Propagation effect of broadband frequency-chirped THz wave pulse in periodically poled lithium niobate

Broadband frequency-chirped multi-cycle terahertz wave (THz) pulses have been generated from periodically poled lithium niobates (PPLNs). Up- and down-chirped THz pulses with temporal frequency shifts from 1 to 1.7 THz and 2 to 1 THz, respectively, were measured. In the waveforms of the both chirped THz pulses, large fluctuation of THz electric field amplitude was observed. Since the fluctuation disturbs exact estimation of temporal frequency shift of chirped THz pulses, suppressing the fluctuation is desired for applications using chirped THz pulses. For this purpose, the origin of the fluctuation of chirped THz pulses have been investigated.