Nikolai V. Nikonorov

Experimental determination of the upconversion rate in erbium-doped silicate glasses

A new experimental method for direct determination of the upconversion coefficient C(up) in Er-doped glasses is presented. This method is based on measurement of the dependence on pump power of the fluorescence quantum yield at 1.54 microm and of the excited-state absorption. Two methods are used for determination of the population of the excited Er ions. The first is based on the measurement of the variation in stimulated emission and on the variation in ground-state absorption for the (4)I(15/2)<-->(4)I(13/2) transition range. In the second, the excited-state absorption is measured for the (4)I(13/2) -->(4)F(7/2) transition. This method is successfully applied to Er-doped silicate glass fibers. The value of C(up) experimentally obtained is in good agreement with previously published results.

New possibilities of photosensitive glasses for three-dimensional phase hologram recording

Refractive index variation due to photothermoinduced crystallization of polychromatic glass has been found. This effect is used for 3-D phase hologram recording. Optical properties of holograms are stable in the wide spectral and temperature range. Holograms have high diffraction efficiency and angle selectivity.

Effect of pumping on spectral characteristics of Er-doped glasses

The fluorescence and absorption variation of spectra of Er- and Yb/Er-doped phosphate and silicate glasses under CW Ti- sapphire laser were investigated. On pumping, the differential spectra demonstrated variations of spectral profiles. The reason of these variations is heating effect under high pump power. These variations were explained by a redistribution of the populations of the Stark sublevels of the 4I15/2 ground and the 4I13/2 excited manifolds. The heating effect under pumping was taken into account for measurement of quantum yield and determination of absolute values of up-conversion coefficients. Several techniques that reduce the heating effect on fluorescence, excited state absorption, and ground state absorption spectra due to pumping were proposed.

Measuring the gain/loss spectra in high-concentration ytterbium-erbium-doped laser glasses

The gain/loss spectra of ytterbium-erbium-doped laser glasses have been investigated in the 1.5-µm region. A direct experimental method has been developed for determining the population of the excited metastable 4I13/2 level, the contour of the gain/loss spectrum, and its variation at various pumping levels. The experimental and calculated spectra are compared.

Steady-state characterization of up-conversion quenching in Er-doped glasses with the use of hypersensitive bands of ESA and GSA spectra

A steady-state method was used for characterization of up- conversion quenching in Er-doped glasses. This method is based on measurement of pumping dependencies of quantum yield and the population of the 4I13/2 metastable manifold. The population was determined from absorption spectra variation under the pump of semiconductor laser. The feature of the method consists in measurement of absorption spectra variation in short-wave spectral range of 300 - 520 nm. In this spectral region, a hypersensitive excited state absorption (ESA) band ((lambda) equals 478 nm) for 4I13/2 yields 4G9/2 transition was detected. The following parameters characterizing absolute intensity of ESA band were determined: line strength, integral cross- section, cross-section in maximum, and oscillator strength. This band was used for evaluation of the population of the 4I13/2 metastable manifold and up-conversion coefficients. The up-conversion coefficient, Cup equals 1.7 X 10-17 cm3s-1, was obtained for an Er3+ concentration of 6.8 X 1020 cm-3.

Effect of heating on spectral characteristics of Er-doped laser glasses

The absorption and fluorescence spectra of Er-doped phosphate and silicate laser glasses were investigated in a temperature range of 20 - 300 degree(s)C. On heating, the differential spectra demonstrated variations of spectral profiles. The effects of heating for silicate and phosphate glasses are similar. The contours of the absorption and luminescence bands varied nonmonotonically with the temperature. These variations were explained by a redistribution of the populations of the Stark sublevels of the 4I15/2 ground and the 4I13/2 excited terms. The heating resulted in 5 - 10% decrease of oscillator strengths of spectral bands. On the base of temperature variations of spectral profiles we proposed an energy levels model, which allowed to explain the thermal variation of spectrum of Er-doped laser at 1.54 micrometers . According to this model, the transitions in two range of lasing (1534 and 1542 nm) come from two Stark sublevels of the 4I13/2 excited manifold to two sublevels of the 4I15/2 ground manifold. The effective energy gaps between neighboring Stark components are equal to 50 cm-1 and 100 cm-1 for the 4I13/2 and the 4I15/2 states, respectively.

Polarized fluorescence of Er3+ in laser glasses

The partial polarization of luminescence in phosphate and silicate erbium glasses in the range of 1.5 μm under the stimulation by the linearly polarized laser light (532 nm, 790-990 nm) has been detected. The degree of polarization depends both on a spectral range of excitation and on a spectral range of registration, reaching maximum value ~1%. The concentration of depolarization has been studied.

Study of optically waveguiding structures formed in potassium titanyl phosphate by ion exchange

Ion-exchanged KTiOPO 4 (KTP) planar optical waveguides are formed in X , Y , and Z cuts of KTP single crystals with Rb + -> K + , Cs + -> K + , and Ag + -> K + ion exchanges from nitrate melts. Waveguide modes, index profiles, and birefringence of the waveguides are studied with the integrated optics technique. Electron probe microanalysis is applied to determine an elemental composition of the ion-exchanged structures and x-ray diffractometry is used to study crystalline structure of the waveguides. The research enabled us to produce KTP optical waveguides by silver ion diffusion for the first time. In addition, the residual potassium concentrations after the ion exchange are measured and the distribution profiles of Cs and Rb atoms and positions of the atoms in the KTP lattice are characterized. A study of the unit cell deformations accompanied by birefringence measurements enabled us to clarify differences in Rb + -> K + and Cs + -> K + ion exchanges. A novel approach that would produce a KTP optical waveguide with higher index increase and better crystalline perfection than Rb + -> K + and Cs + -> K + ion exchanges is proposed.

Influence of ion exchange treatment on laser-induced damage of glass surface

This work is devoted to the investigation of questions that can be useful for development of standard for the determination of laser induced damage threshold. It is shown that low- temperature ions exchange is a prospective approach for improving and stabilizing of laser damage thresholds of glasses surfaces. The radiation parameters and exposure conditions which are necessary to obtain the reproducible breakdown thresholds have formulated. The powerful laser system for damage testing designed on the basis of these requirements are described.

Photoinduced chi recording in two- and multicomponent lead-silicate glasses for optical waveguides

The possibility of recording second-order nonlinear susceptibility in commercial and specially synthesized lead-silicate glasses was investigated. Effective photoinduced SHG in glasses with lead content from 10 to 40 mol% was found. Optical waveguides by ion-exchange were made in these glasses. Optimal content of Na2O in lead-silicate glasses for optical waveguides was found.