  Interference fringes of total atomic density with period $\lambda /4$ and
$\lambda /2$ for optical wavelength $\lambda$, have been produced in de Broglie
atom interferometer and directly imaged by means of an ``optical mask''
technique. The imaging technique allowed us to observe sub-wavelength periodic
patterns with a resolution of $\lambda /16$. The quantum dynamics near the
interference times as a function of the recoil phase and pulse areas has been
investigated.
