New experimental results and new phenomena related to the study of the retrofluorescence spectrum induced by a diode laser at the interface between glass and cesium vapor are presented. The Cs 62P3/2(Fe) hyperfine states are populated with a low-intensity tunable diode laser with a 10-MHz spectral bandwidth. We report an integrated atomic retrofluorescence spectrum in the 852.2-nm (62P3/2–62S1/2) resonance line and 917.2-nm (62D5/2–62P3/2) line generated by energy-pooling collisions. Emission spectra of the molecular fluorescence signal have been observed. At the resonance line a large proportion of the atoms excited by the laser are located in the vicinity of the surface. The interactions between the excited atomic 62P3/2 state and the surface appear as a spectral inhibition of the integrated retrofluorescence spectrum for both the atomic line and the molecular band. This spectral inhibition indicates that the nonradiative transformation process of changing atomically excited energy into thermal energy is preferred. We report the analysis of the dominant processes in the vicinity of the 852.2-nm resonance line, which can influence the retrofluorescence hyperfine spectrum at the boundary between the glass window and the saturated cesium vapor. Only the nonradiative transfer by evanescent waves toward the dissipative surface is retained. Using this mechanism, we formulate, for the first time to our knowledge, a simple model of a backscattered hyperfine fluorescence signal. The glass–vapor interface is considered as two distinct regions: a wavelength-thickness vapor layer joined to the surface and a more remote vapor region. The first region is analyzed as a spectral filter that annihilates the absorbed photons and the second one as a rich spectral light source. The experimental setup is described, and measured integrated retrofluorescence spectra are compared with predictions made by the model. The consistency between theory and experiment is remarkably good considering that the model depends only on two unknown parameters: the nonradiative transfer rate and the absorption shape line of the filtering region.
New experimental results and new phenomena related to the study of the retrofluorescence spectrum induced by a diode laser at the interface between glass and cesium vapor are presented. The Cs 62P3/2(Fe) hyperfine states are populated with a low-intensity tunable diode laser with a 10-MHz spectral bandwidth. We report an integrated atomic retrofluorescence spectrum in the 852.2-nm (62P3/2–62S1/2) resonance line and 917.2-nm (62D5/2–62P3/2) line generated by energy-pooling collisions. Emission spectra of the molecular fluorescence signal have been observed. At the resonance line a large proportion of the atoms excited by the laser are located in the vicinity of the surface. The interactions between the excited atomic 62P3/2 state and the surface appear as a spectral inhibition of the integrated retrofluorescence spectrum for both the atomic line and the molecular band. This spectral inhibition indicates that the nonradiative transformation process of changing atomically excited energy into thermal energy is preferred. We report the analysis of the dominant processes in the vicinity of the 852.2-nm resonance line, which can influence the retrofluorescence hyperfine spectrum at the boundary between the glass window and the saturated cesium vapor. Only the nonradiative transfer by evanescent waves toward the dissipative surface is retained. Using this mechanism, we formulate, for the first time to our knowledge, a simple model of a backscattered hyperfine fluorescence signal. The glass–vapor interface is considered as two distinct regions: a wavelength-thickness vapor layer joined to the surface and a more remote vapor region. The first region is analyzed as a spectral filter that annihilates the absorbed photons and the second one as a rich spectral light source. The experimental setup is described, and measured integrated retrofluorescence spectra are compared with predictions made by the model. The consistency between theory and experiment is remarkably good considering that the model depends only on two unknown parameters: the nonradiative transfer rate and the absorption shape line of the filtering region.
We characterize, for the first time to our knowledge, the laser-induced backward fluorescence (retrofluorescence) spectra that result from energy-pooling collisions between Cs atoms near a dissipative thin Cs layer on a glass substrate. We resolve, experimentally and theoretically, the laser spectroscopic problem of energy-pooling processes related to the nature of the glass–metallic vapor interface. Our study focused on the integrated laser-induced retrofluorescence spectra for the 455.5-nm (72P3/2–62S1/2) and 852.2-nm (62P3/2–62S1/2) lines as a function of laser scanning through pumping resonance at the 852.2-nm line. We experimentally investigate the retrofluorescence from 420 to 930 nm, induced by a diode laser tuned either in the wings or in the center of the pumping resonance line. We present a detailed theoretical model of the retrofluorescence signal based on the radiative transfer equation, taking into account the evanescent wave of the excited atomic dipole strongly coupled with a dissipative surface. Based on theoretical and experimental results, we evaluate the effective nonradiative transfer rate A¯62P3/2→62S1/2sf for atoms in the excited 62P3/2 level located in the near-field region of the surface of the cell. Values extracted from the energy-pooling process analysis are equivalent to those found directly from the 852.2-nm resonance retrofluorescence line. We show that the effective energy-pooling coefficients k˜72P3/2 and k˜72P1/2 are approximately equal. The agreement between theory and experiment is remarkably good, considering the simplicity of the model.
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
A fluorescence radiation inhibition has been observed by absorption of a laser beam at a resonance of 852 nm at the interface of a Pyrex cell containing optically thick Cesium vapor. One observes a hole of GHz magnitude at the center of the retro-fluorescence signal associated with the lines of hyperfine structure 62P312-625112 (F =4,3). This phenomenon of inhibition, similar to a self-reversal of spectral lines, is found in the radiation generated by pooling effect. It occurs without a significant change in the absorption rate of laser energy. This is attributed to a coupling between atoms excited to 62P312 by laser pumping and a deposit of Cesium of atomic dimensions on the glass. At resonance, an important proportion of the atoms excited by the laser is in the vicinity of a thin conducting film. The non-radiating transformation process of the atomically excited energy to thermal energy is therefore favored. The interface lit by a monochromatic laser diode acts as a stop band filter and as a secondary luminous source. The width of the filter at half-height is proportional to the density of the atomic vapor. Sub-Doppler effects in inhibition spectral band have been observed. We present new experimental results and a phenomenon-related study of fluorescence inhibition induced by interfaced laser.
A low-power tunable laser was used to populate the Rb(5P(3/2)) hyperfine-structure levels in a pure optically thick vapour in the presence of a dissipative surface. The retrofluorescence intensities and spectrum profile for the 780 nm (5P(3/2)--> 5S(1/2)) and 795 nm (5P(1/2)-->5S(1/2)) lines were measured and analyzed. The glass-vapor interface was considered as two distinct regions, a wavelength-thickness vapor layer adjacent to the surface and a more remote vapor region The first region was analyzed as a spectral filter that annihilated the absorbed photons and the second one as a rich spectral light source. The authors discussed two possible mechanisms for the 5P(1/2) population in the cell [i.e., mechanism(1): collisions Rb(5P(3/2))+Rb(5S(1/2))-->Rb(5P(1/2))+Rb(5S(1/2)); mechanism(2): collisions Rb(5D)+Rb(5S)-->Rb(5P)+Rb(5P)]. For each one of the possible mechanisms considered, the authors gave the theoretical formulation of the retrofluorescence integrated signal associated with 795 nm(5P(1/2)-->5S(1/2)), which was compared with experiment. Two important characteristic aspects of retrofluorescence spectra must be taken into account when dealing with retrofluorescence signals for atomic process investigation: the retrofluorescence intensity dependence on laser power and sensitized laser retrofluorescence line shapes. When the laser frequency is scanned through the hyperfine resonance line, the sensitized retrofluorescence spectra signal corresponding to the 795 nm line has a profile similar to the profile of the retrofluorescence signal at the 780 nm. The authors have pointed out that mechanism(1) gives the linear dependence of the trtrofluorescence as a function of laser power and the spectrum profile. The population of the 5P(1/2) atomic level in an optically thick vapour can be principally explained by the fine-structure excitation transfer process [mechanism(1)]. It appears from our experimental and theoretical investigations that, the spectral properties of the laser-induced Rb 795 nm sensitized retrofluorescence in a pure optically thick vapour near a dissipative surface cannot be explained by the mechanism(2).
Sub-Doppler signals of the hyperfine Cs[62P3/2(Fe)-->62S1/2(Fg)] transition lines in a diode laser-induced retro-fluorescence spectrum at the interface between glass and Cs vapor are, for the first time to our knowledge, experimentally identified and phenomenologically investigated. We propose a qualitative explanation of the origin of the sub-Doppler hyperfine line, based on kinematic effects of the population of the excited 62P3/2(Fe) atoms of the laser-pumped velocity classes confined in the near-field region of the interface. The role played by different relaxation processes contributing to the retrofluorescent atomic linewidth has been characterized. The effective decay rate of the atomic hyperfine level 62P3/2(Fe=5) near a metallic thin film has been measured by using both sub-Doppler retrofluorescence and frequency-modulated selective reflection spectroscopies. For a saturated Cs vapor in a glass cell at a temperature of 130°C, the effective nonradiative relaxation rate of the 62P3/2(F_e=5) energy hyperfine level due to the coupling with a metallic film is estimated to be AFe=5-->Fg=4nf approximately 3.10^8 s^−1.
The signals of the hyperfine 85Rb[5P3/2(F' = 2,3,4) --> 5S1/2(F = 3)] transition lines in a diode laser induced retrofluorescence spectrum at the interface between glass and Rb vapor were experimentally identified and investigated. The glass-vapor interface was considered as two distinct regions, a wavelength-thickness vapor layer joined to the surface and a more remote vapor region. The first region was analyzed as a spectral filter that annihilates the absorbed photons and the second one as a rich spectral light source. The experimental setup is described. A Rb reference cell (T = 293 K) was used. A part of the laser beam scanned the 5S1/2(F = 3) --> 5P3/2(F' = 2,3,4) transition. The Doppler broadened absorption profile (FWHM = 510 MHz) was determined. The laser detuning of the profile-center relative to the F = 3 --> F' = 4 transition was about 70 MHz. Another laser beam was directed to the entrance cell window. The resonant retrofluorescence S(ob)(upsilon(L)) as a function of laser detuning for a cell temperature approximately 130 degrees C and laser power 0.4 mW was obtained. We can extract the experimental signal sexp(n) (upsilon(L)) originating from the near-field region by subtracting signal S(T) (upsilon(L)) originating from the far-field region from the total experiment signal S(ob)(upsilon(L)). A fit of the normalized profile of the data corresponding to the spectral band centered on the F' = 4 --> F = 3 hyperfine transition line was obtained by using a Lorentzian distribution function with GammaRF = 50 MHz full width at half-maximum. The role played by different relaxation processes contributing to the retrofluorescent atomic linewidth was characterized. The authors summed up the corresponding spectral broadening and obtained the relation GammaRF = Gamman + Gammacoll + Gammanr, where Gammacoll is the resonance collisional broadening of the hyperfine line, and Gammanr is an additional broadening induced by the nonradiative energy-transfer phenomena of the excited atoms near the cell window surface. To evaluate Gammacoll, we used the relation Gammacoll = gammaRb - RbN, where gammaRb - Rb is line broadening parameter, and N is Rb atom number density. The effective nonradiative relaxation rate of the 5P3/2(F' = 4) energy hyperfine level was estimated to be AF(nr) = 4 --> F = 3 = 2.4 x 10(8) s(-1). The value of A(nr) seems relatively large compared to the spontaneous emission rate A(5P3/2 --> 5P1/2) = 1.4 x 10(7) s(-1).