(Inst. for Advanced Studies in Basic Sciences, Zanjan, Iran)
Structured beams, whose intensity, phase, or polarization profiles have very complex structures, are attracting major attention and presenting various applications in many areas of optics. We have recently reported the observation of a new class of accelerating, self-healing, non-diffracting, and shape invariant beams, have numerous phase anomalies and unprecedented patterns, and can be feasibly tuned. In the diffraction of a plane wave from radial amplitude/phase gratings such beams are generated, and due to the beauty and structural complexity of the generated beams, we named them “radial carpet beams” (RCBs).
In this talk, a report on the recent studies we have done on the RCBs will be presented. In the diffraction of a plane wave from an amplitude radial grating we have shown that the boundaries of geometric shadow, near- and far-field diffraction regimes to be curved. It is also shown that the Talbot carpet can be generated at the transverse plane in the diffraction of a plane wave from an amplitude radial grating. In addition, we introduce "diffraction-based rainbow" in the diffraction of a collimated white light wavefront from a radial grating, and formation of colorful radial Talbot carpet at the transverse plane is also investigated.
An exceptional sample for the spectrum-invariant propagation is also presented. An azimuthally-modified linear phase grating is also introduced and generation of varied radial carpet beams over the different diffraction orders with controlled intensity sharing among the generated beams is presented. Existence of the self-imaging in the polar coordinates for the azimuthally periodic Bessel-based structures is proved. We also consider a family of solutions of the homogeneous free-space scalar wave equation, and we named them “combined half-integer Bessel-like beams” which are determined by linear combinations of the half-integer order Bessel functions. It is shown that, this family of beams satisfies a “radial structured” boundary condition at z = 0 plane, therefore they can be produced by the diffraction of a plane wave from suitable “radial structures.” The use of RCBs for "multiple particle trapping" is presented. This type of trapping is very versatile, yet cheap and simple. We also investigate and compare the propagation of Laguerre-Gaussian (LG) and RCBs through an indoor convective air turbulence and atmospheric turbulence under weak to strong turbulence conditions. We show that, under the same turbulence conditions, the RCB experiences less disturbance and is more resilient to the turbulence, especially when it has a complicated structure. It is also shown that a set of RCBs having different values of the main intensity spots can be used as an orthogonal bases for the free-space optical communication. Finally, the strength of the self-healing of RCBs is quantified in terms of the beams’ specifications.