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)cm3/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))=19.9nm2(±29%)3 at T 184℃ was obtained. Our results were compared to other experiments and to theory.
Sodium vapor, in the density range
1013 to 5 \ifmmode\times\else\texttimes\fi{}
1014 ${\mathrm{cm}}^{\ensuremath{-}3}$, was excited by a cw dye laser, tuned 20-150 GHz from either the
D1 or
D2 resonance line. We observed a three-peak scattered spectrum, consisting of the Rayleigh component at the laser frequency, and the two fluorescence components (direct and sensitized) at the atomic resonance-line frequencies. Corrections to the Rayleigh signals for anisotropy and polarization effects, and to the fluorescence signals for radiation trapping, were made in order to obtain the ratio of the sum of the total intensities of the two fluorescence components to that of the Rayleigh component. This ratio combined with a measurement of the line-wing absorption coefficient yields the sodium density and the
D-line self-broadening rate coefficients [${k}_{\mathrm{br}}=4.67\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$
cm3${\mathrm{s}}^{\ensuremath{-}1}$ (\ifmmode\pm\else\textpm\fi{}15%) for the
D2 line and ${k}_{\mathrm{br}}=3.07\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$
cm3${\mathrm{s}}^{\ensuremath{-}1}$ (\ifmmode\pm\else\textpm\fi{}15%) for the
D1 line]. Asymmetry in the self-broadened line wings due to fine-structure recoupling was observed. The measured intensity ratio of the
D lines, combined with pulsed measurements of the effective radiative decay rates in the presence of radiation trapping, yields the fine-structure collisional-mixing cross section [$\ensuremath{\sigma}(3{P}_{\frac{3}{2}}\ensuremath{\rightarrow}3{P}_{\frac{1}{2}})=172$
A˚2(\ifmmode\pm\else\textpm\fi{}18%)] at $T\ensuremath{\cong}300\ifmmode^\circ\else\textdegree\fi{}$ C. Our results are compared to other experiments and to theory.
The cross sections for the excitation energy transfer in the collisional processes Na*(3P 1 2/)+M(nS 1 2/) to or from Na*(3p 3 2/)+m(Ns 3 2/), m being ground-state Rb (n=5) or Cs (n=6) atom, have been measured by laser fluorescence method. With either of the two sodium 3P fine-structure states optically excited, the intensity ratio of the sensitized to direct fluorescence was measured. The polarization effects due to partially polarized and anisotropic direct fluorescence were investigated. The measured cross sections (T=530 K) for the sodium 3P fine-structure excitation transfer induced by collisions with Rb are: sigma ( 1 / 2 to 3 / 2 )=170 AA 2 , with an overall accuracy of 20%. The corresponding values in the Cs case are: sigma ( 1 / 2 to 3 / 2 )=140 AA 2 , sigma ( 3 / 2 to 1 / 2 )=83 AA 2 . The theoretical calculations reveal the decisive role of the dipole-quadrupole interaction. The obtained values are in satisfactory agreement with the experiment only if both the dipole-dipole and dipole-quadrupole interactions are taken into account, while the calculations involving the dipole-dipole term alone yield the cross section values which are as much as one order of magnitude lower than the experimentally observed ones.
We measured the cross section for the collision transfer process Na(4D)+Na (3S)Na(4F)+Na(3S). The 4D state was excited by two photon absorption using a tunable dye laser. Since the direct 4F→3D fluorescence can not be detected with our apparatus, we monitored instead the cascade 3D→3P and 4D→3P fluorescence. Relative intensity of the fluorescence, combined with the measurement of sodium density, yielded cross section σ_(4D)→(4F)=1.3×10~(-14)±28％(cm~2). Our result is compared to other experiments.
We have measured the time-dependent fluorescence of the sodium
D lines following pulsed excitation of one
D line, in the presence of radiation trapping with optical depths
k0L of \ensuremath{\sim}10 to 2000. When collisional coupling of the
3P21 and
3P23 levels and different radiative-escape probabilities for each
D line are taken into account, we obtain excellent agreement with Holstein's theory for the effective radiative decay rates in the Doppler region (${k}_{0}L\ensuremath{\sim}10\ensuremath{-}300$) and in the redistributed Lorentzian region (
k0L>1000). For
k0L between these two regions, we observe an abrupt transition between the two limiting formulas. The buildup rate of the sensitized fluorescence signal also yields a $3{P}_{\frac{3}{2}}\ensuremath{\rightarrow}3{P}_{\frac{1}{2}}$ excitation transfer cross section in agreement with our previously reported cw measurement. Additionally, we have measured the dependence of the
3P fluorescence on laser power and beam diameter, and we explain the observed approach to saturation. We suggest that the previously reported "anomalous" approaches to saturation may be explained in terms of the laser beam burning through the optically thick vapor. Laser-beam spatial intensity variations and self-focusing also contribute to fluorescence signals that deviate from the usual single-atom saturation behavior.
Cross section σ4D→4F was measured for the collision transfer process of Na(4D) +Na(3S)→Na(4F)+Na(3S).The 4D state is excited by two-photon absorption using a tunable dye laser.Since the 4F→3D fluorescence can not be detected directly with the apparatus used the cascade 3D→3P fluorescence is monitored instead.Then the cross-section σ4D→4F=(1.3±0.3)×10^-14cm^2 is got from the relative intensity of the fluorescence.A theoretical evaluation of σ4D→4F is also given and compared with experimental results.
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 .