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21.
57Fe Mössbauer measurements are reported for the series K x Ba1?x Fe2S3, x ≤ 0.3, at temperatures between 4.2 K ≤ T ≤ 294 K. A decrease of the Debye temperature from 435 to 405 K with x, indicates a weakening of the stiffness of the Fe sublattice. The ordering temperatures, taken from the appearance of magnetic hyperfine splitting in the spectra, are approximately 40 K lower for x ≥ 0.1. The values of the centre shift and the small temperature dependence of the quadrupole splitting strongly supports that similar to the border compound BaFe2S3 also the K containing samples should be characterised as mixed valence compounds. 相似文献
22.
We demonstrate what is believed to be the first phase-coherent locking of a high-power broad-area diode to a single-frequency master laser. We use photorefractive double phase conjugation to lock the diode in a self-optimized complex spatial mode while the photorefractive crystal diffracts that complex mode in a near-diffraction-limited beam. 相似文献
23.
B. Wunderlich A. Boller I. Okazaki K. Ishikiriyama W. Chen M. Pyda J. Pak I. Moon R. Androsch 《Thermochimica Acta》1999,330(1-2):21-38
Temperature-modulated differential scanning calorimetry of first-order transitions has led to many new observations. Some of these involve non-linear processes or deal with transformations of practically instantaneous response. The latter may cause serious lags within the calorimeter due to limited thermal conductivity of the sample and the instrument. In both cases the “reversing heat capacity” or a “complex heat capacity” is not a precise representation of the transition since both are computed from abbreviated Fourier transforms, limited to the evaluation of the first harmonic component. One has in these cases to work in the time-domain with the raw output. But even from these analyses in the time-domain many interesting new insights about the transition and the calorimeter performance can be generated. 相似文献
24.
Blue 465-nm radiation is generated by frequency doubling of the output of an InGaAs diode-laser oscillator-amplifier system in critically phase-matched LiB(3)O(5) (LBO). The diode-laser system emitted 4 W of single-frequency 930-nm radiation in a near-diffraction-limited beam (M(2)<1.2) . The laser power is enhanced to values of up to 150 W in a resonant external ring cavity. The LBO crystal is placed at a resonator internal focus. The frequency doubling in the LBO crystal generates blue radiation at 465 nm with a power of 1 W. The spectral width of the blue radiation is less than 3 MHz, and the value of the M(2) beam parameter is less than 1.2. 相似文献
25.
Singly resonant continuous-wave optical parametric oscillator pumped by a diode laser 总被引:1,自引:0,他引:1
We report on what is believed to be the first singly resonant cw optical parametric oscillator (SRO) that is directly pumped by a diode laser. The SRO consists of a 38-mm-long periodically poled LiNbO(3) crystal in a four-mirror signal-resonant ring cavity. Pumped by 2.5 W of 925-nm diode-laser radiation, the SRO generates 480 mW of single-frequency idler radiation at 2.1mum . The wavelengths of the signal and the idler output are tuned in the ranges of 1.55 to 1.70mum and 2.03 to 2.29mum, respectively, by tuning the wavelength of the diode laser from 924.0 to 925.4 nm. 相似文献
26.
The existence of ternary chalcogenides of general composition TlT
2
X
2 (T=Fe,Co,Ni,X=S;T=Fe,Co,Ni,Cu,X=Se) crystallizing in the ThCr2Si2-structure type has been established. The crystal structure of TlCo2S2 was refined from single crystal diffractometer data. The dimensions of the tetragonal unit cells are: TlFe2S2;a=3.755 (1),c=13.35 (1) Å; TlCo2S2:a= =3.7410 (5),c=12.956(5) Å; TlNi2S2:a=3.792 (1),c=12.77 (1) Å; TlFe2Se2:a=3.890 (1),c=14.00(1) Å; TlCo2Se2:a=3.847 (1),c=13.54 (1) Å; TlNi2Se2:a=3.866 (1),c=13.41 (1) Å; TlCu2Se2:a=3.852 (1),c=14.01 (1) Å. These phases are the first chalcogenides found to crystallize in the ThCr2Si2-structure type. Unlike the already known representatives of this structure type they show a pronounced partial ionic character. Interatomic distances as well as the relations to the alkali thiometallates of Co and Mn are discussed. 相似文献
27.
A complex carbide with formula Ta2S2C prepared by sintering can be transformed by mechanical grinding into a modification having a very simple crystal structure. The lattice parameters of this compound (1s-Ta2S2C) were found to be:a=3.265,c=8.537 andc/a=2.615. The atomic positions are (space group \(P\bar 3ml\) ): $$\begin{gathered} 2 Ta in 2 d) (z = 0.141) \hfill \\ 2 S in 2 d) (z = 0.65) \hfill \\ 1 C in 1 a \hfill \\ \end{gathered} $$ A proposal for the atomic arrangement is presented for the high temperature phase 3s-Ta2S2C with the parameters:a H=3.276 c H=25.62 Å andc/a=7.82, space group \(R\bar 3m\) . The crystal structure of Ti4S5 has been determined from single crystal patterns. The lattice parameters are:a=3.439,c=28.93 Å andc/a=8.413. The atomic positions (space group P 63/mmc) are: 2 Ti in 2 a), 2.6 Ti in 4 e) (z=0.1055); 3.5 Ti in 4 f) (z=0.197); 2 S in b); 2 4 S in 4 f) (z=0.052) and 4 S in 4 f) (z=0.649). 相似文献
28.
R. A. Loch A. Lévy T. Ceccotti F. Quéré C. Thaury H. George F. Bijkerk K.-J. Boller Ph. Martin 《The European physical journal. Special topics》2009,175(1):133-138
Enhanced backward-acceleration of ions is experimentally observed when ultra-short, high-intensity and ultra-high-contrast
laser pulses interact with thin foils having thicknesses in the order of the penetration depth of the laser light. Below the
experimentally observed optimum foil thickness for the maximum ion energy versus thickness, there arises a second peak. 1D
simulations on foils with an initial plasma density gradient show a similar trend as the experiment. It appears that in this
regime of extremely thin foils it is important to take into account the limited expansion of the plasma that is formed by
ultra-high-contrast pulses. 相似文献
29.
L.C. Casper H.M.J. Bastiaens P.J.M. Peters K.-J. Boller R.M. Hofstra 《Applied physics. B, Lasers and optics》2007,88(1):61-66
The discharge quality and optimum pump parameters of a long-pulse high-pressure gas discharge excited KrCl laser are investigated.
A three-electrode prepulse–mainpulse excitation circuit is employed as pump source. The discharge volume contains a gas mixture
of HCl/Kr/Ne operated at a total pressure of up to 5 bar. For a plane–plane resonator, the divergence of both output laser
beams is measured. A low beam divergence of less than 1 mrad is measured as a result of the very high discharge homogeneity.
A maximum laser pulse duration of 150 ns (FWHM) is achieved for a pump duration of 270 ns (FWHM) and a power density of 340 kW cm-3. Pumping the discharge under optimum conditions employing a stable resonator results in a maximum specific energy of 0.45 J/l
with a laser pulse duration of 117 ns and an efficiency of 0.63% based on the deposited energy.
PACS 42.55.Lt; 52.25.-b; 52.59.Ye 相似文献
30.
We report on what is to our knowledge the first optical parametric oscillator (OPO) pumped by microsecond pulses from a wavelength-tunable solid-state laser. The singly resonant OPO (SRO) is based on a periodically poled LiNbO3 crystal and pumped with 2.1-micros-long pulses from an actively Q-switched Yb fiber laser. At an average fiber laser power of 3.6 W, the SRO generates 1.9-micros-long pulses with a repetition rate of 25 kHz and an average power of 560 mW at 3360 nm. The SRO was tuned from 1518 to 1634 nm (signal) and from 3145 to 3689 nm (idler) via the crystal temperature and poling period. By all-electronic tuning of the fiber laser wavelength over 19 nm, tuning of the mid-infrared idler wavelength over 195 nm was achieved. 相似文献