Formation of single-crystal opal films from a suspension of monodisperse spherical silica particles in a dynamic
meniscus area is treated as nanocrystallization involving interparticle interaction forces. Preparation of high-quality
photonic-crystal films with a reflection coefficient in the photonic band gap up to 95% is based on the concept of
equilibrium crystallization. In practice, this process occurs through the correction of oppositely directed interparticle
interaction forces down to a quasi-equilibrium state. Two- and three-layer heterostructures have been produced from
single-crystal films with various sizes of silica spheres. Well-resolved allowed ranges within photonic band gaps have
been detected for three-layer heterostructures, suggesting interesting applications of photonic crystals.
Explosive evaporation of metallic Rb or K clusters in the presence of excited atoms stimulated by resonant CW laser
radiation has been observed in a glass cell. Evaporation occurs at low laser-power density. The effect consists of the
generation of optically thick and sharply localized alkali vapor clouds propagating in the cell against the laser beam. The
clouds are charged and exhibit a strong luminescence of Rb or K spectral lines. The explosive evaporation of metallic
clusters is explained by the laser excitation of alkali atoms, which collide onto the surface of the clusters and transfer
their internal energy, which thereby causes other atoms to be evaporated and to continue the avalanche process.
The diffractive optical element as intracavity gradient mirror ofYAG:Nd laser has been offered.
The peculiarity of this element is using of zero order diffraction. The damage threshold of this mirror
is 5-10 J/cm2. There's been noticed that during the work with full aperture of active element divergence of
one-mode radiation of laser with gradient mirror became 1,5x10-4 rad with 30 mJ energy.
Photonic-crystal fibers provide efficient nonlinear-optical transformations of femtosecond Cr: forsterite laser pulses, delivering linearly chirped frequency-shifted broadband light pulses, optimized for pump-probe nonlinear absorption spectroscopy of molecular aggregates. The blue-shifted output of a photonic-crystal fiber with a spectrum stretching from 530 to 680 nm is used to probe one- and two-exciton bands of thiacarbocyanine J aggregates in a polymer film excited by femtosecond second-harmonic pulses of the Cr: forsterite laser.
Thin films of molecular J-aggregates of polymethyn dyes were obtained. Linear and nonlinear optical properties of the films were investigated. These thin films of J-aggregates were successfully used as saturable absorbers for passive mode-locking in YAG:Nd3+ laser for the first time. The reproduced generation of ultra short pulses with a duration of ~13 ps was obtained for two types of dyes forming the J-aggregates.
Mechanisms of the optical limiting effect in the fullerene-doped ?-conjugated organic systems based on polyimide and 2-cyclooctylamino-5-nitropyridine have been studied. Reverse saturable absorption, two-photon absorption, and charge transfer complex formation have been established to be responsible for the limitation of the laser radiation over visible spectral range. The absorption cross-section of the excited state has been determined for complexes based on both systems.
Thin films of molecular aggregates of pseudoisocyanine were obtained. Delocalization length of exciton wave function was measured with an assumption that an absorption line width is defined by disorder induced mixing of the lowest states of the one-exciton band. Predicted effect of size enhancement of the nonlinear optical properties for molecular aggregates was observed. The assumption used to determine the delocalization length is shown to coincide with the observed optical nonlinearity size enhancement phenomenon.
Lasing on the sodium resonance transitions (D1 and D2 lines) at the superluminosity regime was observed upon the nonresonance excitation in the presence of a buffer gas. Dependences of the lasing intensity on the pump radiation intensity and its frequency detuning from the frequencies of resonance transitions were examined. It was found that under the specific experimental conditions (high buffer gas pressure, sufficiently high intensity of pump radiation) upon the large positive frequency detuning of pump radiation with respect to the frequency of resonance (working) transition, contrary to ingrained conceptions, population inversion for the working transition is raised. That results in observed phenomena.
Thin solid films of low-dimensional J-aggregates of amphyphylic cyanine dyes with various lengths of the N-alkyl substituents were obtained. It was shown that the chemical modification of dye helps obtaining the stable thin films of J-aggregates by spin-coating method without any stabilization polymer. The optical properties of the thin films are described.
The dispersion of cubic optical susceptibility of submicron films of cyanine dyes J-aggregates is measured by a z-scan technique. The values of Im(chi) (3), Re(chi) (3) near to J-peak were 10-5 esu. It was found that Im(chi) (3) has a negative sign but at a low-frequency side of J-peak the sign is reversed. The measured dependence of Re(chi) (3) ((omega) ) has compared with the value calculated by Kramers-Kronig transformation. The dispersion dependence of Im(chi) (3), Re(chi) (3) is quite well described on a basis of four-level model for J- aggregates.
The dispersion of cubic optical susceptibility of submicron films of pseudoisocianine J aggregates are measured by a z- scan technique. The values of Im(chi) (3), Re(chi) (3) near to J-peak were approximately 10-5 esu. The measurements have shown that the films near to J-peak have negative sign of Im(chi) (3)((omega) ), which corresponds to nonlinear bleaching of absorption. The maximum Im(chi) (3)((omega) ) is observed for (omega) approximately equals (omega) J. It is found that at low frequency side of J-peak the sign of Im(chi) (3)((omega) ) changes on positive. The measured dependence Re(chi) (3)((omega) ) has compared with the value calculated by Kramers-Kronig transformation. For optical dense samples the contribution of a thermal nonlinearity is displayed. The spectral behavior features of Re(chi) (3)((omega) ) and Im(chi) (3)((omega) ) are explained by four-level model of Frenkel exciton.
The formation of thin-solid J-aggregated films Pseudoisocyanine prepared by spin-coating method is described. The process of dye aggregation was stimulated by addition of anions B10H10-2 and B12H12-2. It is shown that only addition of decahydro-closo-decaborate dianion (B10H10-2) to initial solution of dye give rise the J-aggregation with high efficiency. Obtained films have long storage time and suitable for non-linear optical measurements. The third-order susceptibility close to J-peak of PIC aggregates in films was studied by Z-scan method. Prepared films have a large magnitude of (chi) (3) to approximately 10-5 esu. The thermal contribution to the optical nonlinear response of dye films was estimated by use Kramers-Kronig relationship.
The theoretical investigation of the holographic grating pulse recording in the absorbing photopolymer materials is presented. The analytical models, describing the space-time transformation of holographic grating at the recording and the post-expositional amplification, have been obtained with taking into account the optical absorption and the diffusion processes. It is shown that the optical beams attenuation in the recording process leads to the spatial nonuniformity of index grating profile and its growth kinetics.
The investigations of hologram recording on a basis of photochemical polymerization reaction in polymer films have lead to creation the number of new holographic materials13. It is expected that their application will be realized in the nearest future. The performances of holographic recording useful for practice, such as sensitivity, maximum of diffraction efficiency (DE), storage, spatial resolution and other have been investigated in detail for this films4'5. But the question of mechanism of hologram formation, including the description of kinetic of photochemical and chemical stages of hologram recording is keeping open and discussed5'6. The holographic performances of HPPM-633 which consist of the light absorbing dye (Methylene Blue), initiator (triethanolamine - TEA), monomer (acrylamide -M), cross-linking monomer (hexamethylenbisacrylamide) and polymer binder (polyvinylalcohol) at He-Ne laser continuous recording were described7'8. In the preliminary investigation of hologram recording in HPPM-633 by the He-Ne laser pulses it was established that the DE about 1-5% appear at exposition time 0, 1 s with laser beam power density 0,05-0,1 W/cm2. The Fig. 1 illustrates the pulse hologram growth curves in HPPM633 , The phenomenon of hologram dark amplification (see Fig.2a,b) was observed in this experiment , That fact is in accordance with the mechanism of free-radical polymerization in HPPM. In this case the monomer polymerization in plasticizered polymer may expand independently after initial laser pulse action. It is interesting to know in which way the polymerization accrues at earlier stages. But the employment of pulse setup on the base of He-Ne laser does not allow to investigate the dark processes at time less then 0. 1 sec. To elucidate the material behaviour at the initial stages of the polymerization process immediately after excitation of the absorbing dye to the triplet state it is necessary to record the diffraction grating by laser pulse with durability about 108 sec. The DE growth of hologram under these conditions fall into nonsteady-state case of the polymerization. Thus we must to connect the hologram DE temporal dependence (DE(t)) with kinetic model of polymerization reactions in nonsteady-state case to have a possibility of the chemical interpretation of the obtained experimental date.
Optical properties of molecular J-aggregates of cyanine dyes are investigated intensively at present time. The most characteristic peculiarity of J-aggregates is presence of narrow peak (J-peak) red shifted from the peak of single molecule in absorption spectrum. J-peak is due to exciton absorption (Frenkel's exciton) and its width is defined by effect of motional narrowing) The interest to J-aggregates of pseudoisocyanine (PlC) has been aroused recently by discovery of their huge cubic susceptibility with l)iCOSecOnd decay time.24 The developing of preparation methods for J-aggregates PIG in thin films is actual for practical application. J-aggregates PlC in films of Langmuir-Blodgett or in a polymer matrix have been described recently.58 Temperature and radiation stability of such films allows to carry out investigations of structure, exciton dynamics and their nonlinear-optical properties. One of the methods for study of nonlinear properties of thin films is z-scan technique when real and imaginary parts of third order susceptibility are measured independently . Nonlinear optical properties of two types of i-aggregates prepared in thin films and studied by z-scan technique are described in this paper.
The magnitude and the dispersion of the cubic susceptibility of pseudoisocyanine J-aggregates entrapped in polyvinylpyrrolidone thin films have been determined. (chi) (3)((lambda) ) and (chi) (3)((Delta) (lambda) ) have been measured by four-wave mixing in both degenerate and non-degenerate cases. Z-scan technique was used to separate the Re(chi) (3)((lambda) ) and Im(chi) (3)((lambda) ) contributions to the absolute value of (chi) (3) (DOT) (chi) (3) was found to be approximately (2 divided by 6) 10-6 esu and the relaxation time was 10-13 - 10-12 s.
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