A G Papashvili

Beam-quality improvement of a passively Q-switched Nd:YAG laser with a core-doped rod

We present experimental results that demonstrate the great efficiency of a core-doped Nd:YAG rod (a hexagonal Nd:YAG core surrounded by undoped YAG) in producing high output power and excellent beam quality. An additional improvement in beam quality is clearly observed when the core-doped rod is used in combination with a LiF:F(2)(-) crystal, which acts as a passive Q-switching element. This improvement is quantified by beam-propagation factors as low as M(2) approximately = at a maximum average output power of 9 W. We show that transversally pumped core-doped rods with the addition of LiF:F(2)(-) crystals fulfill the requirements for high-beam-quality, scalable, compact all-solid-state lasers in passively Q-switched operation.

Photoluminescence studies in Sc: CaF2 and Sc,Ce: CaF2 crystals

Abstract Stokes and anti-Stokes UV-visible luminescence was investigated in γ-irradiated Sc and Sc-Ce doped CaF 2 crystals. Wideband Stokes luminescence under laser or CW lamp excitation was measured: (1) at 380 nm (luminescence decay time τ ~ 17 μs ) in Sc : CaF 2 and Sc , Ce : CaF 2 crystals, attributed to Sc 2+ ions and (2) at 300 nm ( τ ~ 40 ns ) in Sc , Ce : CaF 2 crystals, due to Sc-Ce aggregate centers. Anti-Stokes luminescence in the 250–350 nm spectral range with a 1 μs lifetime can be explained by exciton luminescence.

Spectroscopic and laser properties of Nd3+ doped fluoride crystals in 1.3-um region

For a number of neodymium doped fluoride crystals both with regular and disordered structure the Judd-Ofelt analysis of absorption spectra have been performed, and fluorescence and lasing spectra were studied in order to reveal the most promising materials for optical amplification in a 1.3 micrometers telecommunication window. The most suitable crystalline media investigated was found to be cubic disordered fluorides based on (50 - 70%) SrF2 - (50 - 30%) CaF2 solid solutions with Nd3+ optical centers having tetragonal local symmetry. These crystals have (1) low value of excited state absorption line strength, (2) high metastable level lifetime (1.2 - 1.3 ms), (3) high enough emission cross section for fluorescence (approximately 4 X 10-21 cm2), and (4) proper fluorescence peak at about 1310 nm wavelength and comparatively wide fluorescence band with about 20 nm FWHM.

Spectroscopic and laser properties of Tm3+ optical centers in CaF2 crystal under 795 nm diode laser excitation

The dynamics of Tm3+ optical center formation with increasing thulium concentration and the influence of different optical centers on the fluorescence and laser properties of the 2 μm 3F4–3H6 transition under ~795 nm laser diode excitation is studied.

Supersensitive electronic transition in impurity Nd-Nd nanoclusters in CaF2 crystal

A comparison of the theoretical calculations with the results of experiments on high-resolution laser spectroscopy made it possible to reveal the fine structure that arises in the supersensitive 4I9/2↔ 4G5/2 transition as a result of a strong coherent interaction in the Nd3+ ion pair in the CaF2 crystal and construct the level splitting diagram for the ground and excited states of impurity Nd-Nd nanoclusters.

Characteristics of BaF2 Scintillation Crystals

The characteristics of BaF2 barium fluoride crystals, grown from the materials provided by manufacturers, were investigated. The parameters which are important for application of the crystals in low-energy physics, electromagnetic high-energy calorimeters for detecting γ rays and electrons, and measurement of energy in the maximum possible range from tens of MeV up to hundreds of GeV, as well as applications in medicine, instrument building, geology, and so on, were measured. 7 figures, 3 tables, 13 references.

Spectroscopic properties of Tm3+ long-lifetime optical centers at the 1G4–3H5 transition in CaF2 crystal

The spectroscopic properties of Tm3+ optical centers with a long fluorescence lifetime at the magnetic dipole that allowed 1G4–3H5 transition are investigated at low (77 K) temperature.

Cooperative optical phenomena in praseodymium doped CsCdBr3

In CsCdBr3 the trivalent Rare-Earth (RE) ions substitute for the divalent Cd ions. For reasons of charge compensation and the specific crystal structure, RE centers of the form RE3+ - (Cd vacancy) - RE3+ are preferentially formed. These symmetric pair centers are very suitable for studying cooperative effects of RE ions. These include processes between the ions of the pair as well as processes between the coupled pair and the electronic excitations of the host lattice. Experiments will be shown and discussed on: (i) cross relaxation and up-conversion by direct ion-ion interaction; (ii) cooperative cross relaxation of the Pr3+ pairs with the host lattice; and (iii) cooperative vibronic emission of the Pr3+ pairs with high phonon progressions.

Passive Q-switching of 1.3-um Nd-lasers with Nd2+:SrF2 and V3+:YAG crystalline saturable absorbers and application to Raman shifting to the eye-safe region

Passive Q-switching of 1.3 micrometers neodymium lasers with Nd2+:SrF2 and V3+:YAG crystalline saturable absorbers are studied. Giant pulses up to 5 mJ energy and 40 ns duration were obtained. Efficient Raman shifting of the 1.3 micrometers pulses of passively Q-switched lasers to 1.55 micrometers wavelength are realized in Ba(NO3)2 crystal.

Cryogenic-cooled Tm:SBN tunable laser

In this work the temperature dependence of spectroscopic and laser properties of new ac- tive medium Tm:SBN (Strontium-Barium Niobate, SrxBa1−xNb2O6, x = 0.61). The tested sample of Tm:SBN (2 wt. % of Tm2O3) appropriate for generation of laser radiation at 1.88 μm had plan-parallel polished faces without anti-reflection (thickness 6.65 mm). During spectroscopy and laser experiments the Tm:SBN was at- tached to temperature-controlled copper holder and was placed in a vacuum chamber. The transmission and emission spectra of Tm:SBN and the fluorescence decay time were measured depending on temperature range 80 - 350 K. The fluorescence decay time was measured to be 3.5 ms and 2.8 ms at 80 and 350 K, respectively. Longitudinal excitation of Tm:SBN was carried out by a fibre-coupled laser diode (pulse duration 10 ms, rep- etition rate 10 Hz, pump wavelength 793 nm). The laser resonator was hemispherical, 146 mm long, with flat pumping mirror (HR @1.8 - 2.1 μm) and spherical output coupler (r = 150 mm, R = 97.5 % @1.8 - 2.1 μm). The Tm:SBN laser properties were investigated at temperature range 80 - 300 K. The highest slope efficiency with respect to absorbed pumped power was 3 % at 80 K. The maximum output peak amplitude power was 0.12 W at 80 K, i.e. 3.2 times higher than it was measured at 200 K. Tunability of laser wavelength at 80 K in the range of 1827 - 1962 nm was obtained by using SiO2 birefringent filter. At 300 K, wavelength tunability reached 1859 - 1970 nm. Thus, the new Tm:SBN crystal can be an useful laser material in the region of 2 μm.