Direct diode-pumped continuous-wave near-inf rared tunable laser operation of Cr(4+):forsterite and Cr(4+):Ca(2)GeO(4)

Continuous-wave tunable laser operation of direct diode-pumped Cr(4+):Mg(2)SiO(4) (Cr:forsterite) and Cr(4+):Ca(2)GeO(4) (cunyite) crystal were demonstrated. Diode-pumped Cr:forsterite was tunable over the 1236-1300-nm spectral range. The maximum output of 10 mW was measured at 1260 nm for 640 mW of pump power absorbed by the crystal. Diode-pumped laser operation of cunyite was also demonstrated over the 1390-1475-nm range. Free-running 20-mW output was centered at 1410 nm.     

Broadly tunable compact continuous-wave Cr(2+):ZnS laser

We report the development of a continuous-wave, room-temperature Cr(2+) ZnS laser that is compact and tunable over 700 nm. The laser is pumped by a diode-pumped Er-fiber laser and generates 0.7 W of linearly polarized radiation at 2.35microm , at up to 40% slope efficiency. Cr(2+) ZnS directly diode-pumped at 1.6microm yields polarized radiation that is tunable over 400 nm at up to 25 mW of output power. A comparison of Cr(2+) ZnS with Cr ZnSe (70 mW, 350 nm) in a similar setup is given. As opposed to Cr ZnSe, the Cr ZnS laser is intrinsically polarized. Finally, we observe sensitization of the output radiation by a few milliwatts of the visible (470-500-nm) and near-infrared (740-770-nm) radiation.     

Enhanced thermoelectric performance through homogenously dispersed MnTe nanoparticles in p-type Bi_(0.52)Sb_(1.48)Te_3 nanocomposites

In this work,we report that the thermoelectric properties of Bi_(0.52)Sb_(1.48)Te_3alloy can be enhanced by being composited with Mn Te nano particles(NPs)through a combined ball milling and spark plasma sintering(SPS)process.The addition of Mn Te into the host can synergistically reduce the lattice thermal conductivity by increasing the interface phononscattering between Bi_(0.52)Sb_(1.48)Te_3 and MnTe NPs,and enhance the electrical transport properties by optimizing the hole concentration through partial Mn~(2+)acceptor doping on the Bi~(3+)sites of the host lattice.It is observed that the lattice thermal conductivity decreases with increasing the percentage of Mn Te and milling time in a temperature range from 300 Kto 500 K,which is consistent with the increasing of interfaces.Meanwhile,the bipolar effect is constrained to high temperatures,which results in the figure of merit z T peak shifting toward higher temperature and broadening the z T curves.The engineering z T is obtained to be 20%higher than that of the pristine sample for the 2-mol%Mn Te-added composite at a temperature gradient of 200 K when the cold end temperature is set to be 300 K.This result indicates that the thermoelectric performance of Bi_(0.52)Sb_(1.48)Te_3 can be considerably enhanced by being composited with Mn Te NPs.     

钙钛矿锰氧化物La0.7Sr0.3MxMn1-xO3(M=Cr,Fe)的巨磁电阻效应与磁性

研究了溶胶 -凝胶法制备氧化物巨磁电阻材料的工艺 ,制备了La0 .7Sr0 .3 CrxMn1-xO3 (x =0 ,0 .10 ,0 .15 )和La0 .7Sr0 .3 FexMn1-xO3 (x =0 .0 5 ,0 .10 ,0 .16 )两系列的单相钙钛矿锰氧化物多晶样品 ,并研究了Cr ,Fe替代La0 .7Sr0 .3 MnO3 中部分Mn后对其结构、磁性和巨磁电阻性质的影响 .观察到La0 .7Sr0 .3 Cr0 .15Mn0 .85O3 和La0 .7Sr0 .3 Fe0 .0 5Mn0 .95O3 两个样品的电阻 温度曲线都出现了双峰 .定性讨论了可能产生双峰的机制 .随Cr(或Fe)替代量的增加 ,材料的居里温度很快下降 ,铁磁性减弱 ,导电性降低 ,巨磁电阻效应增强 .但与Fe掺杂相比 ,相同数量的Cr掺杂对材料的影响要小 .     

1.9- m and 2.0- m laser diode pumping of Cr(2+) :ZnSe and Cr(2+) :CdMnTe

Efficient diode pumping at wavelengths of 1.9 and 2.0microm of a Cr(2+): ZnSe laser with an output power of 105 mW and a slope efficiency of 35% with respect to the absorbed pump power is presented. In addition, Cr(2+): CdMnTe has been laser diode pumped as well as operated in the continuous-wave regime, to the best of our knowledge for the first time.     

Efficient passively Q-switched laser operation of Yb in the disordered NaGd(WO4)2 crystal host

Efficient passively Q-switched laser operation of the disordered Yb:NaGd(WO(4))(2) crystal is demonstrated for the first time to our knowledge with a Cr(4+):YAG saturable absorber by diode end pumping. 2.05 W of average output power at a pulse repetition frequency of 13.3 kHz was obtained at an absorbed pump power of 7.7 W, with a slope efficiency of 40%. The energy and duration of the generated laser pulse were 154 microJ and 33 ns, respectively, corresponding to a peak power of 4.67 kW. In continuous-wave operation, the Yb:NaGd(WO(4))(2) laser yielded an output power of 5.5 W with an optical-optical efficiency of 51%.     

Cr(2+):ZnSe and Co(2+):ZnSe saturable-absorber Q switches for 1.54-mum Er:glass lasers

Passive Q switching of Er:glass lasers has been demonstrated with Cr(2+):ZnSe and Co(2+):ZnSe saturable absorbers. A pulse duration of ~50ns and an output pulse energy of 5 mJ were obtained with both Co:ZnSe and Cr:ZnSe passive shutters. A Q-switched conversion efficiency of as much as 26% was obtained for Cr:ZnSe. Theoretical modeling exhibits satisfactory agreement with experimental data.     

Efficient grating-tuned mid-infrared Cr2+:CdSe laser

Room-temperature, all-solid-state, broadly tunable laser operation of Cr(2+) -doped CdSe has been demonstrated. Pumping with a Q -switched Tm, Ho:YLF laser running at a 1-kHz repetition rate achieved broadband output of 500 mW at 2.6mum with 48% absorbed power slope efficiency. With reduced efficiency, as much as 815 mW of power was obtained. With a diffraction grating, the Cr(2+): CdSe laser was tuned from 2.3 to 2.9mum with 10-nm bandwidth (FWHM) and output power up to 350 mW.     

End-pumped, passively Q-switched Yb:YAG double-clad waveguide laser

We present a diode-pumped, double-clad Yb:YAG waveguide laser that contains an integrated section of a Cr(4+): YAG saturable absorber for passive Q switching. Using two 4-W polarization-coupled, broad-striped diode-pumped lasers, we obtained 30-microJ pulses of 1.6-ns duration at repetition rates of as much as 77 kHz. The slope efficiency was ~50% with respect to absorbed pump power, with a maximum output average power of 2.3 W and a peak power of ~18 kW . The output beam was single lobed, with M(2) values as great as 1.5x1.3 . We also demonstrate a passively Q -switched Nd:YAG waveguide laser of similar design, operating at 1.064 microm and 946 nm.     

Density functional studies on the ferromagnetic properties of (Zn,Cr)Te

We have investigated the electronic and magnetic properties of the room temperature ferromagnetic diluted magnetic semiconductor (DMS) (Zn,Cr)Te with density functional calculations. The electronic and magnetic properties of (Zn,Cr)Te are very similar with those of the typical DMS (Ga,Mn)As. The stronger ionicity of ZnTe plays a key role in the electronic and magnetic properties of (Zn,Cr)Te.     

Ultralow-pump-threshold, femtosecond Cr(3+):LiSrAlF(6)laser pumped by a single narrow-stripe AlGaInP laser diode

We report what we believe to be the first demonstration of a Kerr-lens mode-locked Cr(3+):LiSrAlF(6)laser that is pumped by a single narrow-stripe AlGaInP laser diode with a diffraction-limited output beam. A novel low-loss three-mirror laser cavity design is described in which strong, localized Kerr lensing was exploited such that 75-fs-duration pulses were obtained for only 36mW of incident pump power. This pump power was maintained for 18h by just three AA batteries as the electrical power source. We have shown that mode locking can be sustained for pump powers as low as 22mW.     

Erbium fiber laser-pumped continuous-wave microchip Cr(2+):ZnS and Cr(2+):ZnSe lasers

Efficient continuous-wave (cw) lasing of Cr(2+):ZnS and Cr(2+):ZnSe crystals in external hemispherical cavities and in a microchip configuration under Er-fiber-laser pumping at room temperature are reported. The key result is what is believed to be the first successful demonstration of cw Cr(2+):ZnS and Cr(2+):ZnSe microchip lasers with maximum output powers of 63 and 100 mW at 2320 and 2520 nm, with slope efficiencies of 53% and 20%, respectively.     

YAG晶体中Cr4+和Yb3+的光谱和荧光特性研究

报道了（Ｃｒ＾４＋,Ｙｂ＾３＋）：ＹＡＧ晶体的吸收光谱和荧光光谱特性。在室温下,（Ｃｒ＾４＋,Ｙｂ＾３＋）：ＹＡＧ晶体在９３７ｎｍ和９６８ｎｍ处存在两个吸收带,能与ＩｎＧａＡｓ激光二级管有效耦合：而且在１０３０ｎｍ处有一Ｃｒ＾４＋吸收峰,可以实现对Ｙｂ＾３＋的自调Ｑ激光输出。（Ｃｒ＾＋,Ｙｂ＾３＋）：ＹＡＧ 荧光光谱与Ｙｂ＾３＋：ＹＡＧ晶体一样,发光中心也是位于１０２９ｎｍ,但其强度比Ｙｂ＾３＋：     

Binary alloys of Ge and Te: order, voids, and the eutectic composition

The liquid and amorphous structures of Ge0.15Te0.85 and GeTe alloys are characterized using combined density functional/molecular dynamics simulations. Te is threefold coordinated, in contrast with predictions of the "8-N rule," and Ge atoms (fourfold coordinated) show octahedral and tetrahedral bonding angles. Cubic local environment occurs in both materials, and GeTe shows a pronounced alternation of atomic types. Tetrahedral Ge coordination is more common in the eutectic Ge0.15Te0.85, which comprises corner- and edge-sharing GeTe4 units surrounded by Te. There is no Te segregation, and the material resembles neither GeTe nor Te. The ubiquitous cavities (voids) have been overlooked in Ge0.15Te0.85, where they comprise over 25% of the volume.     

Hg_(0.8)Cd_(0.2)Te光电二极管的外差量子效率的研究

介绍了n~+-P型离子注入Hg_(0.8)Cd_(0.2)Te光电二极管的敏面上外差量子效率分布函数η(x,y)的正则化分析方法,并通过CO_2相干激光探测的方法测量了η(x,y).     

Local spin density in the Cr(7)Ni antiferromagnetic molecular ring and (53)Cr-NMR

We present (53)Cr-NMR spectra collected at low temperature in a single crystal of the heterometallic antiferromagnetic (AF) ring Cr(7)Ni in the S?=?1/2 ground state with the aim of establishing the distribution of the local electronic moment in the ring. Due to the poor S/N we observed only one signal which is ascribed to three almost equivalent (53)Cr nuclei in the ring. The calculated spin density in Cr(7)Ni in the ground state, with the applied magnetic field both parallel and perpendicular to the plane of the ring, turns out to be AF staggered with the greatest component of the local spin ?s? for the Cr(3+) ions next to the Ni(2+) ion. The (53)Cr-NMR frequency was found to be in good agreement with the local spin density calculated theoretically by assuming a core polarization field of H(cp)?=-?11?T/μ(B) for both orientations, close to the value found previously in Cr(7)Cd. The observed orientation dependence of the local spin moments is well reproduced by the theoretical calculation and evidences the importance of single-ion and dipolar anisotropies.     

Neutron powder diffraction investigation on the crystal and magnetic structure of (Ho(0.50+x)Ca(0.50-x))(Mn(1-x)Cr(x))O3

The crystal and magnetic structure of (Ho(0.50+x)Ca(0.50-x))(Mn(1-x)Cr(x))O(3) (x = 0.00, 0.01, 0.02, 0.03) has been investigated between 5 and 300 K by means of neutron powder diffraction followed by Rietveld refinement and dc magnetic measurements. During cooling an orthorhombic to monoclinic phase transition occurs on account of the charge and orbital ordering taking place in the Mn sub-lattice; at low temperature phase separation takes place and the main monoclinic phase coexists with a secondary orthorhombic phase, whose amount slightly increases with the increase of Cr content. Cr(3+) is not involved in orbital ordering or superexchange interactions. The charge and magnetic ordering are decoupled: the Mn moments order according to a CE-type structure in all samples.     

High-energy self-starting femtosecond Cr(4+):Mg(2)SiO(4) oscillator operating at a low repetition rate

We describe a self-starting high-power femtosecond laser based on the Cr(4+):Mg(2)SiO(4) crystal that produces 17-nJ pulses of 40-fs duration at 26.5-MHz repetition rate. This low repetition rate is achieved by employment of a one-to-one telescope in the cavity. The pulse energy is five times greater than with a short-resonator laser. To our knowledge, the laser produces the highest energy ever achieved from this type of laser directly from the resonator without cavity dumping or external amplification. We believe that this laser source can be used for many applications, including nonlinear optics, microscopic imaging, and micromachining of silicon and other semiconductor materials.     

Spin and orbital quantization of electronic states as origins of second harmonic generation in semiconductors

Basically different mechanisms of optical second harmonic generation (SHG) in semiconductors, induced by an external magnetic field H, have been identified experimentally by studying the diluted magnetic semiconductor (Cd,Mn)Te. For paramagnetic (Cd,Mn)Te the SHG response is governed by spin quantization of electronic states, in contrast with diamagnetic CdTe with its dominating orbital quantization. The mechanisms can be identified by the distinct magnetic field dependence of the SHG intensity which scales with the spin splitting in the paramagnetic case as compared to the H2 dependence observed for the diamagnetic case.     

Investigation of the Emission Cross-sections and the Spectra of (Cr~(4 ), Yb~(3 ) ): YAG Crystal

l introductionIn recent years, Cr4 --doped crystals have attracted a great deal of attention aspassive Q--,wit,h.,[l~4]. These Cr4 --dOPed crystals include Cr4 : YAG[l'21 ) Cr4 :GSGG[s], Cr4 : YSO['] etc. They have a large absorption cross section and lOwsaturable intensity at the laser wavelength. In comparison with previously usedsaturable absorbers such as dyes['] and LiF: FZ-- [6] cOlor center crystals, Cr4 -dopedcrystals are more photO--chemically and thermally stable and h…