Positive and negative subnatural-width resonances ͑SNWR͒ were observed in the absorption and fluorescence of rubidium vapor under excitation by two copropagating optical waves with variable frequency offset. The two optical fields resonantly couple Zeeman sublevels, belonging to the same ground-state hyperfine level ͑GSHL͒, to an intermediate excited state. The SNWR present opposite signs depending on which GSHL participates in the interaction with the two optical waves. For both Rb isotopes an increase in the transparency with reduced fluorescence occurs for the lower GSHL while the absorption and fluorescence are increased for the upper GSHL. The influence of external magnetic field, polarization, and intensity of applied optical fields on the SNWR is examined. The narrowest observed resonance has a width of 10 kHz ͑full width at half maximum͒. The origin of the SNWR is discussed in terms of coherent processes involving ground-state Zeeman sublevels. ͓S1050-2947͑98͒06703-1͔

A large increase in atomic absorption due to coherent interaction with resonant radiation is predicted for a closed transition between two degenerate atomic levels verifying 0ϽF g ϽF e (F g and F e are the total angular momentum of the ground and the excited levels, respectively͒. In good agreement with the theoretical prediction, a total absorption enhancement by a factor 1.7 was obtained on the D 2 line of 85 Rb in a vapor cell experiment. ͓S1050-2947͑99͒04106-2͔

We investigate frequency up-conversion of low power cw resonant radiation in Rb vapour as a function of various experimental parameters. We present evidence that the process of four wave mixing is responsible for unidirectional blue light generation and that the phase matching conditions along a light-induced waveguide determine the direction and divergence of the blue light. Velocity-selective excitation to the 5D level via step-wise and two-photon processes results in a Doppler-free dependence on the frequency detuning of the applied laser fields from the respective dipole-allowed transitions. Possible schemes for ultraviolet generation are discussed.

Steep dispersion of opposite signs in driven degenerate two-level atomic transitions have been predicted and observed on the D2 line of 87 Rb in an optically thin vapor cell. The intensity dependence of the anomalous dispersion has been studied. The maximum observed value of anomalous dispersion (dn/dν ≃ −6× 10 −11 Hz −1 ) corresponds to a negative group velocity Vg ≃ −c/23000. 42.50. Gy, 32.80.Qk, 42.62.Fi, Investigations of coherent effects in resonant media, namely coherent population trapping (CPT) and electromagnetically induced transparency (EIT) [1,2], which can dramatically modify the absorptive and dispersive properties of an atomic vapor, have caused a rebirth of interest in the problem of light propagation through a dispersive medium. In the last decade, the study of the dispersive properties of coherently prepared media was always under attention due to fundamental and practical interest.An ultra-large index of refraction in coherently prepared resonant gas was predicted [3] and a refractive index variation as large as ∆n ≈ 1 × 10 −4 was demonstrated in a dense Rb vapor [4]. It was also shown that a coherently driven medium exhibits large dispersion [5]. A high normal dispersion (up to dn/dν ≃ 1 × 10 −11 Hz −1 ) was measured on the Cs D 2 line in a vapor cell [6] and in an atomic beam [7]. Recently, extremely slow light group velocity (17 m/s) associated with normal dispersion was demonstrated in an ultracold atomic sample [8]. However, the same order of magnitude of group velocity (90 m/s) was observed in a hot dense vapor cell [9].All these investigations were carried on alkaline atoms where the absorption is strongly suppressed and dispersion is steep and normal (D ≡ dn/dν > 0) due to CPT between the two ground state hyperfine levels (Λ scheme). However, atomic coherence among Zeeman sublevels belonging to the same ground-state hyperfine level can led not only to usual EIT, but also to an absorption enhancement named as electromagnetically induced absorption (EIA) [10,11]. Since EIT/EIA effects in degenerate two-level systems can produce a significant variation in the absorption with subnatural width, one can predict a large absolute value of dispersion in this case. Notice that at resonance dispersion would be normal (D > 0) for EIT and anomalous (D < 0) for EIA. In both cases the absolute value of the dispersion can be several orders of magnitude greater than for a linear medium. In this letter we present the first observation of steep anomalous and normal dispersion in coherently prepared degenerate two-level atomic system.Refractive index and dispersion were analyzed with the model recently used to study subnatural EIA resonances [12]. In this model, two monochromatic optical fields, a drive field and a weak probe field with amplitudes E d , E p and frequencies ω d , ω p respectively are incident on motionless two-level atoms with resonance frequency ω 0 and electric dipole moment µ. The atomic levels are degenerate. The configuration is closed. The spontaneous decay rate is Γ. Finite interact...

We report on the loading and trapping of ultracold atoms in a one dimensional permanent magnetic lattice of period 10 µm produced on an atom chip. The grooved structure which generates the magnetic lattice potential is fabricated on a silicon substrate and coated with a perpendicularly magnetized multilayered TbGdFeCo/Cr film of effective thickness 960 nm. Ultracold atoms are evaporatively cooled in a Z-wire magnetic trap and then adiabatically transferred to the magnetic lattice potential by applying an appropriate bias field. Under our experimental conditions trap frequencies of up to 90 kHz in the magnetic lattice are measured and the atoms are trapped at a distance of less than 5 µm from the surface with a measured lifetime of about 450 ms. These results are important in the context of studies of quantum coherence of neutral atoms in periodic magnetic potentials on an atom chip.