Ferroelectric Exchange Bias Affects Interfacial Electronic States

In polar oxide interfaces phenomena such as superconductivity, magnetism, 1D conductivity, and quantum Hall states can emerge at the polar discontinuity. Combining controllable ferroelectricity at such interfaces can affect the superconducting properties and sheds light on the mutual effects between the polar oxide and the ferroelectric oxide. Here, the interface between the polar oxide LaAlO₃ and the ferroelectric Ca-doped SrTiO₃ is studied by means of electrical transport combined with local imaging of the current flow with the use of scanning a superconducting quantum interference device (SQUID). Anomalous behavior of the interface resistivity is observed at low temperatures. The scanning SQUID maps of the current flow suggest that this behavior originates from an intrinsic bias induced by the polar LaAlO₃ layer. Such intrinsic bias combined with ferroelectricity can constrain the possible structural domain tiling near the interface. The use of this intrinsic bias is recommended as a method of controlling and tuning the initial state of ferroelectric materials by the design of the polar structure. The hysteretic dependence of the normal and the superconducting state properties on gate voltage can be utilized in multifaceted controllable memory devices.     

Impurity local phonon nonradiative quenching of Yb3+fluorescence in ytterbium-doped silicate glasses

We have studied the concentration quenching of Yb³⁺ ion fluorescence in Yb-doped silicate glasses containing up to 3.4×10 ²¹ cm^-3 Yb³⁺ ions. The absorption and fluorescence spectra are similar to those obtained for the Yb³⁺ ion in many different matrices, with a radiative lifetime of approximately 1400 μs. The fluorescence decay curves were different among samples, with strong dependence on the Yb concentration. The decay curves could always be resolved into two exponential components, indicating that the ions reside in two different sites, each of a different characteristic nonradiative decay mechanism. The fast decay times ranged between 6 and 300 μs, and the slow ones ranged between 190 and 1250 μs in different samples. The sites where ions exhibit the fast decay most probably consist of pairs of Yb³⁺ ions. The nonradiative decay probabilities for each site mere directly proportional to the Yb³⁺ concentration in the same site. We propose that the fluorescence quenching occurs by multiphonon nonradiative transitions involving polar local phonon bands created by the presence of the Yb³⁺ ion     

Energy Transfer Between Multi-Sites in Chromium-Thulium-Doped Yttrium Aluminum Garnet

We consider the energy transfer between different sites in chromium-thulium-doped yttrium aluminum garnet. Subtle changes in the spectroscopic levels allow us to selectively excite different sites, with considerably different dynamic and spectral behavior. A new analytical model is developed to account for the complicated energy transfer mechanisms in this crystal.     

激光二极管抽运高浓度掺杂Yb:YAG晶体获得3.8 W连续激光输出

在热力学性质优良的YAG晶体中,Yb3+离子仅有的两个电子态产生Stark分裂后,形成准三能级的激光能级,具有高的激光效率和掺杂浓度,较Nd3+离子的四能级分布更容易在激光二极管抽运下产生高功率激光输出.     

Comparative Performance of Passively Q-Switched Diode-Pumped Yb 3+-Doped Tungstate and Garnet Lasers Using Cr 4+:YAG Saturable Absorber

We investigated the continuous wave (CW) free-running and repetitive modulation in the kilohertz frequency domain of a passively Q-switched diode-pumped Yb:YAG, Yb:GGG, and Yb:KYW lasers by using Cr⁴⁺:YAG as a saturable absorber. The results presented in this paper are focused on the design of a passively Q-switched Yb-doped garnets or Yb-doped tungstates microlasers. The free-running performance of Yb:YAG, Yb:GGG, Yb:KGW, and Yb:KYW were characterized, and experimental parameters such as gain and loss were evaluated. We carried out a fit between our experimental results and an existing numerical model, which relates the experimental and the physical parameters of the ytterbium diode-pumped system to the minimal threshold pumping power. The best performance among the laser crystals was obtained for Yb:YAG laser. A maximum peak power of ap4.5 kW at an average output power of 1.32 W was extracted with an extraction efficiency of ap25%.     

The effect of the geometry of the active medium on the performanceof SF6+H2 pumped HF laser

Experimental study of a pulsed, electric-discharge-initiated, SF ₆+H₂ pumped HF chemical laser is presented. The reactants were premixed and the laser medium was preionized by means of a plasma cathode. The laser pulse energy, as a function of the discharge voltage, was measured for various laser medium parameters. It was concluded that the ratio between the width and height of the active volume is an important issue in the laser performance     

Passively Q-switched diode-pumped Yb:YAG laser using Cr-doped garnets

We investigate the repetitive modulation in the kHz frequency domain of a passively Q-switched, diode-pumped Yb:YAG laser, by Cr⁴⁺:YAG, Cr⁴⁺:LuAG, and Cr⁴⁺:GSGG saturable absorbers. The results presented here are focused towards the design of a passively Q-switched Yb:YAG microlaser. The free-running performance of both rod and a disk Yb:YAG is characterized and experimental parameters such as gain and loss are evaluated. These values, together with the value of the stimulated emission cross-section, e.g. σ_em=3.3×10⁻²⁰ cm² were found to fit between our experimental results and an existing numerical model which relates the experimental and physical parameters to the minimal threshold pumping power. Q-switched pulses with maximum peak power of ≈10.4 kW, with energy of ≈0.5 mJ/pulse, were extracted with 30% extraction efficiency.