Analysis of low power spatial light modulation characteristics of bacteriorhodopsin

Abstract

Summary We present a detailed and accurate analysis of low power spatial light modulation characteristics of bacteriorhodopsin (bR) based on nonlinear intensity induced absorption. Amplitude modulation of probe laser read beam transmissions at 410 nm and 640 nm, corresponding to the peak absorption of MII and O states of D96N bR and WT bR respectively, by the modulation laser write beam intensity-induced population changes at 570 nm has been analyzed, considering all intermediate states with both forward and backward transitions in the respective bR photocycles, using the rate equation approach. The SLM characteristics are shown to be sensitive to the normalized small signal absorption coefficient β, rate constants of MII and O intermediate states and the absorption cross-section of the initial B state at the probe wavelength (σBp). There exists an optimum value of β for which maximum percentage modulation can be achieved. It is shown that for extended MII state lifetime of 250 s in D96N bR and O state lifetime of 2.2 s in WT bR, with σBp= 0, 100% modulation of read beam transmissions can be achieved, leading to high dynamic range and sensitivity for low laser write beam intensities of 50 μW/cm2 and 4 mW/cm2 at 570 nm, respectively.