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We analyze the conical second-harmonic generation via Cerenkov-type phase matching in two-dimensional decagonal nonlinear photonic quasi-crystals for linear, circular, and elliptical polarized fundamental beams. Depending on the polarization state, we observe either centrosymmetric or noncentrosymmetric intensity modulation of the second-harmonic rings. We explain this effect by employing the concept of effective quadratic nonlinearity combined with the hexagonal symmetry of the individual ferroelectric domains.

International audience; We demonstrate experimentally the generation of cross-polarized femtosecond pulses in BaF2 crystal in the UV region. We show that unsaturated cross-polarized wave generation in the UV is six times more efficient than in the visible region, and we deduce the corresponding wavelength dispersion of the third-order nonlinearity.

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.

A new cubic nonlinear optical effect in which a linearly polarized wave propagating in a single quadratic medium is converted into a wave that is cross polarized to the input wave is observed in BBO crystal. The effect is explained by cascading of two different second-order processes: second-harmonic generation and difference frequency mixing.

We investigate efficient fourth-harmonic generation in a single two-dimensional (2D) quadratically nonlinear photonic crystal. We propose a novel parametric process that starts with phase-matched generation of a pair of symmetric second-harmonic waves, which then interact to produce a fourth-harmonic wave that is collinear to the fundamental. We show that this process is more efficient than conventional fourth-harmonic-generation schemes by a factor that reaches 4 at low intensities and discuss how to design and optimize the nonlinear 2D photonic crystals that are implemented in LiNbO(3) and LiTaO(3) .

We demonstrate that simultaneous phase- and group-velocity-matched cascaded parametric processes can be achieved in two-dimensional quadratic nonlinear photonic crystals by proper matching of noncollinear processes with front tilting of the fundamental pulse. We present examples of cascaded third- and fourth-harmonic generation in a poled LiNbO3 planar structure.

Most of the known methods to measure the nonlinear optical properties of materials deal with the bulk properties, but there are many demanding applications that require those measurements to be done on a single particle or a single molecule. We report a novel application of nonlinear optics to measure the third-order nonlinear optical susceptibility of nanoparticles in solutions. By measuring the power of the third harmonic generated in a diluted solution of nanoparticles, both the size and chi(3) can be extracted from a simple set of measurements.

We suggest a novel scheme for multistep cascaded parametric processes based on a periodically poled nonlinear directional coupler and derive the conditions for simultaneous phase matching of the second-harmonic generation and sum-frequency mixing processes. We predict an efficient wavelength conversion by the cascaded third-harmonic generation from the third optical communication window (1.53-1.56 microm) to visible in a LiNbO3 poled waveguide coupler.

We introduce novel types of spatial vector soliton that can be generated in anisotropic optical media, such as tetragonal crystals with third-order nonlinear susceptibility. We demonstrate that these vector solitons provide a nontrivial generalization to both conventional vector solitons of birefringent cubic media and parametric solitons supported by third-order cascaded nonlinearities.

Collinear third-harmonic generation at 526.7 nm was realized by the simultaneous phase matching of two second-order processes in a single quadratic crystal: second-harmonic generation (SHG) and sum-frequency mixing (SFM). The measured conversion efficiency was 12%. As a nonlinear medium a LiNbO(3) nonlinear photonic crystal with short-range order was used that allowed simultaneous phase matching by use of discrete reciprocal vector (for the SHG process) and continuous reciprocal vectors (for the SFM process). It was demonstrated that the third harmonic could be generated efficiently in such a crystal even if the intermediate process of SHG was not perfectly phase matched.

International audience; We propose a highly efficient scheme for temporal filters devoted to femtosecond pulse contrast enhancement. The filter is based on cross-polarized wave generation with a spatially suger-Gaussian-shaped beam. In a single nonlinear crystal scheme the energy conversion to the cross-polarized pulse can reach 28%. We demonstrate that the process enables a significant spectral broadening. For an efficiency of 23% the pulse shortening is estimated to 2.2, leading to an intensity transmission of the nonlinear filter of 50%.

We demonstrate simultaneous phase matching of two different nonlinear processes, using a noncollinear interaction in periodically poled crystal with single grating. The noncollinear scheme provides phase-matching solutions over continuous regions of the optical spectrum and can be used for multiple-harmonic generation as well as all-optical effects. We have demonstrated experimentally third-harmonic generation of a 3 microm pump wavelength in a noncollinear configuration using a periodically poled LiNbO3 crystal. We observed, in good agreement with theoretical calculation, very broad spectral and thermal acceptance bandwidths, as well as a relatively narrow angular bandwidth.

International audience; We argue for a different physical interpretation of the results given in the recent Letter by Chvykov et al. [Opt. Lett.31, 1456 (2006)] in which a double nonlinear crystal scheme for cross-polarized wave generation is analyzed. We discuss the most important factors that explain the origin of the two-crystal scheme's increased efficiency, namely, the Kerr lensing effect and a Gouy phase shift. The position and orientation of the second crystal relative to the first one are unambiguously defined; related effects are illustrated by already published works on the subject.

We present a simplified, potentially portable, and highly efficient blue-light source from a periodically poled KTP waveguide crystal with a compact femtosecond Cr:LiSAF laser. This light source generates 5.6 mW of blue average output power at 424 nm with 27 mW of incident fundamental in a single-pass extracavity arrangement at room temperature. The overall system efficiency of electrical power to blue light is 0.5%, and the internal second-harmonic generation conversion efficiency is as high as 37%. The slope efficiency of 5.5% pJ(-1) at low pulse energies is, to our knowledge, the highest slope efficiency yet reported for frequency conversion into the blue spectral region.

Intensity-dependent polarization rotation that results from the simultaneous action of two third-order processes, self-phase modulation and four-wave mixing, is observed. The effect is recorded along the fourfold axis of a YVO(4) crystal. The angle of rotation is proportional to the square of the input intensity-crystal length product. This is to the authors' knowledge the first experimental evidence showing that intensity-dependent polarization rotation can be related to the real part of cubic susceptibility.

We describe a novel type of second-order cascading by which the signal that is cross polarized to the pump can be split with an efficiency of more than 100%. The process requires the simultaneous phase matching of two second-order parametric interactions, whcih can easily be achieved with recently fabricated two-dimensional nonlinear photonic crystals.

A method of intensity-dependent polarization switching is proposed. The effect is based on simultaneous action of two phase-matched second-order processes in a quadratic medium. Using analytical and numerical techniques, we demonstrate that a single linearly polarized fundamental wave, when it is propagating in such a medium, can efficiently generate a new fundamental wave of orthogonal polarization. The polarization switching is explained by an effective four-wave-mixing process that is performed through second-order cascading.

We introduce a novel class of parametric optical solitons supported simultaneously by two second-order nonlinear cascading processes, second-harmonic generation and sum-frequency mixing. We obtain, analytically and numerically, the solutions for three-wave spatial solitons and show that the presence of an additional cascading mechanism can change dramatically the properties and stability of two-wave quadratic solitary waves.