Theoretical study on the generation of THz sub-comb via surface-emitted optical rectification of ultra-short pulse in periodically poled lithium niobate

In this paper, we proposed a method for THz sub-comb generation based on optical rectification. The result of our calculation indicated that THz pulse train, generated by surface-emitted optical rectification (OR) of femtosecond (fs) laser pulse in a periodically poled lithium niobate (PPLN), has a comb-like spectrum. The theoretical analysis was based on radiating antenna model. The characteristic of this THz sub-comb was analyzed both in frequency and time domain. The mechanism of this phenomenon was explained both by spectral interference between early and late pulses and by high-order quasi phase matching. THz sub-comb generated by this method can cover a large bandwidth and have a wide free spectral range.