Search

Russian science icon, Pyotr Lebedev, is well known for first proving the existence of light pressure by measuring its action on both solids and gases. His experiments are discussed here as well as ...

We report the experimental observation of the periodic switching of topological edge states between two dimerized fs-laser written waveguide arrays. Switching occurs due to the overlap of the modal fields of the edge states from topological forbidden gap, when they are simultaneously present in two arrays brought into close proximity. We found that the phenomenon occurs for both strongly and weakly localized edge states and that switching rate increases with decreasing spacing between the topological arrays. When topological arrays are brought in contact with nontopological ones, switching in topological gap does not occur, while one observes either the formation of nearly stationary topological interface mode or strongly asymmetric diffraction into the nontopological array depending on the position of the initial excitation. Switching between topological arrays can be controlled and even completely arrested by increasing the peak power of the input signal, as we observed with different array spacings., Comment: 8 pages, 6 figures

Intense white-light color emission of lanthanide-doped core-shell structured particles at microscale level was presented under 980 nm excitation. The prepared NaYF4:Yb/Er@ NaYF4:Yb/Tm microcrystals not only can effectively prevent the deleterious cross-relaxation that occurs between the Er3+ and Tm3+ due to the location of the activator ions within different layers, but also possess a high luminescence efficiency due to dimensions of the micro-scale structure. The core-shell structured microcrystals presented satisfactory capacity for color control in the white region. The results show great potential in attaining white light-emitting diodes within the field emission display on specific device applications. Furthermore, the core-shell microcrystals emit white-light that presents obvious and distinct lifetimes of green, red, and blue emissions, which could achieve multicolor emissions by setting a suitable delay time. This feature demonstrates that the core-shell structured microrods offer practical use as security ink to prevent forgery, such as in identifying currency.

We have studied the effect of spherical SiO2 nanoparticles with sizes of 20, 50, and 80 nm embedded in a PEDOT : PSS buffer layer on the performance of organic solar cells (OSCs) based on star-shaped oligomers. The current–voltage characteristics and absorption spectra of samples have been measured and analyzed; the morphology of the buffer layer surface with embedded nanoparticles has been studied. It has been shown that an increase in the OSC performance occurs in the case of embedded nanoparticles with a diameter of 20 and 50 nm and weakly depends on the concentration of the nanoparticles in the layer.

Multicolor flexible materials are in growing interest owing to the prominent fluorescence tunability and flexible adaptability. However, narrow band response and finite color transition limit the diverse application of multicolor flexible materials. Herein, flexible lanthanide ions-doped dual GdF3 composite with broadband light source response is successfully constructed via the inspiration of natural color-mixing strategy. Surfactant modification and collaboration of dual GdF3 effectively enhance the photoluminescence emission and color-tunable ability. Further by the excitation of light sources in the ultraviolet (274, 348, 395 nm) and near-infrared (980 nm) regions, the accurate multimodal photoluminescence transition can be clearly observed. Benefiting from such effective strategy, the flexible composite is further implemented in the application of bionic butterfly, flower and leaf, showing good adaptability and color-tunable behaviors. Based on above outstanding performances, the flexible composite can make up for deficiency of traditional color-tunable materials and greatly expand the applications in the optical storage, industrial detection, and anti-counterfeiting fields.

We studied the radiation-directivity pattern and the near-field polarization of a spheroidal metallic nanoparticle located over a silicon substrate by interaction with a linearly and circularly polarized field. It is shown that the directivity pattern of the spheroidal particle near the silicon substrate becomes strongly asymmetric and forward scattering is predominant compared with the symmetric diagram of a particle in free space. The change of the near-field polarization of the nanoparticle in presence of the substrate is studied for different wavelengths in the vicinity of the plasmonic resonance. The near-field polarization is described using the generalized Stokes parameters, which allow pictorial visualization of results.

The near-field polarization structure of a high-refractive-index dielectric nanosphere in a nonmagnetic and nonabsorbing medium is studied numerically in free space and in the vicinity of a flat dielectric substrate. Polarization patterns of the near field are obtained for linear and circular polarizations of the incident light and visualized using the polarization degree and three-dimensional Stokes parameters. Calculations are performed using the finite-element method and verified analytically using the Mie solution for scattering by a sphere with an extension of Weyl's method allowing description of reflection by a flat substrate. It is shown that the nanosphere drastically affects the polarization leading to a complex butterflylike structure. For instance, the near-field polarization is found to be qualitatively modified near the Mie electric and magnetic dipole and quadrupole resonances: linear polarization of the incident field results in circular polarization in some areas around the particle and vice versa. The areas of strong polarization change are found to be spatially localized in certain places around the particle making it possible to perform an experimental mapping. It is shown how a dielectric substrate affects the polarization distribution of the near-field of the particle. Also, several schemes of potential experiments to map the near-field intensity and polarization have been discussed.

The effect of spherical SiO2 nanoparticles (NPs) embedded in the electrode layer of PEDOT:PSS on the efficiency of organic solar cells (OSC) based on small molecules was studied in detail. We show that embedding SiO2 NPs of 50 nm in diameter increases the power conversion efficiency (PCE) by 15%, and this increase weakly depends on the NPs concentration in the buffer layer. Also, we calculated the interaction of radiation with a model three-layer system (ITO, buffer layer, active layer) with embedded NPs in buffer layer and analyzed the directional patterns of spherical SiO2 NPs of various sizes in such a three-layer system. The calculation results allow interpreting the experimental results on increasing the PCE as a result of light scattering by the NPs.

A simple finite-dimensional geodynamo model, obtained from the equations of the mean field electrodynamics and reproducing the phenomenon of geomagnetic reversals, is proposed. It has been indicated that the reversal scale obtained in the scope of this model is rather close to the observed scale in its properties. The reversal mechanism is related to the α-effect fluctuations. It is not necessary to substantially change the hydrodynamic parameters of the problem so that a reversal originates in the scope of such a model, but it is only sufficient to take the α-effect fluctuations into account. If the rms deviation of fluctuations accounts for 10% of the average α value, a fluctuation of two-three standard deviations is sufficient for the origination of a reversal, which quite agrees with the concept that reversals are rather rare phenomena. Another factor resulting in the regime with reversals is that the model can generate magnetic fields with different behaviors in different regions of the parametric space in linear mode: monotonically increasing fields and fields increasing with oscillations.

We suggest a simple dynamical system which mimics a nonlinear dynamo which is able to provide (in specific domains of its parametric space) the temporal evolution of solar magnetic activity cycles as well as evolution of geomagnetic field including its polarity reversals. A qualitative explanation for the physical nature of both phenomena is presented and discussed.

The dual-mode emission and multicolor outputs in the time domain from core-shell microcrystals are presented. The core-shell microcrystals, with NaYF4:Yb/Er as the core and NaYF4:Ce/Tb/Eu as the shell, were successfully fabricated by employing the hydrothermal method, which confines the activator ions into a separate region and minimizes the effect of surface quenching. The material is capable of both upconversion and downshifting emission, and their multicolor outputs in response to 980 nm near-infrared (NIR) excitation laser and 252 nm, and 395 nm ultraviolet (UV) excitation light have been investigated. Furthermore, the tunable color emissions by controlling the Tb3+- Eu3+ ratio in shells and the energy transfer of Ce3+→Tb3+→ Eu3+ were discussed in details. In addition, color tuning of core-shell-structured microrods from green to red region in the time domain could be obtained by setting suitable delay time. Due to downshifting multicolor outputs (time-resolved and pump-wavelength-induced downshifting) coupled with the upconversion mode, the core-shell microrods can be potentially applied to displays and high-level security.

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 concept of entangled quantum measurement was demonstrated by the example of the fundamental value of the experiment on quantum nondemolition measurement of a photon in a resonator with the use of a probe atom [1]. The quantum-information analysis of this experiment was performed. A mechanism of information transmission in the nondemolition measurement scheme in the case of the classical and quantum formalism was demonstrated. The results were shown to coincide in both cases. This is the result of copying the classical part of the initial quantum information attributed to a set of quantum object states.

The universal algorithm of choosing the train of short laser pulses, which could selectively excite the specific enantiomers in a racemic mixture of rotationally cold molecules, is proposed. Its application is illustrated on example of laser control of content of different chiral conformations in the mixture of hydrogen peroxide molecules. Methods of detection of racemity breaking in case of dynamical chirality are also discussed.

The results of frequency-modulation (FM) spec- troscopy of coherent dark resonances from the Zeeman sub- levels of the transition F = 2 ↔ F = 1o fD1 line in absorp- tion of 87 Rb atoms are presented and discussed in detail. By contrast with the conventional spectroscopy of coherent dark resonances employing two laser beams, relative frequency of which can be varied, these data has been obtained with the help of a single frequency-modulated laser field. Varia- tion of the modulation frequency plays then a similar role as the variation of the relative frequency in conventional spec- troscopy. Experimental data are fit to the theoretical calcu- lations, which are based on the theory of FM spectroscopy of coherent dark resonances recently developed by us. Fea- sibility of using such experimental technique for accurate measurements of magnetic fields is also discussed.

The interaction of a three-level atom in the A configuration with a frequency-modulated (FM) field is analyzed theoretically for the first time. The two-frequency model for solving the problem of frequency modulation spectroscopy of coherent dark resonances is described and analyzed for a three-level A system. The effectiveness of the two-frequency model is demonstrated by comparing the results obtained using this model with the results of solving the exact problem of interaction of a A system with an FM field, which can be solved by the density matrix method. It is shown that the simple two-frequency model corresponds to the exact solution and is in qualitative agreement with experimental data.

It is shown that the combined effects of electrostatic and resonant laser fields on a molecular ensemble can be used to control the orientation of molecules by changing their internal state. In contrast to most other schemes for controlling molecular orientation, the proposed method does not require rotational cooling and can be highly efficient at room temperature.

Information aspects of copying quantum states via stimulated emission of an optical quantum amplifier are considered. It is shown that the measurable information very rapidly decreases after amplification of a single photon up to a level of several photons. Spontaneous emission, which leads to such behavior, is also discussed.

We clarify the microscopic structure of the entangling quantum measurement superoperators and examine their possible physical realization in a simple three-qubit model, which implements the entangling quantum measurement with an arbitrary degree of entanglement., Comment: 6 pages, 2 fihures

The concept of an entangling measurement as the most general form of ideal quantum measurement is introduced. The mathematical definition of an entangling measurement is given in the form of a superoperator transformation, which projects the initial states of an object-apparatus system on the corresponding entangled states appearing after a measurement. The mathematical properties of the superoperator of an entangling measurement are considered. The spectrum of superoperator eigenstates is studied analytically on the example of a two-level system. The algebraic relation ℳ2=ℳAM between the superoperators of entangling and standard measurements is ascertained. The coherent information obtained in the course of measurement is analyzed and the relevant potentialities of entangling measurements are discussed.

A universal theory for calculating coherent population trapping resonances in multilevel atoms is suggested. The theory allows arbitrary schemes of multilevel atoms and their excitations to be calculated tak- ing into account the influence of relaxation effects in atoms, applied magnetic field, and the Doppler effect. The experimental data obtained by high-precision diode spectroscopy of coherent dark resonances in samar- ium vapor are systematically analyzed using the suggested theory. In the absence of a magnetic field, the model of samarium is based on consideration of a degenerate Λ system of the 4 f 6 6 s 2 ( 7 F 0 ) 4 f 6 ( 7 F )6 s 6 p ( 3 P 0 ) 9 4 f 6 6 s 2 ( 7 F 1 ) active transitions. If the fourth 4 f 6 6 s 2 ( 7 F 2 ) level is taken into account, this Λ system becomes open. Numerical simulation of coherent population trapping resonances shows that the open character of the system decreases the contrast of resonance curves in absorption spectra without changing resonance widths. The system under applied external longitudinal and transverse magnetic fields is correctly described by 7- and 12-level models of atomic transitions, respectively. © 2003 MAIK "Nauka/Interperiodica".

A new mechanism for controlling chiral states in simple chiral molecules with internal rotation, which employs the coherent quantum entanglement of the rotational–torsional states of the molecules, is proposed. It requires no preliminary spatial alignment of the molecules in a solution. A novel scenario for the preferential laser synthesis of enantiomers from a racemic solution of chiral molecules employing this new mechanism of inducing chirality is proposed and analyzed in detail and experimental scheme realizing this scenario is discussed. It is suggested that a non-linear optical activity coherent anti-Stokes Raman scattering (NOA-CARS) spectroscopic technique is used for both inducing the gyration wave in the medium (vapor) of chiral molecules and detecting this photoinduced gyration wave in the medium by registering the NOA-CARS signal. All numerical estimates are made for the hydrogen peroxide and deuterated hydrogen peroxide chiral molecules. Copyright © 2002 John Wiley & Sons, Ltd.

It is demonstrated that the interaction of a two-level quantum emitter (atom, molecule, etc) with a plasmonic nanoparticle (prolate nanospheroid) in an external laser field features either an essential increase (up to a few orders of magnitude) or reduction (up to a few times) of the total decay rate of the emitter in specific areas around the nanoparticle in contrast to its decay rate in a vacuum. It is also shown that the resonance fluorescence spectrum of the emitter in close proximity to a plasmonic nanoparticle is very sensitive to both the location of the emitter around the nanoparticle and to polarization of the near-field, which depends in turn on the polarization of the incident laser field. This can be used in engineering potential quantum optics experiments with quantum emitters in the near-field, as well as for 3D nanoscopy of the near-field by registering the resonance fluorescence spectra of quantum emitters scattered in the vicinity of a plasmonic nanoparticle.

The photon-number statistics from resonance fluorescence of a two-level atom near a metal nanosphere driven by a laser field with finite bandwidth is studied theoretically. Our analysis shows that all interesting physics here takes place in a small area around the nanosphere where the near field and the atom-nanosphere coupling essentially affect the radiative properties of the atom. Computer modeling estimates this area roughly as r≤2a (r is the distance from the center of the nanosphere to the atom), with a being the radius of the nanosphere. At the larger distances, the influence of the nanoparticle vanishes and the atom tends to behave similarly to that in free space. It is shown that the distribution function p(n,T) of the emission probability of n photons in a given time interval T in steady-state resonance fluorescence drastically depends on the atom location around the nanosphere for r≤2a, featuring a characteristic twist in the ridgelike dependence and a convergence time of up to 9μs, two orders of magnitude slower than for the atom in free space. At large distances, the distribution converges to a Gaussian one, as for the atom in free space. The typical convergence time scale at large distances r>2a tends to the convergence time of the atom in free space. There are also two areas symmetrical around the nanosphere in which Ω∼γ and the convergence time goes to zero. This behavior is determined by the interplay of the radiative and nonradiative decay rates of the atom due to the coupling with the metal nanosphere and by the near-field intensity. Additional parameters are the normalized laser frequency detuning from the atomic resonance and the bandwidth of the incoming laser field. (Less)

The problem of directional laser synthesis of enantiomers in an isotropic racemic mixture of chiral molecules is analyzed taking into account rotational degrees of freedom of molecules. It is shown that the chirality of the polarization structure of a laser field is the most general necessary condition for the laser distillation of an isotropic non-racemic mixture of chiral molecules with the isotropic distribution over the Eulerian angles. In the approximation of the electric-dipole interaction, the required field configuration can be provided due to noncoplanarity of the polarization vectors of laser-pump components. A relevant experimental scheme is proposed and calculated for the transformation of an isotropic racemic mixture with the help of a three-component pulsed laser field. It is shown that the possibility of the laser control of chirality in an isotropic medium corresponds to nonzero information on coupling between the input and output in the laser field-chiral molecular state information channel.

A set of very important simple quantum systems is analyzed from the standpoint of the amount of coherent information that is accessible when information channels corresponding to the systems are used. It is shown that for simple quantum models the coherent information can be calculated and used for estimating the potential possibilities of the corresponding quantum channel as a source of physical information in experiments associated with the effects of the coherence of quantum states. The following physical models are studied: a two-level atom in a laser radiation field, an aggregate of two two-level subsystems in a multilevel atom (hydro- gen), a system of two two-level atoms in the process of joint quantum-deterministic evolution and under the action of transformations of quantum measurement and quantum duplication, as well as one and two two-level atoms in the process of emission. © 2000 MAIK "Nauka/Interperiodica".

Effectiveness of using laser field to produce entanglement between two dipole-interacting identical two-level atoms is considered in detail. The entanglement is achieved by driving the system with a carefully designed laser pulse transferring the system's population to one of the maximally entangled Dicke states in a way analogous to population inversion by a resonant $\pi$-pulse in a two-level atom. It is shown that for the optimally chosen pulse frequency, power and duration, the fidelity of generating a maximally entangled state approaches unity as the distance between the atoms goes to zero., Comment: 4 pages, 3 figures; submitted to the proceedings of the III Adriatico Research Conference on Quantum Interferometry, ICTP, March 1-5,1999; replaced with the final submitted version

The feasibility of using nonlinear optical techniques to control the chiral states of molecules is examined with the hydrogen peroxide molecule as an example. Raman excitation of optical activity owing to a transition among states with different chiral symmetries is proposed, along with an experimental scheme for detecting the corresponding photoinduced optical rotation in hydrogen peroxide vapor.

A universal mechanism destroying coherence in a $\ensuremath{\Lambda}$ system driven by two resonant laser fields due to four-photon interactions is analyzed theoretically. It is shown that this mechanism gives rise to novel spectral structures in resonance fluorescence. The ``dark resonance'' in absorption (dispersion) spectra is affected as well.

The resonance fluorescence spectrum of a Λ-system excited by two resonant light fields is calculated using a Markov analysis. Analytical formulas are derived in the strong-field limit within and beyond the rotating wave approximation. It is shown that the resonance fluorescence of the system does not vanish during coherent population trapping. Its spectrum consists of two multiplets which are similar to a triplet in the resonance fluorescence spectrum of a two-level atom and lie at the electronic transition frequencies, together with two triplets located at the frequencies of four-photon processes involving the optical excitation fields. The latter are fundamental in character and impose limits on the lower bound of the dephasing rate for the Raman resonance owing to the effect of radiative decay of the dipole transitions on the dynamics of the ground state. The effect of four-photon dephasing on the absorption spectrum of a Λ-system is analyzed and found to lead to a substantial reduction in the depth of a dip in the absorption spectrum which vanishes as the laser field strength is increased.

The semiclassical theory of atomic dynamics in a three-dimensional pulsed optical dipole trap formed by superimposed trains of short laser pulses (down to a few fs duration), which is based on a stochastic formulation for the dynamics of an open quantum system, is considered in detail. It covers all key features of the atomic dynamics in the trap, including the dipole-dipole interaction (DDI) between trapped atoms due to the exchange of virtual photons between the atoms. Analytical solutions are obtained for the relaxation and laser Liouvillians, which describe the dissipation and laser excitation in the system, respectively. The probabilities of single-atom and two-atom escapes from the trap are analyzed. As an example, the theory is applied to computer simulation of Rb atoms preliminarily cooled in a magneto-optical trap that are trapped in a femtosecond optical dipole trap (pulse duration 100 fs). Our simulations prove that such a trap effectively confines atoms at the pump laser power in the range from a few mW to several kW. It is also shown that a near-resonant DDI, through which atoms that are closely spaced in the micropotential wells interact with each other, can be significantly increased by illuminating the atoms with a near-resonant probe laser beam. By varying both the parameters of the trap and the intensity of the probe laser field, the role of the DDI in the atomic dynamics in the trap and its influence on the single-atom and two-atom escape rates are clarified in detail.

Structure of the near-field intensity and polarization distributions, the latter is described with the generalized 3D Stokes parameters, of a spherical Si subwavelength nanoparticle in a non-magnetic and non-absorbing media near a dielectric substrate has been studied in detail with the help of the Mie theory and an extension of the Weyl's method for the calculation of the reflection of dipole radiation by a flat surface. It is shown that for the nanoparticle near the substrate the interference effects due to the scattering by the nanoparticle and interaction with the substrate play an essential role. We also demonstrate how these effects depend on the dielectric properties of the nanoparticle, its size, distance to the substrate as well as on the polarization, wavelength and incident angle of the external light field.

Modification of the resonance fluorescence spec-trum of a two-level atom driving by a lasermonochromatic field in the close proximity of aplasmonic nanostructure (metal sphere) is studiedin detail. It is shown that one can control thisspectrum varying four key parameters: distancebetween the atom and the nanosphere, atom’s lo-cation around the nanosphere, the radius of thenanosphere, and polarization of the incident ra-diation. These parameters affect the local fieldenchancement, transition frequency shift and themodification of the radiative decay rate of the atominteracting with the nanosphere, which lead tomodification of the resonance fluorescence spec-trum of the atom (frequency shift of the satellitelines in the Mollow-type triplet, widths of the lines,the spectrum intensity) by contrast with that onein free space. The permittivity of the metal thenanosphere is made of is also an additional param-eter, which defines the nonradiative decay. The lat-ter in combination with other parameters allows tocontinuously control the transition from resonancefluorescence enhancement to its quenching. Thecalculation results are generalized to the case ofN two-level atoms, distributed around the nanopar-ticle in the close proximity of its surface. Thecalculations were performed for different positionsof the detector relative to the system nanoparticle-atom(s).

Modification of the resonance fluorescence spectrum of a two-level atom driven by a monochromatic field in the close proximity of a plasmonic nanostructure (metal sphere) is studied in detail. It is shown that one can control this spectrum by varying several key parameters: (i) the radius of the nanosphere, (ii) polarization of the incident radiation, and (iii) the atom's location around the nanosphere (its radial coordinate and polar angle in the spherical coordinate system). These parameters affect the local field enhancement and the modification of the radiative decay rate of the atom interacting with the nanosphere, which leads to modification of the resonance fluorescence spectrum of the atom (e.g., frequency shift of the satellite lines in the Mollow-type triplet, widths of the lines, and the spectrum intensity) by contrast with that in free space. The permittivity of the metal the nanosphere is made of is also an additional parameter, which defines the nonradiative decay. The latter in combination with other parameters allows continuous control of the transition from resonance fluorescence enhancement to its quenching.

The dynamics in the photoisomerization of isolated cis-stilbene, especially the dynamics leading to the intermediate twisted configuration is explored by molecular dynamics simulation. Comparison of the dynamics of the trans and cis isomers shows that for cis-stilbene the time required to reach the twisted configuration is an order of magnitude or two less than for trans-stilbene, due only to the specific steric interactions, and not to any difference in the potential functions or parameters. A barrier of between 510 and 640 cm−1 along the torsional coordinate from the cis side is estimated for isolated molecule, accounting for a transition to the intermediate in approximately 300 fs.

Dynamics of atoms trapped in an optical dipole trap formed by a train of femtosecond laser pulses is studied in detail on example of Rb atoms. In computer simulation, it is proved that such a trap effectively confines the atoms at the pumping laser beam power in between 1 mW and 3 kW (pulse duration 100 fs). It is also shown that the resonant dipole-dipole interaction (RDDI) through which closely spaced in the micropotential wells atoms interact between each other becomes essential and can be significantly increased by shining the atoms with resonant probe laser beam. Varying both the parameters of the trap and intensity of the probe laser field, role of the RDDI in the atomic dynamics in the trap is clarified in detail.

Theoretical study and computer modeling results of the spectra of coherent dark resonances resulted from excitation of Zeeman sublevels of the F g =2→F e =1 transition of the D 1 line in 87 Rb atoms by a frequency-modulated laser field are presented and discussed in detail. The influence of the nonlinear Zeeman effect on the structure of the coherent dark resonances is observed. It is shown that calculated for different values of the magnetic field spectra are in a good agreement with the experimental data.

The results of frequency-modulation (FM) spectroscopy of coherent dark resonances from the Zeeman sublevelsof the transition F =2 $ F =1 of D 1 line in absorption of 87 Rb atoms are presented and discussed in detail.By contrast with the conventional spectroscopy of coherent dark resonances employing two laser beams, relativefrequency of which can be varied, these data has been obtained with the help of a single frequency-modulatedlaser ¯eld. Variation of the modulation frequency plays then similar role with variation the relative frequencyin conventional spectroscopy. Experimental data are ¯t to the theoretical calculations, which are based onthe theory of FM spectroscopy of coherent dark resonances recently developed by us. Feasibility of using suchexperimental technique for accurate measurements of magnetic ¯elds is also discussed.Keywords: Coherent population trapping, absorption, dark resonance, magnetometry, metrology 1. INTRODUCTION The coherent population trapping (CPT) is one of the most intriguing quantum interference phenomena thatcan be most vividly seen in a three-level system in ¤-con¯guration. In this system, if two monochromaticpumping ¯elds are tuned into the resonance with the respective transitions, all the population is captured in thecoherent superposition of two low-lying levels, which gives the name of the phenomenon|coherent populationtrapping [1]. This means that the media of such three-level atoms under CPT will not emit °uorescence and donot absorb photons. In absorption spectra it is revealed as a narrow sharp dip in the absorption pro¯le whilescanning frequency of one of the pumping laser ¯elds. These resonances are called the coherent dark resonances.Due to the rather small spectral width of the dark resonances they found applications in precision spectroscopicapplications, such as metrology

A method for coherent laser control of randomly oriented molecules at high temperatures ! up to room temperature" is suggested, which rests on the technique proposed by us earlier of laser-assisted orientationdependent selection ! ODS "# Phys. Rev. A 77, 011401R ! 2008"$ . It is shown that the ODS is of practical importance for the problem of field-free orientation of molecules. The efficacy of the method is justified by simulations of the photoinduced dynamics of BF molecules via direct numerical solution of the nonstationary Schrodinger equation.

A method of laser-assisted field-free dynamic molecular orientation employing a short, moderately intense three-color phase-locked laser pulse is proposed. Numerical simulations show that it provides an exceedingly effective control of orientation in molecular gases even at room temperatures. The underlying mechanism is based on the specific laser-induced orientation-dependent selective excitation of molecules and subsequent self-transformation of the induced geometrical orientation into a dynamical one. It is shown that this mechanism is significantly more powerful than the widely investigated kick mechanism.

We analyzed the absolute asymmetric synthesis (AAS) of enantiomers from an isotropic racemic mixture of chiral molecules, which employs the laser electrodipole interaction, and revealed a set of basic symmetry-based conditions on the parameters of field-molecule interaction. Using these conditions, we developed a novel scenario of the AAS (through selective photodestruction of the enantiomers of a given type) based on the joint action of the strong multicomponent femtosecond and picosecond laser pulses. Key mechanism of this scenario is the partly modified scheme of laser orientation-dependent selection of molecules proposed by us earlier [D. V. Zhdanov et al., JETP 130, 387 (2006)]. Calculations made on example of chiral molecule SiHNaClF show rather high efficiency and stability of the proposed AAS scenario with respect to the parameters of the incident laser pulses and even feasibility of its realization at room temperature.