Direct Imaging of Periodic Sub-wavelength Patterns of Total Atomic Density

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.