半导体中多光子吸收跃迁速率的全量子理论分析

本文从非线性光学中辐射跃迁速率的表达式出发,在全量子理论下,导出了半导体中任意阶多光子吸收跃迁速率的一般表达式。理论分析结果表明,n光子吸收跃迁速率与光强的n次方和n阶光子相干度成正比。本文在多能带及二能带理论模型下,对多光子吸收跃迁速率的一般表达式进行了化简,并对非线性相互作用项对跃迁速率的贡献,作了讨论。     

Study on infrared multiphoton excitation of the linear triatomic molecule by the Lie-algebra approach

Infrared multiphoton vibrational excitation of the linear triatomic molecule has been studied using the quadratic anharmonic Lie-algebra model, unitary transformations, and Magnus approximation. An explicit Lie-algebra expression for the vibrational transition probability is obtained by using a Lie-algebra approach. The infrared multiphoton vibrational excitation of the DCN molecule is discussed as an example.     

Multiphoton atomic ionization in the field of a very short laser pulse

Closed analytic expressions are derived for the probability of multiphoton atomic and ionic ionization in a variable electric field ?(t), which are applicable for arbitrary Keldysh parameters γ. Dependencies of the ionization probability and photoelectron pulse spectrum on the shape of a very short laser pulse are analyzed. Examples of pulse fields of various forms, including a modulated light pulse with a Gaussian or Lorentz envelope, are considered in detail. The interference effect in the photoelectron energy spectrum during atomic ionization by a periodic field of a general form is examined. The range of applicability of the adiabatic approximation in the multiphoton ionization theory is discussed. The imaginary time method is used in the calculations, which allows the probability of particle tunneling through oscillating barriers to be effectively calculated.     

Multiphoton transitions for the harmonic oscillator

2- and 3-photon electric dipole transitions for the harmonic oscillator are shown to have zero intensity. This is extended to the general cases of Δv?=?n and Δv?=?n???2 for n-photon transitions. Although not proved in general, it seems likely that all multiphoton transition moments vanish. This suggests that electric dipole multiphoton transition intensity is due to anharmonicity.     

High intensity Compton scattering in a strong plane-wave field of general form

Photon emission by an electron embedded in a strong external field of general form is studied theoretically. The external field considered is a plane-wave electromagnetic field of any number of components, period and polarisation. Exact, Volkov solutions of the Dirac equation with the 4-potential of the general external field are obtained. The photon emission is considered in the usual perturbation theory using the Volkov solutions to represent the electron. An expression for the transition probability of this process is obtained after the usual spin and polarisation sums, trace calculation and phase space integration. The final transition probability in the general case contains a single sum over contributions from external field photons, an integration over one of the phase space components and the Fourier transforms of the Volkov phases. The validity of the general expression is established by considering specific external fields. Known specific analytic forms of the transition probability are obtained after substitution of the 4-potential for a circularly polarised and constant crossed external field. As an example usage of the general result for the transition probability, the case of two circularly polarised external fields separated by a phase difference is studied both analytically and numerically.     

Multiphoton resonances in a system of interacting josephson qubits

The behavior of the level population of two coupled qubits as a function of the system parameters and characteristics of the driving field has been studied. In the case where the tunneling splitting of qubit levels is small, the explicit expression for the transition probability describing multiphoton processes of any order and resonance conditions dependent on the qubit coupling constant have been obtained. The possibility of experimentally observing the discovered effects is discussed.     

Convergence of rayleigh-schrödinger perturbation theory in calculations of multiphoton processes

Abstract

We have calculated the high-order ac Stark Shift, multiphoton ionization rates, and nonlinear susceptibilities for high harmonic generation for the hydrogen atom in a radiation field. The calculations are done in the framework of Rayleigh-Schrödinger perturbation theory applied to a complex-rotated Hamiltonian. Our intention is to investigate the limitations of perturbation theory in calculations of multiphoton processes. Comparisons are made with results from nonperturbative calculations. For some frequencies the results of lowest-order perturbation theory are found to disagree with nonperturbative calculations even at moderate to low intensities (I ～ 10¹¹ W cm^?2) and in the absence of resonances. We find that the high-order perturbation expansion theory is not a reliable predictor of the behavior of hydrogen atoms in radiation fields with intensities greater than ～ 10¹² W cm^?2.     

A new integral equation for treating high-intensity multiphoton processes

Summary In the present paper we derive a new integral equation for the non-perturbative evaluation of transition matrix elements for high-intensity multiphoton processes. Our method will be partly based on the Kramers-Henneberger transformation. In the course of the development of our theory we shall relate our approach to previous investigations along similar lines. As a specific example we shall apply our integral equation to the problem of light scattering and present a multiphoton generalization of the Kramers-Heisenberg dispersion formula. We shall then apply this general formula to the study of higher-harmonic generation from a short-range potential with a single bound state, and evaluate the ratesR _n of then-th-order harmonic for a set of specifically chosen parameters. This work has been supported by the East-West Program of the Austrian Academy of Sciences under Project Nr. 45.174/1-46a/93 of the ?sterreichische Bundesministerium für Wissenschaft und Forschung.     

Time-dependent spectrum of thermionic emission from hot C60

Experimental measurements of time-dependent photoelectron spectra observed in thermionic emission of hot C₆₀ excited by multiphoton absorption are presented. Time resolved velocity-map imaging is used to record photoelectron spectra and to disentangle direct and delayed processes. The evolution of the kinetic energy distribution of thermal electrons as a function of the delay after multiphoton excitation is described within the general formalism of the detailed balance theory. Experimental spectra obtained in the near-UV are in excellent agreement with the assumption of thermal equilibrium.     

Logics for quantum mechanics

The two concepts of probability used in physics are analyzed from the formal and the material points of view. The standard theory corresponds toprob ₁ (probability of the coexistence of two properties). A general logicomathematical theory ofprob ₂ (probability of transition between states) is presented in axiomatic form. The underlying state algebra is neither Boolean nor Birkhoff-von Neumann but partial Boolean. In the Boolean subalgebras,prob ₁ theory holds. The theory presented contains the logicomathematical foundations of quantum mechanics and, as degenerate cases, the theories of stochastic games and of Markov chains.     

Theory of laser-induced gas ionization

The mechanism of laser-induced gas ionization is analyzed in the context of the theories presently available, namely multiphoton and cascade theory, and their predictions are shown to be in serious divergence from experimentation. A novel hypothesis is then formulated which considers the classical photon energy expression ε=hν as the limit of a general expression ε=hν/[1?β_ν f(I)],f(I) being a function of light intensity and β_ν a coefficient such that β_ν f(I) significantly differs from zero only for high-intensity laser light. Starting from the new formulation of the photon energy expression, a theory is developed for the laser ionization phenomenon and a few simple relations are found. The successful use of these relations in the verification of the experimental results suggests that the new photon energy expression has a real physical meaning rather than an empirical significance, and some considerations on the physical meaning are presented.     

利用多光子跃迁控制基态HF分子布居转移

采用波包动力学方法研究了HF分子基电子态的多光子跃迁. 激光场由两束频率比为1:2的重合红外脉冲构成. 态|0,0>作为初始态, 态|4,0>与态|4,2>分别作为目标态. 计算结果表明, 通过选取不同的共振频率, 可以控制布居跃迁至不同的目标态. 两束脉冲间的初相位差可以控制布居转移概率. 当初相位差为π/2的偶数倍时, 布居转移概率为最大值. 当初相位差为π/2的奇数倍时, 布居转移概率为最小值. 初相位差对于态|4,0>的布居影响大于态|4,2>. 关键词： 多光子跃迁 初相位 布居转移 波包     

Multiphoton ionization of the hydrogen atom by a circularly polarized electromagnetic field

This paper examines the multiphoton ionization of the ground state of the hydrogen atom in the field of a circularly polarized intense electromagnetic wave. To describe the states of photoelectrons, quasiclassical wave functions are introduced that partially allow for the effect of an intense electromagnetic wave and that of the Coulomb potential. Expressions are derived for the angular and energy distributions of photoelectrons with energies much lower than the ionization potential of an unperturbed atom. It is found that, due to allowance for the Coulomb potential in the wave function of the final electron states, the transition probability near the ionization threshold tends to a finite value. In addition, the well-known selection rules for multiphoton transitions in a circularly polarized electromagnetic field are derived in a natural way. Finally, the results are compared with those obtained in the Keldysh-Faisal-Reiss approximation. Zh. éksp. Teor. Fiz. 116, 807–820 (September 1999)     

Linearly and circular dichroism in a semiconductor with a complex valence band with allowance for four-photon absorption of light

This paper presents a theoretical study of the linear and circular dichroism of multiphoton absorption of light in semiconductors with a complex valence band. Matrix elements of optical transitions between subbands of the valence bands of a p-GaAs semiconductor are calculated. Transitions connected with both nonsimultaneous absorption of single photons and simultaneous absorption of two photons are taken into account. An expression for the temperature dependence of the coefficient of multiphoton absorption of polarized radiation with allowance for transitions between subbands of heavy and light holes is obtained.     

Nonlinear theory of multiphonon relaxation of excited rare-earth ions in laser crystals

A general formula for the probability of multiphonon nonradiative transitions between J multiplets of 4f ^N states of trivalent rare-earth ions in a crystal derived for a nonlinear mechanism is discussed. A technique is developed for calculating the quantities involved in this formula. Particular attention is given to calculating the spectral density J ^(p)(Ω), which is the Fourier transform (at the transition frequency) of the pth power of the correlation function K(t) of host ion displacements. Based on the central limit theorem from probability theory, an approximation is proposed for the spectral density J ^(p)(Ω). The theoretical values of nonradiative multiphonon transition rates are compared with experimental ones.     

飞秒激光激发空气电离的阈值研究

报道在脉宽50fs—22ps,波长800nm脉冲激光作用下的空气电离阈值的研究结果.利用探测等离子体发光信号的方法,实验测量了激发空气电离所需的阈值激光强度.结果表明,当激光脉冲宽度从50fs增加到22ps时,阈值光强I_th从8.7×10¹⁴W/cm²下降到2.7×10¹³W/cm²;I_th经历了由迅速降低逐渐发展为缓慢降低的过程.在50fs—1p 关键词： 飞秒激光 阈值 多光子电离 碰撞电离     

飞秒激光激发空气电离的阈值研究

报道在脉宽50fs—22ps，波长800nm脉冲激光作用下的空气电离阈值的研究结果.利用探测等离子体发光信号的方法，实验测量了激发空气电离所需的阈值激光强度.结果表明，当激光脉冲宽度从50fs增加到22ps时，阈值光强I_th从8.7×10¹⁴W/cm²下降到2.7×10¹³W/cm²；I_th经历了由迅速降低逐渐发展为缓慢降低的过程.在50fs—1p     

On the relativistic theory of tunneling

A relativistic generalization of the semiclassical theory of tunneling and multiphoton ionization of atoms and ions in the field of a high-intensity electromagnetic wave with linear, circular, and elliptic polarization is constructed. The exponential factor in the ionization probability is calculated for arbitrary values of adiabaticity parameter γ. In the case of low-frequency laser radiation, an asymptotically exact formula is derived for the ionization rate of the s atomic level, including the Coulomb, spin, and adiabatic corrections and the preexponential factor.     

Luis Santaló and classical field theory

Considered one of the founding fathers of integral geometry, Luis Santaló has contributed to various areas of mathematics. His work has applications in number theory, in the theory of differential equations, in stochastic geometry, in functional analysis, and also in theoretical physics. Between the 1950’s and the 1970’s, he wrote a series of papers on general relativity and on the attempts at generalizing Einstein’s theory to formulate a unified field theory. His main contribution in this subject was to provide a classification theorem for the plethora of tensors that were populating Einstein’s generalized theory. This paper revisits his work on theoretical physics.

     

On the infinite summation in the theory of atomic multiphoton ionization

The infinite summation through the complete set of real unperturbed atomic states that appears in the Nth-order time-dependent perturbation theory when applied to multiphoton ionization is calculated by using the Green's function method. The cross-sections so obtained are in good agreement with other theoretical values published elsewhere.