Influence of the polarization of radiation on the shape of resonances of coherent population trapping on fine-structure levels

The dependence of the shape of resonances of coherent population trapping (CPT) on magnetic sublevels of thallium atoms, forming a generalized Λ-system with the magnetic sublevels of the fine-structure levels as lower ones, on the polarization of the radiation fields has been numerically studied. The cases of linear, elliptical, and circular polarizations have been considered. The shape and the number of CPT resonances for different polarizations have been compared. It has been concluded that the electromagnetically induced transparency can be changed by changing the polarization properties of the laser radiation. The possibility to decrease the number of observed resonances may be useful in high-resolution spectroscopy.     

Sub-Doppler spectroscopy of atoms excited in the regime of Rabi oscillations in a thin gas cell

We carried out theoretical investigation about velocity-selective atomic excitation on long-lived (metastable) levels of an atomic vapour in a thin cell by a monochromatic laser beam, running in the normal direction. The regime of coherent Rabi oscillations is considered on the light-induced transition from a sublevel of the ground quantum term to a metastable atomic level. On the basis of density matrix equations for the two-level system, we analysed the atomic population density of the metastable level, when the sample is irradiated by resonant monochromatic laser beam with an annular cross-section versus atomic velocities and versus the detuning, the amplitude, and the geometry of the laser beam. It is shown that, in the centre of the annular region, it can be obtained a population distribution on the metastable level as a function of the laser detuning, characterized by a sharp narrow resonance profile, whose width is reduced with respect to the thermal Doppler width roughly by the ratio between the diameter of the irradiated region and the inner thickness of the cell. We suggest high-sensitive schemes, in order to detect these sub-Doppler resonances, by probing the population of the metastable state with a second laser beam, resonant with a transition leaving from the metastable level. The case of ¹S₀ → ³P₁ spin-forbidden transition of Ca is discussed in more detail     

A study of dark resonance splitting for the D 1 line of 87Rb in strong magnetic fields

The process of electromagnetically induced transparency (EIT) is studied using an extremely thin cell with thickness of a vapor column of rubidium atoms L = 794 nm. Wavelengths of resonant laser beams ?? ?? 794 nm. Results of the study of behavior of the EIT resonance (which is also called the ??dark?? resonance) formed in the ?? system of the D ₁ line of ⁸⁷Rb atoms in strong magnetic fields up to 1700 G (0.17 T) are reported for the first time. Three dark resonances are recorded in magnetic fields with induction B < 300 G, two resonances are recorded at B > 650 G, and only one dark resonance is retained at B > 1200 G. A method of the formation of a dark resonance at a given frequency is demonstrated that will allow, under the corresponding conditions, the formation of a dark resonance also at B > 0.2 T. The experimental results are well described by the known theoretical models. Practical applications of these results are indicated.     

Excitation of sodium atoms by 330-nm laser pulses

1/2 ) atoms in a dense sodium vapour irradiated by nanosecond laser pulses tuned near the 3S→4P transition was investigated. It was observed that the population of Na(4P) atoms remained high only within the laser pulse, in spite of the relatively long lifetime of the 4P level (110.ns)The 3P_1/2 level, which is populated as a result of cascade transitions from the higher levels, reached the highest population several nanoseconds after the laser shot. The fast population changes are explained by cascade-stimulated transitions between the excited atomic levels. Received: 16 July 1997/Revised version: 27 October 1997     

Optimization of stabilization regimes in atomic clocks,based on the effect of coherent population trapping

Using the atomic density matrix formalism, we investigate the dynamic regime of formation of the error signal for resonances of coherent population trapping excited in a three-level Λ-system by a bichromatic field. The optimal parameters of harmonic modulation used in the frequency locked loop are determined with allowance for low-frequency noise.     

V.L. Ginzburg’s elliptic screw polarization modes in an optical medium with linear birefringence and twist: Determination of their parameters by the method of Jones matrices

The effect of electromagnetically induced transparency (EIT) has been experimentally implemented for the first time for the (4S _1/2–4P _1/2–4S _1/2) Λ-system of potassium atom levels in a nanocell with a 770-nm-thick column of atomic vapor. It is shown that, at such a small thickness of the vapor column, the EIT resonance can be observed only when the coupling-laser frequency is in exact resonance with the frequency of the corresponding atomic transition. The EIT resonance disappears even if the coupling-laser frequency differs slightly (by ~50 MHz) from that of the corresponding atomic transition, which is due to the high thermal velocity of K atoms. The EIT resonance and related velocity selective optical pumping resonances caused by optical pumping (formed by the coupling) can be simultaneously recorded because of the small (~462 MHz) hyperfine splitting of the lower 4S _1/2 level.     

Splitting of the electromagnetically induced transparency resonance on 85Rb atoms in strong magnetic fields up to the Paschen-Back regime

Electromagnetically induced transparency (EIT) resonance in strong magnetic fields of up to 1.7 kG has been investigated with the use of a 30-??m cell filled with an atomic rubidium vapor and neon as a buffer gas. The EIT resonance in the ?? system of the D₁ line of ⁸⁵Rb atoms has been formed with the use of two narrowband (??1 MHz) 795-nm diode lasers. The EIT resonance in a longitudinal magnetic field is split into five components. It has been demonstrated that the frequencies of the five EIT components are either blue- or red-shifted with an increase in the magnetic field, depending on the frequency ??_P of the probe laser. In has been shown that in both cases the ⁸⁵Rb atoms enter the hyperfine Paschen-Back regime in magnetic fields of >1 kG. The hyperfine Paschen-Back regime is manifested by the frequency slopes of all five EIT components asymptotically approaching the same fixed value. The experiment agrees well with the theory.     

Laser spectroscopy and optical pumping of alkali atoms in superfluid helium

In this paper, our recent works on the alkali atoms in superfluid helim (HeII) are reported. At first we mentions the laser-sputtering method for implantation, which is simple but is very efficient to produce various kinds of neutral atoms and molecules in HeII. Secondly, we report on the laser spectroscopy of alkali atoms in HeII. Optical excitation and emission spectra are found to be roughly explained by a spherical atomic bubble model, but the spectra corresponding to the D₂ lines indicate the quadrupole oscillation of the bubble shape. Optical pumping by a circularly polarized laser beam is found to produce perfect polarization, for both electron and nuclear spins. Using the rf-optical double resonance techniques, the magnetic and hyperfine resonances are observed. It is discussed also about the phenomena which have observed in the experiments done so far but have not been fully explained.     

Dark-line atomic resonances in submillimeter structures

We present measurements of dark-line resonances excited in cesium atoms confined in submillimeter cells with a buffer gas. The width and contrast of the resonances were measured for cell lengths as low as 100 microm. The measured atomic Q factors are reduced in small cells because of frequent collisions of atoms with the cell walls. However, the contrast of coherent population trapping resonances measured in the small cells is similar in magnitude to that obtained in centimeter-sized cells, but substantially more laser intensity is needed to excite the resonance fully when increased buffer-gas pressure is used. The effect of the higher intensity on the linewidth is reduced because the intensity broadening rate decreases with buffer-gas pressure.     

On the capabilities of sub-Doppler photoionization spectroscopy in thin gas cells

A high-sensitivity photoionization method of registration of narrow sub-Doppler resonances in the spectral distribution of a flow of metastable atoms (or molecules) excited from the ground quantum term by a monochromatic laser beam propagating at normal incidence through an ultrathin gas cell (with a micrometer-scale or even nanoscale gas layer thickness) is proposed. Based on density matrix equations for atomic particles, various mechanisms of broadening of the considered resonances, such as time-of-flight, field, and Doppler broadening, are analyzed. The requirements for laser beam parameters and gas cell dimensions that allow obtaining the narrowest resonances are established. The proposed method can be used in ultrahigh resolution spectroscopy of atoms and molecules, as well as high-precision optical frequency standards.     

Dynamics of moving interacting atoms in a laser radiation field and optical size resonances

The forces acting on interacting moving atoms exposed to resonant laser radiation are calculated. It is shown that the forces acting on the atoms include the radiation pressure forces as well as the external and internal bias forces. The dependences of the forces on the atomic spacing, polarization, and laser radiation frequency are given. It is found that the internal bias force associated with the interaction of atomic dipoles via the reemitted field may play an important role in the dynamics of dense atomic ensembles in a light field. It is shown that optical size resonances appear in the system of interacting atoms at frequencies differing substantially from transition frequencies in the spectrum of atoms. It is noted that optical size resonances as well as the Doppler frequency shift in the spectrum of interacting atoms play a significant role in the processes of laser-radiation-controlled motion of the atoms.     

Resonant interaction of femtosecond radiation with a cloud of cold <Superscript>87</Superscript>Rb atoms

The resonant interaction of ⁸⁷Rb atoms in a magneto-optical trap with femtosecond laser radiation in the spectral range 760–820 nm has been investigated experimentally. It has been demonstrated that femtosecond laser radiation with a spectral width of 10 nm interacts with an atomic ensemble as a set of spectrally narrow modes and as an ionizing laser field simultaneously. The dynamics of trap loading in the presence of ionization by femtosecond radiation has been studied, and the 5D _5/2 level population produced by an additional weak laser field has been measured.     

Resonant light pressure forces in a strong standing laser wave

The light pressure forces acting on a two-level atom in a strong standing laser wave are calculated. It is shown that at strong saturation of a resonant atomic transition the velocity dependence of these forces include sharp variations due to multiphoton resonances. At small atomic velocities these multiphoton resonances may even change the sign of the forces. The results obtained are important for many applications of resonant light pressure, e.g. in cooling and trapping of atoms in standing laser waves.     

激光减速原子束频标的建议

本文提出一个激光减速的碱金属原子束频标的方案。用共振激光束对原子束同时进行减速和选态,使原子速率降到10m/s以下,而光抽运作用使原子自动集中到基态超精细结构中具有最大磁量子数的塞曼子能级上。为避免重力场中束轨迹下垂,用偏转磁铁或多束激光使束由水平转成垂直向上,然后用级联磁共振使原子过渡到频标所需的m_F=0能级。利用原子上升和重力场中自由下落两次通过单个微波谐振腔而取得Ramsey共振信号,线宽约为¹Hz。信号用另一束激光检测。予期这种频标的稳定度和准确度可比现有束型频标提高一个数量级以上。文中详细讨论了激光减速和选态的方法,克服横向加热效应的措施,实现级联磁共振的办法,以及获得垂直束装置的设计等。     

Electromagnetically Induced Transparency and optical pumping processes formed in Cs sub-micron thin cell

The Electromagnetically Induced Transparency (EIT) effect in a Λ-system formed by Cs atoms (6S_1/2 ? 6P_3/2 ? 6S_1/2) confined in an extremely thin cell (ETC) (atomic column thickness L varies in the range of 800 nm –3 µm is studied both experimentally and theoretically. It is demonstrated that when the coupling laser frequency is in exact resonance with the corresponding atomic transition, the EIT resonance parameters weakly depend on L, which allows us to detect the effect at L = λ = 852 nm. EIT process reveals a striking peculiarity in case of the coupling laser detuned by Δ from the atomic transition, namely the width of the EIT resonance rapidly increases upon an increase in Δ (an opposite effect is observed in centimeter-scale cells). The strong broadening of the EIT resonance for large values of detunings Δ is caused by the influence of atom-wall collisions on dephasing rate of coherence. The influence of the coupling laser on the velocity selective optical pumping/saturation resonances formed in ETC has been also studied. The theoretical model well describes the observed results.     

Laser phase fluctuations in a four-level atomic system in N-configuration

We discuss here the effect of laser phase fluctuations on coherent spectroscopy of four-level N-system interacting with a trichromatic radiation field of frequencies Ω _i , (i = 1?3). The laser phase variables are described by the Wiener-Levy diffusion process to specify the bandwidths (Γ _i ) and cross-correlations (Γ _ij ) that may exist between pairs of laser fields. A general formalism based on the master equation and theory of multiplicative stochastic processes is developed and used to study three-photon and (2+1)-photon absorptive resonances in model N-system of ⁴⁰Ca⁺ ion. It is observed that the resonances are suppressed or broadened by all Γ _i ,(i = 1?3), while their revival is dependent only on Γ ₁₂ and Γ ₂₃, and yet the revival is only partial even when the relevant fields are critically correlated. In contrast Γ ₁₃ is observed to deteriorate the absorptive resonances. The distinctive features of the steady state and time dependent behavior of the system under three-photon and (2 + 1)-photon resonance conditions and for fluctuating fields are discussed.     

激光微波双共振导致的基态碱原子的非均衡分布

本文求得了激光微波双共振抽运碱原子束时基态原子实现最大非均衡分布的条件,这与新近的实验结果相符。分析了影响非均衡分布的机制,如相干囚禁,指出了消除其影响的途径,与双激光抽运对比,讨论了激光微波双共振抽运过程的特点。 关键词：     

Study of optical narrow-band N-resonance formed in the vapor of isotope 87Rb atoms in an external magnetic field

Narrow-band cascade N-resonance formed in a Λ-system of rubidium atoms was investigated. Radiation of two continuous narrow-band lasers was used, one of which had a fixed frequency, while the second one was a probe laser. N-resonance may have a sub-natural width and exhibits enhancement of absorption. The behavior of N-resonance in an external magnetic field was examined with use of ⁸⁷Rb atomic vapors.     

Implementation of all-optical Toffoli gate in Λ-systems

An optical Toffoli gate is the essential logical element, which permits the implementation of a reversible optical processor. We propose a simple realization of such a gate in films of crystals doped with rare-earth ions. The proposed scheme is based on adiabatic population transfer in a ??-system by means of counterintuitive and intuitive sequences of short laser pulses. We also discuss possibilities for experimental realization of the proposed gate.     

Superlong pulses of laser oscillation on the 6 1P1-5 1D2 transition of the barium atom

A possibility of CW laser oscillation on atomic transitions between a resonance energy level and a metastable one under conditions when lower laser states are deactivated by electron impacts has been theoretically shown. We determined the plasma parameters so that CW laser action on such transitions of Cu, Au, Ca and Ba atoms may be possible. Superlong laser pulses of 6 μs duration were obtained on the 6 ¹P₁-5 ¹D₂ transition of the barium atom.