Nanosecond optical excitation dynamics of long M-state lifetime bacteriorhodopsin films

Dynamic parameters relevant to the performance of bacteriorhodopsin (bR) as an optical cache memory are reported. The thermal relaxation of the M-state photocycle-intermediate has been a barrier to the exploitation of wild-type bR in optical memory devices. Extension of the room-temperature M-state lifetime from 10 ms to ~ 10 s is described. Writing to the long-lifetime material is achieved for nanosecond pulses of less than 1 nJ µm^-2 fluence. Reading, at a contrast-ratio of 1.3:1, is achievable following a 5 ms delay. Erasure is achieved on a 50 µs timescale for pulse fluences similar to those used for the writing stage. Following continuous-wave (cw) excitation, contrast ratios of 200:1 are obtained, with significant photochromic changes remaining after many seconds.