Holograms help build 3D nanostructures
Mar 1, 2002
A new method of building complex nanoscale structures has been demonstrated by Dieter Meschede of the University of Bonn in Germany and colleagues. The team created a three-dimensional interference pattern by shining a laser into a ‘holographic crystal’, and used the pattern as a stencil to position atoms from an atom laser. This technique could be used to construct ultra-small photonic crystals, and could pave the way for all-optical circuits (M Mützel et al 2002 Phys. Rev. Lett. 88 083601-1).
The light field of an interference pattern can induce an electric dipole in certain atoms, and this draws the atoms to the most intense regions of electric field in the pattern – that is, the bright fringes. This effect is widely used to build two-dimensional structures, but the process becomes cumbersome in three dimensions because many lasers are needed to create the interference patterns.
In contrast, the new technique can create a three-dimensional interference pattern using just one laser. To do this, Meschede and co-workers first ‘imprinted’ a crystal with a hologram, by shining three lasers into the crystal and heating it for three hours. When a ‘read-out’ laser was subsequently shone into the crystal, the interference pattern that created the hologram was reconstructed outside the crystal.
The team then fired a caesium atom laser through the interference pattern towards a specially prepared gold substrate behind it. A simple nano-structure then built up on this surface according to the geometry of the interference pattern.
Meschede’s team demonstrated its principle with three lasers, but such crystals could store holograms created by up to a thousand lasers, which will allow more elaborate structures to be built. The crystals can also hold many holograms at the same time, each one created by light of different wavelengths. Every hologram acts as a stencil for different atoms, which means that a single crystal could be used to make a variety of structures.
“The beautiful thing about these holographic crystals is that you can use one laser to reconstruct many holograms”, says Meschede.
Although the regular spacing of interference patterns means that their technique can only be used to make periodic structures, Meschede and colleagues are optimistic that it could become an integral part of the semiconductor industry. Lithography is widely used in the industry to make two-dimensional circuit boards, but a convenient method for creating three-dimensional nanoscale structures has so far been elusive.
About the author
Joseph Hines is Graduate Liaison Officer at the Institute of Physics