In this work, optical pulse amplification by parametric chirped-pulse
amplification (OPCPA) has been applied to the generation of high-energy,
few-cycle optical pulses in the near-infrared (NIR) and infrared (IR)
spectral regions. Amplification of such pulses is ordinarily difficult to
achieve by existing techniques of pulse amplification based on standard
laser gain media followed by external compression. Potential applications
of few-cycle pulses in the IR have also been demonstrated.
The NIR OPCPA system produces 0.5-terawatt (10 fs, 5 mJ) pulses by use of
noncollinearly phase-matched optical parametric amplification and a
down-chirping stretcher and upchirping compressor pair.
An IR OPCPA system was also developed which produces 20-gigawatt (20 fs,
350 uJ pulses at 2.1 um.
The IR seed pulse is generated by optical
rectification of a broadband pulse and therefore it exhibits a
self-stabilized carrier-envelope phase (CEP).
In the IR OPCPA a common laser source is used to generate the pump
and seed resulting in an inherent sub-picosecond optical synchronization
between the two pulses. This was achieved by use of a custom-built Nd:YLF
picosecond pump pulse amplifier that is directly seeded with optical pulses
from a custom-built ultrabroadband Ti:sapphire oscillator. Synchronization
between the pump and seed pulses is critical for efficient and stable
amplification.
Two spectroscopic applications which utilize these unique sources have been
demonstrated. First, the visible supercontinuum was generated in a
solid-state media by the infrared optical pulses and through which the
carrier-envelope phase (CEP) of the driving pulse was measured with an
f-to-3f interferometer. This measurement confirms the self-stabilization
mechanism of the CEP in a difference frequency generation process and the
preservation of the CEP during optical parametric amplification. Second,
high-order harmonics with energies extending beyond 200 eV were generated
with the few-cycle infrared pulses in an argon target. Because of the
longer carrier period, the IR pulses transfer more quiver energy to ionized
free electrons compared to conventional NIR pulses. Therefore, higher
energy radiation is emitted upon recombination of the accelerated electrons.
This result shows the highest photon energy generated by a laser excitation
in neutral argon