V. Giannetas

Two-photon absorption properties of novel organic materials for three-dimensional optical memories

Abstract The two-photon absorption (TPA) properties of a novel group of pyrylium-based compounds were studied. The molecules of this group were synthesized by systematically changing the chemical structure of a specific substituent in an initial chromophore. TPA cross-sections as large as 1.8×10 −47 cm 4 s photon −1 and high quantum yields were obtained. The results combined with the low cost and ease of synthesis of these compounds make them candidates for TPA applications. Particularly, three-dimensional data storage in polymer matrices of the synthesized compounds was realized through the photobleaching process. The high efficiency of recording and the submicron resolution reveal the great potential of this group of molecules as memory materials.

Intensity dependent nonlinear absorption of pyrylium chromophores

Abstract The intensity dependence of nonlinear absorption (NLA) of a series of pyrylium chromophores was studied with femtosecond pulses in their two-photon absorption spectral region to assess their potential as optical limiters. The open z-scan technique using different excitation intensities was employed. Fifth-order effects appear above a critical value of the irradiance and consequently of the first excited singlet-state population. Reverse saturable absorption (RSA) based on two-photon (TPA) and excited-state absorption (ESA) was dominant in most cases. The third- and fifth-order NLA coefficients and high ESA cross-sections of the order of 10 −15 cm 2 are presented at 760, 790 and 840 nm.

Novel class of pyrylium dyes with high efficiency in lasing and two-photon absorption fluorescence

Abstract We report the synthesis of a promising class of pyrylium dyes concerning laser and two-photon absorption action. Three representatives of this class, 4-(2,4-dichlorophenyl)-2,6-bisphenylpyrylium tetrafluoroborate, 4-phenyl-2,6-bis(4-methoxyphenyl)pyrylium tetrafluoroborate, and 4-(2,4-dichlorophenyl)-2,6-bis(4-biphenyl)pyrylium tetrafluoroborate, were investigated. Each dye was synthesized by a convenient and inexpensive method. Efficient laser action was shown at ∼500, ∼560, ∼615 nm. Changing the conjugation length i.e. the length of the oligophenyl moiety, or introducing various substituents on the aromatic rings, the emission maximum can be controlled. Two-photon absorption induced fluorescence was also observed. These pyrylium dyes constitute excellent candidates for laser technology and two-photon absorption applications.

Three-photon induced photobleaching in a three-dimensional memory material

The photobleaching properties of a 3D memory material based on pyrylium salts are studied. It is shown that under ultrashort pulsed irradiation photobleaching occurs through two diverse mechanisms. One is major and causes fast bleaching, whereas the other is minor and causes slow bleaching. Furthermore, it is proved that both mechanisms are three- or more-photon processes. This fact gives the capability of significantly increasing data storage density.

Solvent and branching effect on the two-photon absorption properties of push–pull triphenylamine derivatives

The photophysical and two-photon absorption (2PA) properties of two tri-podal molecules and of their quadrupolar and dipolar counterparts are reported for a series of solvents with varying polarity. The molecules possess a tri-phenylamine electron donating group and mono-cyano acceptors while olefinic and acetylenic π-linkers have been used. Branching led to an increase of the molar extinction coefficient and to a slight bathochromic shift of the absorption spectra while the fluorescence quantum yields decrease but they are maintained to relatively high values. Solvatochromic measurements in the tri-podal molecules revealed an emitting state with a polar nature. The 2PA cross sections in general increase upon branching but the observed behaviour strongly depends on the type of solvent. The highest 2PA cross sections are obtained in solvents of medium polarity and values as high as 1420 GM are reported.

Z-scan analysis for near-Gaussian beams through Hermite-Gaussian decomposition

Gaussian decomposition is used as a theoretical infrastructure with which Z-scan experiments are analyzed. This procedure is extended here to the interesting, from a practical point of view, case in which the laser beam used is not perfectly Gaussian. We follow a perturbative approach to obtain the far-field pattern of the beam after the beam passes through a nonlinear sample. The procedure is based on the decomposition of the electric field at the exit plane of the sample to a linear combination of Hermite–Gaussian functions. To a first-order approximation, each mode of the incident beam is decomposed to a linear combination of different-order modes that do not exceed the order of the original mode. Finally, the effects of the simultaneous presence of first and higher-order refractive nonlinearities or first-order refractive nonlinearity and nonlinear absorption are studied.

Modulation of (non)linear optical properties in tripodal molecules by variation of the peripheral cyano acceptor moieties and the π-spacer

A series of twelve tripodal push-pull molecules with a central triphenylamine donor and peripheral cyano substituted acceptors has been prepared. These molecules possess systematically altered π-linkers as well as cyano acceptors. Based on the experimental properties measured by differential scanning calorimetry, electrochemistry, one and two photon absorption/emission spectroscopy, supported by the DFT calculations, thorough structure–property relationships were elucidated.

Strong two photon absorption and photophysical properties of symmetrical chromophores with electron accepting edge substituents.

Two photon absorption (TPA) and photophysical properties of three new symmetrical chromophores with electron accepting phthalimide edge substituents have been studied. The three chromophores contain fluorene, alcoxy-substituted divinyl benzene, and carbazole moieties as central cores, respectively. The femtosecond time-resolved fluorescence upconversion spectroscopy and two photon excited fluorescence technique have been carried out. The effect of solvent polarity on TPA and on photophysics has also been determined. Ultrafast fluorescence dynamics, with decay times ranging from 1 to 13 ps, are revealed in polar solvents. This is attributed to the relaxation of the chromophores to the intramolecular charge transfer state. The chromophore bearing fluorene central core, being of the type A-pi-A, is the most efficient concerning TPA. Strong TPA, with a cross section value as high as 2100 GM at an excitation wavelength of 770 nm is found in acetophenone which is a solvent of intermediate polarity. The TPA spectra were also reproduced using a sum over states three-state model. A study of the TPA induced photobleaching of the fluorene molecule, doped in a solid poly(methyl-methacrylate) film, has shown that this material is very promising for efficient TPA optical data storage.

Three-dimensional data storage in photochromic materials based on pyrylium salt by two-photon-induced photobleaching

Molecular two-photon absorption (TPA) has gained great interest over recent years owning to each application in various fields, including spectroscopy, microscopy, 3-D optical data storage, optical power limitation and microfabrication. The requirement for organic molecules with large TPA cross-sections is therefore essential. In the present work the two-photon absorption properties of a series of pyrylium-based chromophores were investigated. The molecules of this series were synthesized by systematically changing the chemical structure of a specific substituent of an initial, strong two-photon absorbing, molecule. Very large TPA cross-sections (1800 GM) and high quantum yields were achieved in the visible red and NIR region of the spectrum. The relation between the chemical structure of the molecules and their TPA performance was discussed. Furthermore, the photobleaching efficiency of these molecules doped in polymer matrices was investigated. Parallel successive patterns were recorded in a polymer matrix via photobleaching. The accuracy of recorded patterns reveals the great potential of these chromophores as memory materials.

Electrical discharges investigation in gas-pulsed laser

The electrical discharges which exist in a gas-pulsed laser (ignition system and laser tube) constitute an additional problem to the study of the whole laser system. This is due to their time-dependent behavior during the discharge. An electrical discharge can be symbolized as time-dependent resistance and inductance in the laser electric circuit. The analysis of the circuit is impossible if the resistance and inductance functions in relation to time are not known. This work illustrates a very easy way of finding the resistance and inductance functions in relation to time. This can be achieved by measuring only the waveform of the voltage across the capacitors of the system. By combining this waveform with the differential equation of the system performance, the evolution of the resistance and the inductance in relation to time can be determined. The quantities which can be calculated after that, in relation to time, are the oscillatory frequencies, the damping constants as well as the impedances of the discharges.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.