We have developed a theory of resonance radiation imprisonment in collimated atomic beams. Treating the integral master equation describing imprisonment as a generalized wave (Schrödinger) equation and using the geometrical quantization technique for its solution, we obtained analytical representations for the effective radiative lifetime, mean scattering number, and trapping factors. We apply this theory to explain the recent observation of a dramatic velocity redistribution of excited atoms by radiative excitation transfer after the photofragmentation of Na2. In this process, the fast Na(3p) photofragments transfer their excitation energy efficiently via radiation to the abundant Na(3s) atoms from the primary particle beam. The influence of the hyperfine splitting of the ground state of Na atoms on this process is discussed. The ratio of the number of Na(3p) atoms produced by the radiative excitation transfer to the number of Na(3p) photofragments was found to be 0.13 and 0.19 for photodissociation of Na2 molecules in the vibrational levels v″=17 and v″=23, respectively. This is in good agreement with the corresponding experimental values of 0.16 and 0.22.
We have developed a theory of resonance radiation imprisonment in collimated atomic beams. Treating the integral master equation describing imprisonment as a generalized wave (Schrödinger) equation and using the geometrical quantization technique for its solution, we obtained analytical representations for the effective radiative lifetime, mean scattering number, and trapping factors. We apply this theory to explain the recent observation of a dramatic velocity redistribution of excited atoms by radiative excitation transfer after the photofragmentation of Na2. In this process, the fast Na(3p) photofragments transfer their excitation energy efficiently via radiation to the abundant Na(3s) atoms from the primary particle beam. The influence of the hyperfine splitting of the ground state of Na atoms on this process is discussed. The ratio of the number of Na(3p) atoms produced by the radiative excitation transfer to the number of Na(3p) photofragments was found to be 0.13 and 0.19 for photodissociation of Na2 molecules in the vibrational levels v″=17 and v″=23, respectively. This is in good agreement with the corresponding experimental values of 0.16 and 0.22.
Abstract. The cross sections for the Na.4D/! Na.4F / excitation energy transfer induced by collisions with He, Ar and Na ground-state atoms have been measured. The sodium atoms in the 4D state have been produced by two-photon excitation using cw laser radiation at 578.89 nm. Within a model which takes into account collisional population and depopulation of the 4F level as well as radiative relaxation (direct or cascade) of the 3D, 4P, 4D and 4F states ending in the 3P level, the rate for the Na.4D / ! Na.4F / collisional transfer turns out to be related to the ratio of the steady-state populations created in 3D and 4D states. They have been determined by measuring the fluorescence intensities of the 3D! 3P and 4D! 3P transitions. The measurements yield the following cross section values for those
The cross sections for the excitation energy transfer induced by collisions with He, Ar and Na ground-state atoms have been measured. The sodium atoms in the 4D state have been produced by two-photon excitation using cw laser radiation at 578.89 nm. Within a model which takes into account collisional population and depopulation of the 4F level as well as radiative relaxation (direct or cascade) of the 3D, 4P, 4D and 4F states ending in the 3P level, the rate for the collisional transfer turns out to be related to the ratio of the steady-state populations created in 3D and 4D states. They have been determined by measuring the fluorescence intensities of the and transitions. The measurements yield the following cross section values for those processes investigated: , and , at .
This study carries out an experimental investigation of the radiative decay kinetics of the resonance states of sodium atoms excited by dye laser radiation. The effective radiative decay rates of the resonance states as a function of vapor temperature, primary and impurity gas presssure, and the radius of the cylindrical volume containing the vapor were obtained by computer processing ofthe experimental curves using a kinetic decay model.-The radiative decay rate calculated in the Holstein approximation is compared to the measured values. The mechanisms of optical excitation of metallic vapors in resonance radiation trapping conditions have been investigated theoretically to a sufficient degree.lr At the same time there have been few experimental studies devoted to this problem. The decay kinetics of the atomic resonance states in the vapors of alkali metals have largely been studied for a planar radiating layer,2-6 where the nonideal geometry of the radiating volume made it necessary to introduce a fitting parameter to compare the experimental results to theory. The radiative decay kinetics of the populations of the resonance 3P states of atomic Na under conditions of axial laser excitation of a cylindrical shell are investigated in the present paper for the first time; this made it possible to carry out a comparison to theory without introducing variable parameters, since in this case exact analytic expressions are known for the effective lifetimes. It should also be emphasized that cylindrically configured cells are most commonly used in experimental research and hence these results have a certain interest in such studies. For our analysis we selected a concentration range of normal sodium atoms of 3 X 1013 <;no<;4 X 1015 cm - where selective optical excitation of the fine structure components (FSC) 32Pl/2 and 32P3/2 are accompanied by collisional mixing, which has a substantial effect on the persistence kinetics of the NaD lines. Under these conditions the decay of the directly excited fine structure component is biexponential, while the time dependence of the population of the corresponding level takes the form
The effect of imprisonment of radiation in sodium vapor on the measured lifetime of the 32P states has been investigated in an experiment in which the atoms in the vapor were excited with 10-nsec pulses of resonance radiation and the elapsed times between the exciting and the fluorescent pulses were recorded using a time-to-amplitude converter and kicksorter. At vapor densities below 1010 atoms/cm3, where there is no multiple scattering, the measured lifetime reaches a constant value of (1.63\ifmmode\pm\else\textpm\fi{}0.04)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ sec, equal to the natural lifetime of the 32P states. In the density range 109-1013 atoms/cm3, the variation of the effective lifetime with the vapor density is in good agreement with the predictions of Milne's theory of radiation trapping; agreement with Holstein's theory is observed only in the range 1012-1013 atoms/cm3. The results of a subsidiary Hanle experiment show that a multiply scattered photon of sodium resonance fluorescence loses its original polarization and that, at high sodium vapor pressure, coherence is not preserved.
The dencity of sodium was determined from measurement of optical absorption of the resonance line. Sodium vapour, in the dencity 3×10~(11) to 1.2×10~(12)cm~(-3), was excited by a cw dye laser, tuned 70 GHz from D_2 resonance line. We recorded signal intensities, consisting of The Rayleigh component at the laser frequency and the two fluorescence components (direct and sensitized) at the atomic resonance-line frequencies. D_2 line self-broadening rate coefficient [k_(br,2)=5.44×10~(-7)cm~3/s(±15%)] was yielded. Combined with the effective radiative decay rates in the presence of radiation trapping, we measured excitation-transfer rates in different dencities, for the excitation transfer process Na(3P_(3/2))+Na(3S) Na (3P_(1/2))+Na(3S). The fine-structure collisional-mining cross section [σ_(21)(3P_(3/2)→3P_(1/2))=19.9nm~2(±29%)3 at T 184℃ was obtained. Our results were compared to other experiments and to theory.
The effects of imprisonment of resonance radiation in potassium vapor and of collisions between excited potassium atoms and N2, H2, HD, and D2 molecules, on the measured lifetimes of the 42P states, have been investigated by the method of delayed coincidences. The potassium atoms were excited with short pulses of resonance radiation, and the delays between the exciting and fluorescent pulses were measured with a time-to-amplitude converter. At pure potassium densities below 1010 atoms/cm3, the measured lifetimes approach the constant values 27.8 ± 0.8 and 27.6 ± 0.8 ns, corresponding to the natural lifetimes of the 42P1/2 and 42P3/2 states, respectively. At higher densities the effective lifetimes are in satisfactory agreement with the predictions of Holstein's theory. The decrease in the measured decay rates observed upon addition of the diatomic gases yielded cross sections for quenching collisions with N2, H2, HD, and D2 which equal 34.0 ± 2.0 Å2, 9.4 ± 1.3 Å2, 11.9 ± 1.5 Å2, and 8.0 ± 2.0 Å2, respectively.