-transforming an appropriately apodized Bessel beam whose radial oscillations are chirped by a cubic phase term. Depending on the relation between the chirp rate and the focal distance of the Fourier-transforming lens, it is possible to generate AAF beams with one or two foci, the latter case leading to the formation of an elegant paraboloid optical bottle.

Geometrical interpretation of negative radiation forces of acoustical Bessel beams on spheres

Abstract: Various researchers have predicted situations where the acoustical or optical radiation force on a sphere centered on a Bessel beam is opposite the direction of beam propagation. We develop the analogy between acoustical and optical radiation forces of arbitrary-order helicoidal and ordinary Bessel beams to gain insight into negative radiation forces. The radiation force is expressed in terms of the asymmetry of the scattered field, the scattered power, the absorbed power, and the conic angle of the Bessel beam and is related to the partial-wave coefficients for the scattering. Negative forces only occur when the scattering into the backward hemisphere is suppressed relative to the scattering into the forward hemisphere. Absorbed power degrades negative radiation forces.

Extended focus high-speed swept source OCT with self-reconstructive illumination

Abstract: We present a Bessel beam illumination FDOCT setup using a FDML Swept Source at 1300nm with up to 440kHz A-scan rate, and discuss its advantages for structural and functional imaging of highly scattering samples. An extended focus is achieved due to the Bessel beam that preserves its lateral extend over a large depth range. Furthermore, Bessel beams exhibit a self-reconstruction property that allows imaging even behind obstacles such as hairs on skin. Decoupling the illumination from the Gaussian detection increases the global sensitivity and enables dark field imaging. Dark field imaging is useful to avoid strong reflexes from the sample surface that adversely affect the sensitivity due to the limited dynamic range of high speed 8bit acquisition cards. In addition the possibility of contrasting capillaries with high sensitivity is shown, using inter-B-scan speckle variance analysis. We demonstrate intrinsic advantages of the extended focus configuration, in particular the reduction of the phase decorrelation effect below vessels leading to improved axial vessel definition.

Arbitrary scattering of an electromagnetic zero-order Bessel beam by a dielectric sphere

Abstract: Arbitrary electromagnetic (EM) scattering of a zero-order Bessel beam by a homogeneous water sphere in air is investigated. The radial components of the electric and magnetic scattering fields are expressed using a partial wave series involving the beam-shape coefficients, scattering coefficients of the sphere, and half-conical angle of the wavenumber components of the beam. The 3D scattering directivity plots in the far-field region are evaluated using a numerical integration procedure. It is shown here that shifting the sphere off the axis of wave propagation breaks the symmetry in the directivity patterns. Moreover, the scattering strongly depends on the half-cone angle of the beam. This investigation could provide a useful test of finite element codes for the evaluation of EM scattering and radiation forces, which are important in optical tweezers and related particle manipulation applications.

Microparticle trapping in an ultrasonic Bessel beam.

Abstract: This paper describes an acoustic trap consisting of a multi-foci Fresnel lens on 127 μm thick lead zirconate titanate sheet. The multi-foci Fresnel lens was designed to have similar working mechanism to an Axicon lens and generates an acoustic Bessel beam, and has negative axial radiation force capable of trapping one or more microparticle(s). The fabricated acoustic tweezers trapped lipid particles ranging in diameter from 50 to 200 μm and microspheres ranging in diameter from 70 to 90 μm at a distance of 2 to 5 mm from the tweezers without any contact between the transducer and microparticles.

Goos-Hänchen and Imbert-Fedorov shifts of a nondiffracting Bessel beam.

Abstract: Goos-Hanchen (GH) and Imbert-Fedorov (IF) shifts are diffractive corrections to geometric 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 of how the GH and IF shifts behave for a "nondiffracting" Bessel beam.

Off-axis scattering of an ultrasound bessel beam by a sphere

Abstract: In this paper, the scattering of an ultrasound zero-order Bessel beam by a rigid sphere in the off-axis configuration is studied. The beam is described through the partial wave expansion. The beam-shape coefficients which represent the amplitude of each multipole mode of the partial wave expansion are computed by numerical quadrature. Calculations are presented for both near- and far-field off-axis scattering. The far-field scattering is examined in both Rayleigh and geometrical acoustic limits. Results demonstrate that the scattered pressure in the off-axis case may significantly deviate from that in the on-axis configuration. In addition, the directive pattern of the scattered pressure is highly dependent on the relative position of the beam to the sphere.

Integral localized approximation description of ordinary Bessel beams and application to optical trapping forces

Abstract: Ordinary Bessel beams are described in terms of the generalized Lorenz-Mie theory (GLMT) by adopting, for what is to our knowledge the first time in the literature, the integral localized approximation for computing their beam shape coefficients (BSCs) in the expansion of the electromagnetic fields. Numerical results reveal that the beam shape coefficients calculated in this way can adequately describe a zero-order Bessel beam with insignificant difference when compared to other relative time-consuming methods involving numerical integration over the spherical coordinates of the GLMT coordinate system, or quadratures. We show that this fast and efficient new numerical description of zero-order Bessel beams can be used with advantage, for example, in the analysis of optical forces in optical trapping systems for arbitrary optical regimes.

Microwave Bessel Beams Generation Using Guided Modes

Abstract: A novel method is devised for Bessel beams generation in the microwave regime. The beam is decomposed in terms of a number of guided transverse electric modes of a metallic waveguide. Modal expansion coefficients are computed from the modal power orthogonality relation. Excitation is achieved by means of a number of inserted coaxial loop antennas, whose currents are calculated from the excitation coefficients of the guided modes. The efficiency of the method is evaluated and its feasibility is discussed. Obtained results can be utilized to practically realize microwave Bessel beam launchers.

Efficient generation of Bessel beam arrays by means of an SLM

Abstract: We use a Spatial Light Modulator (SLM) to produce arrays of Bessel beams by using multiple axicon phase-masks on the SLM. This approach utilises the whole of the SLM, rather than just a thin annular region (which is the case if the SLM is in the far-field of the generated Bessel beams). Using the whole SLM rather than just an annular region means that the required intensity on the SLM is an order of magnitude lower for a given power in the Bessel beams. Spreading the power over the whole SLM is important for high-power applications such as laser micromachining. We allow the axicons to overlap and interfere in the hologram, so the axial length of the Bessel beam core is maintained as we add more beams to the array.

Subwavelength plasmonic lens patterned on a composite optical fiber facet for quasi-one-dimensional Bessel beam generation

Abstract: We demonstrate a beam shaping method by engraving plasmonic lens consisted of subwavelength slit-metallic groove structure on the cleaved end facet of a composite optical fiber. The fiber consisted of a single mode optical fiber serially concatenated with a coreless silica fiber segment to expand the beam diameter. The subwavelength slit-groove structure on a gold film was fabricated using focused ion beam milling process. Plasmonic interaction in the film generated a quasi-one-dimensional Bessel-like beam with a beam width of 0.8 μm at the focal length of 2 μm. Detailed two- and three-dimensional finite-difference time-domain analyses showed beam characteristics consistent with experimental observations.

Measuring the topological charge of optical vortices with an axicon

Abstract: We analyzed the spatial spectrum of the diffraction intensity pattern of an ideal Bessel beam and found an implicit rule that the number of the bright rings in the spatial spectrum is equal to the topological charge of the Bessel beam. The radius of the bright and dark rings has some relation with the topological charge and can be determined accurately. It provides us with a new way for measuring the topological charge of an optical vortex through its diffraction intensity pattern after an axicon. The results of simulation coincide with the theory.

Bessel–Gauss beams as rigorous solutions of the Helmholtz equation

Abstract: The study of the nonparaxial propagation of optical beams has received considerable attention. In particular, the so-called complex-source/sink model can be used to describe strongly focused beams near the beam waist, but this method has not yet been applied to the Bessel–Gauss (BG) beam. In this paper, the complex-source/sink solution for the nonparaxial BG beam is expressed as a superposition of nonparaxial elegant Laguerre–Gaussian beams. This provides a direct way to write the explicit expression for a tightly focused BG beam that is an exact solution of the Helmholtz equation. It reduces correctly to the paraxial BG beam, the nonparaxial Gaussian beam, and the Bessel beam in the appropriate limits. The analytical expression can be used to calculate the field of a BG beam near its waist, and it may be useful in investigating the features of BG beams under tight focusing conditions.

Quasi-Gaussian Bessel-beam superposition: application to the scattering of focused waves by spheres.

Abstract: A superposition of zero-order Bessel beams is examined that closely resembles an idealized paraxial Gaussian beam, provided the superposition is not tightly focused. Plots compare wavefield properties in the focal region and in the far field for different values of kw(0), the product of the wavenumber k, and the focal-spot-radius w(0). The superposition (which is an exact solution of the Helmholtz equation) has the important property that the scattering by an isotropic sphere can be calculated without any approximations for the commonly considered case of linear waves propagating in an inviscid fluid. The nth partial wave amplitude is similar to the case of plane-wave illumination except for a weighting factor that depends on incomplete gamma functions. An approximation for the weighting factor is also discussed based on a generalization of the Van de Hulst localization principle for a sphere of radius a at the focus of a Gaussian beam. Examples display differences between the directionality of the scattering with the plane wave case even though for the cases displayed, ka does not exceed 2 and w(0)∕a is not less than 2. Properties of tightly focused wavefields and the partial wave weighting factors are discussed.

Generation of spiraling high-order Bessel beams

Abstract: Spiraling Bessel beams of arbitrary order are created by illuminating an apertured axicon and a hologram with a single-ringed Laguerre–Gaussian beam. The high-order beam rotates around the propagating axis with a hollow center and can be regarded as the hollow spiraling beam. Such beams have distinct advantages, which offer a direct method for micro-fabrication applications, especially for cold atom guiding, due to their inherent central hollow region and their non-diffracting feature.

Demonstration of a Fresnel axicon.

Abstract: We design and manufacture a Fresnel axicon (fraxicon) that generates a quasi-diffraction-free/Bessel beam with a large depth of field. The novel optical element is characterized with both coherent and incoherent light, and its behavior is compared with that of a classical axicon. While the fraxicon exhibits a strong interference pattern in the on-axis intensity distribution, it can be smoothed out when using broadband light, partial spatial coherence light, or by period randomization. As inexpensive, compact/lightweight, and low-absorption elements, fraxicons may find applications in imaging, illumination, and situations where low absorption and dispersion are important.

High-Speed Functional OCT with Self-Reconstructive Bessel Illumination at 1300nm

Abstract: We present a Bessel beam illumination FDOCT setup with FDML buffered swept source at 1300nm. An extended focus is achieved due to the Bessel beam that preserves its lateral extend over a large depth range. Decoupling the illumination from the Gaussian detection improves the sensitivity as compared to double passing the ring filter and enables dark field imaging. Dark field imaging is useful to avoid strong reflexes from the samples surface that adversely affect the sensitivity due to the limited dynamic range of high-speed 8bit acquisition cards. Furthermore, Bessel beams exhibit a self-reconstruction property that allows imaging even behind obstacles such as hairs on skin. Densely sampled volumes of skin in-vivo with high lateral resolution are acquired at up to 440kHz A-Scan rate. In addition the possibility of contrasting capillaries with high sensitivity is shown, using inter-B-scan speckle variance analysis. High-speed imaging is of crucial importance for imaging small details since sample motion artifacts are reduced and high sampling can be maintained while increasing the B-Scan rate.

Terahertz imaging in dielectric media with quasi-Bessel beams

Abstract: Terahertz (THz) imaging is promising for nondestructive evaluation, since many optically opaque dielectrics are transparent to THz waves. Conventional THz imaging systems employ focusing elements such as spherical lenses and off-axis parabolas, but their fixed focal length produces an inherent trade-off between lateral resolution and depth of focus. Furthermore, image quality suffers when imaging objects located inside a dielectric medium. The air-dielectric interface introduces significant spherical aberration that degrades spatial resolution. Bessel beams are known to produce a small spot size over a large depth of focus. The contribution of our work is two-fold: (1) We demonstrate THz imaging with a significantly improved depth of focus using a zero-th order Bessel beam produced by an axicon lens. (2) We also demonstrate, for the first time to our knowledge, that Bessel beams experience reduced spherical aberration when imaging objects embedded in a dielectric medium. Imaging experiments are performed with a time-domain THz system, where a zero-th order quasi-Bessel beam is formed with an axicon lens made from high density polyethylene (HDPE). The HDPE axicon has a 50 mm diameter and an apex angle of 120 degrees. Point spread function (PSF) measurements confirm that lateral resolution is maintained over a 25 mm depth of field in air. The same lateral resolution is achieved over a 35 mm range inside a HDPE substrate. Needle objects embedded inside a thick HDPE substrate are imaged with high spatial resolution. Image contrast is significantly improved by digital filtering to reduce sidelobe levels. These promising results suggest that Bessel beams are well suited for terahertz nondestructive imaging of thick dielectric objects.

Potential-well model in acoustic tweezers-comment [Correspondence]

Abstract: The production of acoustical vortices-based potential wells for particle trapping is not only restricted to the use of a Laguerre-Gaussian beam. Other useful types of vortex beams include an r-vortex beam, a non-diffracting high-order Bessel and Bessel-Gauss beam, a fractional (diffracting) highorder Bessel beam, a non-diffracting high-order Bessel beam of fractional type α, and a hypergeometric beam to name a few. Representative types of vortex beams are chosen here, but the examples are not exhaustive and additional categories of vortex beams may be reported and investigated. Expressions for the incident acoustic pressure field of various vortex beams are provided. The results should assist in the development of a multitude of vortex-based potential-well models for particle entrapment and manipulation.

Method and device for producing diffraction-free Bessel beam array in random order based on phase hologram

Abstract: The invention relates to a method and a device for producing diffraction-free Bessel beam array in random order based on phase hologram, which overcomes the technical defects that the existing method is complex and the service efficiency of light energy is low; the method has the following schemes: a beam of monochromatic plane light waves is used for irradiating a group of phase hologram with the same characteristic value arranged according to the design requirement in a space light modulator; a unique bright ring with centralized energy is produced after the hologram is performed with Fourier transform; the bright ring is filtered through an annular space filter; and Fourier transform is performed again so as to generate diffraction-free Bessel beam array. The device comprises a light wave beam expanding alignment lens group, a space light modulator, a Fourier lens I, an annular space filter and a Fourier lens II that are arranged in sequence along the transmitting direction of the light path. The method and the device have the following advantages: the use efficiency of energy is high; according to the need, the phase hologram in the space light modulator is changed and written so that the diffraction-free Bessel beam array in random order and at random position can be obtained.

Generation of a variable-diameter collimated hollow laser beam using metal axicon mirrors

Abstract: We demonstrate the generation of a collimated hollow beam of variable diameter using a pair of convex and concave metal axicon mirrors. Using these homemade inexpensive convex and concave metal axicon mirrors of equal cone angle, we have generated a good quality hollow beam with high conversion efficiency (∼76%) from a Gaussian input beam. The focusing of the generated collimated hollow beam has been compared with that of a diverging hollow beam.

Self-reconstructing properties of high-order Besssel-Gauss beam

Abstract: Based on the hankel waves theory, formation principle of Bessel beam is analyzed, self-reconstruction behavior of zero-order and high-order Bessel beam is also explained commendably. Based on the diffraction theory and the transmission model under the collins formula conditions, optical intensity of high-order Bessel beam after a circular obstacle is simulated. Result shows that the high order Bessel-Gauss beam have similar self-reconstruction behavior with zero-order Bessel beam. In terms of the experiment, first-order Bessel-Gauss beam is generated by focusing of vortex beam with an axicon. This Bessel-Gauss beam passes though an on-axis circular obstacle, an on-axis square obstacle and an off-axis square obstacle, and the self-reconstruction properties of the high-order Bessel-Gauss beams are verified. Experimental results agree well with the theoretical analysis.

Circular antenna array for microwave Bessel beam generation

Abstract: A circular antenna array (CAA) is proposed and demonstrated for the generation of optimal pseudo-Bessel beams at millimeter-wave frequencies. Numerical simulations show that a 91-element array produces a Bessel beam of a 7λ main lobe width over a distance of 180λ. Based on this report, it is suggested that Bessel beams may provide a unique solution to millimeter-wave quasi-optical systems by providing highly focused beams with small-sized antennas.

High power Bessel beams from EP-VECSELs

Abstract: We report on demonstration of non-diffracting (Bessel) beams from Electrically Pumped Vertical External Cavity Surface Emitting Lasers (EP-VECSELs), with output powers ranging up to hundreds of milliwatts and central lobe diameters of 10-100 μm with propagation lengths up to few tens of centimeters. To our knowledge, this is the best result for Bessel beams generated from semiconductor light sources and is comparable to that achievable from vibronic lasers.

Coherence of Bessel beams propagating in turbulent media

Abstract: In this article, the characteristic features of formation of the Bessel optical beam in a turbulent atmosphere are analyzed. The problem analysis is based on the solution of the equation for the mutual coherence function (the second-order field moment) of a Bessel beam of optical radiation. The behavior of the spatial coherence radius of a Bessel optical beam depending on parameters of a beam and characteristics of the turbulent atmosphere is examined. It has appeared, that at low levels of fluctuations in a turbulent atmosphere the spatial coherence radius of a Bessel optical beam is larger than the spatial coherence radius of a plane optical wave, but it is smaller than the spatial coherence radius of a spherical wave. At high levels of fluctuations in a turbulent atmosphere, the spatial coherence radius of a Bessel beam becomes closer to the similar characteristic of a spherical wave.