Comparative analysis of optical rectification-based multicycle terahertz pulse generation techniques

Numerical investigations of multicycle terahertz pulse generation based on wafer stack and tilted pulse front pumped lithium niobate setups concerning the conversion efficiency and the resulting temporal shape and spectrum were performed. Pumping by Fourier-limited-, chirped-, and intensity-modulated pulses, as well as pulse sequences was considered. Wafer stacks give a maximum efficiency when the pump pulse duration is 0.243 times the temporal period of the generated THz pulse. In wafer stacks, increasing the number of pulses in a sequence drastically increases the efficiency. A five-period wafer stack tailored for a 0.15 THz frequency achieves a maximum efficiency of almost 0.1% when pumped by a single, 1.5 ps pulse with an intensity of 100 GW$^2$/cm$^2$, and 0.3% when pumped by a sequence of five pulses. In a similar wafer stack of 10 periods, the efficiency with the same pulse sequence reaches 0.7%. For a large pump pulse number, the efficiency increase approaches a factor equal to the number of wafer pairs. For a given number of THz cycles, the highest efficiency is obtained when the number of wafer stack periods and pump pulses are equal to half the number of cycles. For relatively small cycle numbers, tilted-pump-front setups were found to yield the highest conversion efficiencies.