  Multi-photon resonant spectroscopies require tunable narrowband excitation to
deliver spectral selectivity and, simultaneously, high temporal intensity to
drive a nonlinear-optical process. These contradictory requirements are
achievable with bursts of ultrashort pulses, which provides both high intensity
and tunable narrowband peaks in the frequency domain arising from spectral
interference. However, femtosecond pulse bursts need special attention during
their amplification [Optica 7, 1758 (2020)], which requires spectral peak
suppression to increase the energy safely extractable from a chirped-pulse
amplifier (CPA). Here, we present a method combining safe laser CPA, relying on
spectral scrambling, with a parametric frequency converter that automatically
restores the desired spectral peak structure and delivers narrow linewidths for
bursts of ultrashort pulses at microjoule energies. The shown results pave the
way to new high-energy ultrafast laser sources with controllable spectral
selectivity.
