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53.
D. Sabourdy V. Kermène A. Desfarges-Berthelemot M. Vampouille A. Barthélémy 《Applied physics. B, Lasers and optics》2002,75(4-5):503-507
The coherent combining of two Nd:YAG lasers using a Vernier–Michelson-type cavity has been demonstrated. The spectral behaviour
and the energetic performance are reported. We firstly show that the combining efficiency is not strongly spoilt by the gain
imbalance between the two amplifying media, and secondly, that despite the interferometric nature of the cavity, the Vernier–Michelson
laser can withstand environmental perturbations without alteration in output power.
Received: 25 April 2002 / Revised version: 18 May 2002 / Published online: 25 September 2002
RID="*"
ID="*"Corresponding author. Fax: +33-5/5545-7253, E-mail: kermene@ircom.unilim.fr 相似文献
54.
Baril N Lewa CJ de Certaines JD Canioni P Franconi JM Thiaudière E 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,154(1):22-27
A new method for NMR characterization of mechanical waves, based upon radiofrequency field gradient for motion encoding, is proposed. A binomial B1 gradient excitation scheme was used to visualize the mobile spins undergoing a periodic transverse mechanical excitation. A simple model was designed to simulate the NMR signal as a function of the wave frequency excitation and the periodicity of the NMR pulse sequence. The preliminary results were obtained on a gel phantom at low vibration frequencies (0-200 Hz) by using a ladder-shaped coil generating a nearly constant RF field gradient along a specific known direction. For very small displacements and/or B1 gradients, the NMR signal measured on a gel phantom was proportional to the vibration amplitude and the pulse sequence was shown to be selective with respect to the vibration frequency. A good estimation of the direction of vibrations was obtained by varying the angle between the motion direction and the B1 gradient. The method and its use in parallel to more conventional MR elastography techniques are discussed. The presented approach might be of interest for noninvasive investigation of elastic properties of soft tissues and other materials. 相似文献
55.
Localized proton spectroscopy without water suppression: removal of gradient induced frequency modulations by modulus signal selection 总被引:1,自引:0,他引:1
Serrai H Clayton DB Senhadji L Zuo C Lenkinski RE 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,154(1):53-59
Most Magnetic Resonance Spectroscopy (MRS) localization methods can generate gradient vibrations at acoustic frequencies and/or magnetic field oscillation, which can cause a time-varying magnetic field superimposed onto the static one. This effect can produce frequency modulations of the spectral resonances. When localized MRS data are acquired without water suppression, the associated frequency modulations are manifested as a manifold of spurious peaks, called sidebands, which occur symmetrically around the water resonance. These sidebands can be larger than the small metabolite resonances and can present a problem for the quantitation of the spectra, especially at short echo times. Furthermore, the resonance lineshapes may be distorted if any low frequency modulations are present. A simple solution is presented which consists of selecting the modulus of the acquired Free Induction Decay (FID) signal. Since the frequency modulations affect only the phase of the FID signal, the obtained real spectrum of the modulus is free from the spurious peaks where quantitative results may be directly obtained. Using this method, the distortions caused by the sidebands are removed. This is demonstrated by processing proton MRS spectra acquired without water suppression collected from a phantom containing metabolites at concentrations comparable to those in human brain and from a human subject using two different localization methods (PRESS and Chemical Shift Imaging PRESS-(CSI)). The results obtained illustrate the ability of this approach to remove the spurious peaks. The corrected spectra can then be fit accurately. This is confirmed by the results obtained from both the relative and the absolute metabolites concentrations in phantoms and in vivo. 相似文献
56.
Three-dimensional microfabrication by two-photon-initiated polymerization with a low-cost microlaser 总被引:3,自引:0,他引:3
Fabrication of submicrometer structures by two-photon-initiated polymerization is performed with an inexpensive and low-power microlaser. This is made possible by the design of photoinitiators with strong two-photon absorption cross sections. We analyze the influence of both material properties and irradiation conditions on the two-photon polymerization rate and show that resins based on our highly sensitive two-photon photoinitiator can be solidified with microlaser excitation, whereas commercial UV photoresins require ultrashort and intense laser pulses. 相似文献
57.
E. Canè G. Di Lonardo L. Fusina W. Jerzembeck H. Bürger J. Breidung 《Molecular physics》2013,111(4):557-577
The high resolution infrared spectrum of 123SbD3 has been recorded in the 20–350?cm?1 range and in the regions of the ν1, ν3 and ν2, ν4 fundamental bands centred at 1350 and 600?cm?1, respectively. Splitting of the K′′?=?3, 6 lines have been observed both in the rotation and ro-vibration spectra. A large number of ‘perturbation allowed‘ transitions with selection rules Δ(k??l) =?±?3,?±?6, and?±?9 have been identified in all fundamental bands. Accurate ground state molecular parameters have been determined by means of a simultaneous fit of the rotational transitions and about 12?000 ground state combination differences from the infrared bands. The A and B reductions of the rotational Hamiltonian provided almost equivalent results. The molecular parameters of the ν i ?=?1 (i?=?1???4) states were obtained as a result of the simultaneous analysis of the ν1 (A1)/ν3 (E) stretching and of the ν2 (A1)/ν4 (E) bending dyads. In fact, the corresponding excited states are affected by strong perturbations due to rovibrational interactions of Coriolis and k-type that have been treated explicitly in the model adopted for the analysis. Improved effective ground state and equilibrium geometries were determined for the molecule and compared to those of 123SbH3. Ab initio calculations at the coupled cluster CCSD(T) level with an energy-consistent large-core pseudopotential and large basis sets were carried out to determine the equilibrium structure, the anharmonic force field, and the associated spectroscopic constants of 123SbH3 and 123SbD3. The theoretical results are in good agreement with the experimental data. 相似文献
58.
59.
Abstract During these last twenty five years a great efforts have been made in the Laboratoire de Chimie du Solide du CNRS in order to develop high oxygen pressure for the stabilization of unusual oxidation state of transition elements. The aims of such research works was to correlate the increase of the Mn+-O bond covalency versus the increase of the oxidation state n+ to the physicochemical properties of resulting oxides [1]. Iridium was an interesting element due to its position (5d) in the Periodic Table. In 1980 Ir(V) (d4) was stabilized in La2LiIrO6 in the perovskite structure [2]. Such a study had underlined the strong value of the spin-orbit coupling associated to Ir(V) [3]. The stabilization of Ir(VI) is interesting from two points of view : (i) its isotropic electronic configuration (d3), (ii) such a high oxidation state could lead to the strongest M-O bond in an oxygen lattice. Selecting, through a specific methodology, the most appropriate local structural and chemical factors and with the help of high oxygen pressure, Ir(V1) was stabilized in the perovskite Ba2CaIrO6. Structural, magnetic and Mössbauer studies have been carried out in order to characterize the physicochemical properties induced by this unusual oxidation state. 相似文献
60.
A system of two coupled oscillators, each of them coupled to an independent reservoir, is analysed. The analytical solution of the non-rotating wave master equation is obtained in the high-temperature and weak coupling limits. No thermal entanglement is found in the high-temperature limit. In the weak coupling limit the system converges to an entangled non-equilibrium steady state. A critical temperature for the appearance of quantum correlations is found. 相似文献