We report a study of fine-structure mixing $\mathrm{Rb}(5{}^{2}{D}_{5/2})\ensuremath{\rightarrow}\mathrm{Rb}(5{}^{2}{D}_{3/2})$ in collisions with ground-state Rb atoms. In the experiment, two-photon cw laser excitation was applied to the Rb vapor cell. The measured cross section for the process was $(5.8\ifmmode\pm\else\textpm\fi{}1.9)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}{\mathrm{cm}}^{2}.$ Theoretical calculations using nonadiabatic collision theory gave a value of $3.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}{\mathrm{cm}}^{2}.$
A diode-laser fluorescence experiment was performed in order to study fine-structure transitions between 5 2 P states of rubidium atoms colliding with ground-state potassium or caesium atoms. The Rb (5 2 P 3 2/) state was optically excited and the intensity ratio of sensitized to direct fluorescence was measured. The obtained cross sections for the excitation energy transfer Rb( 2 P 3 2/) to Rb( 2 P 1 2/) induced by collisions with K and Cs (T=573 K) are sigma =54 AA 2 +or-30% and sigma =15 AA 2 +or-30%, respectively. Assuming detailed balancing, the cross sections for the reverse process Rb( 2 P 1 2/) to Rb( 2 P 3 2/) are sigma =60 AA 2 +or-30%, and sigma =16.5 AA 2 +or-30% for K and Cs, respectively.
Cross sections for inelastic transfer between the 82D3/2 and 82D5/2 fine-structure states in rubidium, induced in resonant collisions with ground-state Rb atoms, have been determined using an experimental method involving two-photon excitation of atomic fluorescence. Rubidium vapor in a fluorescence cell was irradiated with pulses of 641 nm radiation from a N2 laser-pumped dye-laser tuned to excite one of the 82D states. The resulting fluorescence included the direct component originating from the optically excited state and a sensitized component arising from the other fine-structure state populated by collisions. Relative intensities of the fluorescent components, determined by photon-counting techniques, yielded the cross sections for excitation transfer: Q(2D3/2 → 2D5/2) = 8.1 × 10−13 cm2; Q(2D3/2 ← 2D5/2) = 5.5 × 1013 cm2; as well as [Formula: see text], the effective quenching cross section. The excitation transfer cross sections which are considered accurate to within ±20% are in the ratio predicted by the principle of detailed balancing.
Rb atoms were excited to the 5P3/2 level using a single-mode laser diode. The 5P3/2 state atom density was measured by the absorption of line from a Rb hollow-cathode lamp. The excited atom density is combined with measured fluorescence ratio to determine collisional cross section for the energy pooling process [i.e. Rb(5P3/2)+Rb(5P3/2)→Rb(5D)+Rb(5S)]. The cross section is (5.0±1.9)(?)10-14cm2. Cross section for 5P3/2 →5P1/2 transfer in Rb, induced in collision with ground-state Rb atoms, has been determined using methods of atomic fluorescence. The resulting fluorescence included a direct component arising from the optically excited state and a sensitized component due to the collisionally populated fine-structure state and the energy-pooling collisions. Measurement of relative intensities of the two components yielded the following cross section: σ(5P3/2→5P1/2)=(3.0±0.9)×10-15cm2. It is found that the rate for the energy pooling is an order of magnitude more efficient than 5P3/2→5P1/2 mixture. Comparisons of our result with other experiments have been made.
Cross sections for
72D and
82D fine-structure mixing in Rb, induced by collisions with various ground-state atoms and
N2 molecules, have been determined using methods of atomic fluorescence. Rb vapor, pure or mixed with a buffer gas, was irradiated in a glass fluorescence cell with pulses of radiation from a
N2 laser-pumped dye laser, populating a
2D fine-structure state by two-photon absorption. The resulting fluorescence included a direct component arising from the optically excited state and a sensitized component due to the collisionally populated fine-structure state. Measurements of relative intensities of the two components in relation to buffer-gas pressure yielded the following cross sections (in units of ${10}^{\ensuremath{-}14}$
cm2): $Q({7}^{2}{D}_{\frac{3}{2}}\ensuremath{\rightarrow}{7}^{2}{D}_{\frac{5}{2}})=14.1,15.5,\mathrm{and}10.0$; $Q({7}^{2}{D}_{\frac{3}{2}}\ensuremath{\leftarrow}{7}^{2}{D}_{\frac{5}{2}})=9.0,10.5,\mathrm{and}6.9$, for Kr, Xe, and
N2, respectively; $Q({8}^{2}{D}_{\frac{3}{2}}\ensuremath{\rightarrow}{8}^{2}{D}_{\frac{5}{2}})=8.9,4.9,12.4,24.9,25.8,12.1,\mathrm{and}43.1$; $Q({8}^{2}{D}_{\frac{3}{2}}\ensuremath{\leftarrow}{8}^{2}{D}_{\frac{5}{2}})=5.8,3.2,9.4,15.1,17.6,8.3,\mathrm{and}28.5$, for He, Ne, Ar, Kr, Xe,
N2, and Rb, respectively. Cross sections for the effective depopulation of the
2D states were also determined.
Recently we demonstrated lasing at 420 nm and 455 nm inside of rubidium and cesium vapor cells respectively, by non-resonant, two photon absorption at near infrared pump wavelengths. Two photon absorption from the ground S1/2 state to excited D3/2,5/2 or higher lying S1/2 state via virtual states and subsequent infrared stimulated emission pumps the upper laser levels, the second excited P1/2,3/2 states. To better understand the mechanism and phenomenology of this type of laser, this paper presents a method for determining the two-photon absorption (TPA) cross-section for the 5S1/2 −→ 5D5/2 transition in naturally occurring rubidium. For an incident pump intensity of 392 W cm2 and a rubidium concentration of 3.34 × 10 atoms cm3 , a peak absorbance of 0.10 is observed. The concentration of the Rb in the test cell is determined by one photon absorption spectra of the D2, indicating a vapor curve shifted by 14 C from the exterior wall temperature. The incident laser beam is focused to a waist of 75 μm. The beam quality is consistent with an M = 1.05 − 1.09. A model for the intensity as a function of propagation distance is developed to interpret the observed absorption spectrum and determine a cross-section for the two photon absorption.