Local and global properties of lightbound atomic lattices investigated by Bragg diffraction
Abstract
We explore Bragg diffraction from atomic lattices bound by light as a diagnostic tool for studying properties of optical lattices not accessible so far. A weak laser beam at a wavelength of about half the wavelength of the lattice field is diffracted from the (100) and (130) lattice planes of a Rb optical lattice. The observation of welldefined Bragg spots confirms the longrange order in optical lattices. From the acceptance angle for Bragg diffraction we deduce the range over which crystalline order is preserved. The comparison of two Bragg spots diffracted from different lattice planes allows us to directly measure the position spread of the atomic wave packets oscillating in the lightinduced potential wells. By combining conventional probe transmission spectroscopy with Bragg diffraction we study the motion of atoms that are deeply bound inside the potential wells. We show experimentally and theoretically how backaction of the bound atoms on the trapping field influences the lattice constant. We develop a model for the modification of the refractive index by the highly ordered atomic medium. Based on firstorder scattering theory the model explicitly includes the influence of atomic localization on the resulting lattice constant. By measuring the change of the Bragg angle, we observe a decrease of the lattice plane separation for increasing atomic density. We report experimental evidence for the correction to the refractive index due to the finite position spread of the atoms.
 Publication:

Physical Review A
 Pub Date:
 December 1998
 DOI:
 10.1103/PhysRevA.58.4647
 Bibcode:
 1998PhRvA..58.4647W
 Keywords:

 42.25.Fx;
 32.80.Pj;
 42.65.k;
 Diffraction and scattering;
 Optical cooling of atoms;
 trapping;
 Nonlinear optics