Tunable Narrow-band THz Generation by Type-II Difference Frequency Generation with Linearly Chirped Optical Pulses in ZnTe

Bright, tunable sources of narrow-band THz radiation are highly desirable for studies of low energy excitations of various systems such as phonons, strongly correlated electron systems, and the rotational and vibrational states of molecules. Techniques developed so far to obtain narrow-band THz pulses include mixing chirped optical pulses in a photoconductive switch; optical rectification of shaped pulses; and optical rectification in quasi-phase matching nonlinear crystals. For these methods, either loss of optical power in the optical components or parasitic nonlinear effects in the nonlinear media lowers the efficiency of THz generation. In this work, we demonstrate a novel scheme for generation of tunable narrow-band THz pulses, in which the undesirable effects are substantially reduced. We produced narrowband THz pulses via type-II difference frequency generation in ZnTe, where two linearly-chirped and orthogonally-polarized broadband near-IR pulses were employed. We tuned the central frequency by adjusting the time delay between the two optical pulses.