  Amplified bursts of laser pulses are sought for various machining,
deposition, spectroscopic and strong-field applications. Standard frequency-
and time-domain techniques for pulse division become inadequate when intraburst
repetition rates reach the terahertz (THz) range as a consequence of
inaccessible spectral resolution, requirement for interferometric stability,
and collapse of the chirped pulse amplification (CPA) concept due to the loss
of usable bandwidth needed for safe temporal stretching. Avoiding the burst
amplification challenge and resorting to a lossy post-division of an isolated
laser pulse after CPA leaves the limitations of frequency- and time-domain
techniques unsolved. In this letter, we demonstrate an approach that
successfully combines amplitude and phase shaping of THz bursts, formed using
the Vernier effect, with active stabilization of spectral modes and efficient
energy extraction from a CPA regenerative amplifier. As proof of concept, the
amplified bursts of femtosecond near-infrared pulses are down-converted into
tunable THz-frequency pulses via optical rectification.

Optics