<title>Diffraction efficiency of BR holograms under thermal exposure</title>

Abstract

The change ofthe dark relaxation rate of the bacteriorhodopsin (BR) hologram diffraction efficiency with write pulse width is considered. The heating of the BR film with light pulses is shown to be the cause. The effect ofthermal exposure can be reduced by increasing the hologram spatial frequency. . INTRODUCTIONBR-based dynamic photocamers are widely used for holographic data recording in information processing and storage st"2 The performance of such systems is affected essentially by the rate of recording and regenerating the data on the carrier. To acheive fast operation rate, the recording in the metastable state M of BR should be applied. 3 We found, that the thermal energy emitted during the recording in metastable state M can markedly exceed the optical energy losses of recording light pulse. And rapid heating of carrier in recording can initiate the thermal hologram generation.In this paper, the mechanism of carrier heating in recording is discussed. The attention is paid to the features ofthennal hologram which is caused by the thermal change in refractive index ofthe carrier under it's rapid heating. THERMAL EFFECTS IN FAST RECORDiNGFor fast recording (Fig. I), the carrier is preliminarily exposed to continuous reading light beam with wavelength X, ranged into the absorption spectrum of the stable state (Br) of BR (570 nm). By this, BR converts from stable state to metastable state (M) with absorption peak at 412 nm.' The wavelength ? r of recording light is within the M-state sensitivity range. Under exposure to recording light pulse, the metastable M-state converts into the original Br-state. As a result, recorded pattern consists of spatial distributed M and Br states which have different absorption and refractive indeces.5 L. _ recordmg hologram ?Lw ii t diffracted gh 1it reading light BR Ar Fig. 1. Illustration for recording in M-state of BR SPIEVol. 3347. 0277-786X/98/$1O.OO 61 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/27/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx