We investigate the production of ultracold ground state X 1 σ + (v = 0) RbCs molecules in the lowest vibrational level via short-range photoassociation followed by spontaneous emission. The starting point is the laser cooled 85 Rb and 133 Cs atoms in a dual species, forced dark magneto-optical trap. The special intermediate level (5)0 + (v = 10) correlated to the (2) 3 π electric state is achieved by the photoassociation process. The formed ground state X 1 σ + (v = 0) molecule is resonantly excited to the 2 1 π intermediate state by a 651 nm pulse laser and is ionized by a 532 nm pulse laser and then detected by the time-of-flight mass spectrum. Saturation of the photoionization spectroscopy at large ionization laser energy is observed and the ionization efficiency is obtained from the fitting. The production of ultracold ground state 85 Rb 133 Cs molecules is facilitative for the further research about the manipulation of ultracold molecules in the rovibrational ground state.
We have observed short-range photoassociation of
7Li85Rb to the two lowest vibrational states of the $d{\phantom{\rule{0.16em}{0ex}}}^{3}\mathrm{\ensuremath{\Pi}}$ potential. We have also observed several ${a}^{3}\phantom{\rule{0.16em}{0ex}}{\mathrm{\ensuremath{\Sigma}}}^{+}$ vibrational levels with generation rates between $\ensuremath{\sim}{10}^{2}$ and $\ensuremath{\sim}{10}^{3}$ molecules per second, resulting from the spontaneous decay of these $d{\phantom{\rule{0.16em}{0ex}}}^{3}\mathrm{\ensuremath{\Pi}}$ molecules. We observe an alternation of the peak heights in the rotational photoassociation spectrum that depends on the parity of the excited molecular state. Franck-Condon overlap calculations predict that photoassociation to higher vibrational levels of the $d{\phantom{\rule{0.16em}{0ex}}}^{3}\mathrm{\ensuremath{\Pi}}$ potential, in particular, the sixth vibrational level, should populate the lowest vibrational level of the $a{\phantom{\rule{0.16em}{0ex}}}^{3}{\mathrm{\ensuremath{\Sigma}}}^{+}$ state at a rate as high as
104 molecules per second. This work also motivates an experimental search for short-range photoassociation to other bound molecular states, such as $c{\phantom{\rule{0.16em}{0ex}}}^{3}{\mathrm{\ensuremath{\Sigma}}}^{+}$ or $b{\phantom{\rule{0.16em}{0ex}}}^{3}\mathrm{\ensuremath{\Pi}}$, as prospects for preparing ground-state molecules.
One- and two-color resonance-enhanced two-photon ionization (RETPI) is used to detect ultracold ground-state RbCs molecules which are formed via short-range photoassociation from laser-cooled atoms. The transition from the X1Σ+(v = 0) state to the 21Π(v = 10) state of ultracold RbCs molecules shows the consistence of one- and two-color RETPI. A multi-photon photoionization rate model is introduced to interpret the dependence of molecular ion intensity on photoionized laser energy, and can be used to verify the photoionization scheme. This photoionization rate model can be expanded to multi-color photoionization for all kinds of atoms and molecules, which is a powerful method of determining the photoionization scheme.