Ultrafast pulse shaping modulates perceived visual brightness in living animals

Vision is usually assumed to be sensitive to the light intensity and spectrum but not to its spectral phase. However, experiments performed on retinal proteins in solution showed that the first step of vision consists in an ultrafast photoisomerization that can be coherently controlled by shaping the phase of femtosecond laser pulses, especially in the multiphoton interaction regime. The link between these experiments in solution and the biological process allowing vision was not demonstrated. Here, we measure the electric signals fired from the retina of living mice upon femtosecond multipulse and single-pulse light stimulation. Our results show that the electrophysiological signaling is sensitive to the manipulation of the light excitation on a femtosecond time scale. The mechanism relies on multiple interactions with the light pulses close to the conical intersection, like pump-dump (photoisomerization interruption) and pump-repump (reverse isomerization) processes. This interpretation is supported both experimentally and by dynamics simulations.

AN ALGEBRAIC APPROACH TO THE INTERACTION OF A THREE-LEVEL ATOM INTERACTING WITH QUANTIZED RADIATION FIELD

The system of a three-level atom in the Ξ configuration coupled to two quantized field modes with arbitrary detuning and density-dependent multiphoton interaction is studied by dynamical algebraic method. With the help of an su(3) algebraic structure, we diagonalize the Hamiltonian by making use of unitary transformations and obtain the eigenvalues, eigenstates and time evolution operator for the system. Based on this su(3) structure, we also show that the system of a three-level atom in the Ξ configuration can be exactly transformed to an effective two-level Hamiltonian by an unitary transformation. Finally, we show that there exist an su (N) algebraic structure in the system of a N-level atom interacting with N-1 field modes.

POPULATION TRAPPING IN A GENERALIZED JAYNES-CUMMINGS MODEL

In recent literature the expression for the population inversion in the Jaynes-Cummings model was obtained for the most general initial state of the field-atom system, allowing the investigation of the population trapping problem. Here we extend this study to the case of multiphoton interaction where coherent and incoherent trappings are investigated, the mentioned results of literature becoming a particularization of ours.