Nearly single-cycle terahertz pulse generation in aperiodically poled lithium niobate

Abstract

In the present work, an opportunity of nearly single-cycle THz pulse generation in aperiodically poled lithium niobate (APPLN) crystal is studied. A radiating antenna model is used to simulate the THz generation from chirped APPLN crystal pumped by a sequence of femtosecond laser pulses with chirped delays (m = 1, 2, 3 . . . ) between adjacent pulses. It is shown that by appropriately choosing Δt m , it is possible to obtain temporal overlap of all THz pulses generated from positive (or negative) domains. This results in the formation of a nearly single-cycle THz pulse if the chirp rate of domain length d in the crystal is sufficiently large. In the opposite case, a few cycle THz pulses are generated with the number of the cycles depending on δ. The closed-form expression for the THz pulse form is obtained. The peak THz electric field strength of 0.3 MV/cm is predicted for APPLN crystal pumped by a sequence of laser pulses with peak intensities of the separate pulse in the sequence of about 20 GW/cm 2 . By focusing the THz beam and increasing the pump power, the field strength can reach values in the order of few MV/cm.