Pump Pulse Width and Temperature Effects in High Energy Lithium Niobate THz Sources

Abstract

Intense terahertz source development in the last decade allowed the growth of new areas of research. Tilted-pulse-front pumping of inorganic LiNbO3 (LN) shows good characteristics to achieve the highest possible pulse energies below 1 THz. Ultrafast carrier dynamics of semiconductors were measured by THz pump - THz probe measurements, molecule alignment with an intense field and electron wave streaking were also demonstrated. THz-assisted attosecond pulse generation, would also benefit from intense terahertz pulses. The above mentioned applications require peak electric fields on the order of 100 kV/cm. However, newly emerging areas as acceleration, longitudinal compression, and undulation of relativistic electron bunches, post-acceleration of laser-generated proton and ion beams with potential applications for hadron therapy, multispectral single-shot imaging, THz-enhanced attosecond-pulse generation with increased cut-off frequency would benefit from field strengths higher than currently provided. Multi-mJ and multi-10-MV/cm level sources are needed for these applications. Today extremely high field strengths up to 100 MV/cm are available only in the frequency range above 10 THz. Although the mentioned applications would highly benefit from low frequency THz sources, so that longer wavelength is preferably matching typical transversal sizes of particle beams, pulse energies and peak electric fields necessary for these applications is presently not available. Therefore, it is a priority to optimize THz pulses generated by optical rectification of fs laser pulses with tilted-pulse-front pumping in lithium niobate. Theoretical studies predict an increase in effciency with optimization of pump pulse duration and cryogenic cooling of LN source crystal.