Coherent interferometric detection of infrared emission from bacteriorhodopsin
Abstract
We have developped resonance coherent emission experiments where the ensemble of charge displacements upon photon absorption is monitored and time resolved. We have recently succeeded in directly visualizing the ultrafast (~10 fs) charge separation process in bacteriorhodopsin by interferometrically monitoring the associated low-frequency emission in macroscopically ordered films. The retinal isomerization subsequently takes place in few hundreds femtoseconds and appears associated with a relaxation of the dipole moment. In addition to the instantaneous broadband infrared emission, characteristic of electronic optical rectification, long lasting modulations at positive time can be distinguished that reflect the infrared-active vibrational response of the retinal/protein system.