  Femtosecond dual-comb lasers have revolutionized linear Fourier-domain
spectroscopy by offering a rapid motion-free, precise and accurate measurement
mode with easy registration of the combs beat note in the RF domain. Extensions
of this technique found already application for nonlinear time-resolved
spectroscopy within the energy limit available from sources operating at the
full oscillator repetition rate. Here, we present a technique based on time
filtering of femtosecond frequency combs by pulse gating in a laser amplifier.
This gives the required boost to the pulse energy and provides the flexibility
to engineer pairs of arbitrarily delayed wavelength-tunable pulses for
pump-probe techniques. Using a dual-channel millijoule amplifier, we
demonstrate programmable generation of both extremely short, fs, and extremely
long (>ns) interpulse delays. A predetermined arbitrarily chosen interpulse
delay can be directly realized in each successive amplifier shot, eliminating
the massive waiting time required to alter the delay setting by means of an
optomechanical line or an asynchronous scan of two free-running oscillators. We
confirm the versatility of this delay generation method by measuring chi^(2)
cross-correlation and chi^(3) multicomponent population recovery kinetics.
