Two-photon photoassociation spectroscopy of an ultracold heteronuclear molecule

We report on two-photon photoassociation (PA) spectroscopy of ultracold heteronuclear LiRb molecules. This is used to determine the binding energies of the loosely bound levels of the electronic ground singlet and the lowest triplet states of LiRb. We observe strong two-photon PA lines with power broadened linewidths greater than 20 GHz at relatively low laser intensity of $30\mathrm{W}/\mathrm{c}{\mathrm{m}}^2$. The implication of this observation on direct atom to molecule conversion using stimulated Raman adiabatic passage is discussed and the prospect for electronic ground-state molecule production is theoretically analyzed.

Figure 1

(a) Scheme used for Raman-type two-photon PA spectroscopy. The frequency ${\nu }_{\mathrm{PA}}$ of the PA laser is kept fixed while the frequency ${\nu }_{\mathrm{R}}$ of the Raman laser is scanned. (b) Electronic ground-state PECs at large $R$ [37].

Figure 2

(a) A typical one-photon PA spectrum. (b) A two-photon PA spectrum when the frequency of the Raman laser is scanned, with the ECDL locked to the 2(1), $v^{\prime }=-4\mathrm{PA}$ line indicated by the arrow in (a).

Figure 3

Two-photon PA spectra measured using the REMPI detection scheme. The PA laser is tuned to the 2(1) $(v^{\prime }=-5)$ level and the REMPI laser (frequency $17871.5\mathrm{c}{\mathrm{m}}^{-1}$) ionizes molecules produced in the $a{}^3{\mathrm{\Sigma }}^{+}(v^{\prime \prime }=13)$ state by spontaneous emission. (a) The two-photon PA resonance corresponding to the $a{}^3{\mathrm{\Sigma }}^{+}(v^{\prime \prime }=12)\leftrightarrow 2\left(1\right)(v^{\prime }=-5)$ transition. The triplet structure due to hyperfine splitting of the $a{}^3{\mathrm{\Sigma }}^{+}(v^{\prime \prime }=12)$ level is indicated by arrows. (b) The $a{}^3{\mathrm{\Sigma }}^{+}(v^{\prime \prime }=13)\leftrightarrow 2\left(1\right)(v^{\prime }=-5)$ transition measured using different Raman laser powers as indicated in the legends.

Figure 4

(a) Scheme for free-to-bound STIRAP (see text for details). (b) Laser pulse sequence employed in the simulations for STIRAP. (c) Solution of the time-dependent Schrödinger equation for the proposed STIRAP scheme, for the case when the final state of the molecules is the $a{}^3{\mathrm{\Sigma }}^{+}(v^{\prime \prime }=13)$ level.