Aleksandr I Landman

Ultrasonic evaluation of the Jahn–Teller effect parameters. Application to ZnSe:Cr2 +

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.

A compact Er:YLF laser with a passive Fe 2+ :ZnSe shutter

This paper describes an experimental study of the lasing of an Er:YLF laser at wavelengths 2.66, 2.71, and 2.81 µm under selective pumping by the radiation of laser diodes at wavelength 0.98 µm and passive Q-switching of the cavity by a shutter based on an Fe2+:ZnSe crystal. Single pulses are obtained with energy 3 mJ and width 30 ns at wavelength 2.81 µm.

Tunable single-frequency CW Cr2+:CdSe laser

Continuous tuning of the lasing wavelength from 2350 to 3450 nm in the cw Cr2+:CdSe laser is demonstrated. It is shown that the laser efficiently operates at a wavelength of 3.28 µm, 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.

Passive Q-switching of the diode-pumped Er:YAG laser cavity with the Q-switch based on the Fe2+:ZnSe crystal

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.

Relaxation Attenuation of Ultrasound by the Jahn-Teller Centers in ZnSe:Cr in High Magnetic Fields

The magnetic field dependence of ultrasonic attenuation α (B) of slow shear waves in the ZnSe:Cr2+ crystal at a number of fixed temperatures from T=1.4 K to 20 K in magnetic fields of up to B=14 T were investigated. For magnetic fields B above 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 at B=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.

Continuous-wave Cr{sup 2+}:CdS laser

Continuous-wave lasing is obtained for the first time in a Cr{sup 2+}: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 Cr{sup 2+}:CdS and Cr{sup 2+}:CdSe lasers are compared. A Cr{sup 2+}: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%. (lasers)

A Cr{sup 2+}:CdS laser tunable between 2.2 and 3.3 {mu}m

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.

A continuous-wave Fe{sup 2+}:ZnSe laser

A continuous-wave oscillation is obtained for the first time in a Fe{sup 2+}:ZnSe laser. The laser wavelength was in the range from 4.04 to 4.08 {mu}m. A liquid-nitrogen-cooled active element was pumped by a Cr{sup 2+}:CdSe laser at 2.97 {mu}m. 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 Fe{sup 2+}:ZnSe crystal did not exceed 0.024 cm{sup -1} during lasing. (lasers. amplifiers)

Efficient cw lasing in a Cr{sup 2+}:CdSe crystal

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%.