Multistate polarization addressing using a single beam in an azo polymer film

Laser beam shaping using a photoinduced azopolymer droplet-based mask

The dewetting of an azopolymer droplet, followed by the photostructuration of the evaporated droplet, is employed to create an amplitude mask. This straightforward process yields a large area featuring periodic micro- and nanostructures. The resulting pattern is utilized to generate a nondiffracting beam. Starting with a Gaussian beam illuminating the amplitude mask, the critical aspect is the production of a bright, ring-shaped beam with a high radius-to-width ratio and symmetric central laser spots, each with the same intensity. This alternative approach to shaping a laser beam is demonstrated as a rapid and cost-effective fabrication technique.

Topological reconstruction of a stretched transparent surface relief grating via an optical diffraction pattern

The optical characterization of transparent and stretchable patterned surfaces replicated from the fabrication of quasicrystal structures on azopolymer thin films is presented. The complexity of the quasicrystal surface fabrication is obtained by superimposed multiple light exposures. Azopolymer surface patterns are used as a replica molding master. The microscopic elongation of nanocavities induced by macroscopic stretchings of the elastomeric quasicrystal replication is characterized via optical diffraction. An original numerical method is presented to reconstruct the structured surface deduced from the optical diffraction measurements. The measurements show that drastic topologic changes, e.g., going from cavities to a canal, happens on the surface. This could be ingeniously used for creating actionable structured surfaces or nanoparticles trapping surfaces.

Self-enhancement and suppression of optical pulses by use of photochromism in elastomer

When violet or green pulses were launched into an elastomer containing photochromic diarylethene, two competitive absorption bands emerged at around 400 and 520 nm. The violet pulses suppressed the former and enhanced the latter, whereas the green pulses induced the opposite reaction. Consequently, these signals self-formed their optical path in the elastomer (self-enhancement). By contrast, blue pulses exhibited either a self-enhancement or suppression characteristic depending on whether the elastomer had been irradiated by the violet or green signal before the blue signal transmission. Measurement of the transient spectra during the irradiation process revealed that the blue photons were absorbed by both 400 and 520 nm bands inducing two competitive photochromic isomerizations simultaneously.

Photoinduction of spontaneous surface relief gratings on Azo DR1 glass

Surface relief gratings were spontaneously photoinduced from a collimated Nd:YAG laser beam at 532 nm on thin films of a disperse red 1 functionalized glass-forming compound. Pattern formation was studied by measuring the diffraction intensity of a He-Ne laser probe beam at 633 nm and by atomic force microscopy (AFM). The dependence of pattern formation on both irradiation time and intensity was studied. The gratings could be erased both optically and thermally. The orientation of the gratings is influenced by the polarization of the writing beam, and it is accompanied by strong diffraction of the incident light into the sample plane, thereby providing a way to couple and trap the light into the substrate. Interestingly, photobleaching upon prolonged irradiation yields transparent gratings, and the process is partially reversible upon thermal erasure.

How does the motion of the surrounding molecules depend on the shape of a folding molecular motor?

A simplified model of the DR1 molecule is used to realize a systematic study of the surrounding molecules motions dependence on the motor's length and width.

Light mediated emergence of surface patterns in azopolymers at low temperatures

Polymer thin films doped with azobenzene molecules do have the ability to organize themselves in spontaneous surface relief gratings (SRG) under irradiation using a single polarized beam. To shed some light on this still unexplained phenomenon, we use a new method that permits us to access experimentally the very first steps of the pattern formation process. By decreasing the temperature, we slow down the formation and organization of patterns, due to the large increase in the viscosity and relaxation time of the azopolymer. As a result, decreasing the temperature allows us to access and study much shorter time scales, in the physical mechanisms underlying the pattern formation, than those previously reported. We find that the patterns organize themselves in sub-structures which size increases with the temperature, following the diffusion coefficient evolution of the material. This result suggests that the pattern formation and organization are mainly governed by diffusive processes, in agreement with some theories of SRG formation. Upon decreasing the temperature further, we observe the emergence of small voids located at the junction of the sub-structures.

Multifractal characteristics of optical turbulence measured through a single beam holographic process

We have previously shown that azopolymer thin films exposed to coherent light that has travelled through a turbulent medium produces a surface relief grating containing information about the intensity of the turbulence; for instance, a relation between the refractive index structure constant C(n)2 as a function of the surface parameters was obtained. In this work, we show that these films capture much more information about the turbulence dynamics. Multifractal detrended fluctuation and fractal dimension analysis from images of the surface roughness produced by the light on the azopolymer reveals scaling properties related to those of the optical turbulence.

Simple turbulence measurements with azopolymer thin films

A simple method to measure the influence on the laser beam propagation by a turbid medium is proposed. This measurement is based on the inscription of a surface relief grating (SRG) on an azopolymer thin film. The grating obtained with a single laser beam after propagation into a turbulent medium is perturbed and directly analyzed by a CCD camera through its diffraction pattern. Later, by scanning the surface pattern with an atomic force microscope, the inscribed SRG is analyzed with the Radon transform. This method has the advantage of using a single beam to remotely inscribe a grating detecting perturbations during the beam path. A method to evaluate the refractive index constant structure is developed.

Photoinduced self-structured surface pattern on a molecular azo glass film: structure-property relationship and wavelength correlation

In this study, three series of star-shaped molecular azo glasses were synthesized, and self-structured surface pattern formation on the azo compound films was studied by laser irradiation at different wavelengths. The molecular azo glasses were synthesized from three core precursors (Tr-AN, Tr-35AN, Tr-H35AN), which were prepared by ring-opening reactions between 1,3,5-triglycidyl isocyanurate and corresponding aniline derivatives. The star-shaped azo compounds were obtained through azo-coupling reactions between the core precursors and diazonium salts of 4-chloroaniline, 4-aminobenzonitrile, and 4-nitroaniline, respectively. By using the two-step reaction scheme, three series of azo compounds with different structures were obtained. The core precursors and azo compounds were characterized by using (1)H NMR, FT-IR, UV-vis, mass spectrometry, and thermal analyses. The self-structured surface pattern formation on films of the azo compounds was studied by irradiating the azo compound films with a normal-incident laser beam at different wavelengths (488, 532, and 589 nm). The results show that the photoinduced surface pattern formation behavior is closely related to the structure of the azo compounds, excitation wavelength, and light polarization conditions. The absorption band position of the π-π* transition is mainly determined by the electron-withdrawing groups on the azo chromophores. When the excitation wavelength is between λ(max) and the band tail at the longer wavelength side, the self-structured surface patterns can be more efficiently induced to form on the films. The 3,5-dimethyl substitution on azo chromophores inhibits the surface pattern formation for certain excitation wavelengths. Increasing molecular interaction also shows an effect of restraining the surface pattern formation. The irradiations with linearly and circularly polarized light cause significant differences in the alignment manner of the pillarlike structures and their saturated height.

Photo-responsive polymer with erasable and reconfigurable micro- and nano-patterns: an in vitro study for neuron guidance

The interaction of cells with nanoscale topography has proven to be an important modality in controlling cell responses. Topographic parameters on material surfaces play a role in cell growth. We have synthesized a new bio compatible polymer containing photoswitching molecules. Stripepatterned (groove/ridge pattern) were patterned and erased with ease on this bio azopolymer with two different set-ups: one with the projection of an optical interference pattern and the other one by molecular self-organization with one single laser beam. These two set-ups allow the re-writing of pattern after erasing and its inscription in vitro. PC12 cells were cultured on the bio-photoswitching patterned polymer and compared with PC12 cells growing on a well know substrate: poly-L-lysine. This result is of interest for facilitating contact guidance and designing reconfigurable scaffold for neural network formation in vitro.

Self-structured surface patterns on molecular azo glass films induced by laser light irradiation

In this work, formation of photoinduced self-structured surface pattern and its correlation with chromophoric structures were studied by using a series of star-shaped azo compounds, which exist as stable molecular glass at room temperature. For the synthesis, a star-shaped precursor (Tr-AN) was prepared by a ring-open reaction between 1, 3, 5-triglycidyl isocyanurate and N-methylaniline. The star-shaped azo compounds were then synthesized through azo-coupling reactions between the precursor and diazonium salts of 4-nitroaniline, 2-methyl-4-nitroaniline, and 4-aminobenzonitrile, respectively. Through these steps, three azo compounds were obtained to bear different donor-acceptor type azo chromophores at the peripheral positions. The formation of the photoinduced self-structured patterns was investigated by irradiating solid thin films of the molecular azo glass with a uniform laser beam (532 nm, 200 mW/cm(2)) at normal incidence. For comparison, formation of surface-relief-gratings (SRGs) was also investigated by exposing the thin films to an interference pattern of the laser beams (532 nm, 80 mW/cm(2)). The results show that SRGs can be inscribed on the films of all three star-shaped azo compounds, but self-structured surface patterns is only observed on film of the azo compound containing 4-cyanoazobenzene moieties (Tr-AZ-CN) under the same irradiation condition. The electron-withdrawing groups, which control the absorption band position, show a significant influence on both the self-structured pattern formation and SRG inscription rate. Under proper experimental conditions, both self-structured surface pattern and SRG can simultaneously be observed on the Tr-AZ-CN films. The observations can lead to a deeper understanding of the photoinduced effects, especially their correlation with molecular structures.

Cognitive ability experiment with photosensitive organic molecular thin films

We present an optical experiment which permits us to evaluate the information exchange necessary to self-induce cooperatively a well-organized pattern in a randomly activated molecular assembly. A low-power coherent beam carrying polarization and wavelength information is used to organize a surface relief grating on a photochromic polymer thin film which is photoactivated by a powerful incoherent beam. We demonstrate experimentally that less than 1% of the molecules possessing information cooperatively transmit it to the entire photoactivated polymer film.