S. Martellucci

Optically induced reorientational birefringence in an artificial anisotropic Kerr medium

Abstract A laser induced optical birefringence has been obtained for the first time in an anisotropic artificial Kerr medium. This consists of an aqueous suspension of dielectric microellipsoids which reorientate under electromagnetic and brownian torques. The measured effective optical Kerr coefficients, n 2 , is 4.0x10 -4 cm 2 /MW while the response time is 2.6 ms. These values agree with the ones obtained from a simple Debye model assuming rigid anisotropic rotors in a statistical environment.

Diffraction Patterns of Self-Phase-Modulated Laser Beams

Transverse optical intensity redistribution phenomena like self-focusing, self-defocusing and ring generation happen when a Gaussian laser beam is focused onto a nonlinear medium. We introduce a method for the evaluation of the diffraction pattern that is very simple, quick and suitable for computer implementation.

Soret effect in forced Rayleigh scattering

In forced Rayleigh scattering of mixtures or suspensions the temperature gratings generate, by the Soret effect, concentration gratings that may be very important since they produce both a phase and an amplitude grating superimposed on the principal one. The experimental evidence of their influence was given by Thyagarajan and Lallemand using a mixture of carbondisulfide and ethanol. In this paper we study the temporal behaviour of the concentration grating versus the sample properties and its effect on the detected diffracted beam. Explicit expressions are given for the output intensity taking into account both the generated amplitude and phase gratings.

Surface states studies in semiconductors by photothermal deflection spectroscopy

A method based on the analysis of both the amplitude and phase of the photothermal deflection spectroscopy signal which enables one to locate surface states on the front or rear surface of semiconductor wafers and to measure their absorption. The procedure also allows the determination of the sample thermal conductivity.

Third-order nonlinearity enhancement in an artificial Kerr medium through bulk intrinsic birefringence.

Laser-induced circular birefringence measurements have been performed on a liquid suspension of polymer microellipsoids in order to study its optical nonlinearity as a function of the host liquids refractive index n(h). The results show that the large values obtained for the chi1221((3)) term (1.6 x 10(-8) esu for n(h) = 1.330) can be explained with an intrinsic birefringence of the microellipsoids relative to their geometrical axes. The obtained values for the refractive indices are n || = 1.391 and n perpendicular = 1.368.

Photothermal deflection spectroscopy study of defects in semi-insulating GaAs

Subgab absorption measurements carried out by photothermal deflection spectroscopy in semi-insulating GaAs are used to study the concentration of defects found in as-grown and in heat treated material. Measurements carried out in ion-implanted and furnace-annealed samples prove to be a useful tool for monitoring the successful recovery of the ion implantation damage.

Stable hysteretic reflection of light at a nonlinear interface

We have observed a hysteretic (bistable) reflection of a Gaussian laser beam at the interface between glass and a liquid solution of polystyrene microspheres as nonlinear medium with both branches of the hysteretic curve being stable, in contrast to the results of previous experiments.

Experimental results on the photophoretic motion and radiometric trapping of particles by irradiation with laser light

An experimental observation of the photophoretic motion of micro-sized particles suspended in air has been performed using the radiometric force from a continuous laser beam. The irradiation was used to trap the particles in a confined optical field and to levitate them. Complex photophoretic motion of the particles was observed in the focus of the beam.

Spatial filtering in the detection of transverse phase modulation through a nonlinear thin film

Abstract In thermal lens spectroscopy, improvement of the signal to background ratio can be achieved by the introduction of a circular stop operating as a spatial filter. In this communication we introduce a mathematical model for the signal interpretation and show its validity by comparison with experimental data and, where available, with an analytical solution.

Laser induced thermal profiles in thermally and optically thin films

The temperature field generated by the weak absorption of a gaussian laser beam in an optically and thermally thin film bounded by two transparent plates is discussed. An analytical solution of the problem is presented together with an algorithm for the numerical integration. The influence of the finite thermal conductivity of the plates is shown in an example.