Probe field spectroscopy in three-level Λ systems under arbitrary collisional relaxation of low-frequency coherence

We investigate theoretically the spectrum of weak probe field absorption by three-level atoms with the Λ configuration of levels in the field of a strong electromagnetic wave acting on an adjacent transition and colliding with buffer gas atoms. Analysis is carried out for the general case of arbitrary collisional relaxation of low-frequency coherence at a transition between two lower levels. It is shown that, in the absence of collisional relaxation of low-frequency coherence, the probe field spectrum always exhibits clearly manifested anisotropy with respect to mutual orientation of wavevectors of the strong and probe radiation (even under small Doppler broadening). It is found that the probe field spectrum may acquire under certain conditions supernarrow resonances with a width proportional to the diffusion coefficient for atoms interacting with radiation. This fact may form the basis for a spectroscopic method for measuring transport frequencies of collisions between absorbing and buffer particles. A large-amplitude supernarrow resonance (with an amplitude much larger than the amplitude of the resonance near the line center), which is observed in the far wing of the absorption line, exhibits collisional narrowing (a nonlinear spectroscopic analog of the Dicke effect) at collision frequencies several orders of magnitude lower that the Doppler linewidth. Simple working equations proposed for describing the probe field spectrum are convenient for experimental data processing.     

Spectral specific features of the interaction of two fields of arbitrary intensity with three-level Λ-systems

The spectrum of absorption of a probe field of arbitrary intensity by three-level atoms with the Λ configuration of levels in the field of a strong electromagnetic wave acting on an adjacent transition is studied theoretically. It is shown that the supernarrow resonance, revealed earlier by us, in the absorption spectrum of the probe field far from the resonance with the atomic transition is retained as the probe field intensity increases. The dependence of the amplitude and of the width of the supernarrow resonance on the probe-field intensity is elucidated. The resonance contrast decreases insignificantly (by only a factor of several), even when the probe-field intensity becomes comparable with the intensity of the strong field.     

Resonances of orientation and alignment of atoms in the case of inclined optical pumping

It is shown that, with pumping inclined relative to a constant magnetic field H₀, the radio-frequency (RF) magnetic field rotating at frequency Ω induces new resonances ω₀ = γ H ₀ and 2Ω for the Fourier components of orientation and ω₀ = ?Ω, Ω/2, 3Ω/2, 2Ω, and 3Ω for the components of alignment. New resonances excited by the oscillating RF field are also considered.     

The role of a dipole-coupled but not dipole-probed state in probe absorption with multilevel coupling

We study the impact on weak-probe spectra from the presence of a state for which the electric-dipole transition is allowed for coupling but forbidden for probing. Such is the ⁸⁵Rb ²P_3/2(F′ = 1) state, providing D2-line hfs transitions in Λ-configurations are considered with the 5²S_1/2(F = 2) and 5²S_1/2(F = 3) states in the role of the ground-states for coupling and probing, respectively. The multilevel EIT/Autler-Townes spectra were simulated with coupling field frequency fixed at various values in the range encompassing the atomic resonances. Collisionless (cold) atoms are assumed, and all decoherence rates, other than those related to the natural decay rates, are neglected. The general conclusion is that a state which is not directly involved in probe absorption can still considerably shape absorption spectra (due to multiphoton transitions), and its influence (negative for some applications) has to be carefully considered, even for the coupling-field-induced Rabi frequency values not exceeding the natural linewidth. A particular attention is paid to how the F′ = 1 state effects the narrow resonances, such as those of EIT origin or a “distant wing” of the Autler-Townes splitting, because resonances of these types are of interest, e.g., for developing quantum memory protocols [Sheremet et al., PRA82 (2010) 033838].     

New evidence for supernarrow dibaryons production in pd interactions

The analysis of new experimental data, obtained at the Proton Linear Accelerator of INR, with the aim to search for supernarrow dibaryons in the pd↦ppX ₁ and pd↦pdX ₂ reactions is presented. Narrow peaks with an experimental width of 5 MeV at masses of 1904±2, 1926±2, and 1942±2 MeV have been observed in missing mass M _pX1 spectra. In the missing mass M _X1 spectra, the peaks at M _X1 = 966±2, 986±2, and 1003±2 MeV have been found. The analysis of the data obtained leads to the conclusion that the observed peaks in M _pX1 spectra are most likely supernarrow dibaryons, the decay of which into two nucleons is forbidden by the Pauli exclusion principle. An alternative interpretation of the spectra by assuming a decay of the supernarrow dibaryons in “exotic baryon states” with masses M _X1 is discussed. Received: 22 October 2001 / Accepted: 15 November 2001     

Narrowing of a two-photon resonance due to elastic collisions

The lineshape of two-photon absorption in a standing-wave field during elastic collisions is studied. It has been found that the transit broadening of the two-photon resonance on vibrational-rotational molecular transitions is sharply decreased because of an increase in the time of interaction of particles with the electromagnetic field due to elastic collisions. The effect considered allows one to obtain supernarrow optical resonances of two-photon absorption in a low-pressure gas with high intensity.     

Supernarrow saturated absorption resonances in weakly coupled two resonant optical cavities

The advantages of the weakly coupled two resonant optical cavities (hereinafter referred to as three-mirror cavity) used for observation of the supernarrow saturated absorption resonances are shown. Among these advantages we can name: (a) the possibility to control the intensity in the cavity with the inside absorbing cell which is important when the gain and absorption saturation parameters differ significantly; (b) the resonances observation from the ‘passive’ side of the three-mirror cavity permits us to decrease drastically the influence of the reflected signal from the detector; (c) if instead of the absorbing cell an active system is put in (gain plus absorption), it is possible by tuning the operating mode of the active interferometer to obtain many-fold gain of the supernarrow resonance amplitude. Received: 11 January 2000 / Revised version: 20 June 2000 / Published online: 9 February 2001     

Using Lorentz’s theorem for studying the propagation wave packets in a nonlinear medium

We obtain integral relationships expressing the amplitude of wave-packet field on the output surface of a layer via the field amplitude on the input surface, the field on the side surface of the layer, and the integral of the nonlinear currents inside the layer at the previous times in the spectral and spatiotemporal forms. These relationships allow one to perform studies and develop numerical simulation algorithms of propagation and interaction of wave packets which have wide frequency and angular spectra, including calculations of excitation of evanescent waves in the case of sharp focusing or formation of supernarrow filaments. Using the obtained relationships, we propose an algorithm that employs a simple iteration of the first order and allows one to significantly speed up the calculations. The possibility of using the fast Fourier transform to develop algorithms for numerical simulation of the boundary-value problems of nonlinear optics is demonstrated.     

Speckle diagnostics of multiple scattering media with the use of frequency-modulated laser radiation

A method for probing randomly inhomogeneous multiple scattering media with the use of frequency-modulated laser radiation is considered. The method is based on analysis of the dependence of the blinking index of time-averaged speckles formed upon scattering of the probing radiation in a medium on the frequency modulation depth of the probing radiation. In the case of a binary frequency modulation, the blinking index of the detected speckle-modulated radiation is determined by the cosine Fourier transform of the probability density of the optical path-length difference of partial components of the scattered field in the probed medium. The values of the probability density of the optical path-length difference reconstructed with the use of the proposed method from the measured blinking index of speckles for model scattering media (fluoroplastic layer and layer of TiO₂ particles on a glass substrate) are in a good agreement with the results of statistical simulation of the probing radiation transfer in multiple scattering media.     

Recording of a hologram by using the second-order nonlinearity

The observation of “spatial-modulation” resonances of saturated absorption in the interaction of iodine-127 vapors with a superposition of frequency-nondegenerate TEM₀₁ and TEM₁₀ transverse modes of a linear laser is reported. The modulation of the total radiation power of the probing wave, recorded at twice the beating frequency of transverse modes of the laser, is interpreted to be the result of the transformation of modulation of the spatial distribution of the field into its amplitude modulation under the action of nonlinearly absorbing iodine vapors. Resonances of saturated absorption of the weak line R(127)11-5 of iodine-127 (633 nm) in an extracavity cell are observed by the method proposed.     

Zeeman effect in the polarization spectroscopy of Na

The Doppler-free polarization spectrum of the D₁ line has been studied in fields of about 50 G and in zero field. Although the principal Zeeman resonances are resolved, the signals are confusing because of the very large number of cross-over resonances. Cross-over resonances also seriously distort well-resolved resonances in zero field. An interpretation is given, based on combining a first-order theory of optical pumping with the theory of Faraday rotation and dischroism.     

Critical slowing down in the single crystalline relaxor SBN75

The dielectric susceptibility of strontium-barium niobate, Sr_0.75Ba_0.25Nb₂O₆, reveals strong relaxor behaviour. It is shown that the relationship between the frequency of the ac probing field and the temperature, at which the real part of the susceptibility passes through a maximum, satisfactorily follows the activated dynamic scaling law predicted for the random-field Ising model. Applicability of a power law as suggested by the dynamic scaling theory is discussed.     

Frequency modulation spectroscopy of coherent dark resonances of multi-level atoms in a magnetic field

The resonances of coherent population trapping (CPT) excited by a frequency-modulated (FM) field at the Zeeman sublevels during the transition F _g = 2 → F _e = 1 of the ⁸⁷Rb D ₁-absorption line were studied theoretically. The influence of the nonlinear Zeeman effect on the structure of the observed resonances was considered. The spectra of CPT resonances were calculated for different values of magnetic field induction and compared with the experimental data.     

The shape of saturated-absorption polarimetric resonances caused by transitions between degenerate states of the neon atom

We have studied experimentally and theoretically the shapes of spectropolarimetric resonances of a linearly polarized probe wave for the transitions 1s ₅-2p ₂ and 1s ₅-2p ₄ in the neon atom in the presence of a strong counterpropagating circularly polarized wave of the same frequency. Physical processes that lead to a change in the shape of polarimetric resonances under the action of a longitudinal magnetic field have been determined.     

Terahertz wave polarization rotation in bianisotropic metamaterials

Utilizing a polarization sensitive terahertz detection method where the detector is rotated by either 0° or 90° to measure the electric field E_{p, s} (t) of each polarization component, we have characterized the properties of split ring resonators. The strong polarization dependence of the bianisotropic-circular-current-driven and linear-polarization-induced resonances is in excellent agreement with the simulation when the p-polarized terahertz transmission is measured. However, these electromagnetic responses vanish when the s-polarized terahertz transmission is measured. There is only a transmission minimum at 1.64 THz and the terahertz polarization rotation angle of about 90° is observed. The polarized terahertz transmission amplitudes and spectra detected at orthogonal orientations show that these behaviours are probably attributed to the birefringent effect of the sample.     

Specific features of the electron paramagnetic resonance spectrum in the vicinity of the convergence of the transitions of gadolinium centers in Pb5(Ge1 − x Si x )3O11

An anomalous electron paramagnetic resonance spectrum of the transitions ?1/2 ? +1/2 of four Gd³⁺-Si dimer clusters in the Pb₅(Ge_{1 ? x} Si _x )₃O₁₁ crystals doped with gadolinium has been found in the vicinity of the orientation of the magnetic field along the optic axis of the crystal. It has been assumed that this spectrum is caused by rapid transitions between the spin packets of the initial resonances due to the crossrelaxation. A computer simulation of the spectrum has been carried out. The results obtained adequately describe the experiment.     

Laser-field-induced coherent molecular librations in liquid

The temperature evolution of rotational spectra is demonstrated for four-photon scattering in water in the interval 0.1–8 cm^?1 (3–240 THz). A detailed numerical simulation of the spectra is performed. The best agreement is reached using the frequencies of the rotational resonances of free molecules. It is demonstrated that the contribution of coherent librations into the measured signal increases proportionally to the decrease in the shear viscosity of water. The four-photon-scattering spectra of water corresponding to an increase in the temperature and dilution with H₂O₂ are compared.     

Correlation of momenta of electrons and the nucleus in atoms

The process of resonant multiphoton ionization of a hydrogen atom in the ground 1s state is studied by direct numerical integration of the nonstationary Schrödinger equation for a quantum system in an electromagnetic field. The dependence of photoionization probability on the radiation intensity is found to be nonmonotonic. It is established that the minima of ionization correspond to multiphoton resonances between the ground state and one of the excited (Rydberg) atomic states perturbed by the laser field. It is shown that ionization is suppressed due to rearrangement of Rydberg states in a strong electromagnetic field and is accompanied by efficient Raman Λ transitions, which connect a set of closely lying Rydberg states via the continuum.     

Influence of atomic alignment on crossover signals in saturation spectroscopy

The crossover resonance between the atomic transitions² S _1/2(F=2)→² P _1/2(F′=1, 2), observed in the saturation spectrum of sodium, was found to be sensitive to the atomic orientation of the ground state, produced by velocity selective optical pumping. For zero magnetic field and the same linear polarization of saturating and probing beam, a negative signal was recorded for the crossover, corresponding to an increase in absorption of the probing beam. Application of a sufficiently strong magnetic field perpendicular to the polarization vector causes the destruction of the alignment, leading to a change in sign for the crossover intensity, i.e., to an enhanced transmission of the probing beam. It was shown experimentally that an increase in the atomic transit time has the same effect. Using optical pumping theory all qualitative features could be accounted for.