A. N. Nakladov

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.

Thulium fiber pumped tunable Ho:CaF 2 laser

The paper reports the first room-temperature operation of the in-band pumped Ho:CaF2 laser. A set of Ho:CaF2 crystals varying in holmium concentrations (from 0.1 up to 2.5xa0mol. % of HoF2), synthesized using the Bridgeman technique, was used for lasing and related spectroscopy investigation. A pulsed 1.94xa0μm thulium fiber laser system was used for Ho:CaF2 longitudinal pumping. For 1.5xa0mol. % of Ho:CaF2, the maximal wavelength tunability (from 2073 to 2114xa0nm) and output energy (1.6xa0mJ at 2113xa0nm) were obtained for absorbed pumping energy 34xa0mJ. Without the tuning element, the slope efficiency up to 30% in respect to absorbed power was obtained using this sample.

Specific spectroscopic and laser properties of Tm3+ ions in hot-formed CaF2 laser ceramics

The formation of new Tm3+ tetragonal optical centers with spectroscopic properties different from those for regular ones in hot-formed CaF2 ceramics is observed. The influence of the new centers formation on the fluorescence and laser properties of the 2 μm 3F4–3H6 transition under ~795 nm laser diode excitation is studied.

Transition from crystal-like to glass-like behavior of thermal conductivity in the Sr0.16Ba0.54La0.30F2.30 solid solution

Using a steady-state axial flow technique, we have measured the thermal conductivity of single crystals of congruently melting SrF2-BaF2-LaF3 solid solutions from 50 to 300 K: Ba0.66Sr0.34F2 (minimum in the melting curves), Ba0.70La0.30F2.30 (maximum in the melting curves), and Sr0.16Ba0.54La0.30F2.30 (saddle point on the melting surfaces). The thermal conductivity of the isovalently doped fluorite solid solution is typical of crystals containing point defects. Heterovalent substitution leads to glass-like behavior of thermal conductivity.

InGaN diode pumped Pr:SrF2 laser at 639 nm wavelength

We report on Pr:SrF2 single crystal laser operation at 639nm wavelength under blue laser diode pumping. The laser system was operated in the pulsed regime at 100 Hz repetition rate and 2 ms pulse duration. Using 3.5W InGaN laser diode as a pump source, 6mW of the mean output power at 639nm was extracted from the Pr:SrF2 sample. The corresponding slope efficiency related to the absorbed mean power was 16.4 %.

Formation of new Tm3+ tetragonal symmetry optical centers in CaF2 hot-formed laser ceramics

By means of time-resolved site-selective spectroscopy the formation of new Tm3+ optical centers with modified local environment and presumably tetragonal local symmetry in CaF2 hot-formed laser quality ceramics is observed. The spectroscopic properties of these new Tm3+ optical centers are investigated and shown to differ strongly from that for regular tetragonal optical centers.

Effect of cryogenic temperature on spectroscopic and laser properties of Er,La:SrF2-CaF2 crystal

The laser and spectroscopic properties of crystal Er,La:SrF2-CaF2 at temperature range 80 - 300 K, which is appropriate for generation of radiation around 2.7 um is presented. The sample of Er,La:SrF2-CaF2 (concentration Er(0.04), La(0.12):Ca(0.77)Sr(0.07)) had plan-parallel face-polished faces without anti-reflection coatings (thickness 8.2 mm). During spectroscopy and laser experiments the Er,La:SrF2-CaF2 was attached to temperature controlled copper holder and it was placed in vacuum chamber. The transmission and emission spectra of Er,La:SrF2-CaF2 together with the fluorescence decay time were measured in dependence on temperature. The excitation of Er,La:SrF2-CaF2 was carried out by a laser diode radiation (pulse duration 5 ms, repetition rate 20 Hz, pump wavelength 973 nm). Laser resonator was hemispherical, 140 mm in length with at pumping mirror (HR @ 2.7 µm) and spherical output coupler (r = 150 mm, R = 95 % @ 2.5 - 2.8 µm). Tunability of laser at 80 K in range 2690 - 2765 nm was obtained using MgF2 birefringent filter. With decreasing temperature of sample the fluorescence lifetime of manifold 4I11/2 (upper laser level) became shorter and intensity of up-conversion radiation was increasing. The highest slope efficiency with respect to absorbed power was 2.3 % at 80 K. The maximum output of peak amplitude power was 0.3 W at 80 K, i.e. 1.5 times higher than measured this value at 300 K. The wavelength generated by Er,La:SrF2-CaF2 laser (2.7 µm) is relatively close to absorption peak of water (3 µm) and so, one of the possible usage should be in medicine and spectroscopy.

Influence of cellular substructure on the thermal conductivity of heterovalent solid solutions of fluorides

The thermal conductivity of single-crystal samples of Sr0.88La0.09Nd0.03F2.03 and Sr0.80La0.15Nd0.05F2.20 solid solutions, both with a cellular substructure and without it, have been investigated by the method of stationary longitudinal heat flow in the temperature range of 50–300 K. An anisotropy of thermal conductivity (related to the substructure) is established for a Sr0.995Nd0.005F2.005 single crystal.

Site Selective Spectroscopy and Laser Oscillations of Yb 3+ Ions inBaF 2 -SrF 2 -CaF 2 Single Crystals of SolidSolution

Optical centers of Yb3+ ions in SrF2 crystal and CaF2-SrF2 and BaF2-SrF2 solid solutions were determined by means of site-selective spectroscopy and their spectroscopic and laser properties were investigated and compared to known CaF2:Yb3+ crystal.