72 research outputs found
Accelerating beams
We demonstrate that any two-dimensional accelerating beam can be described in a canonical form in Fourier space. In particular, we demonstrate that there is a one-to-one correspondence between complex functions in the real line (the line spectrum) and accelerating beams. An arbitrary line spectrum can be used to generate novel accelerating beams with diverse transverse shapes. The line spectra for the special cases of the families of Airy and accelerating parabolic beams are provided
Elliptical beams
A very general beam solution of the paraxial wave equation in elliptic cylindrical coordinates is presented. We call such a field an elliptic beam (EB). The complex amplitude of the EB is described by either the generalized Ince functions or the Whittaker-Hill functions and is characterized by four parameters that are complex in the most general situation. The propagation through complex ABCD optical systems and the conditions for square integrability are studied in detail. Special cases of the EB are the standard, elegant, and generalized Ince-Gauss beams, Mathieu-Gauss beams, among others
Normalization of the Mathieu-Gauss optical beams
A series scheme is discussed for the determination of the normalization constants of the even and odd Mathieu-Gauss (MG) optical beams. We apply a suitable expansion in terms of Bessel-Gauss (BG) beams and also answer the question of how many BG beams should be used to synthesize a MG beam within a tolerance. The structure of the normalization factors ensures that MG beams will always be normalized independently of the particular normalization adopted for the Mathieu functions. In this scheme, the normalization constants are expressed as rapidly convergent series that can be calculated to an arbitrary precision
Nondiffracting Accelerating Waves: Weber waves and parabolic momentum
Diffraction is one of the universal phenomena of physics, and a way to
overcome it has always represented a challenge for physicists. In order to
control diffraction, the study of structured waves has become decisive. Here,
we present a specific class of nondiffracting spatially accelerating solutions
of the Maxwell equations: the Weber waves. These nonparaxial waves propagate
along parabolic trajectories while approximately preserving their shape. They
are expressed in an analytic closed form and naturally separate in forward and
backward propagation. We show that the Weber waves are self-healing, can form
periodic breather waves and have a well-defined conserved quantity: the
parabolic momentum. We find that our Weber waves for moderate to large values
of the parabolic momenta can be described by a modulated Airy function. Because
the Weber waves are exact time-harmonic solutions of the wave equation, they
have implications for many linear wave systems in nature, ranging from
acoustic, electromagnetic and elastic waves to surface waves in fluids and
membranes.Comment: 10 pages, 4 figures, v2: minor typos correcte
Comment on 'Exact solution of resonant modes in a rectangular resonator'
We comment on the recent Letter by J. Wu and A. Liu [Opt. Lett. 31, 1720 (2006)] in which an exact scalar solution to the resonant modes and the resonant frequencies in a two-dimensional rectangular microcavity were presented. The analysis is incorrect because (a) the field solutions were imposed to satisfy simultaneously both Dirichlet and Neumann boundary conditions at the four sides of the rectangle, leading to an overdetermined problem, and (b) the modes in the cavity were expanded using an incorrect series ansatz, leading to an expression for the mode fields that does not satisfy the Helmholtz equation
Airy-Gauss beams and their transformation by paraxial optical systems
We introduce the generalized Airy-Gauss (AiG) beams and analyze their propagation through optical systems described by ABCD matrices with complex elements in general. The transverse mathematical structure of the AiG beams is form-invariant under paraxial transformations. The conditions for square integrability of the beams are studied in detail. The model of the AiG beam describes in a more realistic way the propagation of the Airy wave packets because AiG beams carry finite power, retain the nondiffracting propagation properties within a finite propagation distance, and can be realized experimentally to a very good approximation
Topological Photonic Quasicrystals: Fractal Topological Spectrum and Protected Transport
We show that it is possible to have a topological phase in two-dimensional
quasicrystals without any magnetic field applied, but instead introducing an
artificial gauge field via dynamic modulation. This topological quasicrystal
exhibits scatter-free unidirectional edge states that are extended along the
system's perimeter, contrary to the states of an ordinary quasicrystal system,
which are characterized by power-law decay. We find that the spectrum of this
Floquet topological quasicrystal exhibits a rich fractal (self-similar)
structure of topological "minigaps," manifesting an entirely new phenomenon:
fractal topological systems. These topological minigaps form only when the
system size is sufficiently large because their gapless edge states penetrate
deep into the bulk. Hence, the topological structure emerges as a function of
the system size, contrary to periodic systems where the topological phase can
be completely characterized by the unit cell. We demonstrate the existence of
this topological phase both by using a topological index (Bott index) and by
studying the unidirectional transport of the gapless edge states and its
robustness in the presence of defects. Our specific model is a Penrose lattice
of helical optical waveguides - a photonic Floquet quasicrystal; however, we
expect this new topological quasicrystal phase to be universal.Comment: 12 pages, 8 figure
Higher-order moments and overlaps of Cartesian beams
We introduce a closed-form expression for the overlap between two different Cartesian beams. In the course of obtaining this expression, we establish a linear relation between the overlap of circular beams with azimuthal symmetry and the overlap of Cartesian beams such that the knowledge of the former allows the latter to be calculated very easily. Our formalism can be easily applied to calculate relevant beam parameters such as the normalization constants, the M2 factors, the kurtosis parameters, the expansion coefficients of Cartesian beams, and therefore of all their relevant special cases, including the standard, elegant, and generalized Hermite–Gaussian beams, cosh-Gaussian beams, Lorentz beams, and Airy beams, among others
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