Theory of THz generation by Optical Rectification using Tilted-Pulse-Fronts

TL;DR

This paper presents a comprehensive model for THz generation via optical rectification with tilted-pulse-fronts, accounting for complex optical effects and validated by experiments, to improve efficiency and guide source development.

Contribution

It introduces a detailed 2-D model that includes spectral broadening, spatio-temporal distortions, and nonlinear interactions, advancing understanding of THz generation mechanisms.

Findings

Optical pump beam broadens in transverse-momentum due to spectral effects.

Group velocity dispersion causes pulse break-up, limiting THz generation.

Optimization depends critically on pump pulse shape and spectral properties.

Abstract

A model for THz generation by optical rectification using tilted-pulse-fronts is developed. It simultaneously accounts for (i) the spatio-temporal distortions of the optical pump pulse, (ii) the nonlinear coupled interaction of THz and optical radiation in two spatial dimensions (2-D), (iii) self-phase modulation and (iv) stimulated Raman scattering. The model is validated by quantitative agreement with experiments and analytic calculations. We show that the optical pump beam is significantly broadened in the transverse-momentum (kx) domain as a consequence of the spectral broadening caused by THz generation. In the presence of this large frequency and transverse-momentum (or angular) spread, group velocity dispersion causes a spatio-temporal break-up of the optical pump pulse which inhibits further THz generation. The implications of these effects on energy scaling and optimization of optical-to-THz conversion efficiency are discussed. This suggests the use of optical pump pulses with elliptical beam profiles for large optical pump energies. It is seen that optimization of the setup is highly dependent on optical pump conditions. Trade-offs of optimizing the optical-to-THz conversion efficiency on the spatial and spectral properties of THz radiation is discussed to guide the development of such sources.