Simulation of THz generation through optical rectification in bulk lithium niobate (LiNbO3) crystals

Abstract

Terahertz (THz) generation is an active area of research due to its applications in material characterization, medical imaging, and telecommunications among several. One mechanism, optical rectification (OR) in electro-optic materials like lithium niobate (LN) with Cherenkov phase-matching scheme, is ideal for generating THz pulses due to its high electro-optic coefficient resulting in ultrafast modulation, low-voltage operation, and low optical losses. In this work, we considered the nonlinear polarization induced by the LN slab to simulate THz emission. Then, we matched the temporal duration of the experimental data that we had with the simulations, and proceeded with parametrizing the slab thickness d and optical pulse duration τ. We found that d must satisfy the Cherenkov condition for efficient THz pulse generation; we observed an oscillatory trend on the peak THz field as d thickens. On the other hand, as τ became higher, the peak THz field became lower by a factor of 1/τ² due to the second-order nonlinear property of OR, but decayed more slowly due to detector response.