Generation of pump pulse trains by Gires-Tournois etalons for efficient multicycle terahertz pulse generation.

Wafer stacks of lithium niobate are frequently used to generate multicycle terahertz (THz) pulses with high energy via optical rectification of ultrafast optical pulses. However, using a single pump pulse, the THz generation efficiency of such devices is relatively low. In this article, the use of Gires-Tournois etalons (GT) to create pump pulse trains for higher THz generation efficiencies is introduced and systematically studied using numerical simulations. The use of one etalon results in a 120% efficiency increase, while introducing a second one provides a further 59% increase, resulting in more than tripling of the efficiency by two GTs together. Optimal conditions for the thickness of the etalons, their stability, and behavior when used in cascade are studied. Using GT results in a narrower and clearer THz spectrum. Preliminary experiments demonstrated a 111% efficiency increase in the case of using one etalon.