Generation of tunable ultrashort THz radiation up to 5.5 THz

Abstract

We report on the generation of tunable, ultrashort THz radiation between 2.0 and 5.3 THz by optical rectification of femtosecond laser pulse trains in the highly nonlinear crystal 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST). Femtosecond pulse trains with a THz repetition rate are successfully synthesized from a single laser pulse using a zone plate which consists of a stack of thin glass plates. Using four glass slides we could experimentally demonstrate a substantial narrowing of the spectral bandwidth of the THz radiation. The spectral characterization of the THz pulses is accomplished using a Michelson interferometer. By simply tilting the zone plate the peak frequency is tuned from 2.0 to 5.3 THz. Even though higher and lower frequencies can be generated, the reported range is limited by the spectral characteristics of our detector. To our knowledge, our work demonstrates the first application of a zone plate for the generation of ultrashort THz pulses, tunable over a very large spectral range.