An intense short laser pulse or a millimetre wave propagating through a plasma channel may act as a wiggler for the generation of shorter wavelengths. When a relativistic electron beam is launched into the channel from the opposite direction, the laser radiation is Compton/Raman backscattered to produce coherent radiation at shorter wavelengths. The scheme, however, requires a superior beam quality with energy spread less than 1% in the Raman regime.

Innate behaviours, although robust and hard wired, rely on modulation of neuronal circuits, for eliciting an appropriate response according to internal states and external cues. Drosophila flight is one such innate behaviour that is modulated by intracellular calcium release through inositol 1,4,5-trisphosphate receptors (IP3Rs). Cellular mechanism(s) by which IP3Rs modulate neuronal function for specific behaviours remain speculative, in vertebrates and invertebrates. To address this, we generated an inducible dominant negative form of the IP3R (IP3RDN). Flies with neuronal expression of IP3RDN exhibit flight deficits. Expression of IP3RDN helped identify key flight-modulating dopaminergic neurons with axonal projections in the mushroom body. Flies with attenuated IP3Rs in these presynaptic dopaminergic neurons exhibit shortened flight bouts and a disinterest in seeking food, accompanied by reduced excitability and dopamine release upon cholinergic stimulation. Our findings suggest that the same neural circuit modulates the drive for food search and for undertaking longer flight bouts.

The self focusing of a quadruple Gaussian laser beam, comprising four coherent identical Gaussian beams with axes parallel to ẑ but shifted from z-axis by −x0x̂,x0x̂,−x0ŷ,x0ŷ in a collisionless plasma, is investigated in the paraxial ray approximation. The nonlinearity arises through the ponderomotive force led plasma density redistribution. As the beam propagates, it maintains the shape of its intensity profile with spot size r0 of each of the four distributions modified from r0 to r0f, x0, modified to x0f and the axial intensity enhanced by 1/f2, where f is the beam width parameter. In the regime of quadratic nonlinearity, the threshold beam power for self focusing, Pth, increases with x0 as the laser intensity gradient decreases and the ponderomotive force becomes weaker. At beam power greater than Pth, the beam focuses in an oscillatory manner, i.e., f varies periodically with z due to the saturating effect of nonlinearity. The locations of intensity maxima of the four beams also vary periodically with z. As x0 increases from 0 to 0.6r0, the transverse intensity gradient becomes weaker and the rate of self focusing, i.e., the rate of variation of f with z decreases.

No abstract