Read times for bacteriorhodopsin-film optical cache memory

We report measurements of nonlinear-optical responses of bacteriorhodopsin (BR) films of long intermediate-state lifetimes. Nanosecond-duration pulses were used as the excite beam and cw monochromatic light was used as the probe beam in excite–probe experiments. The results reveal that, whereas the response time of the BR films is of the order of milliseconds at the probe wavelength of 633 nm used in earlier experiments, it is of the order of 100 µs at probe wavelengths of 600 nm and below. Contrast ratios and insertion losses were also measured at different probe wavelengths and probe irradiance levels; the maximum contrast ratio was found to be ∼3:1. The implications of these results for the application of BR films as optical cache memory devices are discussed.