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1.
It is shown that LiF crystals with F 2 ? colour centers may be used in lasers for cavity Q-switching and in high-power Nd: glass laser systems for, increasing the contrast and the self-excitation threshold. Also Lif crystals with F 2 ? centers are successfully used for the generation of ultrashort pulses, for the generation of difference frequencies in the ir spectral range and in intracavity spectroscopy experiments.  相似文献   

2.
Intense, directional, and narrow-bandwidth 1130-nm emission was generated from LiF crystal at room temperature by the pumping with radiation in the wavelength region of the absorption band of the F2 color center. The emission was observed by the pumping with radiation of pulse energy above 5 mJ, and the divergence angle of the beam was about 16 mrad. This emission is attributed to the amplified spontaneous emission by the F2 center. Received: 8 April 1999 / Revised version: 18 May 1999 / Published online: 16 September 1999  相似文献   

3.
Ba x Me1 ? x F2 binary fluoride films (“Me” denotes calcium or magnesium fluoride) are studied. A method of processing the reflection and transmission spectra is proposed to determine the optical constants. The dispersion dependences of the refractive indices and absorption coefficients of films in the range of 1.3–12 μm are found. Dispersion in films in the regions of additional absorption bands, which are absent in single crystals, is observed for the first time. It is shown that the films of binary fluorides have a higher packing density, a lower absorption, and better operating characteristics than do films of pure fluorides. The films are promising for application as optical interference coatings in the mid-IR spectral region.  相似文献   

4.
Abstract

Despite numerous studies on the BF4 ? anion 1-6 indicating to its complex behavior in different solutions in the presence of different cations, it is still quite difficult to explain this unambiguously. This is ostensibly due to the incompleteness of experimental data both for temperature dependencies and for solution compositions3. Taking this into account, we measured the dependencies of 19F NMR spectra in a broad range of temperatures and concentrations in aqueous and water-acetone solutions of Co2+, Ni2+ and Zn2+ tetrafluoroborate salts on “RYA-2305” and “SWL 2-31/10” instruments in spherical and cylindrical ampoules. The said dependencies were recorded both for BF4 ? and BF3OH? signals, the latter forming in insignificant quantities due to the hydrolysis of the tetrafluoroborate anion in positively hydrated cation solutions1.  相似文献   

5.
Abstract

Pair defects consisting of F centres and CN? molecules as substitutional impurity anions (FH(CN?) centres) exhibit a strong coupling between the F centres and the CN? molecules. This leads to an optical pumping of the CN? vibrations via the F centre absorption band. We performed an Electron Nuclear Double Resonance (ENDOR) investigation in order to analyse the microscopic structure of these aggregate centres. The CN? molecule occupies a [110] nearest anion position with respect to the F centre in two dynamic dipole orientations even at low temperature.  相似文献   

6.
Frequency-tunable generation by means of F 2 + and F 2 ? colour centers in a LiF crystal is reported. Colour centers were created by illuminating LiF crystals with electrons of 3 meV energy at the electron current density of 1 μA/cm2. The pumping source was a ruby laser with a peak power of 20 MW, a pulse duration of 20 ns, and a repetition rate of 1 Hz. The frequency tuning is obtained in the range of 0.88–1.25 μm. Discussed are the ways of pumping of colour centers and the possibility of lasing in the spectral region of 0.85 to 2 μm in the type of colour centers under investigation.  相似文献   

7.
The decay process τ ?φπ ? ν τ is investigated on the basis of the method of chiral phenomenological Lagrangians. It is shown that the calculated value of the decay probability is very sensitive to variations in the angle of ω?φ mixing. The resulting value of this probability is compared with available experimental data and with the results of other theoretical calculations.  相似文献   

8.
We report on measurements of the Seebeck-effect, the Nernst-effect, and the magnetoresistance in the mixed state of ac-axis oriented expitaxial film of Y–Ba–Cu–O. In contrast to conventional superconductors we find a large Seebeck-coefficientS, which is comparable in magnitude to the Nernst-effect. The broadening of the super-conducting transitions of magnetoresistance and Seebeck-effect are rather similar with respect to (1) the temperature dependence, (2) the dependence on the direction between magnetic field and crystal axis and (3) the dependence on the direction between magnetic field and driving forces. The large Seebeck-effect has to be attributed to dissipation due to normal quasiparticle-excitations, since the vortex-contribution to the Seebeck-effect is by far too small to account for the observed magnitude ofS. It is argued that such a quasiparticle contribution to the dissipation is large in the high-T c superconductors because of the small coherence lengths and thus the small vortex cores. Another possibility is that granularity leads to dissipation proportional to the normal state transport properties. The Seebeck-voltage depends on all dissipative processes other than vortex motion, whereas the Nernst-effect depends only on the vortex motion. Therefore by measurements of thermomagnetic effects the various dissipative properties may be separated.  相似文献   

9.
We report the synthesis, characterization and superconducting temperature of high-temperature superconducting Y0.3Ba0.7CuO3, Y0.4Ba0.6CuO3 and Y1.2Ba0.8CuO4. The volume fraction of the superconducting phase is estimated to be of the order of 10%.HighT c superconductivity withT c -onsets up to 125 K (midpoint 102 K, zero resistance: 90 K) is observed in multi-phase Y–Ba–Cu–O oxygen defect compounds with the nominal composition of Y1.2Ba0.8CuO4–y (0y0.4).  相似文献   

10.
11.
Recently, angle-resolved photoelectron spectra have been measured by exposing negative F? ions to linearly or circularly polarized infrared femtosecond laser fields. We compare the experimental results with numerical calculations carried out in the framework of a Keldysh-type theory modified to account for both the time shape and the spatial inhomogeneity of the pulse. In order to account for the finite duration of the laser pulse, our results have been obtained through calculations of photodetachment probabilities. By using the saddle-point method it is possible to show that the transition amplitude may be written as a coherent sum of terms giving rise to interferences. This circumstance suggests that some particular features of the experimental results may be described in terms of quantum interferences in the time domain.  相似文献   

12.
Abstract

In this work we present new data on the formation and destruction of the laser active (F2 +)  相似文献   

13.
XPS and UPS photoemission experiments on the highT c superconductors (T c ≈90 K) with nominal composition YBa2Cu3O9-y (y≈2) show the following:
  1. The density of electronic states at the Fermi energy is very small, much smaller than in pure Cu.
  2. The Cu 2p spectra show only a Cu2+ contribution.
  3. The Ba core levels show a structure with two components of nearly equal magnitude, which leads to the suggestion that these compounds have large O2? vacancies coordinated to Ba2+ sites.
  4. Annealing at 400°C under UHV conditions leads possibly to a partial reduction of Cu2+ to lower Cu valence states and to a small increase of the O2? vacancy component of the Ba2+ line.
  相似文献   

14.
15.
Neutron diffraction, neutron spectroscopy and magnetization measurements have been employed to study the structural, electronic, and magnetic behavior of eleven compounds with the general formula Nd1+y Ca v Ba2–y–v Cu3O x (0y0.5; 0v0.25; 6x7). The structure turned out to react to oxygen reduction similar as other 123-compounds, yielding discontinuities close to the metal-insulator-transition and the well-known relations of bond lengths as a function ofT c. The crystalline electric field (CEF) interaction, splitting the 10-fold degenerate ground-state J-multiplet of the Nd3+-ions into five doublet states, was investigated by neutron spectroscopy. The derived CEF parameters have been used to determine changes in the electronic surroundings of the Nd3+ ions. In addition, with the help of the CEF parameters the thermodynamic magnetic properties of these compounds were calculated which turn out to be in good agreement with the experimental data.  相似文献   

16.
The (p) mass distribution is calculated for the reactionK dp at rest and in flight at 700 MeV/c, for both BDI-1 and NRS-F potentials, with results which do not discriminate strongly between them. The in flight calculations can be brought into satisfactory agreement with experiment after some modification of the¯KNY amplitudes, but the at rest calculations show a strong disagreement with experiment which is not yet resolved, but which may partly reflect the experimental procedures adopted. The discrepancy with the earlier work reported by Dalitz, Hemming and Morris is accounted for, with the conclusion that further physics input may be needed to reach agreement with the data.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.  相似文献   

17.
18.
Effective orange Sm3+-doped Sr2.5Ba0.5AlO4F phosphors excited at 254 and 408 nm excitation were prepared by the solid-state method. The excitation and emission spectra of Sr2.5?3x/2Ba0.5SmxAlO4F and Sr2.5?3x/2Ba0.5SmxAlO4?αF1?δ (x=0.001~0.1) based on photoluminescence spectroscopy are investigated. The defects in anion-deficient Sr2.5?3x/2Ba0.5SmxAlO4?αF1?δ (x=0.001, 0.01) are monitored by broad-band photoluminescence emission centered near 480 nm along with the orange emission transitions of Sm3+. CIE values and relative luminescent intensities of Sr2.5?3x/2Ba0.5SmxAlO4F and Sr2.5?3x/2Ba0.5SmxAlO4?αF1?δ by changing the Sm3+ content (x=0.001~0.1) are discussed.  相似文献   

19.
The effect of yttrium substitution at the lanthanum site on the superconducting properties of La1?xYxO0.9F0.1FeAs (‘x = 0, 0.10, 0.20, 0.30, 0.50 and 0.60) oxypnictides has been studied. Powder X-ray diffraction studies confirm single phases till x = 0.1 beyond which minor amount of Y2O3 is observed. The temperature dependence of resistivity measurements confirm the superconducting transition temperature (Tc) of 34.8 (±0.05) K and corresponding Meissner transition at 34.3 K in the ‘x = 0.3 composition which is higher than that reported for the parent phase (LaO0.9F0.1FeAs (Tc = 28 K)). Further increase in the concentration of yttrium leads to broadening and suppression of the superconducting transition. The value of Hc2 at zero temperature is estimated to be about 60.5 T. The Seebeck coefficient (S) shows a negative sign indicating that the major contribution to the conductivity is by electrons. The Hall coefficient (RH) also remains negative throughout the temperature range supporting the thermopower results. The lattice parameters (a and c) decreases and the charge-carrier density increases with yttrium doping.  相似文献   

20.
A technique of spatial coherence control, based on the synchronous amplification of a radiation in LiF crystals with F 2 ? color centers, is demonstrated. Spatial radiation distributions of stimulated Raman scattering (SRS) in oxide crystals were investigated under picosecond laser excitation. Low spatial radiation coherence was revealed for both the transient and quasi-stationary SRS. Spatially incoherent SRS was transformed to spatially coherent radiation as a result of phase—locked picosecond synchronous laser pumping of nonlinear Raman and LiF: F 2 ? crystals and the Stokes radiation amplification in the color center crystal.  相似文献   

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