L. Moi

An experimental method for the observation of r.f. transitions and laser beat resonances in oriented Na vapour

SummaryA method which allows a direct picture of phenomena involving line broadening, light shifts and many-photon transitions in the ground state of sodium atoms pumped by dye-laser is reported. A new phenomenon due to light beats between the different dye-laser axial modes has been easily evidenced by the method.RiassuntoSi presenta un nuovo metodo che permette l’esame diretto di transizioni a più fotoni, di allargamento di righe e di spostamento di risonanze prodotto da intensa radiazione laser in vapori di sodio orientati otticamente. Con questo metodo si è messo in evidenza un fenomeno dovuto a battimenti tra modi di un laser a coloranti usato per il pompaggio ottico.РезюмеПредлагается новый метод, который позволяет непосредственно исследовать многофотонные переходы, уширение линий и смещение резонанса, образованного интенсивным излучением лазера в оптически ориентированных парах натрия. С помощью этого метода подтверждается явление биений мод лазера в красителях, используемых для оптической накачки.

Electronic energy transfer induced by collision between two excited sodium atoms

Abstract We have observed the sodium doublets arising from the 3 2 D, 5 2 S, 4 2 D, 6 2 S, 5 2 D→3 2 P and 4 2 P→3 2 S transitions, whenever sodium vapour is illuminated with a cw dye laser tuned to the wavelength of one of the D-lines. The phenomenon is interpreted as an excitation transfer induced by collision between two excited atoms.

Molecule formation and energy transfer processes in a vapor with high density of 3P-excited sodium atoms

Abstract A rich fluorescence spectrum extending between 4000 and 8200 A has been observed whenever sodium vapor is excited by dye laser light tuned to the 3 2 S → 3 2 P transition. Molecule formation due to collisions between excited and unexcited atoms is manifested by the presence of an emission band of sodium in the spectral range 4160–4570 A.

Nonabsorption hyperfine resonances in a sodium vapour irradiated by a multimode dye-laser

SummaryThe fluorescence intensity of a sodium vapour excited by a multimode dye-laser is observed as a function of the applied magnetic field: a resonant decrease of the fluorescence occurs when the frequency difference between two laser modes coincides with the frequency of an hyperfine transition of the ground state. An experimental proof is reported which evidences the coherent nature of the phenomenon.RiassuntoLa fluorescenza di un vapore di sodio, eccitato con un laser multimodo, è osservata in funzione del campo magnetico applicato: si ha una diminuizione risonante della fluorescenza quando la differenza in frequenza fra due modi del laser coincide con la frequenza di una transizione iperfina dello stato fondamentale. È riportata una prova sperimentale che evidenzia la natura coerente del fenomeno.РезюмеИсследуется интенсивность флуоресценции паров натрия, возбужденных многомодовым лазером на красителях, как функция приложенного магнитного поля. Имеет место резонансное убывание флуоресценции, когда разность частот между двумя модами лазера соввадает с частотой сверхтонкого перехода для основного состояния. Приводится экспериментальное доказательство, которое подтверждает когерентную природу этого явления.

Light Induced Atom Desorption

In the present paper we report experimental evidence of a new effect, observed for the first time by Gozzini et al. on sodium vapour, in which an important rubidium vapour density increase (larger than one order of magnitude) is observed when silane-coated cells are shined by non-resonant and weak light. The effect is due to non-thermal light-induced atom desorption. A preliminary analysis of its dependence on the light power density and on the wavelength has been carried out.

Cesium coherent population trapping magnetometer for cardiosignal detection in an unshielded environment

We present encouraging results obtained with an experimental apparatus based on coherent population trapping and aimed at detecting a biological (cardiac) magnetic field in a magnetically compensated but unshielded volume. The work includes magnetic-field and magnetic-field-gradient compensation and uses differential detection to cancel common mode magnetic noise. Synchronous data acquisition with a reference (electrocardiographic or pulse-oximetric) signal makes possible improvement of the signal-to-noise ratio in off-line averaging. The setup has the significant advantages of working at room temperature with a small-size head, and the possibility of fast adjustments of the dc bias magnetic field, which makes the sensor suitable for detecting a biomagnetic signal at any orientation with respect to the axis of the head and in any position on the patients chest, which is not the case with other kinds of magnetometers.

New laser-excited bands in Na2

Abstract We report new emission bands of molecular sodium in the visible and in the infrared regions. The diffuse bands already observed in the violet are also reconsidered.

All optical sensor for automated magnetometry based on coherent population trapping

An automated magnetometer suitable for long lasting measurement under stable and controllable experimental conditions has been implemented. The device is based on Coherent Population Trapping (CPT) produced by a multi-frequency excitation. CPT resonance is observed when a frequency comb, generated by diode laser current modulation, excites Cs atoms confined in a π/4× (2.5) × 1 cm, 2 Torr N2 buffered cell. A fully optical sensor is connected through an optical fiber to the laser head allowing for truly remote sensing and minimization of the field perturbation. A detailed analysis of the CPT resonance parameters as a function of the optical detuning has been made in order to get high sensitivity measurements. The magnetic field monitoring performances and the best sensitivity obtained in a balanced differential configuration of the sensor are presented. OCIS 120.4640, 020.1670, 300.6380. This work has been submitted to JOSA B for publication [Josa B (7) 2007]An automated magnetometer suitable for long lasting measurement under stable and controllable experimental conditions has been implemented. The device is based on coherent population trapping (CPT) produced by a multifrequency excitation. CPT resonance is observed when a frequency comb, generated by diode laser current modulation, excites Cs atoms confined in a π/4×(2.5)2×1 cm3, 2 TorrN2 buffered cell. A fully optical sensor is connected through an optical fiber to the laser head allowing for truly remote sensing and minimization of the field perturbation. A detailed analysis of the CPT resonance parameters as a function of the optical detuning has been made in order to get high sensitivity measurements. The magnetic field monitoring performances and the best sensitivity obtained in a balanced differential configuration of the sensor are presented.

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.

Diode laser spectroscopy of methane overtone transitions

With the aid of commercial room-temperature AlGaAs diode lasers, frequency modulation absorption spectroscopy was performed on the 7900 A and 8600 A rovibrational combination overtone bands of methane. Three weak transitions are reported in the range around 8610 A that, to our knowledge, have not yet been observed and measured. Self-broadening and pressure-broadening coefficients of one ofthese new absorption features (at 8608.93 A) were derived from CH(4) and for CH(4) immersed in N(2) and He buffer gases. An evaluation of the methane detection sensitivity is given for favorable laboratory conditions as well as for an open-path situation.