Natalia E. Noginova

Short-pulsed stimulated emission in the powders of NdAl 3 (BO 3 ) 4 , NdSc 3 (BO 3 ) 4 , and Nd:Sr 5 (PO 4 ) 3 F laser crystals

Short (>300-ps) pulses of stimulated emission were found from powders of NdAl3(BO3)4, NdSc3(BO3)4, and Nd:Sr5(PO4)3F laser crystals during 532- and 805-nm excitation. Study of stimulated emission in the mixture of two powders has shown that the different components influence each other. That implies a collective behavior of emitting particles. The main features of experimentally observed stimulated emission are described with a simple model accounting for 4F3/2 excited-state concentration and emission energy density. The threshold of stimulated emission in powders is shown to be inversely proportional to the small-signal amplification along the photon path in the pumped volume.

Optical characterization of Mn:YAlO 3 : material for holographic recording and data storage

Photoinduced coloration and the holographic grating recording associated with it are experimentally studied in Mn-doped yttrium orthoaluminate (Mn:YAlO3). High diffraction efficiency is demonstrated in visible and in infrared light. The diffraction efficiency at 514.5 nm exceeds 50%. The strong energy exchange between the writing beams observed in a two-wave mixing experiment suggests that diffraction in Mn:YAlO3 is due to mainly nonlocal holographic effect and an electro-optical effect. Mn:YAlO3 is shown to be a promising material for holographic recording and optical storage.

Holographic current study in laser and photorefractive crystals

Summary form only given. We generalized the theory behind the light-induced grating (LIG) electro-motive force (EMF) technique for material characterization and interferometry, first introduced by Petrov et al. In particular, we have accounted for the screening length, that allowed us to describe adequately the dependence of the amplitude, and the decay-time.

Study of photoconductivity and holographic current in rare-earth-doped Y 3 Sc 2 Ga 3 O 12 laser crystals

The photoconductivity and holographic current have been studied in Er-, Tm-, and Ho-doped Y3Sc2Ga3O12 laser crystals under visible and infrared excitation. Kinetics and spectroscopic studies have shown that photoconductivity is linearly proportional to the concentration of excited 4f states. The holographic current was described with a model accounting for the energy transfer between the rare-earth and ligand electronic shells, ionization, recombination, and the diffusion and drift currents in the conduction band. The dependence of the holographic current on the modulation frequency, grating vector, etc. were used to determine the carriers’ diffusion length and the screening length in Er-doped crystals.

Organic compounds with nonlinear optical response enhanced by microparticles prepared at low gravity

We will present the results of study of nonlinear optical organic compounds based on dye doped polymeric micron size spherical particles. These particles are generated on the ground at artificial low gravity. Free falling drops of polymer solution or metal take on the shape close to spherical. The fabrication at real low gravity can substantially improve the sphericity of the particles and their identity. We show that the particles, being combined with different organic chromophores, can potentially increase their nonlinear optical response in practical applications. This effect is associated with the break of symmetry at the particle surface and the interaction of the resonant modes with non-symmetrical molecules at the particle surface. Constructive light interference in an array of microspheres additionally enhances nonlinear response. In our experiments we used polystyrene microspheres with diameter from 1.7 to 5.3 microns. Two- dimensional quasi-crystals were fabricated from polystyrene microspheres and characterized for their structural and nonlinear optical properties. The quasi-crystals were produced with the method based on Langmuir-Blodgett thin film technique. As possible dopants we studied a NPO dye, derivatives of DIVA, disperse dyes. Some of the create Langmuir-Blodgett films combined with spherical particles in the same technological process.

Two-dimensional microsphere quasi-crystal: fabrication and properties

2D quasi-crystals were fabricated from polystyrene microspheres and characterized for their structural, diffraction, and non-linear optics properties. The quasi- crystals were produced with the method based on Langmuir- Blodgett thin film technique. Illuminating the crystal with the laser beam, we observed the diffraction pattern in the direction of the beam propagation and in the direction of the back scattering, similar to the x-ray Laue pattern observed in regular crystals with hexagonal structure. The absorption spectrum of the quasi-crystal demonstrated two series of regular maxima and minima, with the spacing inversely proportional to the microspheres diameter. Illumination of the dye-doped microspheres crystal with Q- switched radiation of Nd:YAG laser showed the enhancement of non-linear properties, in particular, second harmonic generation.

Material characterization by holographic current, beam coupling and spin dependent conductivity

Effects of optical self-organization in photorefractive KNbO3 are observed and studied by optical and electro- motive force methods. The crystal is characterized by monitoring the electric currents induced in the crystal due to applied illumination. A theoretical model of the observed effects is suggested. Spin dependent conductivity in photorefractive crystals with paramagnetic centers is discussed.

Holographic photocurrent in photorefractive crystals

A transient photo-electric current was investigated in photorefractive crystals of Sr1-xBaxNb2O6 (SBN) and Bi12TiO20 (BTO) as a response to a step-like modulation of the light grating phase. Different dependencies of the photocurrent relaxation time on the grating period were observed for SBN and BTO crystals. It is explained theoretically taking into consideration kinetics of the photoexcitation of carriers, charge transfer and trapping. A number of important parameters characterizing the crystals are estimated.

Dynamic memory in phase conjugation of nonoverlapping in time picosecond pulses

It was demonstrated experimentally, that recording of photorefraction gratings BaTiO3 crystals can be realized with nonoverlapping in time 80 ps pulses of Nd:YAG laser ((lambda) equals 532 nm). This phenomenon of dynamic memory is explained by asymmetry of writing-reading mechanisms with simultaneous phase-conjugation.