Abstract

Two self-mode-locked sub-100-fs Ti:sapphire lasers operating at 700-1000 nm generate the pump and probe pulses for an ultrafast pump-probe apparatus. The asynchronous optical sampling approach is employed to perform these studies. To provide an optical delay line the difference in the two cavity lengths is precisely adjusted to give a constantly increasing walk-off between the two laser pulses. The step size of the walk-off provides the time resolution, variable from source-limited 100 fs to a few nanoseconds. The laser beams are sent to a BBO crystal that generates sum frequency pulses when the pulses from the two lasers temporarily overlap. This pulse is then used to define the time-zero position and to initiate a micrometer-millisecond data acquisition process. Data are digitized at the probe laser repetition rate and are then transferred to a micro-computer for storage and analysis. Several laser dyes with excited state lifetimes of picoseconds to nanoseconds have been studied to verify instrument performance. With a uniquely designed cavity length stabilization system, the relative time jitter of the two laser pulses is maintained near 100 fs. By adding frequency doubling crystals, 350-500 nm wavelength coverage can be accessed.

© 1992 Optical Society of America