D. V. Malakhov

Two-Photon Single-Beam "Bit-by-Bit" Writing and Fluorescent "Page-by-Page" Reading 2.5D Femtosecond Optical Data Storage System.

A novel scheme of rewritable multilayered (2.5D) optical data storage based on single-beam femtosecond two-photon consequent writing and fluorescent parallel readout has been developed. The table-top prototype is created to demonstrate writing-reading-erasing the information in dual-layer polymer photochromic matrices with equivalent information density of 50 Mbit/cm2 per layer.

Enhancement of two-photon-initiated coloration by energy transfer from dye to photochromic molecules in polymer films

The method of increasing writing efficiency in 3D optical data storage system is proposed. This method is based on the energy transfer from material with high two photon absorption (TPA) to the photochromic molecules in thin polymer film. This method allows us to increase the writing efficiency of informative media more than one order of magnitude.

Two-photon destruction of photochromatic fulgides

The two-photon induced photo-destruction of indolyl fulgides, which are rather stable under single-photon excitation are investigated. The mechanism of this type destruction is proposed on the basis of semiempirical calculations of potential energy surfaces (PES). It was shown that the photodestruction of indolyl fulgides is connected with the triplet state population.

Efficiency enhancement of writing information in 3D optical memory devices using second harmonic generation in thin nonlinear organic films

New (two-stage) method of writing information in 3-D optical memory devices, using second harmonic generation (SHG) of femtosecond laser pulses in thin nonlinear films, and new informative (two-component) media consisted of nonlinear optical and photochromic materials, was realized. As a result for this two-component media, the 32x increasing of writing efficiency was obtained. It was shown, that the best photochromic substances (without additional requirement for two-photon absorption cross sections) can be used in 3-D optical memory devices.

Two-photon polymerization as a method for fabrication of three-dimensional periodic microstructures

It is demonstrated that two-photon polymerization can be employed as a basis for a technology for the fabrication of 3D micro- and submicrostructures, including structures with a periodically alternating refractive index. The rate of polymerization, energy expenditure, and required radiation doses characteristic of two-photon polymerization are estimated. The possibility to apply two-photon polymerization in the bulk of a medium to fabricate 3D photonic crystals in the optical range is discussed.

Photoisomerization quantum yields of naphthacenequinones in thin polymer films

The influence of three effects on the behavior of photoisomerization quantum yields of organic photochromic molecules embedded into polymer matrices have been investigated by computer simulation and compared with the experimentally observed quantum yields. First, the reverse photoreaction, second, the non-uniformity of the intensity along the direction of light propagation in the sample volume due to high optical density of the medium and third, the kinetic nonequivalence of photochromic molecules. All three effects cause the decreasing of the quantum yield during reaction. The main effect causing the diminishment of quantum yield during photobleaching of 6- phenoxynaphthacenequinone is the kinetic nonequivalence of photochromic molecules in the polymer host. It is shown that the drop of quantum yield observed in this case leads to significant difficulty of erasing the information while the possible number of readout cycles is increased. The fall of quantum yield of naphthacenequinone embedded into polymer film during photocoloration is caused mainly by the reverse reaction and kinetic nonequivalence of molecules.

Write-read-erase kinetics in 2.5-D multilayer polymer structures based on naphtacenepyridone molecules

Photoisomerization kinetics of naphtacenepyridones (NP) embedded into polymer films have been investigated. It is found that the kinetics of photocoloration reactions under single-photon excitation both in cw and femtosecond pulse regimes are similar while they are significantly different from kinetics under two-photon excitation. In the last case it proves to transform only about 12% of the photochromic molecules into colored form. This distinction in photocoloration kinetics seems to be attributable to the differences in photoabsorption cross sections of isomers under single- and two-photon excitation. According to the two-level model of excitation the value of two-photon cross section of NP molecules in form A is estimated to be approximately 0.1 (DOT) 10-50 sm4s at wavelength of 860 nm. The value of quantum yields of photoisomerization and photodestruction was demonstrated experimentally not to be conserved during both writing and erasing photoreactions. It is suggested that the decrease of quantum yields during erasing is due to the kinetic nonequivalence of naphtacenepyridones molecules embedded into polymer host. For this reason a number of readout cycles increases while the erasing process becomes more hard. Two-photon bit-by-bit writing and page-by-page fluorescent reading of information have been realized in multilayered polymer matrices consisting of 1.5 - 2 micrometers photochromic layers separated by 30 micrometers inert polymer layers.

Specialized setup for implementation of principles of two-photon writing and fluorescence reading in 3D optical memory systems based on multilayer polymer structures containing fluorescing photochro

Specialized setup for implementation of principles of two- photon writing and fluorescence reading in 3D optical memory systems based on multilayer polymer structures containing fluorescing photochromes has been developed. Modeling of the recording, readout and erasing processes have been realized. This prototype is also intended to test the photosensitive materials.

PHOTOISOMERIZATION QUANTUM YIELDS OF NAPHTHACENEQUINONES EMBEDDED INTO POLYMERIC MATRICES

The differential photoisomerization quantum yield (QY) behavior of four derivatives of naphthacenequinone in toluene solution and in polymethyl methacrylate (PMMA), polyvinyl butirale (PVB) and polybutyl methacrylate (PBM-5) polymer films during direct and reverse reactions has been investigated. It was discovered that in all cases the initial QY in polymer matrices is higher than the QY in toluene solution.