Limitations to THz generation by optical rectification using tilted pulse fronts

TL;DR

This paper investigates the limitations of terahertz generation via optical rectification with tilted pulse fronts, highlighting how cascading effects and angular dispersion significantly reduce efficiency in lithium niobate.

Contribution

The study introduces comprehensive 1-D and 2-D models that incorporate multiple physical effects, revealing the impact of cascading and angular dispersion on THz generation efficiency.

Findings

Cascading effects cause spectral broadening of the pump pulse.

Angular dispersion enhances phase mismatch, limiting THz output.

Excluding cascading effects overestimates conversion efficiency.

Abstract

Terahertz (THz) generation by optical rectification (OR) using tilted-pulse-fronts is studied. One-dimensional (1-D) and 2-D spatial models, which simultaneously account for (i) the nonlinear coupled interaction of the THz and optical radiation, (ii) angular and material dispersion, (iii) absorption, iv) self-phase modulation and (v) stimulated Raman scattering are presented. We numerically show that the large experimentally observed cascaded frequency down-shift and spectral broadening (cascading effects) of the optical pump pulse is a direct consequence of THz generation. In the presence of this large spectral broadening, the phase mismatch due to angular dispersion is greatly enhanced. Consequently, this cascading effect in conjunction with angular dispersion is shown to be the strongest limitation to THz generation in lithium niobate for pumping at 1 micron. It is seen that the exclusion of these cascading effects in modeling OR, leads to a significant overestimation of the optical-to-THz conversion efficiency. The simulation results are supported by experiments.