Nanostructured metasurfaces offer unique capabilities for subwavelength control of optical waves. Based on this potential, a large number of metasurfaces have been proposed recently as alternatives to standard optical elements. In most cases, however, these elements suffer from large chromatic aberrations, thus limiting their usefulness for multiwavelength or broadband applications. Here, in order to alleviate the chromatic aberrations of individual diffractive elements, we introduce dense vertical stacking of independent metasurfaces, where each layer is made from a different material, and is optimally designed for a different spectral band. Using this approach, we demonstrate a triply red, green and blue achromatic metalens in the visible range. We further demonstrate functional beam shaping by a self-aligned integrated element for stimulated emission depletion microscopy and a lens that provides anomalous dispersive focusing. These demonstrations lead the way to the realization of ultra-thin superachromatic optical elements showing multiple functionalities—all in a single nanostructured ultra-thin element.

A hologram is an optical element storing phase and possibly amplitude information enabling the reconstruction of a three-dimensional image of an object by illumination and scattering of a coherent beam of light, and the image is generated at the same wavelength as the input laser beam. In recent years, it was shown that information can be stored in nanometric antennas giving rise to ultrathin components. Here we demonstrate nonlinear multilayer metamaterial holograms. A background free image is formed at a new frequency—the third harmonic of the illuminating beam. Using e-beam lithography of multilayer plasmonic nanoantennas, we fabricate polarization-sensitive nonlinear elements such as blazed gratings, lenses and other computer-generated holograms. These holograms are analysed and prospects for future device applications are discussed.

-We demonstrate strong coupling between molecular excited states and surface plasmon modes of a slit array in a thin metal film. The coupling manifests itself as an anti-crossing behavior of the two newly formed polaritons. As the coupling strength grows, a new mode emerges, which is attributed to long range molecular interactions mediated by the plasmonic field. The new, molecular-like mode repels the polariton states, and leads to an opening of energy gaps both below and above the asymptotic free molecule energy. plasmons is similar to that in microcavities [17][18][19][20], where the cavity modes dispersion relations are replaced by the plasmonic ones. In the strong coupling regime, energy exchange between the molecular and plasmonic modes is observed, giving rise to two new 'polariton' eigenmodes. Strong coupling manifests itself as an avoided crossing of the polariton modes as a function of the plasmon frequency, with an observed Rabi splitting (RS) which is a non-negligible fraction of the molecular transition frequency

We introduce a new scheme for controlling the sense of molecular rotation. By varying the polarization and the delay between two ultrashort laser pulses, we induce unidirectional molecular rotation, thereby forcing the molecules to rotate clockwise/counterclockwise under field-free conditions. We show that unidirectionally rotating molecules are confined to the plane defined by the two polarization vectors of the pulses, which leads to a permanent anisotropy in the molecular angular distribution. The latter may be useful for controlling collisional cross-sections and optical and kinetic processes in molecular gases. We discuss the application of this control scheme to individual components within a molecular mixture in a selective manner.

When a wave is reflected from a moving object, its frequency is Doppler shifted 1 . Similarly, when circularly polarized light is scattered from a rotating object, a rotational Doppler frequency shift may be observed 2,3 , with manifestations ranging from the quantum world (fluorescence spectroscopy, rotational Raman scattering and so on 3,4 ) to satellite-based global positioning systems 5 . Here, we observe for the first time the Doppler frequency shift phenomenon for a circularly polarized light wave propagating through a gas of synchronously spinning molecules. An ensemble of such spinning molecules was produced by double-pulse laser excitation, with the first pulse aligning the molecules and the second (linearly polarized at a 458 8 8 8 8 angle) causing a concerted unidirectional rotation of the 'molecular propellers' 6,7 . We observed the resulting rotating birefringence of the gas by detecting a Doppler-shifted wave that is circularly polarized in a sense opposite to that of the incident probe.In his famous 1905 paper on special relativity 8 , Einstein derived the frequency shift Dv for linearly polarized light of frequency v reflected from a mirror moving with speed n and showed that in the non-relativistic limit Dv ¼+2kv, where k ¼ v/c, c is the speed of light, and the sign depends on the relative direction of motion. When an anisotropic polarizable object rotates with angular velocity V, a rotational Doppler frequency shift may be observed in the scattering of a circularly polarized (CP) electromagnetic wave. The scattered field consists of a CP component with the same frequency and handedness as the incident one and a CP wave of the opposite handedness 9-13 with a frequency shift of Dv ¼+2V, where the sign depends on the relative sense of rotation. To date, table-top observations of this phenomenon have made use of mechanical rotation of anisotropic optical elements 10,11,14 and electro-optic effects in a nonlinear crystal subject to a rotating microwave electric field 15 . In the present study, we observe the rotational Doppler frequency shift (RDS) from molecules rotating unidirectionally at terahertz frequencies, which is many orders of magnitude larger than that observed in mechanically rotated systems.We induce molecular unidirectional rotation (UDR) by applying two time-delayed, ultrashort, linearly polarized laser pulses (Fig. 1). This two-pulse technique was demonstrated by Kitano et al. 7 and subsequently generalized [16][17][18] . Although UDR persists for as long as the molecules do not collide, the field-free anisotropy of the angular distribution gradually disappears because of angular velocity dispersion. The cigar-like shape of the angular distribution reappears periodically because of quantum revival of the rotational wave packets 19-21 with a revival period of T rev ¼ 1/(2Bc), where B is the rotational constant. Substantial anisotropy of the angular distribution is also observed at fractions of T rev , especially near T rev /2. Probing the ensemble at full or fractional revival enables...

Tin disulfide pellets were laser ablated in an inert gas atmosphere, and closed cage fullerene-like (IF) nanoparticles were produced. The nanoparticles had various polyhedra and short tubular structures. Some of these forms contained a periodic pattern of fringes resulting in a superstructure. These patterns could be assigned to a superlattice created by periodic stacking of layered SnS(2) and SnS. Such superlattices are reminiscent of misfit layer compounds, which are known to form tubular morphologies. This mechanism adds up to the established mechanism for IF formation, namely, the annihilation of reactive dangling bonds at the periphery of the nanoparticles. Additionally, it suggests that one of the driving forces to form tubules in misfit compounds is the annihilation of dangling bonds at the rim of the layered structure.

Spectroscopy aims at extracting information about matter through its interaction with light. However, when performed on gas and liquid phases as well as solid phases lacking long‐range order, the extracted spectroscopic features are in fact averaged over the molecular isotropic angular distributions. The reason is that light–matter processes depend on the angle between the transitional molecular dipole and the polarization of the light interacting with it. This understanding gave birth to the constantly expanding field of “laser‐induced molecular alignment”. In this paper, we attempt to guide the readers through our involvement (both experimental and theoretical) in this field in the last few years. We start with the basic phenomenon of molecular alignment induced by a single pulse, continue with selective alignment of close molecular species and unidirectional molecular rotation induced by two time‐delayed pulses, and lead up to novel schemes for manipulating the spatial distributions of molecular samples through rotationally controlled scattering off inhomogeneous fields and surfaces.

Metasurfaces, and in particular those containing plasmonic-based metallic elements, constitute an attractive set of materials with a potential for replacing standard bulky optical elements. In recent years, increasing attention has been focused on their nonlinear optical properties, particularly in the context of second and third harmonic generation and beam steering by phase gratings. Here, we harness the full phase control enabled by subwavelength plasmonic elements to demonstrate a unique metasurface phase matching that is required for efficient nonlinear processes. We discuss the difference between scattering by a grating and by subwavelength phase-gradient elements. We show that for such interfaces an anomalous phase-matching condition prevails, which is the nonlinear analogue of the generalized Snell's law. The subwavelength phase control of optical nonlinearities paves the way for the design of ultrathin, flat nonlinear optical elements. We demonstrate nonlinear metasurface lenses, which act both as generators and as manipulators of the frequency-converted signal.