D. Sarkisyan

Cooperative Lamb Shift in an Atomic Vapor Layer of Nanometer Thickness

We present an experimental measurement of the cooperative Lamb shift and the Lorentz shift using an atomic nanolayer with tunable thickness and atomic density. The cooperative Lamb shift arises due to the exchange of virtual photons between identical atoms. The interference between the forward and backward propagating virtual fields is confirmed by the thickness dependence of the shift which has a spatial frequency equal to 2k, i.e. twice that of the optical field. The demonstration of cooperative interactions in an easily scalable system opens the door to a new domain for non-linear optics.

Exploring the van der Waals atom-surface attraction in the nanometric range

The van der Waals atom-surface attraction, scaling as C3z?3 for z the atom-surface distance, is expected to be valid in the distance range 1?1000?nm, covering 8?10 orders of magnitudes in the interaction energy. A Cs vapour nanocell allows us to analyze the spectroscopic modifications induced by the atom-surface attraction on the 6P3/2 ? 6D5/2 transition. The measured C3 value is found to be independent of the thickness in the explored range 40?130?nm, and is in agreement with an elementary theoretical prediction. We also discuss the specific interest of exploring short distances and large interaction energy.

Saturation effects in the sub-Doppler spectroscopy of cesium vapor confined in an extremely thin cell

Saturation effects affecting absorption and fluorescence spectra of an atomic vapor confined in an extremely thin cell (cell thickness L<1 {mu}m) are investigated experimentally and theoretically. The study is performed on the D{sub 2} line ({lambda}=852 nm) of Cs and concentrates on the two situations L={lambda}/2 and L={lambda}, the most contrasted ones with respect to the length dependence of the coherent Dicke narrowing. For L={lambda}/2, the Dicke-narrowed absorption profile simply broadens and saturates in amplitude when increasing the light intensity, while for L={lambda}, sub-Doppler dips of reduced absorption at the line-center appear on the broad absorption profile. For a fluorescence detection at L={lambda}, saturation induces narrow dips, but only for hyperfine components undergoing a population loss through optical pumping. These experimental results are interpreted with the help of the various existing models and are compared with numerical calculations based upon a two-level modeling that considers both a closed and an open system.

Hyperfine Paschen–Back regime realized in Rb nanocell

A simple and efficient scheme based on a one-dimensional nanometric-thin cell filled with Rb and strong permanent ring magnets allows direct observation of the hyperfine Paschen-Back regime on the D(1) line in the 0.5-0.7 T magnetic field. Experimental results are perfectly consistent with the theory. In particular, with σ(+) laser excitation, the slopes of the B-field dependence of frequency shifts for all 10 individual transitions of (85,87)Rb are the same and equal to 18.6 MHz/mT. Possible applications for magnetometry with submicron spatial resolution and tunable atomic frequency references are discussed.

Maximal refraction and superluminal propagation in a gaseous nanolayer.

We present an experimental measurement of the refractive index of high density Rb vapor in a gaseous atomic nanolayer. We use heterodyne interferometry to measure the relative phase shift between two copropagating laser beams as a function of the laser detuning and infer a peak index n=1.26±0.02, close to the theoretical maximum of 1.31. The large index has a concomitant large index gradient creating a region with steep anomalous dispersion where a subnanosecond optical pulse is advanced by >100 ps over a propagation distance of 390 nm, corresponding to a group index n(g)=-(1.0±0.1)×10(5), the largest negative group index measured to date.

Investigation of atomic transitions of cesium in strong magnetic fields by an optical half-wavelength cell

It has been demonstrated that the use of the λ/2 method allows one to effectively investigate individual atomic levels of the D2 line of Cs (with the most complicated spectrum among all alkali metals) in strong magnetic fields up to 7 kG. The method is based on strong narrowing of the absorption spectrum (which provides sub-Doppler resolution) of a cesium-filled thin cell with the thickness L equal to a half-wavelength (L = λ/2) of the laser radiation (λ = 852 nm) resonant with the D2 line. In particular, the λ/2 method has allowed us to resolve 16 atomic transitions (in two groups of eight atomic transitions each) and to determine their frequency positions, fixed (within each group) frequency slopes, the probability characteristics of the transitions, and other important characteristics of the hyperfine structure of Cs in the Paschen-Back regime. Possible applications are mentioned. Two theoretical models have been implemented. The values of the magnetic field have been indicated at which the models describe the experiment well.

Saturated absorption spectroscopy: Elimination of crossover resonances with the use of a nanocell

It is demonstrated that the velocity-selective optical pumping/saturation resonances of the reduced absorption in a Rb vapor nanocell with thickness L = λ, 2λ, and 3λ (resonant wavelength λ = 780 nm) allow for the complete elimination of crossover (CO) resonances. We observe well-pronounced resonances corresponding to the Fg = 3 → Fe = 2, 3, and 4 hyperfine transitions of the 85Rb D2 line with line widths close to the natural width. A small CO resonance located midway between Fg = 3 → Fe = 3 and Fg = 3 → Fe = 4 transitions appears only for L ≥ 4λ. The D2 line (λ = 852 nm) in a Cs nanocell exhibits a similar behavior. From the amplitude ratio of the CO and VSOP resonances, it is possible to determine the thickness of the column of alkali vapor in the range of 1–1000 μm. The absence of the CO resonances for nanocells with L ∼ λ is attractive for the frequency reference application and for studying the transitions between the Zeeman sublevels in external magnetic fields.

Three-photon electromagnetically induced transparency using Rydberg states

We demonstrate electromagnetically induced transparency in a four-level cascade system where the upper level is a Rydberg state. The observed spectral features are sub-Doppler and can be enhanced due to the compensation of Doppler shifts with AC Stark shifts. A theoretical description of the system is developed that agrees well with the experimental results, and an expression for the optimum parameters is derived.

Complete hyperfine Paschen-Back regime at relatively small magnetic fields realized in potassium nano-cell

A one-dimensional nano-metric-thin cell (NC) filled with potassium metal has been built and used to study optical atomic transitions in external magnetic fields. These studies benefit from the remarkable features of the NC allowing one to use

Sub-Doppler spectroscopy of cesium vapor layers with nanometric and micrometric thickness

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