共查询到20条相似文献,搜索用时 609 毫秒
1.
The dynamics of high-harmonic generation and atom ionization by a strong and superstrong laser field are studied. In contrast to many earlier works, the present theory does not impose limitations on the laser field’s strength. We solve the nonrelativistic problem of a single hydrogen-like atom’s ionization from the ground state by a short laser pulse of subatomic, atomic, and superatomic field strength. Within the framework of the proposed method, we investigated the matrix elements of the ionization transition and revealed its substantially nonlinear dependence on the laser field strength. Both ionization and recombination processes are taken into account. The proposed method enables us to take into account the arbitrary order multiphoton ionization processes. 相似文献
2.
V. Yu. Argonov 《JETP Letters》2009,90(12):739-743
The correspondence between the statistical properties of the evolution of a quantum system and Lyapunov instability and the
chaos of its semiclassical analog has been demonstrated. The results of the analyses of atomic motion in a laser field in
the semiclassical approximation (dynamics is described by several nonlinear equations) and without this approximation (dynamics
is described by an infinite system of linear equations) are compared. In the ranges of the parameters for which the semiclassical
dynamics of point-like atoms is unstable, the fast “spreading” of quantized wave packets in the momentum space is observed.
Thus, deterministic chaos “imitates” the statistics of the quantum nondeterministic effects, although the semiclassical and
quantum solutions are fundamentally different. 相似文献
3.
Vladimir Kalitvianski 《Central European Journal of Physics》2009,7(1):1-11
We show that the electrostatic potential of an atomic nucleus “seen” by a fast charged projectile at short distances is quantum
mechanically smeared due to nucleus motion around the atomic center of inertia. For example, the size of the “positive charge
cloud” in the Hydrogen ground state is much larger than the proper proton size. For target atoms in excited initial states,
the effect is even larger. The elastic scattering at large angles is generally weaker than the Rutherford scattering since
the effective potential at short distances is softer than the Colombian one due to a natural “cutoff”. In addition, the large-angle
scattering leads to target atom excitations due to pushing the nucleus (⇒ inelastic processes). The Rutherford cross section
is in fact inclusive rather than elastic. These results are analogous to those from QED. Non-relativistic atomic calculations
are presented. The difference and the value of these calculations arise from nonperturbatively (exact) nucleus “dressing”
that immediately leads to correct physical results and to significant technical simplifications. In these respects a nucleus
bound in an atom is a simple but rather realistic model of a “dressed” charge in the QFT. This idea is briefly demonstrated
on a real electron model (electronium) which is free from infinities.
相似文献
4.
A quantum hydrodynamical study is made of the dynamical changes of a helium atom interacting with lasers of two different
intensities, but having the same frequency. Under the intense laser field, electron density oozes out of the helium atom by
absorbing laser photons and getting promoted to higher excited states including the continuum. Under the superintense field,
electron density partly moves away from the helium nucleus but remains in the “quasi-bound” dressed states along with the
laser field, thus suppressing ionization. 相似文献
5.
A. V. Andreev S. Yu. Stremoukhov O. A. Shutova 《Radiophysics and Quantum Electronics》2011,54(2):128-144
We develop the theory of interaction of the electromagnetic field and a single atom being in an arbitrary state and having
an arbitrary direction of the angular momentum of the atomic electron with respect to the direction of the field polarization
vector. It is shown that the atom response current has a tensor structure and depends on both the direction of the angular
momentum of the atom, and the polarization vector of the external field. The tensor character of the response is determined
by the externally induced anisotropic distribution of the probability density of spatial localization of the atomic electron.
It is shown that the induced-anisotropy effects clarify the harmonic generation mechanism at play during the non-resonance
interaction of laser radiation with atomic media. The developed theory is applied to the analysis of the problem about the
generation of terahertz waves in a two-color laser field. It is shown that the change in the mutual orientation of wave polarization
vectors leads to a significant increase in the efficiency of conversion of high-frequency fields to low-frequency ones. It
is shown for the first time that the generation of terahertz waves is possible in the preionization regime, when the generation
mechanism is related to atomic nonlinearity. 相似文献
6.
G. P. Miroshnichenko 《Journal of Experimental and Theoretical Physics》2009,109(2):193-206
A theory of the discrete photodetection of quantum jumps on the V configuration of atomic levels has been developed. A three-level
source atom is placed in a cavity excited by a resonance fluorescence field. The cavity is tuned to exact resonance with an
atomic transition. The cavity mode state is tested by a flux of unexcited (at the entrance) probe atoms passing through the
cavity. The energy states of the outgoing probe atoms are detected by ionization chambers, which are assumed ideal. This a
posteriori statistical information is indirectly related to the numerical characteristics of a measured quantum system consisting
of the source atom and cavity mode. The “tuning” conditions for a discrete photodetector, i.e., the rules for choosing the
parameters and durations of the interactions of the cavity mode with the probe and source atoms, intensities of the pump and
probe fields that are necessary for observing quantum jumps from the “bright” state to the “dark” one and vice versa, have
been determined. A two-state model that describes the dynamics of a quantum jump has been analyzed. The formulas have been
obtained for the observable characteristics of quantum jumps: the mean residence time of the quantum system in quasistationary
states (durations of the bright and dark periods), probabilities of quantum jumps, mean excitation levels of the quantized
cavity mode, etc. 相似文献
7.
M. Fifirig A. Cionga 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(1):33-39
We study the “coherent phase control” between the three-photon ionization by a fundamental laser field and the one-photon
ionization by its third harmonic for a hydrogen atom in its ground state. The relative phase δ of the harmonic field with
respect to the fundamental laser radiation “modulates” the interference between the two ionization channels, which is important
near the crossing points between the ionization rates of the two individual processes. Numerical results for the total ionization
rate and for the angular distribution of the photoelectrons as a function of the phase δ are presented for frequencies located
in the vicinity of the atomic resonances corresponding to the absorption of two laser photons.
Received 31 August 2000 and Received in final form 6 February 2001 相似文献
8.
This paper investigates stimulated emission and absorption near resonance for a driven system of interacting two-level atoms.
Microscopic kinetic equations for the density matrix elements of N-atom states including atomic motion are built, taking into account atom-field and atom-atom interactions. Analytical solutions
are given for the resulting macroscopic equations in different limits, for a system composed of a strong coherent “pump” field
and a weak counter-propagating “probe” field. It was shown that the existence of a dipole-dipole (long-range) interaction
between atoms separated by distance less than the pump wave-length can cause the formation of periodic polarization and population
structures (gratings in time and space) in the pumped medium without a probe field. The magnitude of pump induced population
grating can have a strong dependence on the relation between the pump field detuning and the polarization decay rate. The
“interaction” between pump and probe induced polarization/population gratings through a dipole-dipole interaction mechanism
causes the absorption line shape asymmetry. Under certain conditions, this asymmetry is revealed in increasing probe gain
for the “red”-shifted (relative to pump) probe and suppressing the gain for the “blue”-shifted probe field when pump is “red”-shifted
relative to the ensemble averaged resonant frequency. The theoretical results are consistent with experimental data for the
probe gain or absorption as the function of frequency and the dependance of the gain on atomic density for sodium vapor when
the pump laser is tuned near the D
2 line. Here the dependance of gain on particle density was explained in the terms of the long-range interaction between the
atoms. 相似文献
9.
A direct test of the so-called “quantum Zeno effect” is proposed for a truly decaying system. It is suggested that the lifetime
of an unstable atom can be extended by illuminating it with an intense laser beam at the frequency of another of its transitions.
The “Zeno” time is also compared to the lifetime 相似文献
10.
Excitation of an n-type GaAs layer by intense ultrashort terahertz pulses causes coherent emission at 2 THz. Phase-resolved nonlinear propagation experiments show a picosecond decay of the emitted field, despite the ultrafast carrier-carrier scattering at a sample temperature of 300 K. While the linear THz response is in agreement with the Drude response of free electrons, the nonlinear response is dominated by the super-radiant decay of optically inverted impurity transitions. A quantum mechanical discrete state model using the potential of the disordered impurities accounts for all experimental observations. 相似文献
11.
A. P. Bogatov 《Journal of Russian Laser Research》1994,15(5):417-453
The electromagnetic field inside a nonlinear active medium of a laser is considered as a system of counterpropagating waves.
Such an approach changes radically an earlier studied behavior of the lateral field instability due to self-deformaion (or
self-focusing). In our calculations we used an expression for a laser field in the form of two “strong” counterpropagating
waves whose complex amplitudes have weak perturbations. Amplitude perturbations of each of the “strong” waves can be presented
by two spatial harmonics corresponding to two weak perturbation waves with wave vectors making some tilted angle ±φ with the
cavity axis. Thus six waves would participate in the interaction: two counterpropagating strong waves and two pairs of weak
waves. Using this approach, we have developed a theory for the propagation of four “weak” perturbation waves in a nonlinear
amplifying medium in the presence of two counterpropagating “strong” waves. It is shown that perturbation waves with tilted
angle φ⋍0.5–1.2° inside the active region, and respecively, with the side lobes of the far-field pattern at ∼1.7–4°, have
the greatest growth increment. These perturbation waves produce lateral intensity modulation with period 10–30 μm for the
0.85 μm lasing wavelength. The appearance of such waves corresponds to the instability threshold of a homogeneous lateral
distribution of optical power in a diode laser.
The present theory makes it possible to investigate the stability of the homogeneous lateral optical intensity distribution
in a diode laser of any design. This allows one to choose a suitable design of a laser with a homogeneous lateral distribution
at high radiation power.
Translated from Preprint No. 43 (1992) of the Lebedev Physics Institute, Russian Academy of Sciences. 相似文献
12.
A. A. Sirotkin S. V. Garnov A. I. Zagumennyi Yu. D. Zavartsev S. A. Kutovoi V. I. Vlasov L. Di Labio W. Lüthy T. Feurer I. A. Shcherbakov 《Laser Physics》2009,19(5):1083-1091
Spectroscopic and lasing properties of c-cut Nd-doped Nd:Gd0.7Y0.3VO4, Nd:YVO4, and Nd:GdVO4 crystals were investigated. Spectral tuning from 1062 to 1067 nm was demonstrated. CW, Q-switching and mode-locking regimes for two-color laser operations were realized. A novel THz source based on Q-switch two-color diode-pumped solid state c-cut Nd:GdVO4 laser with Filter Lio as selective element and the GaSe nonlinear optical crystals as convertor was demonstrated. Terahertz radiation with wavelength 436 mm (0.56 THz) was detected. One picosecond laser pulses in mode-locking diode pumped c-cut vanadat lasers with a Kerr-lens and PbS-doped glasses as saturable absorbers are observed. 相似文献
13.
A method using expansion of the wave function in the basis of photonic and free atomic eigenstates is proposed for calculating the emission spectrum of an atom in a laser field. The wave function is constructed using the Kramers?Henneberger transformation so that the expression for the transition S matrix explicitly includes the nonlinear interaction with the laser field. The expansion coefficients are determined by the residual interaction, which depends on the coordinates of the classical free electron motion in the laser field. Resonances at the atomic transition frequencies explicitly arise in the emission spectrum when the residual interaction is considered in the first order. The numerical solution of the timedependent Schro¨ dinger equation for the hydrogen atom within the semiclassical approach is used to obtain emission spectra for laser pulses of different intensities and durations. 相似文献
14.
A theory of the nonlinear optical response of an atom interacting with a superposition of arbitrarily polarized fields is
developed. The theory is based on the analytical solution of the boundary-value problem for an electron moving in a spherically
symmetric intraatomic field and in the field of an external electromagnetic field. By means of the example of an argon atom
interacting with a bichromatic field formed by the first and second harmonics of a Ti:sapphire laser, it is shown that, when
an atom interacts with the field of two polarized pulses the polarization directions of which are not collinear, the response
spectrum significantly depends on the laser radiation parameters—the duration and intensity of pulses, the time of delay between
them, and the angle between the directions of polarization vectors. Generation of THz radiation is shown to be possible in
the ionization-free regime due to intraatomic nonlinearity. 相似文献
15.
M. Z. Smirnov 《Journal of Experimental and Theoretical Physics》1998,87(2):260-265
The nonlinear dynamics of an open quantum system consisting of a “dressed” atom, i.e., an atom coupled with an external multifrequency
electromagnetic field, and a single quantized mode of an electromagnetic field is studied. At different crossing points of
the quasilevels of the dressed atom, the average number of photons in the quantized mode may either increase without limit
with the passage of time or oscillate within finite limits. In the latter case a decrease of the number of photons is accompanied
by regularization of their statistics, which may become sub-Poissonian.
Zh. éksp. Teor. Fiz. 114, 474–483 (August 1998) 相似文献
16.
Effect of laser focus in two-color synthesized waveform on generation of soft x-ray high harmonics
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yanbo Chen 《中国物理 B》2023,32(1):14203-014203
Synthesis of multi-color laser pulses has been developed as a promising way to improve low conversion efficiency of high-order harmonic generation (HHG). Here we systematically study the effect of laser focus in a two-color waveform on generation of macroscopic HHG in soft x-rays. We find that the dependence of HHG yields on laser focus at low or high gas pressure is sensitive to the characteristics of single-atom harmonic response, in which "short"-or "long"-trajectory emissions can be selectively controlled by changing the waveform of two-color synthesized laser pulse. We uncover the phase-matching mechanism of HHG in the gas medium by examining the propagation of the two-color waveform and the evolution of time-frequency emissions of high-harmonic field. We further reveal that the nonlinear effects, such as geometric phase, atomic dispersion, and plasma defocusing, are responsible for modification of two-color waveform upon propagation. This work can be used to find better macroscopic conditions for generating soft x-ray HHG by employing two-color optimized waveforms. 相似文献
17.
A. V. Andreev S. Yu. Stremoukhov O. A. Shutova 《Journal of Experimental and Theoretical Physics》2018,127(1):25-36
The change in the polarization state of the atomic response due to the appearence of the longitudinal component, which has been predicted in [A. Andreev, S. Stremoukhov, and O. Shoutova, Europhys. Lett. 120, 14003 (2017)], has been studied. The dependence of the vector properties of the atomic current induced in an atom with unit angular momentum in the ground state on the properties of a two-color laser field with orthogonally polarized components has been analyzed. It has been shown that the variation of the delay time between the frequency components of the laser field makes it possible to efficiently control the polarization of the components of the atomic response field. The effect of the mutual orientation of the electric component of the laser field and the angular momentum of the atom on the longitudinal component of the atomic current and on the polarization properties of the generated radiation has been demonstrated. 相似文献
18.
We illustrate the crucial role played by decoherence (consistency of quantum histories) in extracting consistent quantum probabilities
for alternative histories in quantum cosmology. Specifically, within a Wheeler-DeWitt quantization of a flat Friedmann-Robertson-Walker
cosmological model sourced with a free massless scalar field, we calculate the probability that the universe is singular in
the sense that it assumes zero volume. Classical solutions of this model are a disjoint set of expanding and contracting singular
branches. A naive assessment of the behavior of quantum states which are superpositions of expanding and contracting universes
suggests that a “quantum bounce” is possible i.e. that the wave function of the universe may remain peaked on a non-singular
classical solution throughout its history. However, a more careful consistent histories analysis shows that for arbitrary
states in the physical Hilbert space the probability of this Wheeler-DeWitt quantum universe encountering the big bang/crunch
singularity is equal to unity. A quantum Wheeler-DeWitt universe is inevitably singular, and a “quantum bounce” is thus not
possible in these models. 相似文献
19.
In order to have well defined rules for the perturbative calculation of quantities of interest in an interacting quantum
field theory in curved spacetime, it is necessary to construct Wick polynomials and their time ordered products for the noninteracting
theory. A construction of these quantities has recently been given by Brunetti, Fredenhagen, and K?hler, and by Brunetti and
Fredenhagen, but they did not impose any “locality” or “covariance” condition in their constructions. As a consequence, their
construction of time ordered products contained ambiguities involving arbitrary functions of spacetime point rather than arbitrary
parameters. In this paper, we construct an “extended Wick polynomial algebra”– large enough to contain the Wick polynomials
and their time ordered products – by generalizing a construction of Dütsch and Fredenhagen to curved spacetime. We then
define the notion of a local, covariant quantum field, and seek a definition of local Wick polynomials and their time ordered products as local, covariant quantum fields. We introduce a new notion of the scaling
behavior of a local, covariant quantum field, and impose scaling requirements on our local Wick polynomials and their time
ordered products as well as certain additional requirements – such as commutation relations with the free field and appropriate
continuity properties under variations of the spacetime metric. For a given polynomial order in powers of the field, we prove
that these conditions uniquely determine the local Wick polynomials and their time ordered products up to a finite number
of parameters. (These parameters correspond to the usual renormalization ambiguities occurring in Minkowski spacetime together
with additional parameters corresponding to the coupling of the field to curvature.) We also prove existence of local Wick
polynomials. However, the issue
of existence of local time ordered products is deferred to a future investigation.
Received: 27 March 2001 / Accepted: 6 June 2001 相似文献
20.
A quantum field theoretic formulation of atomic collision phenomena involving non-relativistic free and bound systems is developed
and a calculational procedure in terms of Feynman diagrams is prescribed. Matrix elements of several atomic collision processes
have been calculated. In most cases standard quantum mechanical results are reproduced. But in some cases new terms appear
in the scattering matrix whose contribution though negligibly small in the low energy region, become important at higher energies.
A large portion of this work formed material for an invited talk delivered by one of us (T.P.) at the Second National Workshop
on Atomic and Molecular Physics at Visva-Bharati, Santiniketan (India) held from 18–23 November 1979. 相似文献