Photoinitiated collisions between cold Cs Rydberg atoms

Experimental studies of a photoinitiated collision in an ultracold Cs Rydberg gas are presented. The process is characterized by measuring the laser intensity dependence of the absorption, the number of particles leaving each collision, and the recoil velocity of the collision fragments. The results of the experiment are compared to ab initio Rydberg pair interaction potentials.

Figure 1

Ions per laser shot vs laser $B$ frequency. The two spectra are taken at $I_B=50\mathrm{W}∕{\mathrm{cm}}^2$ (higher yield) and $I_B=100\mathrm{mW}∕{\mathrm{cm}}^2$ (lower yield).

Figure 2

(a) The peak ion production rate for $89D_{3∕2}$ (solid circles) and the PI collision (open circles) vs laser $B$ intensity at a $1\text{−}\mathrm{kHz}$ repetition rate. (b) The ratio of two-ion to one-ion detections for the PI collision and $89D_{3∕2}$. The 2:1 ion detection fraction for the PI collision, $0.46\pm 0.06$, is in good agreement with $P_D$ and a two-atom process. (c) The PI collision rate vs $6P_{3∕2}$ density at a $30\text{−}\mathrm{Hz}$ repetition rate. The line is a quadratic fit to the data.

Figure 3

The full width at half maximum (FWHM) of the fragment expansion vs expansion time. The data for the PI collision resonance and the control measurement of the temperature are shown. The lines are fits using the analysis in [17]. The small squares are the Monte Carlo data.

Figure 4

(Color online) (a) Comparison of the ion yield spectra and the $M=0$ pair potentials [1]. The uncertainty in the energy of the spectra is $\pm 10\mathrm{MHz}$. The different asymptotes correspond to the possible $m_j$ atomic pair states which are split by the electric field $E=20\mathrm{mV}∕\mathrm{cm}$. The numbers on the right refer to the $j$’s of each atom pair state. (b) PI collision circled in (a). The percentage of $89D$ character, as determined from the eigenvectors [1], and the squared nuclear wave function at the top of the barrier are shown.