Ultrafast spectroscopy of bacteriorhodopsin

Bacteriorhodopsin (bR) is a retinal protein with the function of a light-driven proton pump in a halobacterial cell membrane. The photocycle of bR is one of the most investigated biological photoinitiated reactions. The primary process in the cycle is the all-trans to 13-cis isomerization of the retinal moiety of bR. In the present work, pump and probe pulses were generated by a NOPA (Non-collinear Optical Parametric Amplifier) seeded by a white-light continuum with a 5-fs pulse compressor system. Both of the spectra of pump and probe pulses are nearly the same and cover a spectral range from 500 to 710 nm with a nearly constant phase. All measurements were performed at room temperature (294K). The spectrograms of the real-time traces probed at 585 nm corresponding to the bleaching spectral range is shown in Fig. 1. It is modulated both in terms of frequency and intensity.