  Several ways to electronically synchronize different types of amplified
femtosecond laser systems are presented, based on a single freely programmable
electronics hardware: Arbitrary-detuning asynchronous optical sampling, as well
as actively locking two femtosecond laser oscillators, albeit not necessarily
to the same round-trip frequency. They allow us to rapidly probe a very wide
range of timescales, from picoseconds to potentially seconds, in a single
transient absorption experiment without the need to move any delay stage.
Experiments become possible that address a largely unexplored aspect of many
photochemical reactions, in particular in the context of photo-catalysis as
well as photoactive proteins, where an initial femtosecond trigger very often
initiates a long-lasting cascade of follow-up processes. The approach is very
versatile, and allows us to synchronize very different lasers, such as a Ti:Sa
amplifier and a 100~kHz Yb-laser system. The jitter of the synchronisation, and
therewith the time-resolution in the transient experiment, lies in the range
from 1~ps to 3~ps, depending on the method. For illustration, transient IR
measurements of the excited state solvation and decay of a metal carbonyl
complex as well as the full reaction cycle of bacteriorhodopsin are shown. The
pros and cons of the various methods are discussed, with regard to the
scientific question one might want to address, and also with regard to the
laser systems that might be already existent in a laser lab.
