The magnetic field dependence of ultrasonic attenuation α (B) of slow shear waves in the ZnSe:Cr2+crystal at a number of fixed temperatures fromT=1.4 K to 20 K in magnetic fields of up toB=14 T were investigated. For magnetic fieldsBabove 5 T we found that the attenuation increases with B monotonically, and at a given temperature it is proportional to the magnitude of relaxation attenuation atB=0. We show that the magnetic field dependent attenuation is due to the change in populations of the lowest energy levels of the impurity centers CrZn4Se, produced by the Jahn-Teller effect and split by the spin-orbital interaction and the magnetic field. The calculations carried out without fitting parameters are in good agreement with the experimental data.

A laser based on a Fe2+ : ZnS crystal is demonstrated for the first time. Lasing in this crystal is obtained at room temperature under pumping by 40-ns pulses of an Er : YAG laser at a wavelength of 2.94 nm. The slope effciency of the Fe2+ :ZnS laser with respect to the absorbed pump energy was 32%, and the output energy reached 3.4 mJ. Continuous tuning of the laser wavelength within the range of 3.4-4.65 nm was achieved using an intracavity dispersion prism.

A method is constructed that uses ultrasonic experiments to evaluate the parameters of the Jahn-Teller (JT) effect in impurity centers in crystals. The method is based on measurements of temperature dependent attenuation and phase velocity and does not require assumptions about mechanisms of relaxation. The results are illustrated by measurements performed on the impurity system ZnSe:Cr(2+), in which the Cr(2+) ion has a threefold degenerate T term in the ground state, subject to the [Formula: see text] JT problem. Ultrasound propagation anomalies show that the main JT distortions of the tetrahedral environment of the Cr(2+) ion are of tetragonal E type and hence the lowest branch of the adiabatic potential energy surface (APES) is formed in accordance with the [Formula: see text] problem. With dopant concentration 3.8 × 10(18) cm(-3) the modulus of the constant of linear vibronic coupling to tetragonal E type vibrations is determined by two independent experiments: |F(E)| = 5.49 × 10(-5) dyn revealed from attenuation measurements, while a slightly different value |F(E)| = 5.57 × 10(-5) dyn emerges from phase velocity measurements. Contributions of other active vibronic modes to the elastic modulus C(l) = (C(11) + C(12) + 2C(44))/2 are analyzed and it is shown that the influence of the totally symmetric mode is negligible. Using additional information about this system obtained from independent sources, we also estimated the primary force constant in the E direction (K(E)≈(1.4-4.2) × 10(4) dyn cm(-1)) and orthorhombic and trigonal saddle points of the APES in the five-dimensional space of the tetragonal and trigonal coordinates, their stabilization energies being E(JT)(O)≈81-450 cm(-1) and E(JT)(T)≈48-417 cm(-1), respectively (the variations of the K(E), E(JT)(O) and E(JT)(T) values are due to different literature data for E(JT)(E)). With these data the APES of the JT linear [Formula: see text] problem for the Cr(2+) ion in the ZnSe:Cr(2+) system is revealed.

Continuous tuning of the lasing wavelength from 2350 to 3450 nm in the cw Cr 2+ :CdSe laser is demonstrated. It is shown that the laser efficiently operates at a wavelength of 3.28 µ m, which is promising for the methane optical frequency standard. The single-frequency mode of the laser with a lasing linewidth not exceeding 60 MHz is implemented in this spectral range.

A method is constructed that uses ultrasonic experiments to evaluate the parameters of the Jahn–Teller (JT) effect in impurity centers in crystals. The method is based on measurements of temperature dependent attenuation and phase velocity and does not require assumptions about mechanisms of relaxation. The results are illustrated by measurements performed on the impurity system ZnSe:Cr2 + , in which the Cr2 + ion has a threefold degenerate T term in the ground state, subject to the JT problem. Ultrasound propagation anomalies show that the main JT distortions of the tetrahedral environment of the Cr2 + ion are of tetragonal E type and hence the lowest branch of the adiabatic potential energy surface (APES) is formed in accordance with the problem. With dopant concentration 3.8 × 1018 cm − 3 the modulus of the constant of linear vibronic coupling to tetragonal E type vibrations is determined by two independent experiments: |FE| = 5.49 × 10 − 5 dyn revealed from attenuation measurements, while a slightly different value |FE| = 5.57 × 10 − 5 dyn emerges from phase velocity measurements. Contributions of other active vibronic modes to the elastic modulus Cl = (C11 + C12 + 2C44)/2 are analyzed and it is shown that the influence of the totally symmetric mode is negligible. Using additional information about this system obtained from independent sources, we also estimated the primary force constant in the E direction (KE≈(1.4–4.2) × 104 dyn cm − 1) and orthorhombic and trigonal saddle points of the APES in the five-dimensional space of the tetragonal and trigonal coordinates, their stabilization energies being EJTO≈81–450 cm − 1 and EJTT≈48–417 cm − 1, respectively (the variations of the KE, EJTO and EJTT values are due to different literature data for EJTE). With these data the APES of the JT linear problem for the Cr2 + ion in the ZnSe:Cr2 + system is revealed.

Repetitive-pulse generation of the diode-pumped Er:YAG laser (λ = 2.94 µm) in the free mode and in the mode of cavity passive Q-switching was achieved using a Q-switch based on the Fe2+:ZnSe crystal. When using pump pulses 3 ms long, the pulse-average output power of the Er:YAG laser in the free generation mode was 0.5W. In the passive Q-switching mode, giant pulses 180 ns long with an energy of 3 µJ were obtained.

Continuous-wave lasing is obtained for the first time in a Cr2+:CdS crystal pumped by a thulium fibre laser at 1908 nm. The output power of the laser at 2534 nm achieved 0.81 W with the slope efficiency with respect to the absorbed pump power equal to 52.3%. The parameters of Cr2+:CdS and Cr2+:CdSe lasers are compared. A Cr2+:CdSe crystal generated 1.7 W of cw radiation at 2638 nm with the slope efficiency with respect to the absorbed power equal to 53.4%.

Ultrasonic experiment was done at the frequency of 54 MHz on ZnSe:Cr2+ crystal with concentration of the dopand 3.8 x 10(18) cm(-3). Giant peak of attenuation of slow shear wave propagating along (110) crystallographic direction was observed at low temperatures (about 13 K). The Peak proved to be due to relaxation process in the Jahn-Teller system. Magnitude of the peak is proportional to the concentration of the dopand. This circumstance forms the basis for a new non-destructive method of characterization of the diluted crystals, which particularly could be useful for determining the low concentration of the Jahn-Teller ions. Estimation showed that the concentration of the dopand an be registered in ZnSe:Cr2+ crystal of the order of 10(16) cm(-3). Other Jahn-Teller ions prospective for such characterization are suggested. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

By using the seeded physical vapour transport (SPVT) method the CdS:Cr single crystals were grown. Doping concentration up to 5x10(18) cm(-3) was achieved. The emission lifetime of the exited state, E-5, of Cr2+ in CdS host was measured to be 0.93 mu s at room temperature and 7.3 mu s at liquid nitrogen temperature. The measured values of peak absorption and emission cross sections were found to be 1.4x10(-18) and 1.1x10(-18) cm(2) respectively. Tuning possibility and efficiency of pulsed Cr2+:CdS laser was described. CW laser operation with slope efficiency of 52 % and output power up to 0.79 W was obtained. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Seeded free growth method with physical transport was used for preparation of large-size II-VI single crystals uniformly doped by transition metals directly during the growth. The growth crystals possess small intrinsic losses. Based on these crystals new results on development of mid-IR lasers were achieved. With the CdSe:Cr crystal pumped at the room temperature (RT) by a continuous wave (CW) 1.908 mu m thulium fiber laser, output laser power at 2.6 mu m was increased up to 1.7 W CW lasing from the ZnSe:Fe crystal was achieved using the 2.97 mu m CW Cr(2). CdSe laser as at pump sources. In this case the output power as high as 0.2 W was obtained at 4.1 mu m and T = 80 K. Broad spectral tuning of the Cr(2+) CdSe (2.26-3.61 mu m) and Fe(2) ZnSe (3.95-5.05 mu m), laser was achieved at RT in the pulsed operation. The RT laser action from CdS Cr and CdSe Fe was demonstrated for the first time. The output power of the CW Cr(+2) CdS laser was 0.81 W. The pulsed Fe2+ CdSe laser was tuned in the 4.6-5.9 mu m spectral range. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We report the spectroscopic characteristics and laser properties of Cr2+:CdS. The emission lifetime of the exited state, 5E, of Cr2+ in CdS host was measured to be 0.93 µs at room temperature and 7.3 µs at liquid nitrogen temperature. The measured values of peak absorption and emission cross sections were found to be 1.4×10−18 and 1.1×10−18 cm2 respectively. Room-temperature pulsed-laser operation was obtained under pumping by the 1.94 µm output of a Tm:YAP laser. The output of the free-running Cr2+:CdS laser was centered at ∼2.6 µm, and an absorbed energy slope efficiency of 38.8% was demonstrated. The passive crystal losses were measured to be less than 0.049 cm−1 at the lasing wavelength. With an intracavity prism, the Cr2+:CdS laser was tuned from 2.18 to 3.32 µm.

The temperature dependence of ultrasonic attenuation is proposed to use for determining concentration of dopand in a diluted magnetic semiconductor. This non-destructive method can be used for the crystal in which attenuation is caused by relaxation in the Jahn-Teller system. Attenuation coefficient per the impurity ion beta obtained at a fixed frequency was introduced as a parameter characterizing sensitivity of the method. This parameter was determined for a number of II-VI: 3d semiconductors: ZnSe:Ni2+, ZnTe:Ni2+, ZnSe:V2+, ZnSe:Cr2+, and ZnSe:Fe2+ at 54 MHz. Anomalously large value of beta = 23 x 10(-18) dB cm(2) was found for Cr2+ in ZnSe. (C) 2009 Elsevier B.V. All rights reserved.

Single crystals of CdSe:Cr and CdS:Cr with the doping level up to 1019cm−3 were grown by a vapor phase contact-free technique. An efficient room-temperature pulsed and continuous wave (CW) lasing with the CdSe:Cr crystal was achieved. First a pulsed lasing with the CdS:Cr crystal was also demonstrated. The slope efficiency on the absorbed energy was as high as 46.5% for Cr2+:CdSe and 39% for Cr2+:CdS lasers. Using an intra-cavity prism, the Cr2+:CdSe laser wavelength was continuously tuned from 2.26 to 3.61μm while the Cr2+:CdS laser from 2.2 to 3.3μm. For the laser wavelength, the crystal passive loss coefficient was estimated to be smaller than 0.045cm−1 for CdSe:Cr crystals and 0.039cm−1 for CdS:Cr crystals. For the Cr2+:CdSe laser, the CW output power up to 1.07W was achieved.

The efficient lasing of a Cr2+:CdSe single crystal pumped by 1.94-μm, 300-μs pulses from a Tm:YAP laser was obtained. The Cr2+:CdSe laser with a nonselective resonator emitted up to 17 mJ at a wavelength of ∼2.65 μm with the quantum slope efficiency of 63% with respect to the absorbed pump energy. The absorption coefficient of the Cr2+:CdSe crystal at the laser wavelength did not exceed 0.045 cm-1. By using a resonator with a dispersion prism, the laser wavelength was continuously tuned in the spectral range from 2.26 to 3.61 μm.

A continuous-wave oscillation is obtained for the first time in a Fe2+:ZnSe laser. The laser wavelength was in the range from 4.04 to 4.08 μm. A liquid-nitrogen-cooled active element was pumped by a Cr2+:CdSe laser at 2.97 μm. The maximum output power of the laser was 160 mW with the 56% slope efficiency. The minimum absorbed pump power threshold was 18 mW. The intrinsic losses in the Fe2+:ZnSe crystal did not exceed 0.024 cm-1 during lasing.

Lasing in a Cr2+:CdS crystal is demonstrated for the first time. The output power of a Cr2+:CdS laser pumped by a pulsed Tm:YAP laser at 1.94 μm achieved 4 mJ and the slope efficiency with respect to the absorbed pump energy was 39%. The continuous tuning was obtained from 2.2 to 3.3 μm in the laser with a dispersion prism resonator.

Continuous wave lasing in a Cr2+:CdSe crystal is obtained for the first time. The Cr2+:CdSe crystal pumped by a 1.908-μm thulium fibre laser generated 1.07 W at 2.623 μm with the quantum slope efficiency with respect to the absorbed power equal to 60%.

A Fe2+:ZnSe laser emitting in the spectral range between 3.77 and 5.05 μm is used for the first time for intracavity laser spectroscopy. The intracavity absorption spectra of methane in the 4.1-μm region are recorded at different instants of lasing (0–80 μs) and the dynamics of spectral holes during lasing is investigated. It is found that an intracavity absorption signal linearly increases with time during lasing in the time range from 0 to 80 μs, which provides the effective absorption length up to 24 km.