Alexander A. Zhilin

Cobalt-doped transparent glass ceramic as a saturable absorber Q switch for erbium:glass lasers

A new saturable absorber Q switch for 1.54-mum Er:glass lasers is presented. The saturable absorber is a transparent glass ceramic that contains magnesium-aluminum spinel nanocrystallites doped with tetrahedrally coordinated Co(2+) ions. We obtained Q-switched pulses of up to 5.5 mJ in energy and 80 ns in duration at 1.54 mum. The relaxation time of (4)A(2) ?(4)T(1)((4)F) transition bleaching was measured to be (450 ? 150) ns. Ground-state and excited-state absorption cross sections at 1.54-mum wavelength were estimated to be (3.2 ? 0.4) x 10(-19) cm(2) and (5.0 ? 0.6) x 10(-20) cm(2), respectively.

Magnesium- and zinc-aluminosilicate cobalt-doped glass ceramics as saturable absorbers for diode-pumped 1.3-μm laser

Q switching of a diode-pumped Nd3+:KGd(WO4)2 laser at 1.35 microm by use of cobalt-doped magnesium- and zinc-aluminosilicate glass ceramics as saturable absorbers is demonstrated. Q-switching efficiency up to 40% has been obtained. Ground-state absorption cross sections for Co2+ ions at the wavelengths of 1.35 and 1.54 microm are estimated to be (3.5-4.0) x 10(-19) cm2. Bleaching relaxation times under the excitation of the 4A2 --> 4T1(4F) transition of tetrahedrally coordinated Co2+ ions are of 280 +/- 50 ns and 700 +/- 80 ns for magnesium- and zinc-aluminosilicate glass ceramics, respectively.

Formation and Passive Q-Switch Performance of Glass-Ceramics Containing Co2+-Doped Spinel Nanocrystals

Compositions and heat treatment conditions were determined at which absorption and luminescence properties of aluminosilicate transparent glass-ceramics are defined mainly by tetrahedrally coordinated Co2+ ions located in spinel nanocrystals. Optical properties of cobaltdoped aluminosilicate transparent glass-ceramics have been studied in visible – near infrared (IR) spectral range. It was demonstrated that the concentration of tetrahedrally coordinated Co2+ ions in the spinel nanocrystals is determined by the CoO content in the initial glass and is independent of the heat-treatment schedule. Absorption saturation and bleaching relaxation under excitation of the 4A2→4T1(4F) transition of tetrahedrally coordinated Co2+ ions were studied. The value of groundstate and excited state absorption cross-sections of tetrahedrally coordinated Co2+ ions was estimated. Comparative study of output pulse parameters of Q-switched Er:glass laser using cobaltdoped glass-ceramics and Co2+:MgAl2O4 single crystal is presented.

Holmium lasers passively Q-switched with PbS quantum-dot-doped glasses.

PbS quantum-dot-doped glasses are demonstrated as saturable absorber Q-switches for 2 microm holmium lasers. Q-switched pulses from Ho3+:Y3Sc2Al3O12 and Ho3+:Y3Al5O12 lasers of 50 and 70 ns in duration, respectively, have been obtained demonstrating up to 13% of energy conversion efficiency from free-running to Q-switched output.

Intensity-dependent bleaching relaxation in lead salt quantum dots

Bleaching relaxation in lead salt (PbS) quantum dots (QDs) of various sizes and under different pump intensities has been studied. The observed bleaching relaxation features (particularly, shortening of the bleaching relaxation times with a decrease in the QD size and an increase of the pump-light intensity) are explained in the context of the proposed spectroscopic model. The model takes into account transitions of the excited-charge carriers both within the system of quantum-confined energy levels and the defect states of the QDs. The characteristic times of the direct electron-hole recombination, carriers trapping to the defect states, and their subsequent relaxation from these states as well as the cross sections of the ground-state and excited-state absorption of charge carriers can be evaluated from the experimental data for PbS QDs of different sizes and under different pumping conditions using this model.

Anomalously Low Light Scattering in the Na2O-Nb2O5-SiO2 Glass-Ceramics

An evolution of the structure of three glasses of Na2O-Nb2O5-SiO2 system in the course of isothermal heat treatments at 660–700°C and the extinction coefficient of the material were studied. Spinodal phase separation was found to be a primary process followed by precipitation of nano-sized NaNbO3 crystalline phase. It was found that the spectral dependence of the extinction coefficient in the wavelength range λ= 400–800 nm corresponds to light scattering by spinodal structure at the phase separation stage and by independent Rayleigh scatterers (NaNbO3 nanocrystals) at the early stage of crystallization. The extinction coefficient increases at the first half of the crystallization stage and then decreases. At the late stage of crystallization and for the final glass-ceramics, the extinction coefficient α is 10–20 times smaller than that calculated for independently scattering nanocrystals and is characterized by anomalous wavelength dependence (α ∝ λ−6). The model for calculation of extinction coefficient is proposed, in which the interference effects in light scattering by nanocrystals are taken into account. On this basis, the variation of extinction coefficient in the course of crystallization and its wavelength dependence are explained.

Influence of reducing-oxidizing conditions on the optical properties of Co 2+ -doped magnesium aluminosilicate glass ceramics and their use as an effective saturable absorber Q switch

Nonlinear optical properties of Co(2+)-doped magnesium aluminosilicate glass ceramics prepared under normal and reducing conditions are studied in the range of the 4A2 --> 4T1(4F) transition of tetrahedral Co2+ ions. The results of passive Q switching of a 1.54-microm Er3+:glass laser with saturable absorbers made of Co(2+)-doped glass ceramics prepared at different conditions are presented. Q-switched pulses of 60 ns in duration and of 4.6 mJ in energy, corresponding to approximately 20% of the Q-switching conversion efficiency, are achieved.

Nonlinear optical properties of PbS and PbSe quantum dots in glassy matrices

Intensity dependent transmission and excited state relaxation measurements of PbS and PbSe quantum dots in silicate and phosphate glasses and their applications for mode-locking of Nd:YAG laser at 1.064 micrometers as well as for Q-switching of Nd:KGW at 1.067 micrometers and 1.35 micrometers and Er:glass at 1.54 micrometers lasers with diode and flash-lamp pumping are presented.

1 mJ single-rod fiber Er:glass laser for rangefinding

We demonstrate a compact Er:glass single-rod fiber laser for rangefinding with 1 mJ energy Q-switched at 1.54μm. Double-pass pumping with 16 W power and 5 ms pulse duration was used. Active medium was enveloped with diffuse reflector. Thus efficient output power operation achieved. Free-running mode output pulse energy was 12 mJ with a slope efficiency of 16%. Transparent glass-ceramics containing Co2+:MgAl2O4 nanocrystals were selected as the optimal passive gate to ensure Q-switching in a temperature range and transverse mode selection. The Q-switch mode had steady operation at 1 Hz repetition rate with thermal effects playing no visible role.

Pulse-burst Er:glass laser

We demonstrate a pulse-bursting phenomenon in Yb:Er glass laser operating at 1.54 μm. Glass-ceramic material with a low value of saturation threshold based on Co2+:β-ZnSiO4 nanocrystals was used as a passive gate for pulse-burst operation. The bursts of pulses were 1.5 ms long, each burst consisted of 40-55 pulses with 9-30 μJ energy per pulse and 0.2-3 μs pulse width. Bursting outputs arise via a coupling between slow switching arising via a slow pump modulation and fast pulsations resulting from Q-switch mechanism. We show that absorption cross-section strongly affects the mode of laser operation ranging from relaxation oscillations corresponding to low cross-section values to bursting and conventional Q-switch operation in the case of their higher values.