Optically Reconfigurable Surface Microstructures on Polymeric Thin Films

Reversible photopatterning of thin film ptical microstructures would enable dynamic and spatially-addressed control of the diffractive and reflective response of the thin film. Azobenzene-polymers are promising reversible light-addressable surfaces [1-2]. Because the surface deformation process originates in the cyclic isomerization-rotation of the azobenzene and involves no irreversible photochemistry, the light-induced surface patterns can be modified by additional exposure and/or photoerased. A surface relief pattern is formed by two laser beams k
₁
and k
₂
that overlap in the film, producing an optical grating with wavevector Kg = k
₁
-k
₂
, which is subsequently transferred to the film as the period of the resulting surface relief grating (fig. 1a). In general, such structures can be generated with intensities of order 20 mW and exposures of less than 2 minutes. The films need no further processing and the photopatterned structures are stable in ambient conditions.