共查询到20条相似文献,搜索用时 9 毫秒
1.
《Superlattices and Microstructures》2001,29(4):301-307
The time-resolved differential absorption of the ZnSe/ZnSTe superlattice is studied using femtosecond pump-probe measurements. Transient spectral hole burning due to the initial nonthermal carrier distribution is observed at zero time delay and the carriers are thermalized within 0.5 ps. The high-energy tail of the differential absorption spectra was used to deduce the effective temperature of the thermalized carriers. Rapid hot-carrier cooling from a temperature of 763 to 450 K within the first 4 ps is observed, with carrier cooling slowing down hence. This initial fast hot-carrier cooling is consistent with the strong carrier–phonon interaction in large gap II–VI semiconductors. 相似文献
2.
Légaré F Litvinyuk IV Dooley PW Quéré F Bandrauk AD Villeneuve DM Corkum PB 《Physical review letters》2003,91(9):093002
Ionization of D2 launches a vibrational wave packet on the ground state of D+2. Removal of the second electron places a pair of D+ ions onto a Coulombic potential. Measuring the D+ kinetic energy determines the time delay between the first and the second ionization. Caught between a falling ionization and a rapidly rising intensity, the typical lifetime of the D+2 intermediate is less than 5 fs when an intense 8.6 fs laser pulse is used. We simulate Coulomb explosion imaging of the ground state wave function of D2 by a 4 fs optical pulse and compare with our experimental observations. 相似文献
3.
Quantum calculations of a (1+1)-dimensional model for double ionization in strong laser fields are used to trace the time evolution from the ground state through ionization and rescattering to the two-electron escape. The subspace of symmetric escape, a prime characteristic of nonsequential double ionization, remains accessible by a judicious choice of 1D coordinates for the electrons. The time-resolved ionization fluxes show the onset of single and double ionization, the sequence of events during the pulse, and the influences of pulse duration and reveal the relative importance of sequential and nonsequential double ionization, even when ionization takes place during the same field cycle. 相似文献
4.
System for nanosecond and picosecond laser synchronization using high-voltage semiconductor switches
N. G. Basov V. L. Vasin M. P. Kalashnikov G. Korn M. Yu. Mazur A. M. Maksimchuk Yu. A. Mikhailov G. V. Sklizkov V. N. Puzyrev S. I. Fedotov S. A. Chaushanskii 《Journal of Russian Laser Research》1989,10(2):87-103
Results are presented on the development and investigation of a system for the synchronization of the emission of a nanosecond laser, used for plasma heating, with the emission of a diagnostic picosecond laser. The system is based on the use of the fast-semiconductor-switch technology, and ensures a temporal synchronization instability not higher than 100 psec.Laser-Plansma Laboratory and Special Design Office. Lebedev Physics Institutes, Academy of Sciences of the USSR. Translated from Preprint No. 85 of the Lebedev Physics Institute, Academy of Sciences of the USSR, Moscow, 1988. 相似文献
5.
Intracavity laser absorption spectroscopy (ICLAS) with an evacuated Cr2+:ZnSe laser is performed with a high-resolution time-resolved Fourier transform interferometer with a minimum detectable absorption coefficient equal to 4 x 10(-9) cm(-1) Hz(-1/2) in the 2.5 microm region. This represents the extreme limit currently reached in the infrared by ICLAS with Doppler-limited resolution. The broad gain band of the crystal allows a spectral coverage at most equal to 125 nm, wide enough to see entire vibration bands. Weak CO2 bands observed up to now only in the Venusian atmosphere are recorded for the first time, to our knowledge, in a laboratory. An H2O detection limit down to 0.9 parts per billion by volume is also demonstrated. 相似文献
6.
Mibaile Justin Gambo Betchewe Serge Y. Doka J. Yves Effa Timoleon Crepin Kofane 《Current Applied Physics》2013,13(7):1209-1212
We introduce a new spatially-extended semiconductor carriers transport equation model, based on generation–recombination process of the band-trap impact ionization under a longitudinal electric field. By means of numerical studies, we demonstrate the existence of chaos. Also, we present many results such as, the lyapunov spectrum, the bifurcation diagram, the phase portrait and the Poincaré surface of section. In addition the basic electric circuit used is found to be helpful in the implementation of a simple and autonomous chaotic oscillator circuit. Furthermore, the obtained results are interesting in the way that they could be useful in avoiding of undesirable chaotic regime in some switching and memory electronic devices. 相似文献
7.
Hansen JL Stapelfeldt H Dimitrovski D Abu-samha M Martiny CP Madsen LB 《Physical review letters》2011,106(7):073001
A nanosecond laser pulse confines the spatial orientation of naphthalene in 1D or 3D while a femtosecond kick pulse initiates rotation of the molecular plane around the fixed long axis. Time-dependent photoelectron angular distributions (PADs), resulting from ionization by an intense femtosecond probe pulse, exhibit pronounced changes as the molecular plane rotates. Enhanced 3D alignment, occurring shortly after the kick pulse, provides strongly improved contrast in molecular-frame PADs. Calculations in the strong-field approximation show that the striking structures observed in the PADs originate from nodal planes in occupied valence orbitals. 相似文献
8.
Podlipensky AV Shcherbitsky VG Kuleshov NV Mikhailov VP Levchenko VI Yakimovich VN 《Optics letters》1999,24(14):960-962
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. 相似文献
9.
A. S. Kyuregyan 《Journal of Experimental and Theoretical Physics》2010,110(4):637-652
The existence of generalized self-similar solutions to the system of continuity and Poisson equations is analyzed for the
problem of evolution of impact ionization waves (IIWs). It is shown that, for any physically reasonable electric-field dependence
of the impact ionization coefficients, there exist only exponentially self-similar (“limiting”) asymptotic solutions. These
solutions describe IIWs whose spatial scales and propagation velocities increase exponentially with time. Conditions are found
for the existence of plane, cylindrical, and spherical waves of this type; their structure is described; analytical relations
between the key parameters are derived; and effects of recombination (or attachment) and tunnel ionization are analyzed. It
is shown that these IIWs are intermediate asymptotics of numerical solutions to the corresponding Cauchy problems. The most
important and interesting type of exponentially self-similar IIWs are streamers in a uniform electric field. The simplest
comprehensive and explicit model describing their evolution is a spherical IIW. 相似文献
10.
S. A. H. Seif el Nasr D. Berényi Gy. Bibok 《Zeitschrift für Physik A Hadrons and Nuclei》1974,271(3):207-210
The positron impact ionization cross section for theK-shell was determined in the case of Ni, Y and Ag at 670 and 490 keV as well as for theL-shell in the case of Yb, Ta, Au and Pb at 490 keV using a beta-ray spectrometer as a source of monoenergetic electrons and anX-e + coincidence arrangement. The results for theK-shell are compared with the theoretical calculations according to Kolbenstvedt and with the earlier experimental values. 相似文献
11.
E. Adomaitis Z. Dobrovolskis A. Krotkus 《Applied Physics A: Materials Science & Processing》1985,38(2):145-149
The impact ionization in p-type indium antimonide at 77 K was investigated both experimentally and theoretically. The dc pulse measurements with the time resolution of 50 ps and the high-field Hall measurements produced clear evidence that the impact ionization inp-InSb is initiated by equilibrium holes. The calculated hole generation rate gives good agreement with the experimental results. 相似文献
12.
The triply differential cross section of molecular hydrogen for ionization by 50 eV positrons has been determined, for the first time, for both the ejected electron in coincidence with the remnant ion and for the scattered projectile. Asymmetries in the energy sharing between the two light particles in the final state are observed, with the electron spectrum being shifted to significantly lower (and the scattered positron to correspondingly higher) energies than expected. A similar shape is observed in the case of the ejected electron spectrum from a helium target at the same excess energy. 相似文献
13.
14.
The experimentally observed growth of the plasma density in a high-current high-voltage pulsed discharge in a liquid medium is compared with the results of calculations based on the effective cross sections for electron-impact ionization and other elementary processes. It is found that, in the initial stage of the discharge, the plasma density grows linearly with time, whereas at densities above 3 × 1010 cm?3, the growth becomes exponential due to the collective acceleration of plasma electrons. The gas-vapor fraction of the water medium is ionized by two groups of electrons: low-energy electrons, with energies about several tens of electronvolts, and high-energy ones, with energies in the kiloelectronvolt range. The energy spent on water ionization is estimated and is found to be several times higher than the energy required to ionize a rarefied gas. 相似文献
15.
A binary encounter model with Vriens' expression for σΔE and quantum mechanical velocity distribution for the bound electron has been used to calculate electron impact ionization cross sections for ions. The calculated cross sections agree well with experimental observations. 相似文献
16.
I. Tóth R. I. Campeanu V. Chiş L. Nagy 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,48(3):351-354
Cross sections for the ionization of N2, CO and O2 diatomic molecules by electron impact are calculated. The applied distorted wave model is based on our previous studies for
positron impact, the molecular orbitals being described by Gaussian wavefunctions. Our study emphasizes the importance of
electron exchange and of using correct distorted waves for the ejected electron. 相似文献
17.
Electron impact single ionization cross sections of copper have been calculated in the binary encounter approximation using
accurate expression for σ
ΔE as given by Vriens and Hartree-Fock momentum distribution for the target electron. The BEA calculation based on the usual
procedure does not show satisfactory agreement with experiment in this case but a striking modification is found to be successful
in explaining the experimental observations. The discrepancy is linked with the ionization of the 3d
10 electrons and probably effective single ionization does not take place from 3d shell of copper leading to smaller values of experimental cross sections. 相似文献
18.
《Physics letters. A》2004,325(1):66-69
We have carried out distorted wave calculations of positron ionization of molecular oxygen in order to compare with experimental measurements. In this work the oxygen molecule was represented by a Gaussian wave function which includes contributions from alpha and beta electrons. We find that our CPE model produces results which are in good agreement with the combined measurements for total ionization and positronium formation. 相似文献
19.
D. H. H. Hoffmann C. Brendel H. Genz W. Löw S. Müller A. Richter 《Zeitschrift für Physik A Hadrons and Nuclei》1979,293(3):187-201
K-, L andM-shell ionization cross sections have been measured for 23 elements, 12≦Z≦92, after bombardment with relativistic electrons, 15≦E 065MeV, by means of high resolution semiconductor detectors and a recently developed gas-scintillation proportional counter. For constant electron bombarding energyE 0 the ionization cross sections follow a power law dependence,σ∽Z ?α, and forE 0=50MeV we deducedα =2.45±0.02 for theK shell andα=3.00 ±0.09 for theL shell. The observedZ dependence exhibits significant systematic deviations from theoretical predictions which exceed the experimental values up to 15 % at lowZ elements for theK shell and on the average about 11% for theL andM shell. The same behaviour of too low experimental values, i.e. an overestimation by the theory, is observed for the energy dependence of the cross sections for all shells. A scaling behaviour describing theZ andE 0 dependence for allK-, L andM-shell data points is observed which also predicts the experimental values by other groups at lower and higher energies correctly. The comparsion of the measuredLΒ/Lα, andLγ/Lα intensity ratios for highZ elements with the values obtained by other groups in the energy range 0.3≦E0≦1,000 MeV exhibits an increase with bombarding energy that cannot merely be explained by the energy dependence of the subshellionization cross sections for theL shell. An attempt to explain this effect with the change of the Coster-Kronig transition probability is described. 相似文献