  Deriving single or few cycle terahertz pulse (THz) by intense femtosecond
laser through cascaded optical rectification in electro-optic crystals is a
crucial technique in cutting-edge time-resolved spectroscopy to characterize
micro-scale structures and ultrafast dynamics. In the past decade, lithium
niobate (LN) crystal implementation of wave-front tilt scheme has been
prevalently used, while painstaking efforts have been invested in order to
achieve higher THz conversion efficiency. In this research we developed a brand
new type of LN crystal possessing dual-face-cut and Brewster coupling, and
conducted experimental and simulative investigation systematically to optimize
the multi-dimensionally entangled parameters in THz generation, predicting the
extreme conversion efficiency of 10% is potentially promising at the THz
absorption coefficient of 0.5cm-1. More remarkably, we first discovered that
the chirp of the driving laser pulse plays a decisive role in the wave-front
tilt scheme, and the THz generation efficiency could be enhanced tremendously
by applying an appropriate chirp.
