The absolute timing of the high-harmonic attosecond pulse train with respect to the generating IR pump cycle has been measured for the first time. The attosecond pulses occur 190+/-20 as after each pump field maxima (twice per optical cycle), in agreement with the "short" quantum path of the quasiclassical model of harmonic generation.

We propose a simple means for compressing optical pulses with second-harmonic generation. Aperiodic quasi-phase-matching gratings impart a frequency-dependent phase shift on the second-harmonic pulse relative to the fundamental pulse and can be engineered to correct for arbitrary phase distortions. The mechanism is discussed, and a detailed analysis of the compression of quadratic phase (linear...

A near-surface structural phase transition on a SrTiO3 single crystal, occurring at T(*) about 45 K above the bulk cubic-to-tetragonal transition, is observed by means of optical second harmonic generation. The temperature dependence of the second harmonic field in the vicinity of T(*) is described with a phenomenological Landau-type model.

We analyze second-harmonic generation (SHG) at a thin effectively quadratic nonlinear interface between two linear optical media. We predict multistability of SHG for both plane and localized waves, and also describe two-color localized photonic modes composed of a fundamental wave and its second harmonic coupled together by parametric interaction at the interface.

We study the second-harmonic generation and localization of light in a reconfigurable waveguide induced by an optical vortex soliton in a defocusing Kerr medium. We show that the vortex-induced waveguide greatly improves conversion efficiency from the fundamental to the second-harmonic field.

We report a robust method of coherent detection of broadband THz pulses using terahertz induced second-harmonic (TISH) generation in a laser induced air plasma together with a controlled second harmonic optical bias. We discuss a role of the bias field and its phase in the process of coherent detection. Phase-matching considerations subject to plasma dispersion are also examined.

Microresonator-based frequency comb generation at or near visible wavelengths would enable applications in precise optical clocks, frequency metrology, and biomedical imaging. Comb generation in the visible has been limited by strong material dispersion and loss at short wavelengths, and only very narrowband comb generation has reached below 800 nm. We use the second-order optical nonlinearity ...

We derive general conditions for 100% frequency conversion in any doubly resonant nonlinear cavity, for both secondand third-harmonic generation via χ (2) and χ (3) nonlinearities. We find that conversion efficiency is optimized for a certain “critical” power depending on the cavity parameters, and assuming reasonable parameters we predict 100% conversion using milliwatts of power or less. Thes...

Nonlinear optical phenomena on rough self-affine metal surfaces are theoretically studied. Placing nonlinearly polarizable molecules on such surfaces results in strong enhancement of optical nonlinearities. A quasistatic approximation is used to calculate local-enhancement factors for the second and third harmonic generation, degenerate four-wave mixing, and nonlinear Kerr effect. The calculati...

The second hyperpolarizability 7 of a molecule plays a role in non-linear optical processes [ 1,2] as well as in intermolecular interactions [3,4]. Usually y(--wo; WI, ~2, ~3) is measured by optical methods such as the dc Kerr effect, electric-field-induced second-harmonic generation (ESHG) of third-harmonic generation (THG), where these processes differ in the choice of the frequency arguments...