A. Débarre

Highly excited levels of neutral ytterbium. I. Two-photon and two-step spectroscopy of even spectra

Highly excited even levels of ytterbium have been investigated using both a two-photon absorption, and a two-step process from the 6S2 1S0 ground state. Resonances are detected by the thermoionic-diode method. Most of the observations are between the J=O and J=2 even levels: the series 6sns1S0, and 6snd1D2 and 6snd 3D2 have been observed from n=10 to n=65, n=8 to n=80 and n=10 to n=61 respectively. Several levels of the 4f135d6s6p and 6p2 configurations have been identified. In the autoionising region lines showing a Fano profile have been observed and analysed. The authors observed many lines corresponding to absorption from the excited levels 6s6p 1P1 degrees , 5d6s3D2 and 5d6s3D3. Some J=2, 3 and 4 odd levels have been observed with this method.

Optical information storage in condensed matter with stochastic excitation

We have performed a temporal structure analysis of subpicosecond signals retrieved in the time domain from a spectral modulation engraved in a photochemical hole-burning material. Two situations are examined experimentally. The first one corresponds to a spectrally programmed stimulated-photon-echo configuration, and the second one corresponds to simple optical data storage. The results are obtained in a sample of octaethylporphine molecules embedded in a polystyrene matrix. Broadband stochastic excitations are used both to write the modulation inside the inhomogeneous width of the ground level of the zero-phonon line and then to read the spectral information. An original field cross-correlation technique is used to sample the retrieved signals.

High-resolution study of light-induced collisional energy transfer in Na-Ca mixture

The experimental study of a laser-induced energy transfer for a dipole-dipole collisional interaction in a Na-Ca mixture is reported. A specific excitation scheme is used in this experiment for which the virtual level is optically excited. A comparison with the case of a dipole-dipole interaction in the Eu-Sr mixture where the virtual level is excited by collisional energy transfer is presented.

Observation of laser-induced collisional two-photon ionisation in a strontium-caesium mixture

Laser-induced collisional ionisation of caesium is observed in a strontium-caesium vapour mixture. In their initial state both atomic species are in the ground level. The ionisation of caesium is achieved when the system is illuminated by an intense laser light, the frequency of which is tuned across the resonance line of strontium. The process involves photoabsorption during the collisional interaction. It is monitored by the observation of optical fluorescence after Cs+, e- recombination. The laser-induced collisional ionisation profile, i.e. the variation of the ionisation yield against the laser wavelength is recorded under various experimental conditions.

Field cross-correlation retrieval of optically stored data

A new method is studied for reading data that have been optically stored within the inhomogeneous spectral width of a material. The memory element is illuminated by a broad-bandwidth laser pulse. The signal that results from this excitation is analyzed by cross correlation with the field of a reference pulse, which is nothing but a delayed replica of the read pulse. Theoretical and experimental aspects of this process are discussed.

Highly excited levels of neutral ytterbium. II. Multichannel quantum defect analysis of odd- and even-parity spectra

For pt.I see ibid., vol.13, no.6, p.1073 (1980). Data on the bound even-parity spectrum of Yb have been presented in the preceding paper (Carnus et al., 1980). These data provide an excellent opportunity for the application of multichannel quantum defect theory (MQDT) to this spectrum. The bound even-parity J=0, 2 spectra and the bound odd-parity J=1 spectrum are analysed with MQDT models. The behaviour of the even-parity 4f146sns 1S0 (n>or=7) and 4f146snd 1.3D2 (n>or=8) Rydberg series perturbed by levels of the 4f146p2 and 4f135d6s6p configurations is well interpreted; in the same way the known bound levels of the 4f146snp 1.3P1 Rydberg series (n>or=12) perturbed by levels of the 4f135d26s configuration are well interpreted. The mutual interaction of the singlet and triplet levels of J=1 and J=2 Rydberg series is analysed. Some assignments of levels are changed and predicted energy values are given for many levels.

Storage of a spectrally shaped hologram in a frequency selective material

A spectral holography experiment is performed in a hole-burning material. A shaping device is used to tailor the spectrum of the pulses which engrave the hologram. The resolution of the spectral shaping technique is investigated both theoretically and experimentally.

Experimental evidence of coherences produced by a radiative collision process

Recently, a theoretical calculation has been presented assuming that coherences can be produced in a radiatively assisted inelastic collision. The author reports the observation of final-state coherences in the simple case of dipole-dipole interaction in a strontium-europium mixture illuminated by a pi -polarised laser field. The author has measured the polarisation ratio P of the fluorescence emitted from the final degenerate Zeeman states of strontium. The result P=0.43+or-0.05 is in good agreement with theoretical predictions P=0.45.

Two-photon absorption spectroscopy in ytterbium

Highly excited levels of ytterbium have been investigated using two-photon absorption spectroscopy and space-charge detection. The authors tuned the 0.2 cm-1 dye laser radiation over the range 3900-4100 AA and observed the even-parity states J=0 and J=2 belonging to the series 4f146s ns 1S0, 4f146s nd 1D2, 4f146s nd 3D2 from n=13-62, from n=11-64 and from n=11-21, respectively. Many strong perturbations appear due to configurations with a 4f13 core.

Observation of 0π-pulse formation with incoherent light

Observation of 0π-pulse formation with incoherent light through field cross-correlation is theoretically and experimentally demonstrated. The experiment illuminates some of the properties of this new incoherent light technique, which is used to analyze the fast temporal variations of the signal. In particular, the technique’s time resolution, signal-to-noise ratio, and sensivity to dispersion are investigated.