Spatial light modulation with pharaonis phoborhodopsin

A detailed and accurate analysis is presented of the low power spatial light modulation (SLM) characteristics of pharaonis phoborhodopsin (ppR) based on nonlinear intensity induced excited-state absorption. Amplitude modulation of probe laser read beam transmissions at 390 and 488 nm, corresponding to the peak absorption of ppR_M and ppR_L states of the ppR photocycle by write beam intensity-induced population changes at 498 nm, corresponding to the peak absorption of the initial ppR state, have been analysed using the rate equation approach. The SLM characteristics are shown to be sensitive to the normalised small signal absorption coefficient (β), the rate constants of intermediates and absorption cross-section of the ppR state at probe wavelength (σ_1p). There is an optimum value of β for which maximum percentage modulation can be achieved. It is shown that for ppR_M and ppR_L states, at typical values, modulation up to 35.9% and 97.2% can be achieved for a laser write beam intensity of 5 mW/cm² and 1 W/cm² respectively. It is shown that 100% modulation of the read beam can be achieved for σ_1p=0. SLM with ppR can be achieved at lower pump powers compared to wild type bacteriorhodopsin. The analysis demonstrates the usefulness of ppR for device applications due to its unique spectral characteristics, especially as a UV filter.