Abstract

In polymeric films of bacteriorhodopsin (BR) a photoconversion product, which was named the $F620$ state, was observed on excitation of the film with $532\mathrm{nm}$ nanosecond laser pulses. This photoproduct shows a strong nonlinear absorption. Such BR films can be used for write-once–read-many (WORM) optical data storage. We demonstrate that a photoproduct similar or even identical to that obtained with nanosecond pulses is generated on excitation with $532\mathrm{nm}$ femtosecond pulses. This photoproduct also shows strong anisotropic absorption, which facilitates polarization storage of data. The product is thermally stable and is irretrievable to the initial B state either by photochemical reaction or through a thermal pathway. The experimental results indicate that the product is formed by a two-photon absorption process. Optical WORM storage is demonstrated by use of two polarization states, but more polarization states may be used. The combination of polarization data multiplexing and extremely short recording time in the femtosecond range enables very high data volumes to be stored within a very short time.

© 2005 Optical Society of America

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