Interference between femtosecond pulses observed via time-resolved spontaneous fluorescence

We study spontaneous fluorescence excited by a series of phase-controlled f emtosecond pulses in an inhomogeneously broadened medium containing a frequ ency comb of sharp spectral holes. We show that evolution of the spontaneou s fluorescence on picosecond time scale is sensitive to interference betwee n the excitation pulses and that varying the relative phase between the exc itation pulses changes the time evolution of the fluorescence. (C) 2000 Els evier Science B.V. All rights reserved.