We observe optical trapping and manipulation of dielectric microparticles using autofocusing radially symmetric Airy beams. This is accomplished by exploiting either the inward or outward transverse acceleration associated with their chirped wavefronts. We experimentally demonstrate, for the first time to our knowledge, that such Airy beams morph into nondiffracting Bessel beams in their far-field. Furthermore, the ability of guiding and transporting microparticles along the primary rings of this class of beams is explored.

2Controlling light transport in soft-matter systems could be crucial in many and diverse fields of science and technology. For example, in colloidal suspensions, this can be accomplished through optical radiation forces capable of manipulating particle concentration and molecular kinetics at the mesoscopic level 2,7,11,12 . In principle, such optically induced processes can be exploited for initiating and regulating chemical reactions, for sorting different species of nanoparticles, and for influencing diffusion and osmotic pressure effects, to mention a few These issues can be addressed by first considering how the particle polarizability is related to optical nonlinearities that are solely mediated by radiation pressure effects. In general, a particle displays a positive polarizability (PP) whenever its refractive index exceeds that of the background medium, while in the converse case its polarizability is negative (NP). As indicated in several studies Fig. 1(c)], one could synthesize soft-matter systems with a tunable polarizability, optimized nonlinear response, and enhanced light transmission.In this study, we experimentally demonstrate a new class of synthetic colloidal suspensions capable of exhibiting negative polarizabilities. This is accomplished in a stabilized mixture of Polytetrafluoroethylene (PTFE) particles in a glycerin-water solution. We show that by judiciously introducing NP particles in conventional PP colloidal suspensions, the resulting "mixed" polarizability can be fine-tuned, thereby enabling us to modify the nonlinear response of these systems. In particular,we observe robust propagation and up to a fourfold-enhanced transmission of an optical beam when traversing an NP suspension as compared to that in a typical PP suspension. Such light penetration through otherwise strong scattering environment is attributed to the interplay between optical forces and 4 self-activated transparency effects while no thermal effect is involved. Our experimental observations are in agreement with a previously derived thermodynamic model that takes into account the interplay between the optical intensity and the osmotic pressure in the presence of particle-particle interactions 19 .These findings may pave the way towards synthesizing soft-matter systems with customized optical nonlinearities that can enable an intensity-dependent reduction in scattering losses.To understand light-particle dynamics in colloidal dispersions, we first consider the optical gradient force that typically dominates the interaction process. To first order, this component of the optical force is given 2,16 by = ∇ /4, where I is the optical intensity and α is the polarizability of the particle. In the dipole regime, = 3 ( − 1)/( + 2), where V is the particle's volume, = / is a measure of the contrast between the refractive index of the particle and that of the background fluid . Therefore, PP dielectric particles with > ( > 0) will be attracted towards

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.

We report interesting anomalies in the temperature dependent Raman spectra of FeSe 0.82 measured from 3K to 300K in the spectral range from 60 to 1800 cm -1 and determine their origin using complementary first-principles density functional calculations. A phonon mode near 100 cm -1 exhibits a sharp increase by ~ 5% in frequency below a temperature T s (~ 100K) attributed to strong spin-phonon coupling and onset of shortrange antiferromagnetic order. In addition, two high frequency modes are observed at 1350 cm -1 and 1600 cm -1 , attributed to electronic Raman scattering from (x 2 -y 2 )to xz / yz d-orbitals of Fe.

We demonstrate optical trapping and manipulation of aerosols with an optical bottle beam generated by the moiré techniques. We observe stable trapping and back-and-forth transportation of a variety of absorbing carbon particles suspended in air, ranging from clusters of nanosized buckminsterfullerene C₆₀ to micrometer-sized carbon powders.