Multiphoton pi pulses
George N. Gibson, University of Connecticut
Single photon interactions are well understood, including pi pulses -
pulses of light that produce a 100% population transfer to an excited
state. Multiphoton pi pulses would be very useful for producing
population inversions on highly excited states. However, it is also
well known that small multiphoton excitation rates, large AC Stark
shifts and ionization all inhibit efficient population transfer. In
this talk, I will present a novel 3-level system in which the AC Stark
shift is greatly reduced and the multiphoton coupling strength is
greatly enhanced over a 2-level system, to such an extent that higher
order pi pulses are achievable. To demonstrate the feasibility of this
process, I will present a fully correlated 2-electron calculation in a
model 1-D molecular potential, including ionization that shows a
12-photon pi pulse driven with 800-nm photons. In other words, a single
excited state 18.6 eV above the ground state can be populated with over
90% efficiency with little ionization while the ground state is almost
completely depopulated. This creates a prompt population inversion in
the vacuum-ultraviolet spectral region that may be suitable for
amplifying femtosecond laser pulses created by high harmonic generation.
Moreover, this 3-level configuration may open the door to other
effects previously restricted to single photon interactions, such as
adiabatic passage and inner shell ionization.