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Over the past decades, optical parametric amplification (OPA) has become one of the most promising sources of ultrafast Mid-IR laser, owing to its outstanding properties including ultrabroad bandwidth, superior tunability, good beam quality, and scalable energy. In this paper, we review the recent progress in ultrashort laser pulse generation via chirp manipulated OPA, which improves the energy scalability and gain bandwidth by strategically chirping both pump and seed pulses. The gain mechanism is theoretically analyzed and the OPA processes are numerically simulated. In addition, the concept is verified experimentally. Femtosecond pulses with hundreds of mJ are generated in a high energy dual-chirped-OPA (DC-OPA), and ultrabroadband μJ-level spectra supporting sub-2-cycle pulse durations are achieved in BBP-OPA. Furthermore, the obtained pulses show excellent tunability through the NIR to Mid-IR regions, which makes them a suitable seeding source for further amplification as well as powerful tools in various applications such as strong field physics, attosecond science, and ultrafast spectroscopy. [ABSTRACT FROM AUTHOR]

The second-harmonic generation (SHG) in gallium doped ZnO (GZO) nanofilms was studied. The Ga doping in GZO nanofilms influenced the crystal structure of the films, which affected SHG characteristics of the nanofilms. In our experiments, a strong SHG response was obtained in GZO nanofilms, which was excited by 790 nm femtosecond laser. It was observed that the Ga doping concentrations affected, not only the intensity, but also the polarimetric pattern of SHG in GZO nanofilms. For 5.0% doped GZO films, the SHG intensity increased about 70%. The intensity ratio of SHG between the incident light polarization angle of 90° and 0°changed with the Ga doping concentrations. It showed the most significant increase for 7.3% doped GZO films, with an increased ratio of c/a crystal constants. This result was attributed to the differences of the ratios of d33/d31 (the second-order nonlinear susceptibility components) induced by the crystal distortion. The results are helpful to investigate nanofilms doping levels and crystal distortion by SHG microscopy, which is a non-destructive and sensitive method. [ABSTRACT FROM AUTHOR]