Induced resonant transparency of magnetic materials for gamma radiation: Propagation dynamics

The theory of spatiotemporal dynamics of gamma radiation in a resonant medium upon excitation of two-frequency gamma magnetic resonance in magnetic materials is considered. The radiation absorption at the fundamental frequency and the harmonic generation are investigated under conditions when the frequency of gamma radiation is shifted by the half-sum or half-difference of the frequencies of radio-frequency magnetic fields. It is shown that the propagation of gamma radiation through an absorber is characterized by a steady-state gamma intensity (resonant transparency). A consistent radio-frequency spectral analysis demonstrates that the intensities of harmonics drastically change at the transparency region boundaries due to nonlinear interference. The theory of quantum and dynamical beats of synchrotron radiation under conditions of induced resonant transparency is proposed.     

Interference phenomena in Doppler broadened quantum transitions: Amplification of intense radiation without population inversion

We study the effect of nonlinear interference processes on quantum transitions in intense resonant electromagnetic fields with allowance for changes in level populations, relaxation processes, incoherent excitation, and Doppler broadening of the transitions, on the absorption, amplification, and refraction of the interacting fields. The theory is generalized to the case of nonlinear interference interaction of two intense fields in open and closed three-level quantum systems. Using the density matrix, we derive general expressions in the case of stationary interaction that make it possible to analyze the optical characteristics for various configurations of the interfering transitions by a simple substitution of parameters. The possibility of amplifying light without saturated population inversion in a resonant transition is discussed. We formulate the conditions for such amplification and use examples to show that under appropriate changes in the initial level populations and the intensity of the auxiliary light, the inversionless amplification coefficient does not decrease with increasing intensity of the amplified radiation. We also show that allowance for these accompanying processes greatly affects the choice of optimal conditions for interference in optical transitions. As an illustration we list the results of a numerical analysis of possible experiments. Zh. éksp. Teor. Fiz. 113, 445–470 (February 1998)     

Interference effects in Mössbauer spectra of E2 transitions

It is shown that interference effects in Mössbauer transmission experiments with pure E2 and mixed E2/M1 transitions are, generally, due to interference between the internal conversion and the photoeffect. This interference effect is mainly determined by the quadrupole part of the photoabsorption, which is comparable to the dipole part at transition energies of about 100 keV. A noticeable part of the interference effect in the case of E2 transitions can be attributed to the interference between the nuclear resonant scattering and Rayleigh scattering on atomic electrons. The angular distribution of the (, e) reaction cross section has been calculated for E2 transitions.     

Level mixing induced transparency II. Different transition probabilities of the crossing lines

In one of our previous papers (R.N. Shakhmuratov et al. Appl. Phys. B. 81, 883 (2005)) we presented a new type of spatiotemporal interference of gamma radiation propagating in a resonant medium. The excitation scheme consists of two identical V-schemes, each being formed by one type of the transition: one is induced only by the left circular polarized field and the other by the right circular polarized field. The coupling of these V-schemes through level crossing allows resonant scattering of a photon in the forward direction with a change of its polarization. As a result the radiation field, which is resonant with a transition from the ground state to one of the two sublevels of the excited state, develops in a particular combination of radiation fields with left and right circular polarizations, called a normal mode. This combination is much less absorbed in subsequent layers of the absorber. For identical V-schemes, the structure of the modes is fairly simple. In this paper, we show that a similar reduction of absorption is realized for non-identical V-schemes, differing in transition strengths. The structure of the normal modes is found and they have a more complicated form. This general case is actually realized in a level crossing experiment in gamma optics. PACS 42.50.Gy; 33.45.+x     

Dynamics of a three-level atom in a resonant light field

The paper is devoted to a consideration of the motion of a three-level atom in two resonant light waves. A kinetic equation of the Fokker-Planck type for the atomic distribution function is derived, which is valid when the recoil energy is small compared to the linewidths of the resonant transitions. The detailed behaviour of the radiation force and the diffusion tensor are studied numerically. The case of exact resonance and the nonresonant case are both considered. It is shown that a detuning from exact resonance results in a drastic decrease of the resonant light pressure force. For the detuning we determine the condition, under which an efficient action of the light pressure on a three-level atom takes place.     

Basic features of coherent nuclear resonant scattering of synchrotron radiation

The time dependences of spatially coherent nuclear resonant scattering of synchrotron radiation show a wealth of characteristic features which originate from the interference of several radiation components and from dynamical nuclear scattering. These effects will be of importance for the future fields of time domain Mössbauer spectroscopy and of nuclear resonant -ray optics. The basic features are discussed and experimental evidence is reviewed.     

Coherent influence of RF field on the gamma-optical properties of a medium upon crossing-anticrossing of nuclear levels

A new approach to the observation of electromagnetic-induced transparency in gamma optics is proposed. For this purpose, the propagation of a resonant gamma photon in a ⁵⁷Fe magnetic medium affected by an external radiofrequency (RF) field is considered. It is demonstrated that, in the case of crossing-anticrossing, a resonant RF field significantly transforms gamma-optical properties of the medium that become dependent on its parameters. This allows coherent control of the group velocity of gamma photons and controlled filtering of unpolarized gamma radiation in the sample to be realized.     

Modification of Mössbauer reflection spectra of group AIIBVI single crystals with Fe<Superscript>57</Superscript> nuclei under influence of infrared radiation

Interaction of Mössbauer gamma radiation with ultrasound vibrations in group AIIBVI single crystals of CdS and CdSe with Fe⁵⁷ impurity nuclei under action of infrared radiation is investigated. It is shown that the infrared irradiation excites a phonon field in single crystals. Similar to the case of optical irradiation of single crystals the shape of their Mössbauer spectrum is modified. The effect of double modulation of resonant gamma radiation by infrared radiation has been observed.     

A New Way of Looking at Nuclear Resonant Scattering

A new model for nuclear-resonant scattering of gamma radiation from resonant matter has been developed and is summarized here. This “coherent-path” model has lead to closed-form, finite-sum solutions for radiation scattered in the forward direction. The solution provides a unified microscopic picture of nuclear-resonant scattering processes. The resonant absorber or scatterer is modeled as a one-dimensional chain of “effective” nuclei or “effective” planes. The solution is interpreted as showing that the resonant radiation undergoes sequential scattering from one absorber “nucleus” or “plane” to another before reaching the detector. For recoil-free processes the various “paths” to the detector contribute coherently. The solution for this case gives calculated results that are indistinguishable from those using the classical optical model approach, although the forms of the solutions are completely different. The coherent-path model shows that the “speed-up” and “dynamical beating” effects are primarily a consequence of the fact that the single “effective” nuclear scattering processes are 180° out of phase with the incident radiation while the double nuclear scattering processes are in phase with the incident radiation. All multiple scattering paths are, and must be, included. The model can also treat the incoherent processes, i.e., processes involving gamma emission with recoil or conversion-electron emission. The source of the resonant gamma radiation can be from a radioactive source or from synchrotron radiation: both cases are treated. The model is used to explain and understand the results when each of the following experimental procedures is applied: time-differential Mössbauer spectroscopy, time-differential synchrotron radiation spectroscopy, enhanced-resolution resonant-detector Mössbauer spectroscopy, and the “gamma echo”.     

Temporal coherent control of a sequential transition in rubidium atoms

An experimental investigation of the coherent interaction of femtosecond pulses with two resonant sequential transitions of Rb atoms is presented. Fluorescence from the atomic system exhibits beating at a frequency given by difference in the sequential atomic transitions. The results are interpreted in terms of quantum interference in the induced coherence and its interaction with the field that results from a cooperative emission process.     

Heterodyne detection of synchrotron radiation

A time integral method for the study of resonant nuclear scattering of synchrotron radiation in the forward direction is presented. The method relies on the interference of radiation scattered by nuclei in two samples, one moving with respect to the other. The method, termed heterodyne detection of synchrotron radiation, gives the same information on hyperfine parameters as the well known differential method. The general formalism is developed for the case where the reference is a single line sample and the investigated sample has magnetic or quadrupole splitting. The first experiments are discussed. A comparison of time differential synchrotron radiation spectroscopy, heterodyne detection and Mössbauer spectroscopy is given.     

Resonance fluorescence of gamma radiation under conditions of coherent mixing of Mössbauer sublevels

A method is proposed for calculating the resonance fluorescence spectrum of coherent gamma radiation with a finite linewidth under conditions when the sublevels of the ground nuclear state are coupled through a strong field. The spectrum line shape is substantially affected by both the coherent effects induced in the system by a strong field and the finite gamma-radiation width. The results obtained earlier and in this work give impetus to experimental investigations into the coherence of a quantum system and quantum interference of Mössbauer gamma transitions through the excitation of coherent magnetization dynamics or an optical subsystem in solids.     

Light drag in moving media with a high frequency dispersion

The influence of spectral interference of various nature on the effects of radiation drag is studied using as examples electromagnetically induced transparency in pure discrete atomic transitions and the transparency windows of autoionization resonances of gaseous media. The analysis is performed using the Maxwell equations and taking into account the equivalence of the corresponding spatial dispersion of a substance and the optical effects caused by uniform motion. The realization conditions of the drag coefficients in the Lorentz and Laub forms are found from the exact dispersion equations obtained. A direct relation between the monochromatic radiation drag coefficient and the decrease in the pulsed radiation group velocity due to high frequency dispersion of the resonant refractive index is found. The known experimental data on ultraslow light pulses indicate the possibility of interference enhancement of the light drag effect by a factor of 10⁶-10⁷.     

Interference enhancement of resonant magneto-optical effects

The influence of spectral interference of different nature on resonant Faraday rotation is studied using as examples the effect of electromagnetically induced transparency in pure discrete atomic transitions and the transparency windows of autoionization resonances of gaseous media. A common numerical criterion for a substantial effect of spectral interference and coherence of atomic transitions on magneto-optical phenomena is established. A direct relationship between the polarization ellipse rotation angle of cw monochromatic light and reduction of the light pulse group velocity resulting from a strong frequency dispersion of the resonant refractive index is found. The known experimental data on ultraslow light pulses indicate the possibility of interference enhancement of the Faraday effect by a factor of 10⁶?10⁷.     

Theory of the line shape of gamma-photon transitions

There is a discussion of the line shape for the nuclear two-quantum transition due to the simultaneous absorption of a Mossbauer quantum and a quantum from a classical photon source. The problem is solved through the use of density-matrix equations, and an equation is derived for the intensity of absorbed gamma rays. In contrast with the case of the ordinary probabilistic approach, the equation for the intensity of gamma absorption reveals a dependence on the relaxation times within the ground and excited states. The line shape for gamma-photon transitions for low intensities of the incident radiation usually differs little from the shape of the Mossbauer line. However, at large irradiation intensities, a shift and a broadening of the resonant lines occur, proportional to the radiation power. These corrections must be taken into account in, e.g., gamma-magnetic resonance.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 12, No. 7, pp. 24–30, July, 1969.     

Quantum interference of Mössbauer gamma-radiative transitions in magnetic materials

A method is developed for calculating the resonance fluorescence spectrum of coherent radiation with a finite linewidth from a system whose energy levels are coupled through a strong field. In this case, the shape of the spectrum is essentially affected by quantum interference. The results obtained give impetus to investigations into quantum interference of Mössbauer gamma-radiative transitions in magnetic materials under conditions of induced coherent magnetization dynamics.     

Dissipative optical superlattice for confinement of ultracold plasma with resonant ions

The application of resonant light pressure in the presence of nonuniform bichromatic laser fields for the localization and control of ultracold electron-ion plasma in which the quantum transitions of ions are resonant with respect to the laser radiation is analyzed. It is demonstrated that the so-called rectified radiation forces that selectively act upon plasma ions and give rise to a dissipative optical superlattice (for ultracold plasma) whose period is significantly greater than the radiation wavelength can be used for this purpose.     

Effects of Spontaneously Generated Coherence on Intensity-Intensity Correlation in a Driven Y-Type Atom

In this paper, we investigate the spontaneously generated coherence (SGC) effects on the fluorescence fields intensity-intensity correlation in a resonant driven four-level Y-type atomic system. By using a strong control field, in the absense of SGC effects, strong correlation and anticorrelation
fluorescence photons can be produced from two ladder transitions in this system respectively. However, in the presence of SGC effects, the fluorescence fields correlation properties are reversed for the two transitions. The above phenomena can be traced to the quantum destructive or constructive interference in terms of dressed states.     

Interference phenomena at the elastic collision of atoms with formation of the Feshbach resonance in the presence of laser radiation field

Resonant scattering of atoms with formation of the Feshbach resonance in the presence of a laser radiation coupling the levels of two bound atoms (a molecule) is considered. The laser field leads to a second resonance in scattering and broadening of resonances, which facilitates the possibility of experimental observation of asymmetry of the total scattering cross-section arising because of interference between resonant and potential scatterings. The effects associated with interference of the two channels of decay of a bound system of two atoms (a molecule) in the laser field are studied. An expression is obtained for the scattering length in collision of two cold atoms in the field of laser radiation.     

Dynamics of resonant fluorescence from atomic Cs vapor at scanning the frequency of laser radiation in the presence of a constant magnetic field

The dynamics of interaction of laser radiation resonant with the transitions of D₂ line in atomic Cs¹³³ in the presence of an external magnetic field is studied. Populations of levels and dynamics of resonant fluorescence at scanning frequency of the laser radiation with linear and circular polarizations are considered.