Radosław Lisiecki

Near-infrared ultrabroadband luminescence spectra properties of subvalent bismuth in CsI halide crystals

We observed two ultrabroadband near-infrared (NIR) luminescence bands around 1.2 and 1.5 μm in as-grown bismuth-doped CsI halide crystals, without additional aftertreatment. Dependence of the NIR emission properties on the excitation wavelength and measurement temperature was studied. Two kinds of NIR active centers of subvalent bismuth and color centers were demonstrated to coexist in Bi:CsI crystal. The eye-safe 1.5 μm emission band with an FWHM of 140 nm and lifetime of 213 μs at room temperature makes Bi:CsI crystal promising in the applications of the ultrafast laser and ultrabroadband amplifier.

Near-infrared photoluminescence spectra in Bi-doped CsI crystal: evidence for Bi-valence conversions and Bi ion aggregation

Bi-doped CsI crystals exhibited near-infrared ultra-broadband photoluminescence around 1216 nm and 1560 nm, depending on the bismuth doping levels, which were ascribed to Bi+ and Bi2+ centers, respectively. The crystal chemistry of the Bi3+ to Bi+ reduction and Bi2+ dimer formation in CsI lattice were investigated. Thermal treatments including annealing and quenching were carried out to study the thermal behaviors of the two emission bands. The evolution of absorption and emission spectra of Bi:CsI crystals indicating the Bi-aggregation and valence conversions under thermal activation. The process of Bi aggregation was observed to be a second-order reaction with activation energy of 0.33 eV. Bi2+ was identified as the origin of the 1560 nm emission band with ESR spectra. A simple lattice structure diagram was developed to illustrate the physical processes in Bi:CsI crystals induced by thermal activation.

Crystal structure and optical study of Tm:Sc2SiO5 single crystal

Sc2SiO5:4 at. %Tm crystal was obtained by the Czochralski method and the crystal cell parameters were calculated. Sixfold coordinated Sc-ions occupied two different crystallographic sites but the low temperature optical spectra only represented energy transitions originating from Tm ions residing in one site. Room temperature absorption spectrum was analyzed in the framework of Judd–Ofelt theory and the calculated absorption coefficient and cross section were 10.47 cm−1 and 5.55×10−21 cm2 at 791 nm respectively. Stimulated emission cross sections for the F34–H36 transition near 1900 nm were evaluated using the reciprocity method while the luminescence F34 lifetime was measured to be 1.14 ms. We conclude that Tm:Sc2SiO5 is promising for diode-pumped infrared lasers.

Spectral characterization and laser performance of a mixed crystal Nd:(Lu x Y 1-x ) 3 Al 5 O 12

An Nd-doped Lu(1.5)Y(1.5)Al(5)O(12) (Nd:LuYAG) crystal was obtained by Czochralski method. Absorption and emission spectra were recorded at low and room temperature. Continuous wave (CW) and passively Q-switched laser operations of Nd:LuYAG crystal were, to our knowledge, demonstrated for the first time. A CW output power of 1.67 W with slope efficiency of 39.8% was obtained. In the passively Q-switched operation, the shortest pulse width, largest pulse energy, and highest peak power were achieved to be 9.6 ns, 61.7µJ, and 6.4 kW, respectively, with Cr(4+):YAG crystals as the saturable absorbers.

Estimation of low-temperature spectra behavior in Nd-doped Sc2SiO5 single crystal

High optical quality Nd-doped Sc(2)SiO(5) crystal with size of diameter 27 mm x 60 mm was obtained by Czochralski method. An x-ray diffraction pattern of Nd:SSO crystal confirmed that the as-grown crystal was isostructual with the SSO crystal. Absorption and emission spectra were recorded at 10 K. The Judd-Ofelt theory was applied to obtain standard parameters Omega t(t=2,4,6) and the fitting result of experimental absorption line strengths, which provided the F3/24 radiative lifetime (tau(rad)) of 219 micros and the luminescence branching ratio beta of 0.57 for the (4)F(3/2)-(4)I(9/2) laser transition. The stimulated emission cross section of 1.04 x 10(-19) cm(2) at 1074 nm was calculated using the Füchtbauer-Ladenburg equation. The (4)F(3/2) luminescence lifetimes with 215 micros at 10 K and 198 micros at 300 K were determined from luminescence decay curves, indicating high quantum efficiency in the Nd:SSO crystal. All these results showed that Nd:SSO would be a promising gain media in solid-state lasers.

Effect of temperature on spectroscopic features relevant to laser performance of YVO_4:Er^3+ and GdVO_4:Er^3+ crystals

Optical spectra and luminescence decay curves were measured for erbium-doped YVO(4) and GdVO(4) single crystals as a function of temperature in the 300 K-670 K temperature region. In spite of structural similarity the two systems studied display significantly different transition intensities and nonradiative relaxation rates. It was found in particular that the intensity of parasitic upconverted emission excited at 978 nm depends weakly on temperature for YVO(4):Er(3+), whereas it decreases monotonously with increasing temperature for GdVO(4):Er(3+) and becomes negligibly small at 670 K. It was concluded that GdVO(4):Er(3+) may be a promising laser active material operating at high thermal loading conditions encountered in high-power diode-pumped IR lasers.

Spectroscopic properties of Yb-doped CaF2–YF3 solid-solution laser crystal

The spectroscopic properties of Yb:CaF2–YF3 disordered crystals obtained by the vertical Bridgman method were studied. The 3 at.% Yb, 3 at.% Y:CaF2 crystal absorption cross section σabs centered at 974 nm reached 7.2 × 10−21 cm2 and the fluorescence lifetime was 3.54 ms at room temperature. Experimental results show that co-doping Y3+ ions at different Y:Yb ratios can modulate the spectroscopy and lengthen the luminescence lifetime of Yb3+ ions in the CaF2 lattice. There are three main kinds of lattice in the 3 at.% Yb, 3 at.% Y:CaF2 crystal, as concluded from the low-temperature spectra.

Effect of temperature on spectroscopic features relevant to laser performance of YVO4:Tm3+, GdVO4:Tm3+, and LuVO4:Tm3+ crystals.

Optical spectra and luminescence decay curves were measured for thulium-doped YVO(4), GdVO(4), and LuVO(4) single crystals as a function of temperature in the 300-670 K temperature region. In spite of structural similarity, the three systems studied display significantly different transition intensities and nonradiative relaxation rates. It was found, in particular, that the peak value of the pump band absorption intensity diminishes by about 30% for Tm:YVO(4) and Tm:GdVO(4), and the effective emission cross section for the laser transition of Tm(3+) diminishes by a factor of 2 roughly when temperature increases from 300 to 500 K. An unusually small quantum efficiency of the upper laser level in Tm:LuVO(4) has been derived from the analysis of luminescence decay curves.

Spectroscopic properties of the Pr3+ ion in TeO2-WO3-PbO-La2O3 and TeO2-WO3-PbO-Lu2O3 glasses

The goal of this work was to investigate the spectroscopic properties of Pr3+ ions, embedded in two different tellurite glass matrices, TeO2-WO3-PbO-La2O3 and TeO2-WO3-PbO-Lu2O3. The absorption and fluorescence spectra have been recorded and analyzed in terms of the Judd-Ofelt theory along with the luminescence decay of the 3P0 and 1D2 levels of the Pr3+ ion. The spectroscopic studies were completed with ellipsometric measurements providing the dispersion relation of the refractive index of the investigated glasses.

Spectroscopy and laser operation of Ho:CaYAlO4

Single crystals of Ho-doped CaYAlO4 crystals with 1.0% and 0.5% holmium concentration have been grown by Czochralski technique in N2 atmosphere. Due to the randomly distributing of Ca2+ and Y3+ ions in the crystal structure, the doped Ho3+ ions show a broad absorption and fluorescence bands. So it can be efficiently utilized to obtain ultrafast pulse generation in time range of pico- or even femtoseconds. Moreover, Ho:CYA laser was operated pumped by Tm:fiber laser, and the maximum output laser power of 2.38 W for 1.0% Ho:CaYAlO4 was obtained.