Wavelength-shifted reconstruction with bacteriorhodopsin for holographic particle image velocimetry

When large amounts of data are stored in Bacteriorhodopsin (bR), for example with Holographic Particle Image Velocimetry (HPIV), the volatile nature of the medium can be a serious problem. The loss of information has two causes; thermal erasure and photo-induced erasure. The thermal erasure can be reduced by cooling the film. We found that by cooling a film with an optical density of 1.5 (OD570) from 21.2°C to 1.7°C, the thermal erasure time leading to 50% loss of diffraction efficiency was increased from 31 to 185 seconds. The rate of photo-induced erasure does not only depend on the intensity of the reconstruction wave, but also on its wavelength. The influence of the shifted wavelength and the reconstruction intensity on the rate of photo-induced erasure were analysed experimentally and were found to agree with the theory. Reconstructing a hologram with 690 nm can potentially result in a 35 times larger integrated signal to be read from the hologram as when reconstructing with 532 nm.