V. A. Sautenkov

Efficient excitation of Rydberg states in ultracold lithium-7 atoms

This work is aimed at preparing highly excited optically cooled lithium-7 atoms for producing a strongly nonideal plasma and Rydberg matter. A setup implementing a novel nondestructive technique for preparation and diagnostics of highly excited Rydberg atomic states is constructed. The operation of this setup is based on the usage of a cw high-power ultraviolet laser combined with a magneto-optical trap. The diagnostics of highly excited states is performed by the direct recording of the variations in the fluorescence of ultracold lithium-7 atoms in the magneto-optical trap.

Laser cooling of 7Li atoms in a magneto-optical trap

A setup for laser cooling and confining of 7Li atoms in a magneto-optical trap has been built. The possibility of cooling and trapping of 7Li atoms in a wide range of frequency detuning of the cooling laser has been proved experimentally. Independent information on the density and number of ultracold 7Li atoms on various ground-state sublevels, as well as on the temperature of the atoms, has been obtained with the use of a probing tunable laser. This information is important for preparing an ultracold plasma and Rydberg matter.

Laser diagnostics of the energy spectrum of Rydberg states of the lithium-7 atom

The spectra of excited lithium-7 atoms prepared in a magneto-optical trap are studied using a UV laser. The laser diagnostics of the energy of Rydberg atoms is developed based on measurements of the change in resonance fluorescence intensity of ultracold atoms as the exciting UV radiation frequency passes through the Rydberg transition frequency. The energies of various nS configurations are obtained in a broad range of the principal quantum number n from 38 to 165. The values of the quantum defect and ionization energy obtained in experiments and predicted theoretically are discussed.

Preparation of a high concentration of lithium-7 atoms in a magneto-optical trap

This study is aimed at obtaining high concentration of optically cooled lithium-7 atoms for preparing strongly interacting ultracold plasma and Rydberg matter. A special setup has been constructed, in which two high-power semiconductor lasers are used to cool lithium-7 atoms in a magneto-optical trap. At an optimum detuning of the cooling laser frequency and a magnetic field gradient of 35 G/cm, the concentration of ultracold lithium-7 atoms reaches about 1011 cm−3. Additional independent information about the concentration and number of ultracold lithium-7 atoms on different sublevels of the ground state was obtained by using of an additional probing laser.

Forbidden 2P–nP and 2P–nF transitions in the energy spectrum of ultracold Rydberg lithium-7 atoms

Forbidden 2P–nP and 2P–nF transitions in the ranges of the principal quantum number n = 42–114 and n = 38–48 have been detected in the optical spectra of ultracold highly excited lithium-7 atoms. The presence of forbidden transitions is due to induced external electric fields. The quantum defects and ionization energy obtained in various experiments and predicted theoretically have been discussed.

Coherent and non-coherent components of two-photon Rydberg excitation of ultracold Li7 atoms

A study of the optical spectra of ultracold highly excited Li7 atoms has revealed coherent and non-coherent components of two-photon excitation. The high sensitivity of the method makes it possible to record pure coherent resonances at a detuning of 803.5 MHz from the intermediate 2P3/2 resonance.

Quantum defects in Rydberg nD states of optically cooled 7Li atoms

To observe Rydberg transitions we applied a spectroscopic technique based on the observation of the resonance fluorescence of cold atoms in a magneto-optical trap. By using this approach, we estimated the quantum defect in Rydberg nD states of 7Li atoms. The obtained results are in a good agreement with previously published data.

Two-photon Rydberg resonances in lithium-7 obtained by recording reduction of resonance fluorescence

In a magneto-optical trap (MOT) of 7Li, two-photon Rydberg resonances are recorded by using a spectroscopic technique, which based on variation in the resonance fluorescence. The first excitation frequency is detuned by 0.59 GHz from the intermediate 2P3/2 state. Two counter-propagating laser beams are used. The resonances are studied on two-photon transitions 2S1/2 − nl in a range of principal quantum number n from 38 to 120. The widths of the observed resonances are varied from 4.4 to 13 MHz for different MOT parameters.

Preparation of Rydberg states in ultracold Li-7 atoms by using coherent or non-coherent optical excitation

Energy spectra of ultracold Rydberg lithium atoms are discussed. Our technique has been used for the experimental observation of coherent and non-coherent components of two-step excitation in Rydberg states. The high sensitivity of the technique has allowed us to record narrow coherent resonance at 2P-41D. The width of this resonance is 3 times less than width of non-coherent resonance. The coherent resonance is observed when the laser is detuned by ±803.5 MHz from the atomic transition 2P 3/2.