Numerical simulations are established concerning optically stimulated acoustic propagative coherent wavefronts (opto-acoustic transduction) and optically detected acoustic wavefront (acousto-optic transduction). A typical user case is given related to a typical example of a bi-layered system ZnO/GaAs. It corresponds to a typical condensed matter system including a thin film layer deposited on top of a bulk substrate. The numerical study is ab-initio developed into the general context of the thermo-elastic regime, outside of any piezo-electric or deformation potential regime nor charge carrier diffusion, without any required initial software packages, e.g. without introducing any initial (external pre-programmed) software packages and/or requiring a subsidiary sub-model. Transient temporal deformation fields are simulated under homogeneous material conditions. Transient optical reflectivity signals are also simulated, as physically measured signals of interest during the experiments. Limit cases (red/red configuration for pump and probe optical beam, without any thin layer deposited) allow to validate the codes given.

Complete numerical simulations are given under SciLab® and MATLAB® coding environments, concerning propagative acoustic wavefronts, for laser picosecond ultrasonics under multiwavelength conditions. Simulations of the deformation field and its propagation into bulk material are given under different wavelength configurations for optical pump and probe beams, which are used to generate and to detect the acoustic signal. Complete insights concerning the dynamics of the acoustic waves are given, considering the absence of carrier diffusions into the material. Several numerical approaches are proposed concerning both the functions introduced to simulate the wavefront ( Heaviside or error) and the coding approach (linear/vectorized/ Oriented Object Programming), under the pure thermo-elastic approach.

A complete numerical complete toolbox is proposed concerning the simulation of photo-induced propagative mechanical wave, and concerning the optical reflectometric measured response of the material, which is initially exposed to a first pump laser beam that photo-induces the acoustic wavefronts. The deformation field and its propagation into a bulk material are simulated. Based on this field expression, the complex transient reflectivity is given for a medium considered as homogeneous. The real part of this quantity permits afterwards to propose a numerical simulation of the transient reflectivity, which corresponds to the optical signal measured during experimental works. The frequency acoustic spectrum is simulated and successfully compared to the measured frequency spectrum. For the first time, numerical complete developments are explicitly proposed and fully-developed under the SciLab ® environment, related to the simulation of laser-induced picosecond acoustic wavefront photogenerated through an opto-acoustic transduction process (ultrasonics and pretersonics).

The experimental study of the laser induced alignment of linear atmospheric molecules naturally present into the air using an ultra-short (femtosecond temporal range) and ultra-intense (TW · cm –2 fluence range) linearly polarised laser pulse is described. The measurements are conducted under a two-color pump-probe configuration using an IR pump beam and a blue probe pulse (red-blue configuration), which interacts with the molecules after they have been exposed to the IR alignment pulse. The optical birefringence and dichroism polarimetric signals have been both strictly measured into the same experimental conditions into this two-color configuration. A balanced detection permits the heterodyne signal to be got directly. Under the short and intense laser pulse exposure, the molecules present into the atmospheric air (under standard room temperature conditions) aligne, and periodic transient revivals are observed (field free alignment approach into non-adiabatic conditions). The results obtained are in accordance with those obtained in the red-red configuration and confirm the approach proposed as relevant for atmospheric sensing.

Mathematical calculations are given concerning the evaluation of the negative ions photodetachment cross-section \(\sigma \), into a so-called saturation regime. The interaction between a negative ion particle beam and a laser beam is examined under theoretical aspects. A quantitative criterion S is proposed to define the saturation threshold between the linear and the saturated domains, which are both present in this saturation regime. The asymptotic behaviours extracted at the low and high energy limits are used to determine this threshold quantitative criterion S and to evaluate also the photodetachment cross-section \(\sigma \). The case of a symmetric gaussian photodetachment laser beam shape is examined according to the proposed formalism, which can be used either for the photo-detachment or photo-ionization processes, and could be potentially used into technological solutions for negative ion neutralisation processes (such as neutral beam injector) in the future fusion energy devices. Estimations onto the errors related to the use of this methodology are given.

Symmetric top molecules of methyl iodide are irradiated with a terahertz pulse generated by a two-color plasma and shaped by a short propagation in air. Free-induction decay is emitted by the excited molecular sample and then propagates in air before detection. The experimental data show that the input terahertz (THz) pulse undergoes strong reshaping through absorption and dispersion. This leads to narrow wave packets at revival times due to the excitation of high rotational energy levels. Typically, a THz burst of duration similar or equal to 15-20 ps is produced periodically, with a central frequency of similar or equal to 1 THz and a width that can be as narrow as 60-80 GHz. Pulse shaping based on propagation can be useful for quantum control in molecules. We provide a theoretical description of this wave propagation based on the Maxwell-Bloch equation. The observed experimental signal is in good agreement with the numerical simulations.

We experimentally investigate the free induction decay in the asymmetric top molecule H2O after interaction with short terahertz pulses. Two different experimental techniques are used to perform measurements in the gas phase under different experimental conditions: electro-optical detection and terahertz field-induced second-harmonic generation. Simulations of the free induction decay signals are performed with a theoretical approach in which the absorption and dispersion coefficients are evaluated from spectroscopic data pertaining to the water molecule. Experimental and theoretical signals are compared directly in the time domain in two limiting cases. For a short propagation length of similar to 40 cm, both signals show a slightly altered electric field consistent with the approximation of weak absorption and dispersion. For a longer propagation length of similar to 300 cm, the electric field is heavily distorted. A good agreement between experimental and calculated signals is obtained in both cases. Finally, we discuss the advantages and/or disadvantages of the two experimental techniques.

Among the several aspects involved into the synthesis of monocharged nitrogene-vacancy NV− colored centers produced into nanodiamonds ND, the post-annealing cleaning process, such as sulfo-nitric acid cleaning or thermal oxidation under acid conditions, can be seen as a factor impacting the optical response of these NV− colored centers. A significative difference of optical response is in fact noticed modifying the post-annealing treatment conditions, between a pure oxidative treatment at room temperature and a mixed-process including oxidation and thermal activation. Specific chemical processes and surface chemical aspects are proposed to explain the optical signals obtained by fluorescence. Some chemical pathways are then found more efficient than others to limit the fluorescence quenching of these colored NV− emitters.

We investigate experimentally and numerically the field-free orientation of the symmetric-top molecule of methyl iodide at high temperatures using a terahertz radiation generated by a plasma induced by a two-color laser beam. The degree of orientation is measured from the free-induction decay emitted by the sample. The observed experimental signal is reproduced with good accuracy by numerical simulations.

A low frequency and high amplitude rectangular voltage V has been applied during different increased duration to Twisted Surface Stabilized Ferroelectric Liquid crystal (TwFLC) samples in which the alignment layers of the two substrates were rubbed along two different directions between 0° and 90°. The optical bistability properties have been evaluated using the specific Mueller Matrix formalism that allows a simultaneous access, through a single-shot measurement, to different polarimetric coefficients. In this new approach, the ellipticity ϵR and the azimuthal αR polarimetric parameters, extracted from the birefringence Mueller Matrix MR will be considered in priority. Several significant parameters, such as the horizontal offset ΔV, the degree of asymmetry DA, the characteristic area S of the hysteresis loop, are used to characterize the degradation observed into the hysteretic behaviour of the samples, for different values of ψ, at different duration T of exposure to V, before reaching the so-called stripes regime, giving a new experimental point of view concerning the evolution of the dynamic properties of the samples studied. The αR(V) and the ϵR(V) hysteresis loops are specifically examined. Static mapping related to ϵR(T) is given too. Among the different possible physical origins of the observed degradation, the in-plane anchoring energy contribution will be particularly examined, and a theoretical model is proposed that also gives access to different physical parameters, through a new approach.

A method is described to measure photoexcitation cross sections, relying on the expected behavior of the signal in the saturated regime, when excitation is provided by a Gaussian light beam. The method is implemented on a negative ion beam, with a single-mode pulsed Nd:YAG laser, to make a laser measurement of the photodetachment cross section of ${\mathrm{H}}^{\ensuremath{-}}$, at the wavelength 1064 nm. This cross section is of importance both as a photodetachment cross section of the most elementary negative ion and as a key parameter for the production of fast neutral ${\mathrm{H}}^{0}$ or ${\mathrm{D}}^{0}$ atoms, by photodetachment of accelerated anions. The obtained value $4.5(6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{2}$ is greater than the one known from older measurements and most ab initio calculations.

The present work presents, for the first time, the dynamic evolution of the hysteresis loops R(V), specifically based onto the total retardance polarimetric parameter R(t) extracted from the Mueller Matrix (MM) of Twisted Ferro-electric Liquid Crystal (TwFLC) samples. This evolution is given for increased exposure time Texp to a rectangular periodic electric field Eapp preliminary applied to the sample, before performing the polarimetric measurements. The Mueller Matrix formalism used is found as a relevant non-destructive and non invasive full-optical method to characterize and to monitor the Twisted Ferro-electric Liquid Crystal cell dynamic behaviour under external applied electric field, before reaching the so-called stripes regime.

Experimental results are presented related to the dynamic behaviour of Polymer Stabilized Ferro-electric Liquid Crystal (PSFLC) samples under external applied electric field, using Snap-shot Mueller Matrix Polarimetry (SMMP) and Mueller Matrix (MM) formalism. Different polarimetric coefficients are simultaneously extracted from each channeled spectrum measured with this full-optical SMMP technique. The impact of the concentration of polymer present into the liquid crystal cell on this dynamic behaviour is studied, permitting a direct and quick characterisation of the material. The results obtained for PSFLC are compared with those already measured for pure Surface Stabilized Ferro-electric Liquid Crystal (SSFLC) samples, which correspond to a 0% concentration in polymer.

The full-optical set-up snap-shot Mueller matrix polarimeter (SMMP) is used to measure the channelled spectrum Iλ(λ) related to a twisted ferroelectric liquid crystal (TwFLC) studied here with this technique. The samples were preliminarily exposed to a high-amplitude/low-frequency rectangular voltage before all the optical measurements. This voltage applied permits one to work in the specific stripe regime. From the channelled spectrum recorded Iλ(λ), the different Mueller matrix (MM) can be obtained: the depolarization matrix, the retardance matrix and the diattenuation matrix. Several scalar polarimetric parameters are extracted from these MM, and especially αR(t), ϵR(t) and R(t). These relevant scalar coefficients, calculated from the retardance matrix, are used to determine the three hysteresis loops αR(V), ϵR(V) and R(V). We define ψ as the difference of angle between the two rubbing directions of the two symmetrical (top and bottom) substrates and we examine how the hysteresis loops obtained are modified with the value of the geometrical externally controllable parameter ψ, for angles between ψ = 0° and ψ = 90°. The key characteristics of the hysteresis loops and the evolution of these key values with ψ are detailed.

The diethyl carbonate, DEC, is an ester that is used as a solvent in Li-ion batteries, but its behavior under ionizing radiation was unknown. The transient optical absorption spectra, the decay kinetics, and the influence of various scavengers have been studied by using the picosecond laser-triggered electron accelerator ELYSE. In neat DEC, the intense near-IR (NIR) absorption spectrum is assigned to the solvated electron. It is overlapped in the visible range by another transient but longer-lived and less intense band that is assigned to the oxidized radical DEC(-H). The solvated electron molar absorption coefficients and radiolytic yield evolution from 25 ps, the geminate recombination kinetics, and the rate constants of electron transfer reactions to scavengers are determined. The radiolytic mechanism, indicating a certain radioresistance of DEC, is compared with that for other solvents.

We investigated the layer dynamics of a conventional surface-stabilized ferroelectric liquid crystal (SSFLC) using a full-optical snapshot Mueller matrix polarimeter (SMMP) based on wavelength polarization coding. Time-resolved polarimetric measurements were performed with different SSFLC samples, and a strong correlation between the polarimetric parameters and the SSFLC under electric field at different exposure times was found. It has been shown that the SMMP polarimeter is able to determine the evolution of the trajectory of the liquid crystal director between the two addressed states, the reversible motion of the smectic layer while switching, as well as the irreversible transition from chevron to bookshelf texture. (C) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.OE.51.12.123601]

Snapshot Mueller matrix polarimetry was performed for static and dynamic analyses of surface-stabilised ferroelectric liquid crystal cells under an electric field. A strong correlation between the static (at fixed voltage) and dynamic (upon field reversal) polarimetric properties and the texture of ferroelectric liquid crystal cells was established. The birefringence properties were different between a rooftop/zigzag-textured cell and a stripe-textured cell. The trajectory of the optic axis, plotted over the transition between two addressed states, was analysed for each cell. The shape of the trajectories could be explained by a reversible motion of the smectic layers while switching.

An experimental Mueller matrix polarimeter is used to quantify human liver fibrosis by measuring retardance and depolarization of thin biopsies. The former parameter is sensitive to fibrillar collagen, the latter is specifically sensitive to fibrillar collagen around blood vessels, which is not significant for liver fibrosis diagnosis. By using depolarization like a filter, retardance distribution enables distinguishing between disease stages and limits the high degree of observer discrepancy.

Seeking for the new opportunities to efficiently excite GHz-THz coherent acoustic phonons by femtosecond lasers is an active field of research. Several fundamental objectives have to be addressed in order to achieve this acoustic phonons manipulation by femtosecond laser. Among them, the understanding of femtosecond generation of coherent acoustic phonons remains a key route. Several electron-phonon, photon-phonon and phonon-phonon interaction mechanisms are involved in the processes of generation and remain only partially understood up to now. In this paper, we will present a survey of ultrafast photo-generation of coherent acoustic phonon in semiconductors. We will focus first on the generation of the phonons by fs-laser excitation through the photoinduced modifications of nanoscopic internal electric fields (deformation potential) in non-piezo-active [100] GaAs semiconductor. We will show secondly how it is possible to develop more efficient sources by using piezo-active [111], [-1-1-1] and [411] GaAs semiconductors. In that case, generation of GHz acoustic phonon due to inverse piezoelectrical effect is based on ultrafast light-induced screening of the near surface built-in electric field.

Human liver biopsy samples, consisting into a 16 mu m thickness biomaterial chemically fixed into a formaldehyde matrix, and stained by red picrosirius dye, are analysed for different states of fibrosis degeneration. Polarimetric methods, and specially Mueller polarimetry based on wavelength coding, have been qualified as an efficient tool to describe many different biological aspects. The polarimetric characteristics of the media, extracted from a Lu and Chipman decomposition(1,) (2) of their Mueller Matrix (MM), are correlated with the degeneracy level of tissue. Different works and results linked to the clinical analysis will be presented and compared to previous performed works.(3) Polarimetric imaging will be presented and compared with SHG measurements. A statistical analysis of the distribution of polarimetric parameters (such as the retardance R and depolarisation P-d) will be presented too, in order to characterise the liver fibrosis level into the biomaterial under study.