Since the first discovery of carbon nanotubes (CNTs) in 1991, a window to new technological areas has been opened. [1] One of the emerging applications of CNTs is the reinforcement of composite materials to overcome the performance limits of conventional materials. [2,3] Recent developments in CNT/polymer composites have shown the potential for improving the strength of polymers, [2] and this finding has encouraged researchers to use carbon nanotubes as reinforcements for metal and ceramic matrices.[4±7] However, because of the difficulties in distributing CNTs homogeneously in a metal or ceramic matrix by means of traditional composite processes, it has been doubted whether CNTs can really reinforce metals or ceramics.[4±7] Here we report on a CNTreinforced Cu matrix nanocomposite, fabricated by a novel fabrication process called ªmolecular-level mixingº; this nanocomposite shows extremely high strength, several times higher than the matrix. The novel process for fabricating CNT/Cu composite powders involves suspending CNTs in a solvent by surface functionalization, mixing Cu ions with the CNT suspension, drying, calcination, and reduction. This process produces CNT/Cu composite powders, whereby the CNTs are homogeneously implanted within the Cu powders. The CNT/Cu nanocomposite, consolidated by spark plasma sintering of CNT/Cu composite powders, is shown to possess three times the strength of the Cu matrix and to have twice the Young's modulus. This extraordinary strengthening effect of carbon nanotubes in metal is higher than that of any other reinforcement ever used for metal-matrix composites. Several researchers have attempted to fabricate CNT-reinforced metal-or ceramic-matrix composite materials by COMMUNICATIONS

A beam with an angular-dependant phase Φ = ℓϕ about the beam axis carries an orbital angular momentum of ℓℏ per photon. Such beams are exploited to provide superresolution in microscopy. Creating extreme ultraviolet or soft-x-ray beams with controllable orbital angular momentum is a critical step towards extending superresolution to much higher spatial resolution. We show that orbital angular momentum is conserved during high-harmonic generation. Experimentally, we use a fundamental beam with |ℓ| = 1 and interferometrically determine that the harmonics each have orbital angular momentum equal to their harmonic number. Theoretically, we show how any small value of orbital angular momentum can be coupled to any harmonic in a controlled manner. Our results open a route to microscopy on the molecular, or even submolecular, scale.

High harmonic radiation, produced when intense laser pulses interact with matter, is composed of a train of attosecond pulses. Individual pulses in this train carry information on ultrafast dynamics that vary from one half-optical-cycle to the next. Here, we demonstrate an all-optical photonic streaking measurement that provides direct experimental access to each attosecond pulse by mapping emission time onto propagation angle. This is achieved by inducing an ultrafast rotation of the instantaneous laser wavefront at the focus. We thus time-resolve attosecond pulse train generation, and hence the dynamics in the nonlinear medium itself. We apply photonic streaking to harmonic generation in gases and directly observe, for the first time, the influence of non-adiabatic electron dynamics and plasma formation on the generated attosecond pulse train. These experimental and numerical results also provide the first evidence of the generation of attosecond lighthouses in gases, which constitute ideal sources for attosecond pump-probe spectroscopy.