Two-photon ionization cross sections from the rubidium ground state have been measured with both a cw 421-nm laser and a combination of cw 421- and 1002-nm lasers. The measurements were performed within a high-vacuum magneto-optical trap while the trapping lasers were switched off, exploiting the long trap lifetime and also the trap laser confinement. The two-photon cross sections were determined for the blue laser near resonance with the 6P1/2 and 6P3/2 states and compared with the estimates of a theoretical model. In near resonance with the 6P states, large two-photon photoionization cross sections were measured.
We report the measurement of the photoionization cross sections of the
5S1/2 and
5P3/2 states of
87Rb in a two-species Hg and Rb magneto-optical trap (MOT) by the cooling laser for Hg. The photoionization cross sections of Rb in the
5S1/2 and
5P3/2 states at 253.7 nm are determined to be ${1}_{\ensuremath{-}1}^{+4.3}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}20}\phantom{\rule{0.28em}{0ex}}{\text{cm}}^{2}$ and $4.63(30)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}18}\phantom{\rule{0.28em}{0ex}}{\text{cm}}^{2}$, respectively. To measure the
5S1/2 and
5P3/2 state fractions in the MOT we detected the photoionization rate of the
5P3/2 state by an additional 401.5 nm laser. The photoionization cross section of Rb in the
5P3/2 state at 401.5 nm is determined to be $\text{1.18(10)}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}\phantom{\rule{0.28em}{0ex}}{\text{cm}}^{2}$.
We report the measurement of the absolute photoionization cross section for the
6P3/2 state of cesium. Cross sections were determined by measuring the photoionization rate of cesium atoms confined in a magneto-optical trap. The photoionization rate was measured by monitoring the decay of trap fluorescence during exposure to ionizing laser radiation. The measurements were made in the wavelength range 457.9 to 501.7 nm using several lines from an Ar-ion laser. Our results are compared to other experimental measurements as well as to existing theories.
We report the measurement of the absolute photoionization cross section for the 5P 3/2 state of 87 Rb at wavelength of 473 nm, which results in the photoelectron energies of 33 meV above the ionization threshold, using cold atoms confined in a vapor-loaded magneto-optical trap. The 87 Rb 5P 3/2 photoionization cross section at 473 nm is determined to be σ PI = 10.5 ± 2.2 Mb. Considering the spatial distribution of the trapped atoms, the average intensity of the ionization laser seen by an atom in the MOT instead of ionizing laser intensity I PI is used in our calculations for the photoionization cross sections. The excited state fraction is also accurately estimated using the latest experimental result.
Photoionization of rubidium atoms cooled in a magneto-optical trap, characterized by the coexistence of the ground
5S1/2 and excited
5P3/2 states, is investigated experimentally and theoretically with the 400-nm femtosecond laser pulses at intensities of $I=(3\ifmmode\times\else\texttimes\fi{}{10}^{9})\text{--}(4.5\ifmmode\times\else\texttimes\fi{}{10}^{12})$
W/cm2. The recoil-ion momentum distribution (RIMD) of
Rb+ exhibits rich ringlike structures and their energies correspond to one-photon ionization of the
5P3/2 state and two-photon and three-photon ionizations of the
5S1/2 state, respectively. With increasing
I, the dips near zero momentum (NZM) in the experimental RIMDs become shallow dramatically and their peaked
Rb+ momenta ionized from the
5P3/2 state move obviously toward zero while the peaks from the
5S1/2 state do not shift. In addition, the ion-yield ratio of the
5S1/2 state to the
5P3/2 state varies from
I to
I1.5 as
I increases. These features indicate a transition from perturbative ionization to strongly perturbative ionization for the
5P3/2 state. Numerical simulations by solving the time-dependent Schr\"odinger equation (TDSE) can qualitatively explain the measurements of the RIMD, photoion angular distributions, and ion-yield ratio. However, some discrepancies still exist, especially for the NZM dip, which could stem from the electron-electron correlation that is neglected in the present TDSE simulations since we have adopted the single-active-electron approximation.
We describe a new technique for accurate measurement of absolute photoionization cross sections. By measuring the loss rateof atoms from a laser trap in the presence of ionizing light, we directly measure the photoionization rate. The only quantities requiring absolute calibration are the ionizing laser intensity and the fractional population in the relevant state. Our technique is capable of detecting extremely small ionization rates, which means that low-power cw sources can be used. We have applied this method to photoionization from the 5P(3/2) state of rubidium at wavelengths of 413 and 407 nm.The cross sections are 1.36(12) x 10(-17) and 1.25(11) x 10(-17) cm(2) , respectively.