ABSRACTA new type of Bessel-like optical beams, which is distinguished by the dependence on the cone angle from the longitudinal coordinate, is investigated. Such beams have the properties of Bessel beams (ring-spatial spatial spectrum) as well as Gaussian beams (keeping the transverse profile at any distances). This new type of beams can be obtained in optical system composed of lens axicon doublet and conical lens. An experimental set-up for producing such beams is realized. It is shown that depending on its parameters the scheme allows one to produce z-dependent Bessel-like beams, whose spatial spectra change from Bessel function to shifted Gaussian one. It is establish theoretically and confirmed experimentally that on-axial intensity of z-dependent Bessel-like beam could be higher than that of incident Gaussian beam.

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We present a numerical simulation of the response of an expanding relativistic jet to the ejection of a superluminal component. The simulation has been performed with a relativistic time-dependent hydrodynamical code from which simulated radio maps are computed by integrating the transfer equations for synchrotron radiation. The interaction of the superluminal component with the underlying jet results in the formation of multiple conical shocks behind the main perturbation. These trailing components can be easily distinguished because they appear to be released from the primary superluminal component instead of being ejected from the core. Their oblique nature should also result in distinct polarization properties. Those appearing closer to the core show small apparent motions and a very slow secular decrease in brightness and could be identified as stationary components. Those appearing farther downstream are weaker and can reach superluminal apparent motions. The existence of these trailing components indicates that not all observed components necessarily represent major perturbations at the jet inlet; rather, multiple emission components can be generated by a single disturbance in the jet. While the superluminal component associated with the primary perturbation exhibits a rather stable pattern speed, trailing components have velocities that increase with distance from the core but move at less than the jet speed. The trailing components exhibit motion and structure consistent with the triggering of pinch modes by the superluminal component. The increase in velocity of the trailing components is an indirect consequence of the acceleration of the expanding fluid, which is assumed to be relativistically hot; if observed, such accelerations would therefore favor an electron-positron (as opposed to proton rest mass) dominated jet.

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.