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A low-power, monochromatic, tunable diode laser is used to selectively populate the cesium 62P3/2 (Fe = 2, 3, 4, 5) hyperfine-structure levels in a pure optically thick vapour in the presence of a dissipative surface. The integrated retrofluorescence intensities for the 852 nm (62P3/2 → 62S1/2), 894 nm (62P1/2 → 62S1/2)> and 455 nm (72P3/2 → 62S1/2) lines have been measured and analyzed. When the laser frequency is scanned through the [62S1/2(Fg) → 62P3/2(Fe)] hyperfine resonance line, the sensitized retrofluorescence spectral signal corresponding to the 894 nm line has a profile significantly different from the retrofluorescence signal at the 852 nm line, but rather similar to the profiles of the lines associated with the energy-pooling collisions. The population of the 62P1/2 atomic level in an optically thick vapour cannot be explained only by the fine-structure excitation transfer process [Cs (62P3/2) + Cs (62S1/2) ↔ Cs (62P1/2) + Cs (62S1/2)] usually accepted in an optically thin vapour. We have investigated inelastic collisions in the populating mechanisms of 62P1/2 level starting from the 62P3/2 level exited by the monochromatic laser taking into account the presence of an electrically conductive surface. It appears from our experimental and theoretical investigations that, the spectral properties of the laser-induced Cs 894 nm sensitized retrofluorescence in a pure optically thick vapour near a dissipative surface cannot be explained by both the conventional mechanism and cascade collisions. The satisfactory interpretation of the experimental results is an open problem of atomic spectroscopy.PACS Nos.: 32.30, 32.50, 32.70, 32.80, 34.10, 34.50, 42.62

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We have investigated the properties of Hg 0.8 Zn 0.2 Te surfaces after passivation with various treatments, either by electrochemical processes or by immersion in chemical baths. From the C (V ) characteristics of metal-insulator-semiconductor structures, we have determined the density of fixed interface charges deduced from the flat-band voltage. The density of slow traps is obtained from the width of the anticlockwise hysteresis and the energy distribution of fast interface states is reported for all passivation processes. The treatment by immersion in bromine-methanol solution including a small amount of Na 2 S gives the best interface properties. The energy distribution of fast interface states then presents a broad U-shape with a minimum lower than 5 × 10 10 eV −1 cm −2 . The surface roughness as measured by atomic force microscopy is notably reduced after this treatment and the x-ray photoelectron spectroscopy of the samples so obtained reveals the presence of a residual Te layer on the surface.

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