Umberto Bortolozzo

Capillary wave turbulence on a spherical fluid surface in low gravity

We report the observation of capillary wave turbulence on the surface of a fluid layer in a low-gravity environment. In such conditions, the fluid covers all the internal surface of the spherical container that is submitted to random forcing. The surface wave amplitude displays power law spectrum over two decades in frequency, corresponding to wavelength from millimeters to a few centimeters. This spectrum is found in roughly good agreement with wave turbulence theory. Such a large-scale observation without gravity waves has never been reached during ground experiments. When the forcing is periodic, two-dimensional spherical patterns are observed on the fluid surface such as subharmonic stripes or hexagons with wavelength satisfying the capillary wave dispersion relation.

Nematicon Routing in Liquid Crystal Light Valve

Using external beams on the photoconductive layer of a liquid crystal light valve we demonstrate all-optical control of soliton induced waveguides in nematics. Using this approach we implement a half-adder and a 3-bit demultiplexer.

Picometer Displacement Detection by Using Wave Mixing in a Liquid Crystal Light Valve

The large dispersion and narrow frequency bandwidth of the two-wave mixing in liquid crystal light valve is used to realize an adaptive holographic interferometer, by which displacements as small as a few picometers are detected.

Self-pumped phase conjugation in a liquid crystal light-valve with tilted feedback mirror

Since the first demonstration of four-wave mixing in Kerr nonlinear media, a lot of works have been devoted to the realization of self-pumped phase conjugate mirrors (SPPMC), where a single incident beam generates its own phase conjugate replica through the self-generation of the pump waves. The most popular schemes make use of a photorefractive crystal, either inside a resonator cavity or alone with the pumps contained inside the sample by internal reflection at the crystal faces. Here we show a scheme based on a photorefractive liquid crystal light-valve (LCLV) with tilted feedback mirror. The self-generated waves come from the optical feedback, which induces a self- sustained refractive index grating in the liquid crystal layer.

Nonlinear transverse effects in photorefractive liquid crystal light-valves

Photorefractive liquid crystal light-valves (LCLV) are built associating a liquid crystal layer with a thin Bi12SiO20 (BSO) photorefractive crystal [1]. The photoconductive and electro optic properties of the device are separately optimized. While the excellent photosensitivity arises from the photoconductivity of the BSO, the large electro-optic effect is due to the large birefringence of the liquid crystals. Photorefractive LCLVs have been demonstrated as attractive elements for nonlinear optical applications, such as two-wave mixing optical amplification and self-pumped phase conjugation [2]. Recently, we have introduced a new optical oscillator based on a photorefractive LCLV as a gain medium [3]. The large transverse size and high gain of the LCLV allows a large number of longitudinal and transverse modes to be simultaneously amplified in the cavity, thus giving rise to dynamical regimes remained inaccessible up to date. We report different dynamical regimes, in particular high amplitude spatiotemporal pulses that are confined along the three space directions.

Nonlinear effects in a liquid crystal optical oscillator

A nonlinear optical medium results by the collective orientation of liquid crystal molecules tightly coupled to a transparent photoconductive layer made of a BSO photorefractive crystal. The nonlinear medium, called photorefractive liquid crystal light-valve, gives a large two-wave-mixing gain, thus, when inserted in a ring cavity, it results in an unidirectional optical oscillator. Dynamical regimes with many interacting modes are made possible by the wide transverse size and the high nonlinearity of the liquid crystal gain medium. In particular, we show the generation of spatiotemporal pulses, coming from the random superposition of many longitudinal and transverse modes simultaneously oscillating in the cavity.