Ultrafast Parametric Laser Technology for Strong-field science in Long-Wave Infrared

Abstract

Intense, ultrashort-pulse laser sources (USPLs) enable a wide range of applications in remote sensing, laser wakefield acceleration, and directed energy. The extremity of the underlying physical phenomena scales favorably with the wavelength of the laser driver, yet, to-date, most of the investigations in intense light-matter interactions used high-power USPLs operating in the relatively narrow wavelength range in the near infrared (NIR). This applies to the nonlinear self-channeling of USPL pulses in air, known as laser filamentation, the primary motivator for the work discussed in this dissertation. Like several other metrics in intense light-matter interactions, the threshold for self-focusing, which is the prerequisite to filamentation, and the optical power carried by an individual laser filament, both scale in proportion to the wavelength of the laser squared. Recent developments in the ultrafast laser technology have enabled the extension of the studies of air filamentation from the familiar NIR spectral range to the short-wave and mid-wave infrared (SWIR and MWIR, respectively). An interesting effect accompanying MWIR filamentation is the efficient and non-perturbation generation of low odd-order harmonics of the optical driver. As the results of our experiments show, spectral interference of the neighboring harmonics carries information about the carrier-envelope phase (CEP) of the MWIR driver pulses and can be used for the single-shot CEP characterization. Contrary to intuition, the carrier-phase information is preserved through the highly nonlinear propagation through the interaction region in the presence of ionization. The natural extension of these and other studies in strong-field science to LWIR is hindered by the lack of practical optical sources in that wavelength range. To address this shortcoming, we have designed and constructed a source of ultrashort optical pulses operating at the center wavelength of 8.5 um. The source is based on optical parametric chirped-pulse amplification (OPCPA) and currently generates one-millijoule pulses at the repetition rate of ten pulses per second. The optical bandwidth of the generated LWIR emission supports one hundred femtosecond pulse duration, corresponding to multi-gigawatt peak optical power. In this dissertation, I will discuss the principle of operation of this OPCPA source, and the major trade-offs involved in its design.