Hybrid Dispersion Model Characterization of PAZO Azopolymer Thin Films over the Entire Transmittance Spectrum Measured in the UV/VIS/NIR Spectral Region.

Notwithstanding the significant optical applicability of PAZO polymer films, there are no accurate data about their optical characteristics. To remedy this shortcoming, in this study three PAZO polymer thin films are characterized, with dissimilar thicknesses, on glass substrates using only one UV/VIS/NIR transmittance spectrum T(λ) per sample and an original hybrid dispersion model (HDM). HDM is based on the Tauc-Lorentz model, the new amorphous dispersion formula, the Tauc-Lorentz-Urbach model of Foldyna and the Tauc-Lorentz-Urbach model of Rodriguez. HDM with two oscillators is employed in characterizations of the PAZO polymer films in the range [300, 2500] nm, whereby the root-mean-square deviation (RMSD) of the fitted transmittance spectrum with respect to T(λ) does not exceed 1.6 × 10-3. Decreasing RMSD by 2.3% to 94.4% is demonstrated by employing HDM compared with the above mentioned four popular dispersion models, for each one of the studied films. HDM is applicable to amorphous films independent of their thickness as well as to cases of non-transparent substrate.

Reversible supramolecular chiral structures induced in azopolymers by elliptically polarized light: influence of the irradiation wavelength and intensity.

Photoinduced supramolecular chiral structures in azo materials have been extensively studied for the development of all-optical switches and because of their influence on the properties of certain types of polarization holographic gratings. Here, we investigate chiral structures induced by irradiation with elliptically polarized light in thin films of four azopolymers denoted as PAZO, P1, P1-2, which are amorphous, and P2, which is liquid crystalline. Their formation is characterized in real time by the kinetics of azimuth rotation. The influence of the irradiation wavelength and intensity is also analyzed. The largest azimuth rotation per unit thickness is achieved in PAZO (33°/µm) and P1-2 (25°/µm). Reversibility of the chiral structures is demonstrated by a tenfold change in the direction of rotation. Our results also indicate that chiral structures formation occurs significantly faster than the induction of linear birefringence.

Intensity-based dynamic speckle method using JPEG and JPEG2000 compression.

Statistical processing of speckle data enables observation of the speed of processes. In intensity-based pointwise dynamic speckle analysis, a map related to speed's spatial distribution is extracted from a sequence of speckle patterns formed on an object under coherent light. Monitoring of time evolution of a process needs storage, transfer, and processing of a large number of images. We have proposed lossy compression of these images using JPEG and JPEG2000 formats. We have compared the maps computed from noncompressed and decompressed synthetic and experimental images, and we have proven that both compression formats can be applied in the dynamic speckle analysis.

Tautomeric influence on the photoinduced birefringence of 4-substituted phthalimide 2-hydroxy Schiff bases in PMMA matrix.

The photoinduced birefringence of two 4-substituted phthalimide 2-hydroxy Schiff bases, containing salicylic (4) and 2-hydroxy-1-naphthyl (5) moieties has been investigated in PMMA matrix. Their optical behaviour as nanocomposite films was revealed by combined use of DFT quantum chemical calculations (in ground and excited state) and experimental optical spectroscopy (UV-Vis and fluorescence). The results have shown that solid-state reversible switching takes place by enol/keto tautomerization and Z/E isomerization. Birefringence study was performed in the PMMA nanocomposite films using pump lasers at λrec = 355 nm and λrec = 442 nm. Fast response time and high stability of anisotropy up to 58% for (4) and 95% for (5) after turning off the excitation laser, was observed, which makes these materials appropriate candidates for cutting-edge optical information technology materials. The possibility for multiple cycles of recording, reading and optical erasure of the photoinduced birefringence at λrec = 442 nm in 5 has been demonstrated. The obtained results have shown that the maximum value of the measured birefringence is close to the anisotropic characteristics of the most frequently used azo materials.

Quantization of dynamic speckle patterns with spatially varying statistics.

Raw data compression is mandatory for monitoring of processes by dynamic speckle analysis when two-dimensional activity maps are built by pointwise statistical processing of correlated speckle patterns formed on the surface of diffusely reflecting objects under laser illumination. Coarse quantization of speckle patterns enables storage and transfer of a huge amount of images, but it may be inefficient at spatially varying speckle statistics, such as for patterns recorded at non-uniform illumination or reflectivity. We prove efficacy of coarse quantization of the raw speckle data with varying statistics for a normalized algorithm by simulation and a polymer drop drying experiment. Both uniform and non-uniform quantization are proposed for treating such data. Decreasing the bit depth from 8 to 3 is possible without worsening the quality of the activity map.

Dynamic speckle analysis with coarse quantization of the raw data.

Analysis of dynamic speckle formed on the surface of diffusely reflecting objects under laser illumination is a non-contact method for inspection of speed of processes. The paper deals with intensity-based implementation of the method that relies on statistical processing of correlated in time sequences of speckle images. A two-dimensional activity map is built for each sequence to visualize regions of different speed on the object surface at a given instant. A great number of images is required to track a process in time. We propose data compression by coarse quantization of the raw speckle data. Efficacy of quantization is analyzed by simulation and experiment for low- and high-contrast speckle patterns with bell-shaped and long-tailed distributions of intensity, respectively. Non-uniform quantization is proposed for long-tailed speckle intensity distributions. Decreasing the bit depth from 8 to 4 causes no change in the probability density function of the activity estimate.