Development of optical parametric chirped-pulse amplifiers and their applications
In this work, optical pulse amplification by parametric chirped-pulse\namplification (OPCPA) has been applied to the generation of high-energy,\nfew-cycle optical pulses in the near-infrared (NIR) and infrared (IR)\nspectral regions. Amplification of such pulses is ordinarily difficult to\nachieve by existing techniques of pulse amplification based on standard\nlaser gain media followed by external compression. Potential applications\nof few-cycle pulses in the IR have also been demonstrated.\n\nThe NIR OPCPA system produces 0.5-terawatt (10 fs, 5 mJ) pulses by use of\nnoncollinearly phase-matched optical parametric amplification and a\ndown-chirping stretcher and upchirping compressor pair.\n\nAn IR OPCPA system was also developed which produces 20-gigawatt (20 fs,\n350 uJ pulses at 2.1 um. \nThe IR seed pulse is generated by optical\nrectification of a broadband pulse and therefore it exhibits a\nself-stabilized carrier-envelope phase (CEP).\n\nIn the IR OPCPA a common laser source is used to generate the pump\nand seed resulting in an inherent sub-picosecond optical synchronization\nbetween the two pulses. This was achieved by use of a custom-built Nd:YLF\npicosecond pump pulse amplifier that is directly seeded with optical pulses\nfrom a custom-built ultrabroadband Ti:sapphire oscillator. Synchronization\nbetween the pump and seed pulses is critical for efficient and stable\namplification. \n\nTwo spectroscopic applications which utilize these unique sources have been\ndemonstrated. First, the visible supercontinuum was generated in a\nsolid-state media by the infrared optical pulses and through which the\ncarrier-envelope phase (CEP) of the driving pulse was measured with an\nf-to-3f interferometer. This measurement confirms the self-stabilization\nmechanism of the CEP in a difference frequency generation process and the\npreservation of the CEP during optical parametric amplification. Second,\nhigh-order harmonics with energies extending beyond 200 eV were generated\nwith the few-cycle infrared pulses in an argon target. Because of the\nlonger carrier period, the IR pulses transfer more quiver energy to ionized\nfree electrons compared to conventional NIR pulses. Therefore, higher\nenergy radiation is emitted upon recombination of the accelerated electrons.\nThis result shows the highest photon energy generated by a laser excitation\nin neutral argon.