White-light solitons

Optical spatial solitons made from incoherent white light were experimentally observed in 1997 by Mitchell and Segev [Nature (London) 387, 880 (1997)]. We present what is believed to be the first theory describing these solitons and find the characteristic features of their spatiotemporal coherence properties and their temporal power spectrum.     

Experimental observation of self-accelerating beams in quadratic nonlinear media

We present the experimental observation of 1D and 2D self-accelerating nonlinear beams in quadratic media, which are also the first nonlinear self-accelerating beams in any symmetric nonlinearity. Notably, we show that the intensity peaks of the first and second harmonics are asynchronous with respect to one another, but the coupled harmonics exhibit joint acceleration within the nonlinear medium. Finally, we demonstrate the impact of self-healing effects on the jointly accelerating first and second harmonics.     

Quantum‐Dot‐Sensitized Solar Cells

Quantum‐dot‐sensitized solar cells (QDSCs) are a promising low‐cost alternative to existing photovoltaic technologies such as crystalline silicon and thin inorganic films. The absorption spectrum of quantum dots (QDs) can be tailored by controlling their size, and QDs can be produced by low‐cost methods. Nanostructures such as mesoporous films, nanorods, nanowires, nanotubes and nanosheets with high microscopic surface area, redox electrolytes and solid‐state hole conductors are borrowed from standard dye‐sensitized solar cells (DSCs) to fabricate electron conductor/QD monolayer/hole conductor junctions with high optical absorbance. Herein we focus on recent developments in the field of mono‐ and polydisperse QDSCs. Stability issues are adressed, coating methods are presented, performance is reviewed and special emphasis is given to the importance of energy‐level alignment to increase the light to electric power conversion efficiency.     

Cross-phase-modulation nonlinearities and holographic solitons in periodically poled photovoltaic photorefractives

We show that the nonlinearity in periodically poled photovoltaic photorefractives can be solely of the cross-phase-modulation type. The effects of self-phase modulation and asymmetric energy exchange, which exist in homogeneously poled photovoltaic photorefractives, can be considerably suppressed by the periodic poling. Finally, we demonstrate numerically that periodically poled photovoltaic photorefractives can support Thirring-type ("holographic") solitons, which to our knowledge have never been observed.     

Surface lattice solitons

We study theoretically nonlinear surface waves in optical lattices and show that solitons can exist at the heterointerface between two different semi-infinite 1D waveguide arrays, as well as at the boundaries of a 2D nonlinear lattice. The existence and properties of these surface soliton solutions are investigated in detail.     

On powers of nonnegative matrices

We investigate the structure of powers of nonnegative matrices A, and in particular characterize those A for which some power is (essentially) triangular. We also show how the number of irreducible components of A can be determined from its powers.     

Following evolution of bacteriorhodopsin in its reactive excited state via stimulated emission pumping

New information concerning the photochemical dynamics of bacteriorhodopsin (BR) is obtained by impulsively stimulating emission from the reactive fluorescent state. Depletion of the excited-state fluorescence leads to an equal reduction in production of later photoproducts. Accordingly, chromophores which are forced back to the ground state via emission do not continue on in the photocycle, conclusively demonstrating that the fluorescent state is a photocycle intermediate. The insensitivity of depletion dynamics to the "dump" pulse timing, throughout the fluorescent states lifetime, and the biological inactivity of the dumped population suggest that the fluorescent-state structure is constant, well-defined, and significantly different than that where crossing to the ground state takes place naturally. In conjunction with conclusions from comparing the photophysics of BR with those of synthetic analogues containing "locked" retinals, present results show that large-amplitude torsion around C13=C14 is required to go between the above structures.     

Quadratic spatial solitons in periodically poled KTiOPO4

The evolution of fundamental beams into quadratic spatial solitons was investigated in a periodically poled bulk KTiOPO4 crystal near and at phase matching. Various soliton properties, such as trapping efficiency as a function of phase mismatch, poling-induced walk-off, and the effects of pulse width, beam width, and input beam quality, were measured. Effects attributed to the presence of cubic nonlinearities were also observed.