Nonlinear Ellipsometry Research Articles

Наведенное двулучепреломление в квантовых точках CdSe в матрице фосфатного стекла

In this paper, we report on the experimental observation of light-induced anisotropy (the optical Kerr effect) due to third-order nonlinear dielectric susceptibility (3) in a nanocomposite material consisting of CdSe quantum dots in a phosphate glass matrix. The signs and values of the off-diagonal components of the tensor (3) are determined using z-scanning techniques and nonlinear ellipsometry. It was shown that the nonlinear response contains three time components, the fastest of which does not exceed 20 ps, the average has an exponential form and amounted to 90 11 and 38530 ps for different samples, and the longest nonexponential and amounts to times of the order of a few nanoseconds. The switching of an optical signal with a time not exceeding 20 ps is demonstrated.

Nonlinear ellipsometry of Si(111) by second harmonic generation

In this paper we present experimental and simulated data of the second harmonic response for arbitrarily oriented linear input polarization and output polarization on Si(111) surfaces. In contrast to other nonlinear optical ellipsometry experiments (e.g. nonlinear optical null ellipsometry) we azimuthally rotate the sample for additional analysis of the crystal structure. In our study, we used the simplified bond hyperpolarizability model (SBHM) to simulate the observed angular shifts of the nonlinear peaks and the change of symmetry features related to a modification of the beam polarizations. Our findings help to identify the corresponding interface dipolar and bulk quadrupolar SHG sources.

Fluorinated and Non-Fluorinated Electro-Optic Copolymers: Determination of the Time and Temperature Stability of the Induced Electro-Optic Coefficient

Organic fluorinated materials demonstrate their excellent electro-optic properties and versatility for technological applications. The partial substitution of hydrogen with fluorine in carbon-halides bounds allows the reduction of absorption losses at the telecommunication wavelengths. In these interesting compounds, the electro-optic coefficient was typically induced by a poling procedure. The magnitude and the time stability of the coefficient is an important issue to be investigated in order to compare copolymer species. Here, a review of different measurement techniques (such as nonlinear ellipsometry, second harmonic generation, temperature scanning and isothermal relaxation) was shown and applied to a variety of fluorinated and non-fluorinated electro-optic compounds.

Advances in polarization sensitive multiphoton nano-bio-imaging

In this talk, we shall shortly review four main directions of ongoing research in our laboratories, directed at the conception and demonstration of a variety of innovative configurations in nanoscale multiphoton imaging. A common feature to all of these directions appears to be the central role played by the involvement of polarization features, both in- and outgoing, moreover so in view of the tensorial aspects inherent to nonlinear schemes such second-harmonic generation, electro-optic modulation or two-photon fluorescence which will ne emphasized. These advances relate to the new domain of nonlinear ellipsometry in multiphoton imaging (1), of high relevance to fundamental aspects of nanophotonics and nanomaterial engineering as well as towards basic life science issues. The four domains to be shortly reported are: a) polarization resolved second-harmonic generation in semiconductor QD's with record small sizes in the 10-12 nm range (2) b) original use of two-photon confocal polarization resolved microscopy in DNA stained by two photon fluorescent dyes in different LC phases arrangements so as to characterize these as well as ascertain the respective DNA-dye orientation (intercalant or groves) (3) c) elaboration and demonstration of an electrooptic confocal microscope in a highly sensitive interferometric and homodyne detection configuration allowing to map weak electric potentials such as in artificial functionalized membranes, the dynamical investigation of firing and propagation aspects of action potentials in neurones being currently the next step (4) d) original plasmon based enhanced nanoscale confocal imaging involving a dual detection scheme (fluorescence imaging and ATR plasmon coupling in reflection) whereby adequate preparation and switching of the incoming polarization state between radial, linear and azimuthal configurations, entail different images and plasmon enhancement levels (5).

Temperature Stability of the Electro-Optic Response of Highly Fluorinated Side Chain Organic Copolymers

In this work were investigated the second order nonlinear optical properties of a group of Disperse Red 1 based electro-optic fluorinated copolymers, synthesized with two fluorinated monomers: the α -fluoroacrylate monomer bearing the 2,2,2-trifluoroethyl side group and the α -fluoroacrylate monomer bearing the Disperse Red 1 chromophore. By means of nonlinear ellipsometry at λ = 1550 nm, the poling-induced electro-optic tensor main component r 33 was retrieved and the stability of the second order nonlinear properties were measured giving a depolarization temperature T dep = 114°C and an activation energy E A ≈ 60 kcal/mol.

Second order optical nonlinearity of ZnO∕ZnO:Al bilayers deposited on glass by low temperature radio frequency sputtering

The authors report on the measurement of the second order nonlinear optical properties of ZnO films deposited by low temperature radio frequency sputtering on ZnO:Al coated glass substrates. They show that ZnO:Al plays a crucial role as a buffer layer for the successive growth of ZnO. The effect of aluminum doping on the relaxation of the stresses acts as a template for crystallization of ZnO, allowing us to obtain partially oriented ZnO films with relatively large nonlinear coefficients. The measurements of the second harmonic tensor by the Maker fringes method are in good agreement with results for the electro-optic coefficient obtained by nonlinear ellipsometry.

Enhanced stability of the second order optical properties of high-Tg fluorinated electro-optic copolymer

In this work the authors investigated the second order nonlinear optical properties of a group of Disperse Red 1 based electro-optic fluorinated copolymers, synthesized with two fluorinated monomers: the α-fluoroacrylate monomer bearing an adamantane side group and the α-fluoroacrylate monomer bearing the Disperse Red 1 chromophore. By means of nonlinear ellipsometry at λ=1550nm, the poling induced electro-optic tensor main component r33 was determined. The polymer’s thermostability was investigated by means of the temperature scanning and isothermal relaxation techniques, leading to the determination of the depolarization temperature Tdep=136°C, corresponding to an activation energy for the relaxation of the orientational distribution of the active chromophores EA=105kcal∕mol. The increased thermostability of the copolymer, given by the adamantane side group, is then compared with that of other two groups of fluorinated copolymers.

Use of sandwich structures with ZnO:Al transparent electrodes for the measurement of the electro-optic properties of standard and fluorinated poled copolymers at λ = 1.55 μm

We report on the measurement of the electro-optic coefficient r33 of poled polymers at λ=1.55μm via the non-linear ellipsometry technique (or Teng and Man technique). Since the measurements rely on the use of sandwich structures with transparent electrodes, different types of aluminium doped zinc oxide (ZnO:Al) are taken into account in order to ensure transparency at the infrared range wavelength. Results on the disperse red 1/poly-methyl-metacrylate (DR1–PMMA) based side-chain benchmark system, with several different concentrations of active groups from 0.05 to 0.58molar, are reported and demonstrate the reliability of the technique. The measurement technique was then used to evaluate the r33 coefficient of copolymers derived from DR1–PMMA by partial fluorination (FATRIFE). In this case, we measured copolymers with three concentrations of active groups, 0.30, 0.37 and 0.56molar.

Concentration dependence of the optical nonlinearity in extremely doped fluorinated organic copolymers

In this work we investigated the second-order nonlinear optical properties of a group of Disperse-Red-1-based electro-optic fluorinated copolymers, synthesized with two fluorinated monomers: the hexafluoroisopropyl alphafluoroacrylate monomer and the alphafluoroacrylate monomer bearing the Disperse Red 1 chromophore. Copolymers, with a concentration of chromophore substituted groups ranging from 46% to 75% molar, were synthesized and deposited as single films on glass substrates, for second-harmonic generation, and as sandwich structures with electrodes, for nonlinear ellipsometry measurements. For large concentrations of substituted groups, cracking of the films was observed and did not allow for any electro-optic characterization by nonlinear ellipsometry. The second-harmonic generation tensor main component d33 was retrieved by means of second-harmonic generation at λ=1064nm for each concentration. The results obtained for the copolymer with the lowest concentration are compared with those obtained by nonlinear ellipsometry at λ=1550nm and used as a calibration to infer information on the electro-optic properties at large concentrations. Stability of the poling-induced second-order nonlinear properties was checked by means of nonlinear ellipsometry. By using the temperature scanning technique, a depolarization temperature Tdep=124°C was measured, while the use of the isothermal relaxation technique allowed to observe two different decay regimes, a Vogel-Fulcher-Taman-Hesse one for temperatures above 110°C and an Arrhenius one for temperatures below 110°C, with activation energy EA≈58kcal∕mol.

Orientation and nonlinear optical properties of N-4-nitrophenyl-(L)-prolinol crystals on nanostructured poly(tetrafluoroethylene) substrates

Thin crystalline films of N-4-nitrophenyl-(L)-prolinol (NPP) were grown on nanostructured highly oriented poly(tetrafluoroethylene) (PTFE) substrates. Depending on the growth conditions, two types of crystalline orientation were observed. Thinnest samples (<0.2 μm), directly grown from the vapor phase, are made of numerous highly ordered crystallites presenting a (110)NPP∥(100)PTFE interfacial relationship and an almost perfect azimuthal orientation. Thicker layers (>1 μm) could be obtained from deposition–annealing procedures and exhibit a (101)NPP planar orientation but with a lack of azimuthal orientation. The full characterization of these various samples was performed by analysis of x-ray diffraction data obtained in θ–2θ and grazing incidence geometry, the latter being used to determine the azimuthal orientation. Furthermore, the proposed orientations were fully consistent with the nonlinear optical (NLO) properties of the layers, deduced from optical second harmonic generation measurements. The combination of x-ray diffraction and nonlinear ellipsometry technique thus proved once again to be a powerful method to analyze oriented structures obtained with NLO molecules.

Polarization field in optical spatial vector solitons

We report for the first time the experimental observation of polarization field in optical spatial solitons in nonlinear planar waveguide. The measurements have been checked by an improved local method (nonlinear ellipsometry method). The results confirm the uniformity of the polarization field for TE and TM solitons (in 1+1D propagation). In the case of mixed TE–TM input polarization, we have pointed out the existence of spatial vector solitons in such nonlinear waveguides. Their output polarization state distribution is uniform in the transverse section.

Influence of transverse effects on self-induced polarization changes in an isotropic Kerr medium

Allowing for an isotropic optical nonlinearity of third order, we derive approximate Gaussian solutions of the paraxial wave equation. They describe a monochromatic elliptically polarized light signal of finite extension both in space and in time. In contrast to plane-wave results, the state of polarization is found to be strongly nonuniform in the transverse direction. Both the orientation and the shape of the polarization ellipse are not conserved. For low intensities, parameters measuring the induced optical activity depend on the intensity quadratically instead of linearly. For high intensities, saturation sets in. It is argued that by means of nonlinear ellipsometry one can evaluate two tensor components, namely, Re χxyyx(3) and Re χxxxx(3). Upon taking into account transverse as well as temporal effects, the magnitude of these components may decrease by a factor of 10.

Nonlinear ellipsometry: a first approach

We present, for what is to our knowledge the first time, the theoretical calculations of the ellipsometric parameters of a single nonlinear layer–substrate system (Fabry–Perot cavity) and of a nonlinear attenuated total internal reflection configuration. Using an analytical solution of the nonlinear wave equation in a medium with a weak third-order nonlinearity of thermal origin, we can determine theoretically the ellipsometric parameters for an incident linearly polarized monochromatic plane wave. We show that the sensitivity of the ellipsometric parameters with respect to the input flux and to changes of the nonlinear coefficient depends strongly on the sharpness of the linear resonances of the system. We propose ellipsometric experiments that permit the determination of small nonlinear coefficients.

A Comment on Non-Linear Depolarization Effects under the Giant Two-Photon Excitation of Excitonic Molecules in CuCl

Photo-induced depolarization effect of linearly polarized beam in the giant two-photon absorption (GTA) band of excitonic molecules was examined in CuCl with the use of non-linear ellipsometry. After the careful elimination of the instrumental optical anisotropy, no depolarization was observed under the excitation of 1 MW/cm 2 . The stability of the linearly polarized state was also studied by measuring the polarization character for a slightly elliptical beam and a partially polarized beam. Growth of the depolarization was found in both cases and thus the linear polarization is concluded to be an unstable state in the GTA resonance.

Renormalization effects of exciton polaritons in CuCl by non-linear ellipsometry

Induced renormalization of exciton polariton (EP) dispersion due to the formation of г 1-excitonic molecules (EM's) are studied by means of the nonlinear ellipsometry. Real and imaginary parts of the induced change in the complex refractive index are determined, quantitatively. The relation between both parts are discussed in terms of the Kramers-Kronig relation.