Abstract
We report optical parametric amplification (OPA) of phase-stable multi-terahertz pulses which can be
tuned from 16.9 to 44.8 THz (6.7 ~ 17.8 μm). The 255-fs laser output of the Yb:KGW regenerative amplifier
is compressed to 11-fs pulses using a multi-plate broadening scheme, which generates multi-terahertz
pulses with a spectrum extending to approximately 50 THz by intra-pulse difference frequency
generation (DFG) in GaSe. The multi-terahertz pulses are further amplified using a two-stage OPA in
GaSe. The temporal dynamics and photocarrier effects during OPA are characterized in the time domain.
Owing to the intra-pulse DFG, the long-term phase drift of the multi-terahertz pulses after two-stage
OPA is as small as 16 mrad during a 6-h operation without any active feedback. Our scheme using the
intra-pulse DFG and post-amplification proposes a new route to intense multi-terahertz light sources
with extreme phase stability.
