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The use of cyclopropenone derivatives as latent photo-released strained cyclic alkynes is reported for the covalent printing of complex patterns on cellulose paper. Two different approaches using either a UV LED or a laser as light irradiation source are discussed. While the high intensity of the laser damages the grafted molecular layer, the use of a simple UV LED allows the printing in only 8 min at room temperature with a good resolution at the micrometer scale with negligible diffusion. The validity of this strategy is demonstrated through the sequential printing of a QR code and a logo on the same paper sheet. [ABSTRACT FROM AUTHOR]

Optical data storage was performed with various thin polymer films containing coumarin-based derivatives and by using femtosecond laser pulses as well as two-photon absorption processes. Exploring the photodimerization attribute of coumarin derivatives and using appropriate irradiation wavelengths, recording/erasing processes could be carried out in the same area. Second harmonic generation microscopy was used to read the stored information. [ABSTRACT FROM AUTHOR]

We study the dynamics of the emission spectrum of a distributed Feedback Dye Laser in Rhodamine 6G doped polymer films. The optical feedback is provided by Bragg gratings formed in the film by interference patterns created by the pump beams. In this experiment the sample is pumped by two beams in a Lloyd mirror interferometer configuration. Both the delay and the angle between the two beams can be varied. The analysis of the emission spectrum as a function of the delay between the pumps allows measurement of the lifetime of the polarization modulation in the material. The coherent superposition of the pulses produces five laser lines in the emission spectrum. [ABSTRACT FROM AUTHOR]

The authors investigated the optical data and image storage in polymeric materials functionalized with azo-dye molecules. Thin films are initially poled to generate a spatially homogeneous second harmonic signal. The information is locally inscribed through the disorientation of the azo chromophores by successive isomerization cycles induced through the two-photon absorption processes. The resulting micron-scale controlled decrease in second harmonic signal can be exploited to perform optical storage. As a demonstration of the proposed method, they store a picture with an 8 bit gray-scale encoding. This image can only be retrieved through second harmonic detection and not by linear optical imaging techniques. [ABSTRACT FROM AUTHOR]

The recent development of 3D printers allowed a lot of limitations in the field of microfabrication to be circumvented. The ever-growing chase for smaller dimensions has come to an end in domains such as microfluidics, and the focus now shifted to a cost-efficiency challenge. In this paper, the use of a high-resolution stereolithography LCD 3D printer is investigated for fast and cheap production of microfluidic master molds. More precisely, the UV LED array and the LCD matrix of the printer act as an illuminator and a programmable photomask for soft lithography. The achieved resolution of around 100 μm is mainly limited by the pixel geometry of the LCD matrix. A tree-shape gradient mixer was fabricated using the presented method. It shows very good performances despite the presence of sidewall ripples due to the uneven pixel geometry of the LCD matrix. Any design can be brought from concept to realization in under 2 h. Given its sub-€1000 cost, this method is a very good entry point for labs wishing to explore the potential of microfluidic devices in their experiments, as well as a teaching tool for introducing students to microfluidics. [ABSTRACT FROM AUTHOR]

We analyze a simple model of a scalar optical wave with partial coherence. The model is devised to describe the influence on the coherence of the wave, of the statistical properties of its random phase, including both the second-order statistics (phase correlation) — which is classic, but also the first-order statistics (phase distribution) — which is nonclassic. Expectedly, upon increasing the disorder of the fluctuating phase through a reduction of its correlation duration, the model shows that the coherence of the wave is always reduced. By contrast, upon increasing the disorder of the fluctuating phase through an increase of its dispersion, the model reveals that the coherence of the wave can sometimes be enhanced. This beneficial consequence of an increase in disorder is related to the phenomenon of stochastic resonance or improvement by noise in signal processing. [ABSTRACT FROM AUTHOR]

Abstract: An optical setup is proposed for the implementation of compressive sensing with coherent images. This setup specifically exploits the natural multiplicative action of speckle noise occurring with coherent light, in order to optically realize the essential step in compressive sensing which is the multiplication with known random patterns of the image to be acquired. In the test of the implementation, we specifically examine the impact of several departures, that exist in practice, from the ideal conditions of a pure multiplicative action of the speckle. In such practical realistic conditions, we assess the feasibility, performance and robustness of the optical scheme of compressive sensing. [Copyright &y& Elsevier]

Abstract: We analyze image transmission in a coherent imaging system, in the presence of speckle noise modeled with the family of Gamma probability density functions of varying order. It is demonstrated that speckle noise can improve the transmission of a coherent image. Exact analytical expressions are obtained for both the best achievable performance and the optimal amount of speckle noise maximizing the transmission efficacy. These expressions allow us to analyze and control the conditions under which the coherent imaging system can take advantage of the speckle noise. The influence of the contrast in the coherent image, and of the order of the Gamma probability density describing the statistical fluctuations of the speckle, are given special attention. These results make a contribution to the understanding of the mechanisms of improvement by noise in nonlinear information processing. [Copyright &y& Elsevier]

A functionalized polymer film allowing for a complete and straightforward second-harmonic generation (SHG)-assisted high-contrast writing-reading-erasing-writing sequence is proposed. The whole process is supported by the reversible photo-induced dimerization of a coumarin chromophore and enables efficient optical data storage that can be detected only by SHG imaging. [ABSTRACT FROM AUTHOR]

An organogelator based on the Disperse Red nonlinear optical chromophore was synthesized according to a simple and efficient three-step procedure. The supramolecular gel organization leads to xerogels which display a spontaneous second harmonic generation (SHG) response without any need for preprocessing, and this SHG activity appears to be stable over several months. These findings, based on an intrinsic structural approach, are supported by favorable intermolecular supramolecular interactions, which promote a locally non-centrosymmetric NLO-active organization. This is in sharp contrast with most materials designed for SHG purposes, which generally require the use of expensive or heavy-to-handle external techniques for managing the dipoles' alignment. [ABSTRACT FROM AUTHOR]

New poly(methyl methacrylate)s bearing push–pull azo-moieties, with the azo-dye content ranging from 31 wt% to 100 wt%, are synthesized by (co)polymerization of a methacrylamide-based azo-monomer. The high reactivity of the colored monomer allowed well-balanced structures to be achieved, characterized by a suitable thermal stability. The second harmonic generation efficiency of the poled samples is investigated by means of the SHG Maker fringes setup. Features that hinder the translation of the azo-moiety optical nonlinearity in the material at the macroscopic level are debated. The results underline the role of chromophore–chromophore and chromophore–polymer interactions on the alignment of the azo-moieties. The polarity of the polymer matrix is proven to influence the chromophore–chromophore interactions. Two-photon absorption is employed for gray scale encoding of second harmonic signals on poled thin films, thus pointing out the possibility to employ these new materials for optical data storage applications. [ABSTRACT FROM AUTHOR]

We report on a crystalline rotorthat undergoes a reversible phase transition at 145 K. Variable-temperatureX-ray and 1H spin–lattice relaxation experiments,and calculations of rotational barriers, provide a description (i)of the way in which the rotators’ dynamics changes back andforth at the onset of the phase transition and (ii) of the mechanismresponsible for the abrupt switching of the crystalline rotors froma very low-energy 4-fold degenerate equilibrium state, in which therotation is ultrafast (9.6 GHz at 145 K), to a single higher-energystate associated with a slower motion (2.3 GHz at 145 K). Our resultsprovide evidence that the reversible change observed in the rotationalbarriers at the transition is due to a cooperative modulation of theC–Hrotator···Istatorhydrogenbond cloud across a C–Istator···Istator–C halogen bond-mediated phase transition. Inaddition, we report evidence for second-harmonic generation from thismaterial, thereby confirming with a second example the benefit ofusing polarized light to probe the torsional degree of freedom ofchiral helix blades, as well as symmetry and dimensionality of largecollections of chiral rotors in the solid state. [ABSTRACT FROM AUTHOR]

We report on a polymorph (2) of an amphidynamic crystal of molecular rods with two helical 1,4-bis(ethynyl)bicyclo[2.2.2]octane rotators where half of the rod-like molecules appear to be shifted with respect to their closest neighbours. This translation takes cogwheel-like pairs of rotators apart in the lattice in such a way that their motion becomes uncorrelated. This property is to be contrasted with the highly correlated motion found to govern the rotators in a recently-published polymorph 1 of the same material. As with polymorph 1, this motion is shown to take place independently of mutations in the handedness of the rotators and of the 'mutamer'-induced second harmonic generation. [ABSTRACT FROM AUTHOR]

The rod-like molecule bis((4-(4-pyridyl)ethynyl)bicyclo[2.2.2]oct-1-yl)buta-1,3-diyne, 1, contains two 1,4-bis(ethynyl)bicyclo[2.2.2]octane (BCO) chiral rotators linked by a diyne fragment and self-assembles in a one-dimensional, monoclinic C2/c centrosymmetric structure where two equilibrium positions with large occupancy imbalance (88% versus 12%) are identified on a single rotor site. Combining variable-temperature (70-300 K) proton spin-lattice relaxation, 1H T1-1, at two different 1H Larmor frequencies (55 and 210 MHz) and DFT calculations of rotational barriers, we were able to assign two types of Brownian rotators with different activation energies, 1.85 and 6.1 kcal mol-1, to the two 1H spin-lattice relaxation processes on the single rotor site. On the basis of DFT calculations, the low-energy process has been assigned to adjacent rotors in a well-correlated synchronous motion, whereas the high-energy process is the manifestation of an abrupt change in their kinematics once two blades of adjacent rotors are seen to rub together. Although crystals of 1 should be second harmonic inactive, a large second-order optical response is recorded when the electric field oscillates in a direction parallel to the unique rotor axle director. We conclude that conformational mutations by torsional interconversion of the three blades of the BCO units break space-inversion symmetry in sequences of mutamers in dynamic equilibrium in the crystal in domains at a mesoscopic scale comparable with the wavelength of light used. A control experiment was performed with a crystalline film of a similar tetrayne molecule, 1,4-bis(3-((trimethylsilyl)ethynyl)bicyclo[1.1.1]pent-1-yl)buta-1,3-diyne, whose bicyclopentane units can rotate but are achiral and produce no second-order optical response. [ABSTRACT FROM AUTHOR]

Abstract: The second-order nonlinear optical properties of photocross-linkable coumarin-based copolymers were investigated using the optical second harmonic generation (SHG) with the Maker fringes technique. High quality and transparent spin-deposited thin films of various methacrylic copolymers containing 4-methylcoumarin pendant chromophores were prepared and the coumarin units were ordered and oriented by the corona poling technique. Nonlinear optical investigations were performed using a picosecond Q-switched Nd:YAG laser working at the fundamental wavelength (λ =1064nm) and the second order nonlinear optical susceptibilities of the functionalized polymers were determined. The samples were irradiated using two wavelengths (λ =254nm and λ >300nm) promoting the reversible photo-induced dimerisation of coumarin moieties within the film. The latter is shown to have a significant impact on the nonlinear optical response of the corresponding material. A large SHG response of photocross-linkable coumarin-based copolymers is obtained. [Copyright &y& Elsevier]

Comparative study of the nonlinear optical response of pyrrolo-tetrathia-fulvalene polygons has been carried out. These materials are of great importance for photonics, because they can be used as building blocks for more complicated molecular systems like rotaxanes, catenanes which are promising candidates for opto-electronic applications like optical computing, optical switching etc. During this work the third order nonlinear susceptibility (X(3)) has been determined by the Degenerate Four Wave Mixing experiment, while the imaginary part of the (3)) which is related with the nonlinear absorption was determined by "open-aperture" Z-scan measurements. Moreover measurements have been carried out in order to provide information about the optical limiting efficiency of the materials. High (3) has been found reaching 2.30 × 10-21 m²/V², corresponding to second order hyperpolarizability γ values of about 6.5 × 10-45 m5/V² . [ABSTRACT FROM AUTHOR]

This study describes the adaptation of non-linear microscopy for single-particle tracking (SPT), a method commonly used in biology with single-photon fluorescence. Imaging moving objects with non-linear microscopy raises difficulties due to the scanning process of the acquisitions. The interest of the study is based on the balance between all the experimental parameters (objective, resolution, frame rate) which need to be optimized to record long trajectories with the best accuracy and frame rate. To evaluate the performance of the setup for SPT, several basic estimation methods are used and adapted to the new detection process. The covariance-based estimator (CVE) seems to be the best way to evaluate the diffusion coefficient from trajectories using the specific factors of motion blur and localization error. [ABSTRACT FROM AUTHOR]