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Summary: Other optical techniques for the production of photonic crystals
use a tightly focused scanning laser beam to initiate chemical
vapour deposition25
or two-photon photopolymerization26
. Struc-
tures are produced layer-by-layer, so these techniques are relatively
slow; they are currently limited to micrometre length scales.
Semiconductor microfabrication27±29
, which has the required reso-
lution, is an expensive process at the limit of current technology and
has not produced structures more than a few unit cells deep.
Colloidal crystals may be used as templates to make submicrometre
structures14±18
, but the use of close-packed spheres severely restricts
the range of lattices that may be produced30
and allows almost no
freedom to alter the structure of a unit cell. By contrast, the optical
properties of microstructures made by holographic lithography
may be optimized by controlling the form of the interference
pattern. Our fabrication method has the high spatial resolution
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