Femtosecond Coherent anti-Stokes Raman spectroscopy in l2.
The general relationship between macroscopic polarization, P, and incident electronic field, ε, may be written:
For an isotropic medium, the lowest order non-linear term is (ignoring vector properties):
The terms responsible Coherent Anti-Stokes Raman Spectroscopy (CARS)are:
This formula, has the following simple dynamical interpretation. The initial wavepacket,
ψ(0)
interacts with the field at time
t1 and propagates on surface
b for time
t2 - t1
at time
t2 it interacts a second time with the field and propagates on the ground surface
α for time
t3 - t2 ;
at time
t3 it interacts a third time with the field and propagates on surface
b until variable time
t. The third order wavepacket on surface
b is projected onto the initial wavepacket on the ground state; this overlap is a measure of the coherence which determines both the magnitude and phase of the CARS signal.
