We present an indirect and non-destructive optical method for domain statistic characterization in disordered nonlinear crystals, having a spatially random distribution of ferroelectric domains with homogeneous refractive index. This method, based on a combination of numerical simulations and experimental measurements, analyses the wavelengthdependent second harmonic spatial distribution. We apply this technique to the characterization of two different random media, with drastically different statistical distributions of ferroelectric domains.
We propose and demonstrate a novel functionality of chirped mirror for monochromatic light beams: a diffraction control in reflections resulting in focusing or imaging of beams. The chirped mirrors, commonly used for manipulating temporal profiles of pulses, here are applied for manipulating the spatial dispersion of a monochromatic beam. By penetrating into dielectric layers of chirped mirror, the monochromatic beam experiences the negative diffraction, therefore the beam diverge propagating in front and behind the structure in normal diffraction region can be compensated inside this structure with negative diffraction. The result is focusing or imaging of the reflected beam from a flat interface of chirped mirror without optical axis.
We report first experimental evidences of spatial filtering of light beams in three-dimensional photonic crystals. The
photonic crystals were fabricated in a glass bulk, where refractive index was modified by applying femtosecond laser
pulses. We observe the modification of the angular spectra (the far field) in the central diffraction maximum of the
transmitted radiation in accordance with the theory of spatial filtering.
We report and analyze experimental observation of the formation of a narrow, well collimated laser beam at optical
frequency behind the woodpile photonic crystal fabricated using a femtosecond laser multi-photon polymerization
technique. We show that the collimation depends on the input laser beam focusing conditions. We discuss the
experimental results and give theoretical interpretation.
We show that photonic crystals made of materials with normal dispersion allow simultaneous broad angular range and
broad spectral range phase matching in nonlinear wave mixing processes, in particular second harmonic generation. The
configuration proposed ensures subdiffractive propagation regimes for both interacting waves and the slopes of the two
dispersion curves (for the fundamental and second harmonic waves) at the phase-matching frequencies are similar (at
frequencies slightly shifted from the phase-matched one the phase-mismatch remains very small). The numerical
simulations confirm both the broad angular range (by the use of narrow beams, with the width of few wavelengths) and
the broad spectral range (by the spectral width of the generated second harmonic beam) for the phase matching, showing
a significant increasing of the conversion efficiency with respect to the case of plane waves in homogeneous materials.
We demonstrate multifunction operation in a 2D PC slab showing that the same structure may be used for lasing, frequency shifting and switching under appropriate stimulus. Our analytical model, based on a coupled modes nonlinear approach closely describes the main experimental features. The experimental results constitute a first step towards an active reconfiguration of photonic crystal all-optical circuits.