A. Wojciechowski

Optical operation by chromophores featuring 4,5-dicyanoimidazole embedded within poly(methyl methacrylate) matrices.

We have studied photoinduced absorption, birefringence, and optical second-harmonic generation in poly(methyl methacrylate) (PMMA) films doped by organic chromophores featuring 4,5-dicyanoimidazole in the weight content equal to 5%. The chromophores indicated as IM1-IM6 were synthesized from 2-bromo-1-methylimidazole-4,5-dicarbonitrile by either nucleophilic substitution or Suzuki-Miyaura cross-coupling reaction. The samples were obtained as films of several micrometers thickness by the spin-coating method on a quartz substrate. Measurements of the optically induced birefringence were done by the Senarmont method at wavelength 1150 nm, and photoinduced absorption was studied in the spectral range 250-700 nm under optical treatment by 300 mW cw 532 nm laser. Photoinduced optical effects were studied by bicolor 1064 and 532 nm coherent laser pulses. The maximal changes were observed for the ratio between fundamental and writing beam intensities equal to about 7:1. To interpret the observed experimental measurements, theoretical simulations of photoinduced optical properties were performed by quantum chemical computational methods.

Linear and nonlinear optical susceptibilities and the hyperpolarizability of borate LiBaB9O15 single-crystal: theory and experiment.

The single-crystal borate LiBaB9O15 was synthesized by a high-temperature solution reaction and structurally determined by the single-crystal X-ray diffraction technique. It crystallizes in the noncentrosymmetric space group R3c and features a three-dimensional ∞3[B9O15]3– anionic framework, with infinite channels in which the Li+ and Ba2+ cations are located. The linear optical properties were investigated experimentally in terms of the absorption spectrum, which reveals an optical gap of 5.17 eV. In addition we have calculated the linear optical properties using state-of-the-art all-electron full potential linearized augmented plane wave method. The nonlinear optical susceptibilities, namely, the second harmonic generation and the hyperpolarizability of the single-crystal borate LiBaB9O15 are calculated and evaluated at a static limit and at λ = 1064 nm. The calculation shows there exists three second-order nonlinear optical susceptiblities tensors components. We present measurements of the IR spectra in the range 500–2000 cm–1, and the second harmonic generation was performed using a Quantel 15 ns Nd:YAG laser operating at 1064 nm.

Effect of intercalation and chromophore arrangement on the linear and nonlinear optical properties of model aminopyridine push–pull molecules

Three push–pull aminopyridine derivatives having D–π–A, D–(π–A)2, and D–(π–A)3 arrangements were examined as model organic chromophores capable of intercalation into inorganic layered materials (alpha modification of zirconium hydrogen phosphate, zirconium 4-sulfophenylphosphonate, and gamma modification of titanium hydrogen phosphate). The fundamental properties of these dyes, their methylated analogues as well as their intercalates were studied by X-ray analysis, electrochemistry, UV/Vis absorption spectra, TGA, IR spectra, SHG, and were completed by DFT calculations. The synthesis of tripodal tris(pyridin-4-yl)amine is given for the first time. The HOMO–LUMO gap, the position of the longest-wavelength absorption maxima, and the dipole moment of aminopyridines can easily be tuned by attaching/removing pyridin-4-yl electron withdrawing units and their quaternization (pyridine vs. pyridinium acceptors). Their intercalation proved to be feasible affording novel inorganic–organic hybrid materials. The intercalation is accompanied by protonation of the guest, which enhances its ICT and strongly anchors the aminopyridines into the confined space of the layered host. Moreover, this process results in ordering of the organic chromophores and also brings improved thermal and chemical robustness. As a result, the measured SHG efficiencies of the intercalates are larger than those observed for the pure organic push–pull chromophores. Hence, the methodology of intercalation turned out to be very useful strategy for property tuning of NLO-active organic molecules.

IR laser induced spectral kinetics of AgGaGe3Se8:Cu chalcogenide crystals.

The possibility to operate by optical spectra near the absorption edge gap was discovered for the AgGaGe3Se8:Cu semiconducting chalcogenide crystals under influence of microsecond CO2 laser with pulse energy 60 mJ operating at wavelength 10.6 μm. An occurrence of substantial photoinduced optical density was observed at wavelengths in the spectral range of 610-620 nm. Introducing of Cu ions leads to substantial spectral asymmetry in the observed spectra. The process achieves its maximum value after the 80-120 s of CO2 laser treatment and relaxes with almost irreversible changes after the same time. The contribution of thermo heating did not exceed 5-6%. Only the irreversible changes of the samples surface topography were observed during the CO2 laser treatment, which do not influence the treatment. So the surface states do not play a principal role and the effect is prevailingly originated from the. The observed effect may be used for control of the CO2 laser power density.

All-optical operation by optical susceptibilities of Ca4NdO(BO3)3:Yb single crystals

We have found substantial enhancement of the optical second harmonic generation (SHG) in Ca4NdO(BO3)3:Yb (1.9% of Yb in weight units) crystals after 10 min optical treatment by the continuous wave (cw) laser at 532 nm and after 15 min treatment by blue 405 nm cw laser. Treatment by a red laser (660 nm) leads to the suppression of this effect. Principally the effect is only slightly reversible and the successive illumination of the same sample leads to the enhanced SHG, which correlates with changes in the principal absorption bands around 300–330 nm and 400–430 nm corresponding to the optical transitions between the energy levels of Nd3+ ions. The effect does not depend on the photoinducing light polarization. The principal origin of the observed photoinduced optical SHG is caused by photopolarization of the Nd localized levels and formation of the stable polarized states.

Absorption, fluorescence and second harmonic generation in Cr3+-doped BiB3O6 glasses

Synthesis, spectral properties and photoinduced nonlinear optical effects of chromium-doped BiB3O6 glass are studied in the present paper. Absorption, excitation and time resolved luminescence spectra are presented and luminescence decay behavior is discussed. Detailed analysis of the obtained spectra (assignment of the most prominent spectral features in terms of the corresponding Cr(3+) energy levels, crystal field strength Dq, Racah parameters B and C) was performed. A weak photostimulated second harmonic generation signal was found to increase drastically due to poling by proton implantation in the investigated sample.

IR laser induced spectra in novel crystals CdTe–CuInTe2

The novel crystalline alloys CdTe-CuInTe2 were synthesized. The photoinduced spectral changes of the anharmonic phonon modes were explored by cw CO2 laser at power about 2 kW in the vicinity of the 1650 cm(-1) mode. The changes of the intensities for principal phonon modes were found. These modes were assigned both to harmonic as well as anharmonic modes. All the measurements are studied after the Ir illumination. The performed quantum chemical calculations with application of the norm-conserving pseudopotential method and Green functions allow to identify the origin of the content dependent anharmonic phonon modes. Some correlation between the intensities of the corresponding phonon modes at about 1600-1700 cm(-1) and the corresponding IR induced changes were found.

Photoinduced spectra for magneto electric (1 − x)BiFeO3−xCuFe2O4 nanocomposites

In this work, we demonstrate possibility to use spectra of the parametrically tuned laser beam for operation by magnetoelectric properties of the (1-x)BiFeO(3-)(x)CuFe(2)O(4) (BFCI). The role of the photoexcited wavelength is crucial due to photoexcited phonons. It may indicate on a spectral sensitivity of the studied nanocomposites. We have studied spectral dependences of magneto-electric constant versus the magnetic field frequency for different sizes of the nanoparticles with and without the nanosecond laser pulses illumination and we have shown an occurrence of principal spectral shifts in the corresponding magneto-electric maxima. Additionally we have explored relative changes of dielectric permittivity and coercivity versus different photoinducing wavelengths. The performed experiments unambiguously show that the external laser treatment will lead to substantial shift of corresponding dielectric and magnetic parameters in the studied nanocomposites. It is principally the finding of clear spectral dependences for the mentioned dielectric and magnetic parameters. One can see their sensitivity to the photoinduced wavelength which reflects the photoexcitations of different part of wavelengths. One can see the spectral shift up to 100 nm for the two principal spectral maxima with respect to the dielectric and magnetic changes which may indicate on the two principally different contributions to the effects observed.

Influence of pressure on optical absorption of triglycine selenium single crystals

For the first time we have shown that increasing uniaxial pressure on the triglycine selenium single crystals leads to the occurrence of several spectral maxima below the energy gap. It is principal that after interruption of the applied uniaxial pressure one observes remarkable spectral shifts up to 20 nm of the principal spectral maxima at 280 nm and 340 nm. The effect is caused by the changes of inter-molecular interactions of the van der Waals type in such kinds of crystals and occurrence of in elastic interactions. The effect has irreversible character and after applying of uniaxial pressure several times we see that there occur several strains which may be considered as the remaining infer-molecular stresses. The observed phenomenon may be used for creation of the optoelectronic tensors of the pressure with the forces up to 4 kG. The performed investigations have shown that the spectral broadening is not sensitive to the pressure, however their spectral shifts are substantially sensitive to the applied pressure. The observed effect possess a long time reversibility (up to one month). Additional studies of piezooptical effects have shown its sensitivity to the external cw green laser light at power 300 mW. Using the thermoluminescence we have established that the crystals are very sensitive to the number of trapping levels within the energy gap. Additionally there were performed studies of electrooptical effects for the pulsed 10 ns Nd:YAG laser.