Enhanced photoinduced chi((2)) in gamma-ray-irradiated bulk glass

Gamma-ray-irradiated light-flint silicate bulk glass (Schott Glass LF5), which contains a large amount of lead oxide, displays enhanced photoinduced quasi-phase-matched second-harmonic generation (PSHG), whereas nonirradiated glass under the same experimental conditions does not generate this nonlinear effect. The dependence of the efficiency of PSHG on the amount of gamma radiation (up to 530 krad) is experimentally studied, as is the role of thermal recovery (bleaching) of the color centers as a result of seeding with the second harmonic. The effect of long-term fading is studied with a sample that was irradiated 8 years ago. Gamma irradiation of boron-crown silicate glass (BK7) does not show this enhancement.     

Phase matching in nonlinear chi((2)) photonic crystals

We analyze harmonic generation in a two-dimensional (2D) chi((2)) photonic crystal and demonstrate the possibility of multiple phase matching and multicolor parametric frequency conversion. We suggest a new type of photonic structure to achieve simultaneous generation of several harmonics; we also present both general analytical results and design parameters for 2D periodically poled LiNbO(3) structures.     

High-energy pulse compression by use of negative phase shifts produced by the cascade chi((2)):chi((2)) nonlinearity

We report a simple optical pulse-compression technique based on quadratic nonlinear media. Negative nonlinear phase shifts are generated by phase-mismatched second-harmonic generation, and the phase-modulated pulses are then compressed by propagation through materials with normal dispersion. Millijoule-energy pulses from a Ti:sapphire amplifier are compressed from 120 to 30 fs, and calculations indicate that compression ratios of >10 are realistically achievable by use of this approach with optimal materials. The insertion loss of the compressor can be less than 10% of the pulse energy, and scaling to higher pulse energies will be straightforward.     

Enhancement of chi((2)) cascading processes in one-dimensional photonic bandgap structures

We theoretically analyze the nonlinear phase shifts induced by cascaded chi((2)):chi((2)) processes in one-dimensional photonic bandgap structures. We find that the enhancement of the density of modes near the band edge, coupled with a suitable choice of relative phase mismatch, leads to a remarkable new effect: The relative phase shift of the fundamental field on transmission can be of the order of pi over a distance of 7mum , with input intensities of the order of only 10 MW/cm(2).     

Large nonlinear phase shif towing to cascaded chi((2)) in quasi-phase-matched bulk LiNbO(3)

Large nonresonant effective nonlinear indices that are due to cascading have been observed by Z-scan and CCD camera measurements performed on quasi-phase-matched LiNbO(3). Positive and negative values of n(cascad)(2) were measured at temperatures symmetrically displayed with respect to the optimum phase-matching temperatures (2.39 x 10(-13) and -2.37 x 10(-13)cm(2)/W, respectively).     

Soliton structures of a wave field with an arbitrary number of oscillations in nonresonance media

A new class of solitary solutions for a wave field is found. This class describes soliton-like structures of a circularly polarized radiation that propagate in a nonresonance medium and which involve an arbitrary number of field oscillations. A feature peculiar to these solutions is that they undergo a smooth transformation from solitons of the Schrödinger type, which correspond to long pulses involving many oscillations, to extremely short visible pulses, which, in fact, do not extend beyond one period. Realizability of such soliton structures is considered for a field of linear polarization, and their structural stability is shown numerically.     

Unveiling quasiperiodicity through nonlinear wave mixing in periodic media

Quasiperiodicity is the concept of order without translation symmetry. The discovery of quasiperiodic order in natural materials transformed the way scientists examine and define ordered structure. We show and verify experimentally that quasiperiodicity can be observed by scattering processes from a periodic structure, provided the interaction area is of finite width. This is made through a momentum conservation condition, physically realizing a geometrical method used to model quasiperiodic structures by projecting a periodic structure of a higher dimension.     

Complexity in spiral wave dynamics(a))

In closed systems of the Belousov-Zhabotinsky reaction a large number of dynamic states found in open systems is sampled as they evolve in time. During such slow aging processes of thin solution layers, prepared under appropriately chosen chemical conditions, an unexpectedly rich variety of spiral tip behavior was observed experimentally. Within a (concentration, time) parameter plane, the movement of free ends of waves was classified as follows: (a) in a stable domain-periodic rigid rotation with cores of small (200 &mgr;m) or very large (2 mm) diameter; quasiperiodic compound motion along a hypocycle, a straight loopy line or an epicycle; complex meandering composed of possibly more than two components; (b) rectilinear tip motion indicating the boundary of spiral wave stability; and (c) in an unstable domain-shrinking of open ends of wave fronts during propagation. The main properties of these parameters are compared with recently published computer calculations.     

Anomalous wave as a result of the collision of two wave groups on the sea surface

The numerical simulation of the nonlinear dynamics of the sea surface has shown that the collision of two groups of relatively low waves with close but noncollinear wave vectors (two or three waves in each group with a steepness of about 0.2) can result in the appearance of an individual anomalous wave whose height is noticeably larger than that in the linear theory. Since such collisions quite often occur on the ocean surface, this scenario of the formation of rogue waves is apparently most typical under natural conditions.     

Third-harmonic generation in quasi-phase-matched chi(2) media with missing second harmonic

What we believe to be a conceptually novel scheme for third-harmonic generation in engineered quasi-phase-matched chi((2)) optical structures is proposed in which the fundamental-frequency field is directly converted into the third-harmonic field without the intermediate generation of the second-harmonic field. This counterintuitive scheme, which exploits the concept of adiabatic passage and the existence of a nonlinear dark state, bears a close connection to the "stimulated Raman adiabatic passage" technique of population transfer in atomic physics.     

Soliton propagation in heterogeneous and random media of a specific class

The motion of solitons in a medium whose parameters vary randomly but so that a stochastic nonlinear equation remains fully integrable is considered. It is found that, in this case, the position of the soliton maximum executes Brownian motion, while its phase becomes random.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 91–97, April, 1987.     

Soliton regimes of surface magnetostatic wave propagation in a magnet-semiconductor structure

The nonlinear properties of exchange-free surface magnetostatic spin waves in a layered structure containing films of a ferromagnet and a semiconductor are investigated theoretically. The stability of nonlinear surface magnetostatic waves relative to longitudinal disturbances is investigated using the envelope evolution equation in the weak-nonlinearity approximation. It is shown that, under certain conditions, a surface spin-wave pulse propagates in the form of an envelope soliton. Calculations are performed for the case of an yttrium iron-garnet-indium antimonide structure. Fiz. Tverd. Tela (St. Petersburg) 41, 1272–1275 (July 1999)     

Deflection of a phase-conjugate wave in nondegenerate four-wave mixing

The boundary problem for signal phase conjugation at nondegenerated four-wave mixing (FWM) is considered. In contrast to the statements of some authors it is shown that noncollinearity of the incident and the phase-conjugate waves occur. Expressions have been obtained for the deflection angle for a number of configurations of practical importance. Useful analogy between linear and nonlinear reflection at the FWM is noted.     

Distributed feedback in a waveguide by four wave mixing

The theory of four wave mixing, two guided and two radiation modes of planar optical waveguides, with periodic structure of interaction regions is presented. In the degenerate case multiple penetration of the pumping waves through the waveguide enables better utilization of their energy, as compared with the single four wave mixing. In the nondegenerate case the periodic structure enables phase matching between initial and backward guided modes.     

Soliton compression in quadratic media: high-energy few-cycle pulses with a frequency-doubling crystal

We present a soliton effect pulse compression technique that uses self-defocusing cascaded-quadratic nonlinearities, with no fundamental limit to its scalability to high pulse energies and the capability of generating few-cycle pulses with only a frequency-doubling crystal. The conditions for which group-velocity mismatch causes an acceptable perturbation to soliton compression are analyzed and underlie optimization of the compressor. Calculations predict compression to near-single-cycle durations, with compression ratios as high as 100. Initial experiments closely agree with calculations, demonstrating compression to durations under three optical cycles (12 fs) and generation of 600 nm bandwidths.     

Wavelength dependence of phase conjugate reflectivity in absorbing media and thermal grating studies by four wave mixing

The development of optical phase conjugation using thermally formed gratings in absorbing media, especially the dye solutions, has besides the high efficiencies, many other characteristics which are worthy of study. Here the wavelength dependence of phase conjugate reflectivity in relation to absorption spectrum of rhodamine-6G and rhodamine-B in water, methanol and ethanol is reported. Further the Bragg condition has been verified for the dominant diffracted beam which shows that the thermal grating behaves like an optically thick grating.     

Superinelastic electron transfer: electron trapping in H2O ice via the N-2((2)Pi(g)) resonance

We present measurements on the trapping of 0-3 eV electrons in H2O ice films covered with a submonolayer of N2 molecules. At the energy of the N-2((2)Pi(g)) shape resonance, the absolute cross section for electron trapping in ice is approximately 5.5 x 10(-16) cm(2), similar to that for vibrational excitations of gaseous N2 via the resonance. This result, indicating that nearly all electrons from autoionization of N-2((2)Pi(g)) are transferred to electron traps in ice, is explained by superinelastic electron transfer from N-2((2)Pi(g)) into preexisting traps in polar ice, leaving N2 in high vibrational excited states.     

Soliton Solutions and Interaction Between a Line Soliton and a y-Periodic Soliton in Generalized (2+1)-Dimensional Nizhnik-Novikov-Veselov Equation

Using the variable separation approach, many types of exact solutions of the generalized (2 1)-dimensional Nizhnik-Novikov-Veselov equation are derived. One of the exact solutions of this model is analyzed to study the interaction between a line soliton and a y-periodic soliton.     

非旋波耦合条件下微波控制的光学双稳与多稳

研究了在非旋波耦合条件下微波场建立的原子相干对光学双稳与多稳的控制.通过改变微波场的初始相位,可以有效地控制双稳与多稳的存在与否、迟滞环宽度和阈值强度的高低.旋波和非旋波耦合在物理上可视为双色激发,耦合的能级分裂成无穷多个子能级,原来的裸态跃迁变成无穷多个不同频率的跃迁.这些跃迁的相干叠加决定了介质的非线性吸收与色散,相干叠加的结果取决于微波场的相位. 关键词： 原子相干 非旋波耦合 光学双稳与多稳 相位控制     

Efficient, multiwatt, continuous-wave laser operation on the (4)F((3/2))-(4)I((9/2)) transitions of Nd:YVO(4) and Nd:YAG

We report multiwatt, diode-pumped cw operation on the (4)F(3/2)-(4)I(9/2) laser transition at 914.5 nm in Nd:YVO(4), for which an output power of 3.0 W and a slope of efficiency of 22.8% were achieved. For the corresponding laser transition of Nd:YAG at 946 nm an output power of 5.35 W and a slope efficiency of 40.2% were measured. By intracavity frequency doubling, an output power of 1.5 W at 473 nm was generated.