Generation of unipolar half-cycle pulses via unusual reflection of a single-cycle pulse from an optically thin metallic or dielectric layer.

We propose a strikingly simple method to form approximately unipolar half-cycle optical pulses via reflection of a single-cycle optical pulse from a thin flat metallic or dielectric layer. Unipolar pulses in reflection arise due to specifics of one-dimensional pulse propagation. Namely, we show that the field emitted by the layer is proportional to the velocity of the oscillating charges in the medium, instead of their acceleration. Besides, the oscillation velocity of the charges can be forced to keep a constant sign throughout the pulse duration. That is, reflection of ultrashort pulses from broad-area layers with nanometer-scale thickness can be very different from the common reflection in the case of longer pulses and thicker layers. This suggests a possibility of unusual transformations of few-cycle light pulses in completely linear optical systems.

Coupling of polarization and spatial degrees of freedom of highly divergent emission in broad-area square vertical-cavity surface-emitting lasers.

The polarization of highly divergent modes of broad-area square vertical-cavity surface-emitting lasers is shown to be only marginally affected by material anisotropies but determined by an interplay of the polarization properties of the Bragg cavity mirrors and of the transverse boundary conditions. This leads to a locking of the polarization direction to the boundaries and its indeterminacy for wave vectors oriented along the diagonal. We point out a non-Poissonian character of nearest-neighbor frequency spacing distribution and the impossibility of single-wave number solutions.

Generation of sub-5 fs pulses in vacuum ultraviolet using four-wave frequency mixing in hollow waveguides.

We investigate the potential of four-wave mixing in dielectric hollow waveguides for vacuum ultraviolet pulse generation with unprecedented short durations. Taking into account higher-order transverse modes and plasma effects we predict the generation of a 2.5 fs pulse at 160 nm using an intense 10 fs, 800 nm pulse and its weaker third harmonic at 267 nm, both coupled to the fundamental transverse mode. Excitation of higher transverse modes allows an increase of the signal energy (up to by a factor of 20) but with a pulse duration of 13 fs (compressible to 7.7 fs).

Spatiotemporal chaos stimulated by transverse Hopf instabilities in an optical bilayer system.

We study two-dimensional spatiotemporal dynamics in an optical system of two identical nonlinear films irradiated from both sides by equal plane waves and show that a wide variety of chaotic behaviors can be obtained near the subcritical pitchfork bifurcation point. The regimes arising in the vicinity of asymmetrical steady state depend on stability of the symmetrical steady state at the same driving field, on interactions of Hopf and Turing instabilities occurring at the asymmetrical branch of solutions, and on a transverse wave number of the Hopf instability band center. The wave number is controlled by a phase shift of the field passed between two films, and the relative order of the Turing and Hopf bifurcations is controlled by a diffusion of charge carrier in a semiconductor media. Chaotic oscillating patterns are formed mainly by transverse Hopf modes rising due to a time delay in the system.

Eigenmodes and symmetry selection mechanisms in circular large-aperture vertical-cavity surface-emitting lasers.

The characteristics of the spatial eigenmodes of vertical-cavity surface-emitting lasers with a large circular aperture are considered close to the lasing threshold. Experiments yield patterns based on rotational symmetry ("flowerlike" patterns) or on Cartesian symmetry (stripelike patterns) for very close operating conditions. The former are compatible with the boundary conditions whereas the latter are expected in infinite devices. Theoretically, the problem is considered in the framework of an eigenmode analysis of a linear partial differential equation for the optical field valid at threshold. This formulation allows for a simple implementation of asymmetries due to the reflection properties of Bragg mirrors as well as of transverse variations of gain and refractive index due to the device structure or due to imperfections in the growth process. A sharp transition between flowerlike modes and stripelike modes is shown to occur, if the device aperture is increased.