Tunable multiwavelength synchronized femtosecond pulse trains for ultrafast spectroscopy

By using femtosecond optical techniques including self-phase modulation, spectral filtering and dispersion compensation, we constructed a tunable multiwavelength synchronized femtosecond light source from a cw modelocked femtosecond Ti:sapphire laser, and experimentally characterized its performance. Synchronized femtosecond pulses of different central frequencies can be selected independently within a 60-nm FWHM band. Pulse duration can also be programmed from 200 fs to 100 fs by controlling the bandwidth. Synchronization between pulses of different wavelengths are experimentally shown to be within a few femtoseconds. We demonstrate applications of the light source in ultrafast pump-probe spectroscopy with a sensitivity as great as 10^-5 in transient transmission measurements.