Spectral and some nonlinear optical properties of multicomponent solutions, which contain fullerene C60, perylene, and
tetramethylbenzidine, are investigated. In such systems, enhanced optical limiting and all-optical switching are due to a
formation of radical ions by a photoinduced electron transfer. A diagram of electronic states is thermodynamically
calculated and prove for efficiency of the photoinduced electron transfer via the excited singlet state of C60 is shown.
We reveal conditions of collective photoinduced luminescence occurrence in model solutions. Experimental study of
transmission and luminescence of concentrated Rhodamine 101 solutions at excitation by laser pulses in the Stokes and
anti-Stokes spectral area showed that the collective photoinduced luminescence, competing with stimulated emission,
plays a significant role in luminescence formation at high pumping energies. Cooling and heating of the solutions are
estimated. Cooling photodynamics is analyzed for solutions of complex molecules at pulsed, both Stokes and anti-
Stokes, excitation of admixture centers. It is shown, that in anti-Stokes area the competition of the compelled processes
of absorption, two- photon absorption, light suppression and the photoinduced collective cold light result to occurrence
of area in which there is a change of a sign on temperature processes.
A non-covalent solubilization technique allowed us to synthesize original compositions such as suspensions of astralenes in nematic liquid crystal (LC). Study of their spectral luminescent parameters in a planar oriented cell led to discovery of bands in the absorption spectra at 1300 and 1700 nm. In our assumption, they correspond to transitions between van Hove singularities (VHS) in electronic state densities. It gave us the opportunity to pioneer measurement of absorption dichroism in the suspensions of carbon nanoparticles and found existence of different polarizations at transitions, responsible for background absorption and absorption in the van Hove bands. The role of the photochemical factor in photodynamics of optical limiting on carbon nanoheterostructures is discussed.
We have experimentally studied optical limiting in multi-component solutions containing polycyclic compounds (perylene and fullerenes) for which typical processe is photoinduced electron transfer with formation of ion pairs. Founded significant rise of limiting efficiency in such molecular systems is due to increase of absorption in the excited state. Formation of radical ions can be used for widening of spectral range of operating medium limiting.
The use of two-photon absorption (TPA) as mechanism of optical limiting puts a question about material, whose structure would provide effective TPA in initially transparent medium. The advantages of use of impurity mesomorphic systems in the tasks of optical limiting are discussed. It is necessary to take into account various detrimental effects on process of limiting may arise in molecular systems in conditions of high-power photoexcitation and high concentrations of excited fragments.
Influence of electron excitation energy transfer and secondary effects, occurred under action of laser radiation, on dynamics and efficiency of optical limiting is discussed. Two different systems, operating on effects of two-photon absorption and reverse saturable absorption, are considered as an example.
The features of low-threshold limitation are observed. It is shown, that one of the solutions of this task is usage of effect of two-photon absorption in an impurity liquid crystal. It is stipulated by large cross-section of two- photon absorption in cyanobiphenyls. The strategy of usage of mesomorphic microlenses as structural elements of optical limiters is discussed. The experiments on optical limitation in constructions using mesomorphic microlenses are realized.
The advantages of use the problems of optical limiting of impurity mesomorphic systems are discussed. These advantages are caused by existence of the excitonic mechanism of the transport energy electronic excitation in liquid crystals. A dynamic range of optical limiting in such systems can be essentially extending using of two- photon absorption.
Paper presents the results of experimental demonstration of dynamic holographic correction in mid-IR, using optically addressed liquid crystal spatial light modulators and method of two-wavelength holography, when the hologram is recorded at one wavelength and reconstructed at some shifted wavelength. On such a basis one can realize the dynamic interferometer, providing the arbitrary scaling of the wave front distortions and thus to record the dynamic hologram on the differential wavelength, which can be used for dynamic holographic correction of distortions in mid-IR. Method feasibility was confirmed in experiment.
THe paper considers the possibility of application of doped chiral systems with properties of dynamic optical hysteresis as optical limiters. The theoretical analysis of interaction of transmitted radiation with a resonant absorbing chiral system is performed using both two-level and multi-level models of the absorbing center. Experimental values of nonlinearity threshold obtained for the system of ketocyanine - nematochiral liquid crystal were approximately 250 (mu) J/cm2 at the wavelength of 530 nm.
We presented wide range of laser-radiation optical limiters that are based on different physical principles, operating in 400-12000 nm spectral range with rate 100-1 ns and providing wide dynamic range of limiting required for eye and sensor protection. We propose and investigate a method for reduction of the optical limiting threshold due to the Bragg reflection in a system with distributed feedback. The limiting threshold with the Borman effect, accompanying by diffractional absorption suppress and stimulated reflection from the LC Bragg grating, is about (mu) J/cm2 for nano seconds pulse. We investigate nonlinear optical limiters of laser radiation based on fullerene-contained materials, operating on the basis of reverse saturable absorption (RSA) as well as stimulated nonlinear reflection of laser radiation. Fullerenes C60, C70 and C84 were studied with the second harmonic of Nd:YAG laser, 532 nm, single-mode radiation pulses of 30 ns duration and maximum energy 0.35 J. Definite thresholds of RSA limiting vary from 0.05 to 0.1 J/M2) depending on fullerene density and limiting scheme. Dynamic range of limiting sufficiently increases for multi-pass trains, the fluence decreases up to 10000 times.
We elaborate 3000-12000 nm laser-radiation attenuators based on multi-layer interference containing vanadium-dioxide film. It is shown that these attenuators can operate due to both amplitude and diffraction effect. Attenuation is up to 1x103- 1x105 times for 1 MW/cm2 beams, operating time being 30-100 ns. For sensors in cooled optical systems, radiation attenuators can be used with vanadium oxides having the phase transition at cryogen temperatures.
The experimental investigation of the influence of electric field on luminescence of thin liquid crystal layers are presented. It is shown that the observed luminescence quenching is nearsurface phenomena dye to the exiton nature of liquid crystal luminescence.
The abilities of TEA-CO2 laser controlling by LC modulators have been investigated. It is shown, that beam direction, beam profile, energy and time position of the pulse can be controlled by LC modulators. Some problems of interaction of radiation with LC are discussed.
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