We show that it is possible to excite higher rotational states
J>2 in ultracold photoassociation by two laser fields. Usually higher
J states are suppressed in photoassociation at ultracold temperatures in the regime of Wigner threshold laws. We propose a scheme in which one strong laser field drives photoassociation transition close to either
J=1 or
J=2 rotational state of a particular vibrational level of an electronically excited molecule. The other laser field is tuned near photoassociation resonance with
J>2 rotational levels of the same vibrational state. The strong laser field induces a strong continuum-bound dipole coupling. The resulting dipole force between two colliding atoms modifies the continuum states forming continuum-bound dressed states with a significant component of higher partial waves in the continuum configuration. When the second laser is scanned near the resonance of the higher
J states, these states become populated due to photoassociative transitions from the modified continuum.
The photoassociation (PA) spectrum is analysed in the presence of a magnetic Feshbach resonance. A nonperturbative solution of the problem yields analytical expressions for PA linewidth and shift which are applicable for arbitrary PA laser intensity and magnetic field tuning of Feshbach resonance. We show that by tuning the magnetic field close to the Fano minimum, it is possible to suppress power broadening at increased laser intensities. This occurs due to quantum interference of PA transitions from unperturbed and perturbed continuum. Line narrowing at high laser intensities is accompanied by large spectral shifts. We briefly discuss the important consequences of line narrowing in cold collisions.
We present a theory for manipulation of
d-wave interaction of cold atoms with two lasers strongly driving two photoassociative transitions. The theory predicts the occurrence of a coherence between two excited ro-vibrational bound states due to the photoassociative dipole couplings of ground-state
d-wave scattering state to the bound states. We show that this excited-state coherence significantly influences atom-atom interaction. In particular, this leads to the enhancement of
d-wave elastic scattering and to the suppression of inelastic scattering. In the presence of an
s-wave magnetic Feshbach resonance, the two lasers can couple the
s-wave resonance with the
d-wave scattering state, leading to the further enhancement in
d-wave scattering at relatively low energy. Our numerical calculations based on realistic parameters show that
d-wave manipulation would be most effective in case of atoms having excited diatomic states with narrow natural linewidth. We estimate that at an energy of 100 $\ensuremath{\mu}$K the inelastic scattering rate in Yb can be reduced to 20 s${}^{\ensuremath{-}1}$ while the elastic scattering rate can be two orders of magnitude larger.