We combine in this work the measurement of local optical transmission in the near-field with the mapping of the third
harmonic generation of semiconducting polymer samples. The use of a linear method with the scanning near-field optical
microscope (SNOM) and a nonlinear method with the Third Harmonique Generation (THG) microscope reveal the
variation and the nature of the nanomorphology of doped polyaniline thin films.
Although coherent light is usually required for the self-organization of regular spatial patterns from optical beams, we show that peculiar light matter interaction can break this evidence. In the traditional method to record laser-induced periodic surface structures, a light intensity distribution is produced at the surface of a polymer film by an interference between two coherent optical beams. We report on the self-organization followed by propagation of a surface relief pattern. It is induced in a polymer film by using a low-power and small-size coherent beam assisted by a high-power and large-size incoherent and unpolarized beam. We demonstrate that we can obtain large size and well organized patterns starting from a dissipative interaction. Our experiments open new directions to improve optical processing systems. We also discuss the relevance of our experiment to other systems such as social insects, for which a self-assembly or spatial pattern is organized within a collective group, starting from amplified fluctuations.
The holographic optical storage capacity with photopolymer is improved by creating a multigrating onto the surface of a azopolymer thin film with the use of a liquid droplet. We show by this method that three kinds of gratings can be created and controlled by different laser beam parameters as polarization or incident angle.
The orientation and attachment of neuronal cells were controlled by submicron-scale topographical patterns. The surface structure is realized with a laser beam and photo-responsive azobenzene polymer thin films. A surface relief grating (SRG) can be produced by self-organization of molecules under the action of light. The cells are attached onto the SRG and preferentially grown along the groove direction. The use of polymer thin films is good candidate for cellular engineering applications.
The French-Italian interferometric gravitational wave detector VIRGO is currently being commissioned. Its principal instrument is a Michelson interferometer with 3 km long optical cavities in the arms and a power-recycling mirror. This paper gives an overview of the present status of the system. We report on the presently attained sensitivity and the system’s performance during the recent commissioning runs.
The goal of the VIRGO program is to build a giant Michelson type interferometer (3 kilometer long arms) to detect gravitational waves. Large optical components (350 mm in diameter), having extremely low loss at 1064 nm, are needed. Today, the Ion beam Sputtering is the only deposition technique able to produce optical components with such performances.
Consequently, a large ion beam sputtering deposition system was built to coat large optics up to 700 mm in diameter. The performances of this coater are described in term of layer uniformity on large scale and optical losses (absorption and scattering characterization).
The VIRGO interferometer needs six main mirrors. The first set was ready in June 2002 and its installation is in progress on the VIRGO site (Italy). The optical performances of this first set are discussed. The requirements at 1064 nm are all satisfied. Indeed, the absorption level is close to 1 ppm (part per million), the scattering is lower than 5 ppm and the R.M.S. wavefront of these optics is lower than 8 nm on 150 mm in diameter. Finally, some solutions are proposed to further improve these performance, especially the absorption level (lower than 0.1 ppm) and the mechanical quality factor Q of the mirrors (thermal noise reduction).
We present the suitability of the Third Harmonic Generation (THG) technique as a new nonlinear microprobe for non destructive determination of the index profile of new types of optical fibers and particularly for the test of Photonic Bandgap (Bragg type) and microstructured air-silica (MAS) fibers. The complete spatial characteristics such as hole diameter and spacing into MAS fibers or sandwiched layer thickness into Bragg fibers were demonstrated to be attainable anywhere along a bare fiber.
Measurements by Laser scanning Third Harmonic Generation microscopy of Ca<SUP>2+</SUP> dynamic release from internal stores and/or calcium influx in biological cells is presented. The Ca<SUP>2+</SUP> signal consists of a transient increase in the intracellular concentration. A good correlation is found between these measurements and measurements done with microspectrofluorometry.
12 Energetical and spectral characteristics of backward stimulated Raman scattering (BSRS) in water and water solutions of organic liquids (acetone, benzene, ethanol, cyclohexane) at different excitation conditions have been experimentally investigated. Maximum conversion efficiency of laser light into BSRS wave was about 40%. For picosecond range experimental results and calculations are presented showing the BSRS intensity as a function of the main experimental parameters concerning the geometry of excitation and the exciting intensity. Thus it's possible to forecast the best experimental set-up in term of BSRS efficiencies and to estimate the minimum length of water necessary to detect BSRS. Competition with other scatterings is observed. In nanosecond range simultaneously with BSRS stimulated Brillouin scattering has been excited. Possible applications are discussed.
Experimental investigations of the energetical, spatial and statistical properties of stimulated Raman scattering (SRS) pulses, excited in acetone by picosecond laser pulses, are presented. The properties of the SRS pulses propagating in the forward direction and propagating in the backward direction are compared. Changing the geometrical and energetical conditions of excitation one can change the properties of SRS pulses in proper way.
We have observed SRWS without phase modulation and self focusing of the pump beam with use of a Bessel beam excitation. The experiments show at the scattering threshold two types of line spectra, and above the threshold a large band spectrum. These results are interpreted by the presence of four photon processes coupling two exciting photons, one Stokes and one anti-Stokes scattered photon, developing in cascade. This interpretation can be extended to the recent studies of soliton propagation in a planar waveguide.
We report on the observation of far field spatial distortions of a Bessel beam after passing through a Kerr liquid. A coaxial ring structure has been observed to occur at some threshold power. It consists of two closely spaced (1.5 - 3.5 mrad) sharp rings of comparable intensity and a diffuse inner ring of smaller intensity separated by 8 - 9 mrad. Evolution of the far field pattern with moving the sample along the propagation path of the Bessel beam shows strong dependence of beam distortions upon the position of the sample. The phenomenon is supposed to be due to nonlinearly induced phase aberrations resulting in the distortion of angular spectrum.