Andrey A. Lipovskii

Synthesis and characterization of PbSe quantum dots in phosphate glass

The controlled synthesis of PbSe nanocrystal quantum dots with narrow size distributions was achieved through phase decomposition of the PbSe solid solution in a phosphate glass host. Structural characterization by electron microscopy and x-ray diffraction shows that the dots have mean diameters between 2 and 15 nm. The exciton Bohr radius aB=46 nm in PbSe, so these quantum dots provide unusual and perhaps unique access to the regime of strong quantum confinement. The optical absorption spectra are compared to the predictions of a theoretical treatment of the electronic structure. The theory agrees well with experiment for dots larger than ∼7 nm, but for smaller dots there is some deviation from the theoretical predictions.

Optical limiting behavior of a glass–ceramic containing sodium niobate crystallites

The nonlinear absorption properties of a glass–ceramic containing ferroelectric sodium niobate (NaNbO3) crystallites were investigated. Two- and three-photon absorption coefficients were determined using nanosecond pulsed lasers. The optical power-limiting performance for light beams at 1064 and 532 nm was dependent on the volume fraction of NaNbO3 crystallites formed during the heat-treatment process.

Raman spectroscopy and the origin of electrooptical Kerr phenomenon in niobium alkali-silicate glasses

It is shown that magnitudes of the Kerr coefficient and permittivity of 19Na2O–11K2O–2B2O3–2CdO–(66−x)SiO2–xNb2O5 glasses, where 0<x<37, correlate with the content of the Na2O·Nb2O5 groupings, with that content being estimated by Raman scattering data. This allows assigning to these groupings, or to other structural entities containing such groupings (for example, crystal motifs), the responsibility for high-polarizability and Kerr sensitivity of the glasses.

Strong confinement of PbSe and PbS quantum dots

Abstract We synthesized PbSe and PbS quantum dots in strong-confinement regime, and measured energy relaxation time by using pump-and-probe experiments. Energy relaxation time of PbSe dots in phosphate glasses showed clear correlation with the average radius. Smaller dots were shown to have shorter decay times. This dependence is ascribed to the relaxation to the surface of the dots.

Characterization of Er-doped sodium-niobium phosphate glasses

Er-doped sodium-niobium phosphate glasses have been produced by the melting technique. Their optical properties have been fully characterized and show a broad fluorescence band around 1.5 micrometers . The fluorescence lifetime of the 4I13/2 metastable state is long enough to make these glasses suitable to be used in optical ampl9ification devices. Waveguides have been produced by diluted Ag+/Na+ ion exchange and their properties are described here.

Glass doped with PbS quantum dots for passive Q switching of a 1.54-mu m laser

By using a PbS-doped phosphate glass as an intracavity saturable absorber, we achieved passive Q switching of a 1.54-microm Er:Yb:glass laser. We obtained Q-switched pulses with 110-ns duration and 0.2-mJ energy. The saturation intensity at 1.54 microm was estimated to be approximately 60 kW/cm(2).

Raman gain in niobium-phosphate glasses

In this paper, niobium-phosphate glasses doped with rare earths (Er and Sm) are investigated by Raman scattering. The goal of Raman characterization is twofold: (a) to perform a fine structural characterization of the synthesized glasses and (b) to measure the Raman gain coefficient of the samples and to compare it with fused silica. The results reveal the presence of NbO6 octahedra and Nb–O–P–Nb–O mixed chains. A broadening of bandwidth and a significant enhancement (∼24 times) in gain coefficient G with respect to conventional silica glasses are also demonstrated.

Femtosecond absorption dynamics in glass-metal nanocomposites

We report strong optical nonlinearity of glasses embedded with copper and silver nanoparticles. In pump-probe experiments with copper-doped glasses, the observed absorption bleaching with picosecond relaxation time is as high as 22%. Transmission femtosecond measurementsreveal the reverse saturable absorption with nonlinear absorption coefficient of 10(-10)cm/W in both copper- and silver-doped nanocomposites.

New glasses for graded-index optics: influence of non-linear diffusion in the formation of optical microstructures

Abstract We have designed novel glasses for the formation of graded-index diffractive optical structures. In these glasses silver ion exchange and rapid diffusion produce a large refractive-index variation (0.085). We model the non-linearity of the diffusion process by applying the Boltzmann–Matano technique to the optical profiles and use index variation rather than concentration in the second Fick equation. The simulation of graded-index diffraction gratings formed under thermal and electrically assisted diffusion shows that, other conditions being equal, more efficient gratings can be formed when the diffusion coefficient increases with the dopant concentration. According to the simulation, the application of an electric field of about 0.5 V/μm enables one to obtain a phase shift equal to 1.5 π rad if a grating with a period of 4 μm is formed in the novel glass material. For comparison, a phase shift of only 0.9 π is predicted when a similar grating is formed in the commercial BK-7 glass.

Size-dependent picosecond energy relaxation in PbSe quantum dots

We measured the size dependence of the energy relaxation time of PbSe quantum dots at room temperature. The radius of the dots was evaluated by small-angle x-ray scattering. We found a monotonic decrease of the relaxation time from 25 to 1 ps with a decrease of the radius r from 2.9 to 1.4 nm. The 1/r 3 dependence of the relaxation rate was indicated.