Tatiana Kukhtareva

Green Synthesis of Silver Nanoparticles, Their Characterization, Application and Antibacterial Activity †

Our research focused on the production, characterization and application of silver nanoparticles (AgNPs), which can be utilized in biomedical research and environmental cleaning applications. We used an environmentally friendly extracellular biosynthetic technique for the production of the AgNPs. The reducing agents used to produce the nanoparticles were from aqueous extracts made from the leaves of various plants. Synthesis of colloidal AgNPs was monitored by UV-Visible spectroscopy. The UV-Visible spectrum showed a peak between 417 and 425 nm corresponding to the Plasmon absorbance of the AgNPs. The characterization of the AgNPs such as their size and shape was performed by Atom Force Microscopy (AFM), and Transmission Electron Microscopy (TEM) techniques which indicated a size range of 3 to 15 nm. The anti-bacterial activity of AgNPs was investigated at concentrations between 2 and 15 ppm for Gram-negative and Gram-positive bacteria. Staphylococcus aureus and Kocuria rhizophila, Bacillus thuringiensis (Gram-positive organisms); Escherichia coli, Pseudomonas aeruginosa, and Salmonella typhimurium (Gram-negative organisms) were exposed to AgNPs using Bioscreen C. The results indicated that AgNPs at a concentration of 2 and 4 ppm, inhibited bacterial growth. Preliminary evaluation of cytotoxicity of biosynthesized silver nanoparticles was accomplished using the InQ™ Cell Research System instrument with HEK 293 cells. This investigation demonstrated that silver nanoparticles with a concentration of 2 ppm and 4 ppm were not toxic for human healthy cells, but inhibit bacterial growth.

Broadband Dynamic, Holographically Self-Recorded, and Static Hexagonal Scattering Patterns in Photorefractive KNbO3:Fe

We have observed and explained three types of hexagon pattern formation in photorefractive crystal KNbO 3 :Fe. These are: (1) dynamic (laser induced), (2) semipermanent (holographically stored), (3) permanent (induced by a static domain grid) over a wide wavelength range.

Optical, photoelectric, and photorefractive properties of Ti-doped CdTe crystals

The photorefractive characteristics of Ti-doped CdTe semi-insulating crystals were measured. Additional optical and photoelectric measurement confirmed that titanium has advantages over other dopants and that this material has better characteristics for potential applications. The high optical holographic gain coefficient, Γ≈0.60 cm−1, low background absorption, kb≈0.2 cm−1, high optical quality and homogeneity, and almost monopolar (electronic) photoconductivity show that these materials can be effectively used for both optical and photoelectric applications in the near infrared region. Studies of the optical absorption and photodiffusion current made it possible to determine the nature and energy structure of impurity and intrinsic defects as well as to establish their role in the photorefractive effect. It is shown that the excited impurity 4T1(F) state is in resonance with the conduction band. As a result, autoionization of electrons to the conduction band under laser excitation takes place. An energy...

Pyroelectric and photogalvanic crystal accelerators

In this study, we have derived equations for the pyroelectric and photogalvanic contribution to the electrical charging of the photosensitive ferroelectric crystal. Standard photorefractive equations are supplemented by the equation of state for the polarization density following the Devonshire–Ginsburg–Landau (DGL) approach. The photogalvanic voltage and current is considered for a wide intensity range, which includes the cw and the pulsed photoexcitation with high intensities when the impurity is fully ionized and when the traditional linear-recombination approach is not valid. The crystal electrostatic accelerators, based on charging of ferroelectric crystals by pyroelectric and photogalvanic effects, are discussed in relation to the generation of the self-focused electron beam, x rays, and neutrons.

Running gratings in photoconductive materials

Starting from the three-dimensional version of a standard photorefractive model (STPM), we obtain a reduced compact set of equations for an electric field based on the assumption of a quasi-steady-state fast recombination. The equations are suitable for evaluation of a current induced by running gratings at small-contrast approximation and also are applicable for the description of space-charge wave domains. We discuss spatial domain and subharmonic beam formation in bismuth silicon oxide (BSO) crystals in the framework of the small-contrast approximation of STPM. The experimental results confirming holographic current existence in BSO crystal are reported.

Holographic interferometry of oil films and droplets in water with a single-beam mirror-type scheme

Application of single-beam reflective laser optical interferometry for oil films and droplets in water detection and characterization is discussed. Oil films can be detected by the appearance of characteristic interference patterns. Analytical expressions describing intensity distribution in these interference patterns allow determination of oil film thickness, size of oil droplets, and distance to the oil film from the observation plane. Results from these analyses indicate that oil spill aging and breakup can be monitored in real time by analyzing time-dependent holographic fringe patterns. Interferometric methods of oil spill detection and characterization can be automated using digital holography with three-dimensional reconstruction of the time-changing oil spill topography. In this effort, the interferometric methods were applied to samples from Chevron oil and British Petroleum MC252 oil obtained during the Deep Water Horizon oil spill in the Gulf of Mexico.

Photoinduced Optical and Electrical High-Voltage Pulsations and Pattern Formation in Photorefractive Crystals

We review our results on conversion of CW laser Ar-ion beam power into pulsating multi-channel outputs: optical, electric and piezoelectric with simultaneous dynamic pattern formation. We show, that electrical pulsations generate high-voltage signals that may be used as a driving voltage for the conventional electro-optical modulator. We have also demonstrated the possibility of synchronization of two optical pulsators, through regulated optical coupling in a photorefractive LiNbO3 crystal. Spatial distribution of scattered light is self-organized in different patterns (hexagonal and cross-type).

A unified treatment of radiation-induced photorefractive, thermal, and neutron transmutation gratings

We have reviewed different types of periodic structures (superlattices) induced by optical, infrared, and neutron irradiation. Both optical and electrical properties of these superlattices are analyzed, starting from the standard photorefractive model. New results on the thermoelectric and pyroelectric dynamic gratings are discussed in connection to the energy conversion and vibration sensing. For the neutron irradiation both real-time and static grating are analyzed, suggesting transmutation doping as a mechanism of recording.

Laser Beam Shaping by Holographic Optical Elements

For material processing and laser machining, it is important to shape intensity and phase profiles of the laser beams. For dynamic beam shaping, we suggest the method based on energy exchange during self-diffraction of laser beams in the photorefractive materials. For applications, related to use of the powerful lasers we have tested a possibility of beam shaping by holographic optical elements, recorded in Photo-Thermo-Refractive (PTR) glasses, developed in CREOL. The gratings in PTR glasses are stable up to 400°C with laser-induced breakdown energy threshold of 10 J/cm2 in 1 ns pulses at 1064 nm. High diffraction efficiency more than 95% of gratings recorded in PTR glass allows to achieving high energy transfer that is vital for commercial laser applications. Preliminary results show that flattop distribution of laser intensity may be realized in the diffraction orders.

Real-time holography for optical processing using photorefractive crystals

In this paper, we describe different schemes of phase conjugation during formation of the self-organized hexagonal spot array in the photorefractive crystal KNbO3. Both forward and backward phase-conjugated beams are observed in the two-beam coupling geometry. We present also theoretical description of this multiplexed phase conjugation, introducing concept of the scattering wave-vector diagrams that visualize contributions from the transmission and reflection gratings.