Polychromatic liquid crystal laser arrays towards display applications.

Band-edge liquid crystal lasers are of interest for a number of applications including laser projection displays. Herein, we demonstrate simultaneous red-green-blue lasing from a single liquid crystal sample by creating a two-dimensional laser array fabricated from dye-doped chiral nematic liquid crystals. By forming a pitch gradient across the cell, and optically pumping the sample using a lenslet array, a polychromatic laser array can be observed consisting simultaneously of red-green-blue colors. Specifically, the two-dimensional polychromatic array could be used to produce a laser-based display, with low speckle and wide color gamut, whereby no complex fabrication procedure is required to generate the individual 'pixels'.

Separate representations of dynamics in rhythmic and discrete movements: evidence from motor learning.

Rhythmic and discrete arm movements occur ubiquitously in everyday life, and there is a debate as to whether these two classes of movements arise from the same or different underlying neural mechanisms. Here we examine interference in a motor-learning paradigm to test whether rhythmic and discrete movements employ at least partially separate neural representations. Subjects were required to make circular movements of their right hand while they were exposed to a velocity-dependent force field that perturbed the circularity of the movement path. The direction of the force-field perturbation reversed at the end of each block of 20 revolutions. When subjects made only rhythmic or only discrete circular movements, interference was observed when switching between the two opposing force fields. However, when subjects alternated between blocks of rhythmic and discrete movements, such that each was uniquely associated with one of the perturbation directions, interference was significantly reduced. Only in this case did subjects learn to corepresent the two opposing perturbations, suggesting that different neural resources were employed for the two movement types. Our results provide further evidence that rhythmic and discrete movements employ at least partially separate control mechanisms in the motor system.

Instabilities in the oscillatory flow of a complex fluid.

The dynamics of a fluid in a vertical tube, subjected to an oscillatory pressure gradient, is studied experimentally for both a Newtonian and a viscoelastic shear-thinning fluid. Particle image velocimetry is used to determine the two-dimensional velocity fields in the vertical plane of the tube axis, in a range of driving amplitudes from 0.8 to 2.5 mm and of driving frequencies from 2.0 to 11.5 Hz. The Newtonian fluid exhibits a laminar flow regime, independent of the axial position, in the whole range of drivings. For the complex fluid, instead, the parallel shear flow regime exhibited at low amplitudes [Torralba, Phys. Rev. E 72, 016308 (2005)] becomes unstable at higher drivings against the formation of symmetric vortices, equally spaced along the tube. At even higher drivings the vortex structure itself becomes unstable, and complex nonsymmetric structures develop. Given that inertial effects remain negligible even at the hardest drivings (Re < 10(-1)), it is the complex rheology of the fluid that is responsible for the instabilities observed. The system studied represents an interesting example of the development of shear-induced instabilities in nonlinear complex fluids in purely parallel shear flow.

Ultrafast non-thermal electron dynamics in single layer graphene

We study the ultrafast dynamics of non-thermal electron relaxation in graphene upon impulsive excitation. The 10-fs resolution two color pump-probe allows us to unveil the non-equilibrium electron gas decay at early times. © 2012 OSA.

Ultrafast non-thermal electron dynamics in single layer graphene

We study the ultrafast dynamics of non-thermal electron relaxation in graphene upon impulsive excitation. The 10-fs resolution two color pump-probe allows us to unveil the non-equilibrium electron gas decay at early times. © Owned by the authors, published by EDP Sciences, 2013.

Ultrafast non-thermal electron dynamics in single layer graphene

We study the ultrafast dynamics of non-thermal electron relaxation in graphene upon impulsive excitation. The 10-fs resolution two color pump-probe allows us to unveil the nonequilibrium electron gas decay at early times. © OSA 2012.

Two-dimensional liquid crystal laser array

A two-dimensional liquid crystal (LC) laser array has been demonstrated by photopumping a single LC sample using a lenslet array consisting of plano-convex microlenses. A 5 × 5 array of LC lasers (displaying evidence of mutual coherence) spaced by 1 mm inactive regions has been generated, which could be combined to yield a single monomode output and allows an almost 50-fold increase in energy density in comparison to a single-focus LC cavity. Furthermore, we have demonstrated how the individual and recombined emission spectra vary with different sample topologies and how polydomain samples can be used to generate a multiwavelength laser emission. © 2008 Optical Society of America.

Very high modulation efficiency two-sections tapered laser diode at 1060nm for free space optical communications

High-power (more than 500 mW) and high-speed (more than 1 Gbps) tapered lasers at 1060 nm are required in free-space optical communications and (at lower frequencies of around 100 MHz) display applications for frequency doubling to the green. On a 3 mm long tapered laser, we have obtained an open eye diagram at 1 Gbps, together with a high extinction ratio of 11 dB, an optical modulation amplitude of 530 mW, and a high modulation efficiency of 13 W/A. On a 4 mm-long tapered laser, we have obtained an open eye diagram at 700 Mbps, together with a high extinction ratio of 19 dB, a high optical modulation amplitude of 1.6 W, and a very high modulation efficiency of 19 W/A. On a 6 mm-long tapered laser, we have obtained a very high power of 5W CW and a very high static modulation efficiency of 59.8 W/A. © 2011 SPIE.