Development of optical parametric chirped-pulse amplifiers and their applications

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.