Strong Light Field Research Articles

Stabilization of atoms in a strong laser field

The main mechanisms of atomic stabilization in a strong light field are surveyed. The main features and physics of Kramers-Henneberger and interference stabilization are discussed. Some experiments confirming existence of stabilization effects are briefly overviewed. Two-color interference stabilization is described in its connection with the single frequency interference stabilization and effects like the laser-induced continuum structures.

Stabilization and structure of wave packets in Rydberg atoms ionized by a strong light field

New features of the phenomenon of interference stabilization of Rydberg atoms are found to exist. The main of them are: (i) dynamical stabilization, which means that in case of pulses with a smooth envelope the time-dependent residual probability for an atom to survive in bound states remains almost constant in the middle part of a pulse (at the strongest fields); (ii) existence of the strong-field stabilization of the after-pulse residual probability in case of pulses longer than the classical Kepler period; and (iii) pulsation of the time-dependent Rydberg wave packet formed in the process of photoionization.

Analysis of transient interband light modulation by ultrashort intersubband resonant light pulses in semiconductor quantum wells

We explore the transient characteristics of an interband resonant light modulation process by ultrashort intersubband resonant light pulses in semiconductor quantum wells (QW's). The modulation characteristics in a three-level semiconductor QW system, including the effects due to in-plane momentum, have been investigated by a numerical analysis of the coupled Bloch equations using a density-matrix approach. We have studied the effect of the carrier density and the nature of the intersubband coupling light on the transient absorption features of the interband light. The modulation process has been compared in doped and undoped QW's. The switching behavior of the strong interband light field in presence of a train of intersubband light pulses has also been discussed.

Born-Oppenheimer approximation for molecules in a strong light field

A simple model to describe effect of laser field on structure of molecular vibronic spectra is proposed. The change of the internuclear distance which takes place in experiments on Coulomb explosion is estimated. A dispersion curve is calculated for weak probe radiation absorption/emission by molecules exposed to a strong laser field.

Observation of Rydberg transitions induced by optical core dressing

We study experimentally the behaviour of magnesium Rydberg series converging to the and ion states, coupled by a strong () light field that is resonant with the transition between the ion states ( nm). This strong-field version of isolated-core excitation leads to modifications in the photoionization spectrum of the bound Rydberg series and to transitions between bound Rydberg states when the Rabi frequency associated with the core transition becomes larger than the Rydberg spacing.

Generation of coherent hard-x-ray radiation in crystalline solids by high-intensity femtosecond laser pulses.

A process for coherent hard-x-ray generation is suggested, which is based on the idea that high-intensity, ultrashort laser pulses can be coupled into a crystal before the lattice structure is destroyed. In the presence of the lattice periodicity, additional momentum can be transferred to the electrons that are moving in the strong light field. This additional momentum supplied by the crystal results in a substantial decrease of the threshold pump laser intensity required for hard-x-ray generation as compared to free electrons. The lattice is also utilized to select the frequency of the emitted x rays via Bragg coupling. A numerical estimation for the yield of the proposed mechanism gives an output power of some 10 W in the range of 1--10 keV of photon energies by using a state-of-the-art optical pulse with a peak intensity of about ${10}^{17}$ W/${\mathrm{cm}}^{2}$ and a pulse duration of 30 fs.

Strong-Field Phenomena in Atoms - Quasiclassical Approach

A quasiclassical (WKB) approach is used to construct a theory of atomic transitions induced by a strong light field. This approach is used to find the Coulomb-Volkov solutions of the Schrodinger equation in which both the Coulomb and light fields are taken into account. These solutions are shown to be applicable in . a region of low light frequencies, low electron energies and angular momenta.. The found solutions are used to describe two kinds of processes: strong-field photoionization from highly excited (Rydberg) atomic levels, and field-assisted electron-ion scattering. In the photoionization problem the strong-field complex quasi-energies of an atom are found. A problem' of the strong-field stabilization of an atom, as well as the expected behavior of the ionization time in its dependence on the light field strength are discussed.

Squeezing from ghost transitions.

We show that significant squeezing in a strong signal light field can be generated with three-level atoms in a ghost-transition setup by tuning a weak probe beam inside the Autler-Townes doublet created by the strong signal light. Close to the Rabi level, i.e., within the absorption line, processes involving both amplitude quadratures become important. Significant atomic two-photon coherence provides a vehicle for signal-amplitude fluctuations to trigger fluctuations in the probe amplitude. Subsequently, atomic coherence will feed these probe fluctuations back into the signal and enable substantial noise suppression.

Dynamic dipole moment of a molecule in a strong light field

The dynamic dipole moment induced by a strong light field in a linear molecule is calculated. The resonance of the field with the electronic Σ → Σ transition is supposed. It is shown that to induce the stabilized moment a slowly-turned-on mode is necessary. The exactness of resonance and the light field intensity sufficient for inducing the dipole moment are discussed.

Separation of the magnetic quantization axes by lightshift interaction in a Rb/Xe gas mixture

We demonstrate the use of strong light fields in order to create different magnetic quantization axes for rubidium (Rb) and xenon (Xe) atoms in a gaseous mixture. A light-induced fictitious magnetic field is created by means of the Zeeman-lightshift phenomenon only for the Rb atoms by strong optical irradiation off-resonant from the D 1-line of Rb. It is demonstrated that the Zeeman precession of the Rb spin and the Xe nuclear spin occurs in different magnetic fields thus allowing to separate the quantization axes for the two atoms. This effect is used to extend the Hanle condition for the groundstate and to measure the frequency dependence of the Zeeman lightshift.

Self-modulation and nonlinear diffraction of strong light fields in dispersive media

The problem of space-time self-modulation of strong laser fields is solved by the method of successive approximations. The nonlinear diffractional and nonlinear dispersive transformations of beam width and pulse duration are studied with emphasis on the reciprocal effects of nonlinear diffraction and dispersion. The effect of incomplete initial time and space coherence on the space-time parameters of a laser field and the conversion of its coherent properties is examined.

Nonlinear processes in many-electron atomic systems

We formulate the basis of a many-body theory of field-dressed particles and a technique for time-dependent effective potential construction in the case of inhomogeneous quantum systems under the influence of a strong light field. We consider the influence of polarization effects on electron detachment from atomic systems. The resonant enhancement of an external field inside an atom and the modification of bound–free and free–free transitions are studied. In several regions of field parameters a statistical approach to the description of the excitation and ionization of heavy atoms is developed. Finally, we discuss possible directions for future theoretical investigations of heavy atoms in strong laser fields.

Nonperturbative ac Stark shifts in hydrogen atoms

The evolution of low excited states of hydrogen in the presence of a strong light field is investigated by using the complex dilatation method with a finite basis of Slater-type functions. The method is applied for wavelengths of 592, 608, and 616 nm, which have been investigated experimentally. The results of the calculation are in agreement with experimental observations as far as comparison is possible.

Electromagnetic wave propagation in a non-equilibrium ferroelectric in polar phase

In a strong light fields the absorption and velocity of light are different when light propagating along and against the spontaneous polarization in ferroelectric. The first experimental results obtained by special polar photometers and interferometers are given.

Effective interactions in non-linear optics

A new theoretical approach to the problem of non-linear polarisation of matter is suggested. The density matrix equation for a low-density gas in a strong light field has been solved without using the phenomenological relaxation constants. Use is made of the general Hamiltonian that explicitly involves, besides the interaction of atoms with the external field, also their interactions with each other and with the vacuum electromagnetic field. The equation is solved by the canonical transformation method (a variant of the Bogolyubov-Mitropolski method of averages). It is generalised and used in the more complicated case of interacting multilevel atoms (molecules) in a strong light field. An expression for the cubic susceptibility is obtained, enabling analysis of the resonant saturation in both stationary and non-stationary cases. The proposed method provides correct expressions for the dynamic Stark shifts, amplitudes of multiphoton transitions and of radiational collisions, as well as for effective interatomic interactions caused by photon exchange. The proposed theoretical approach can also be used in studying non-linear optical processes in dense gases, liquids and solids.

Theory and observation of Faraday rotation obtained with strong light fields

The authors have observed dramatic changes in both the magnitude and the lineshape of Faraday rotation on an allowed E1 transition in Sm I (4f 66s2 7F0-4f 66s6p 7G1) as a function of laser intensity and buffer-gas pressure. The effect is ascribed to the development of optical and Zeeman coherences and a theoretical treatment, based on the solution of steady-state density matrix equations is given. Effects of optical pumping on the odd isotopes 147Sm and 149Sm, both with I=7/2, are also considered.

Dressed-atom theory of stimulated pair transitions.

We present an exact, analytic solution for the probability of radiative, cooperative transitions of stationary, weakly coupled atoms in strong light fields. Very simple expressions are obtained for pair-emission and -absorption probabilities by use of the ``dressed-atom'' formalism applied to atoms in solids or nearly at rest in optical traps. Analogies between radiative collisions in gases and the pair transitions encountered in solids, which may be viewed as ``frozen'' radiative collisions, are explored. Conditions are predicted for the occurrence of electric dipole decoupling in the presence of a suitable rotating electric field, similar to the well-known phenomenon of ``magic-angle'' decoupling of magnetic spins due to a rotating magnetic field. Observations of this new effect should permit precision determinations of interaction Hamiltonians in optical pair systems.

Atoms in Strong Light Fields

<i>Atoms in Strong Light Fields</i>

Atoms in Strong Light Fields

Atoms in Strong Light Fields

Spectra of a linear molecule in a strong light field

Optical spectra of a linear molecule in a strong monochromatic field are considered within the framework of a numerically solvable quantum-mechanical model. Light field-molecule interaction causes the dynamic Stark splitting of molecular rotational levels. In the strong-field limit the orientational motion obtains a librational character. A new mechanism of the laser cooling of molecular rotation is discussed.