S. Gozzini

Molecule formation in an optically oriented vapor

In this work an experimental observation is reported of the predicted shift in chemical equilibrium between an atom and its dimer in the gas phase upon optical orientation of the atoms. The previously derived relationship between the equilibrium constant and the degree of atomic orientation is also verified.

White-light-induced drift on sodium vapour

We report the first experimental evidence of the white-light-induced-drift effect in one-component active gas. It can be observed in optically thick multilevel systems when an initially flat excitation spectrum is asymmetrically modified by both absorption and optical pumping. The effect has been detected in sodium vapour excited by a laser with a very large bandwidth and a particular cavity configuration (lamp laser).

Magnetic coherence resonance profiles in Na and K

Magnetic coherence resonance profiles, obtained at magetic field B = O in Hanle configuration were examined for Na and K atoms in different cells: evacuated glass cells and buffered, coated and uncoated. At low laser power for all cells the shape of the resonancees is Lorentzian. At power higher than about 100 mW/cm2, some narrowing around the resonance peak is observed for the Na buffered cell, while for the vacuum one the resonance shape is even more complex. Theoretical explanation is proposed for the complex resonance shape evidenced in the vacuum cells. Large resonance contrast in the K absorption at B = 0 is observed, attributed to the low rate of hyperfine optical pumping in K. The detailed investigation of the resonance profiles and contrast is of very high importance for their application.

Lossless formation of electromagnetically induced transparency in sodium atoms

In this paper we propose a simple method for eliminating the population losses of MC resonances by involving all atoms of the Na ground state in the formation of the narrow coherent resonances observed in the fluorescence when scanning around zero value the applied magnetic field. As a result, dark resonances with a contrast up to 100% have been observed. Results are obtained in two different experimental configurations: using laser excitation of linear and circular polarization, leading to different population redistribution among Zeeman and hf levels. Theoretical analysis of the results is also presented. It is shown that at certain conditions complete optical pumping of atoms to levels Fg=2, mFg=2 or mFg=-2 can be achieved, which means complete orientation of the atoms.

Diode laser overtone spectroscopy: a possible atmospheric monitoring technique

By the use of commercial A1GaAs diode lasers and short radiation path-length, frequency modulation (FM) absorption spectroscopy has been performed in the near infrared to study the overtone absorption bands of molecules interesting as environmental sensing tracers. Our measurements concern water vapor resonances around 820 nm, methane around 780 nm and 860 nm, and ammonia around 790 nm. Pressure broadening coefficients have been extracted by using different buffer gases like air, N2 , He, and by varying their pressure between 10 and 760 Torr. A x2 fitting of the absorption line shapes has been used for this purpose by the aid of a simple fitting function. Finally an estimation of the sensitivity of the technique is made.

Influence of anti-relaxation coating of optical cells on the potassium D1 line saturated absorption

In this work we present new features observed in the Saturated Absorption (SA) spectrum on the D1 line of K. In an uncoated optical glass cell containing pure K atoms, excitation by circularly polarized pump beam produces an enhancement of the amplitude of the crossover resonances due to the hyperfine transitions starting from the ground state Fg = 2. This effect appears to be much more relevant when K atoms are contained in a cell coated with an anti-relaxation film. Here, the crossover resonance in the Fg = 2 set of transition is not observed experimentally with linearly polarized pump light, while in case of circular polarization its amplitude is significantly enlarged. The Light Induced Atomic Desorption (LIAD) effect strongly improves the intensities of the SA resonances observed in coated cell.

Inelastic collisions in laser excited alkali atoms

This paper will briefly outline inelastic collisions between two laser excited alkali atoms. Special emphasis will be on recent progress made in our laboratory for heteronuclear systems.

Temperature dependence of coherent resonances in Na and Cs cells

Temperature dependences of coherent resonances in Na and Cs atoms prepared by two coherent laser frequencies or two polarizations of single frequency laser field are presented. It is shown that the temperature dependence of the amplitude or contrast of the resonances in most cases exhibits a maximum. For both types of coherent resonances, a reason for the contrast reduction at higher temperature is the increased absorption of the laser light along the gas cell due to the optical thickness of the medium. Spin-exchange collisions lead to resonance contrast reduction more effectively in a cell with pure alkali atoms.

Influence of the pumping field polarization on the coherent effects at Zeeman sublevels of hyperfine states in Rb

In this communication we present experimental investigation of coherent effects at Zeeman sublevels of hyperfine levels of Rb in dependence on the polarization of the pumping laser field in order to obtain more complete information about the dark and bright CPT resonances. The coherent effects are examined in Hanle effect configuration, exciting Rb vapor cell with a single-frequency diode laser. By means of phase-sensitive detection (PSD) the amplitude and sign of the CPT resonances are registered in the vicinity of the Rb D1 and D2 lines. It is shown that the sign of the CPT resonances changes when the polarization of the exciting beam changes. Theoretical calculations are performed for the population losses of the given transition in order to clarify the observed experimental results.

Diode laser overtone spectroscopy of atmospheric trace species

This work is based on the use of diode lasers as spectroscopic sources for the observation and study of weak overtone bands of the NIR. The diode laser emission wavelength can be scanned around a gas resonance by sweeping its injection current, permitting a direct observation of an absorption line-shape. The resolution is limited principally by the effective laser linewidth, generally approximately equals 20 MHz in free running mode. The signal-to-noise ratio is increased by using the frequency modulation technique, and the excess laser amplitude 1/f noise is reduced by working at high frequencies. Since detectors operating at high frequencies are expensive and less sensitive, a good compromise is the two-tone frequency modulation technique, which uses two close high frequencies and collects the beat signal at lower frequency. Pressure broadening coefficients have been measured for some acetylene and ammonia absorption lines in the 790 nm bands and new lines have been observed. Pressure shift of two acetylene lines have been examined. It is shown that this spectroscopic apparatus can extract very weak signals from the background and can be a good choice when the space occupied by the spectrometer needs to be restricted into small volumes.