Real-time holography in azo-dye-doped liquid crystals

When exposed to an Ar laser at 514 nm, azo-dye molecules in a nematic liquid-crystal host undergo photoisomerization from trans-isomers to cis-isomers. The conformation change of the azo-dye molecules reorients liquid-crystal molecules. Reversible polarization holograms can be recorded dynamically by this effect, with a threshold intensity as low as 3.0 mW/cm2 and a response time from a few hundred microseconds to 100 ms, depending on the spatial frequency of the recorded grating