Increasing bandwidth of Cherenkov-type terahertz emitters by free carrier generation

We found experimentally that Cherenkov-type terahertz radiation produced by optical rectification of ultrashort laser pulses in LiNbO3 can experience strong spectral broadening in the regime of multiphoton laser absorption. The broadening is attributed to the terahertz emission from a surge current of the optically generated carriers. The effect can be used to improve the bandwidth of optical-to-terahertz converters based on optical rectification.