Coupled propagation and Coulomb effects shift optimal phase for THz yield by more than isolated models predict

The study solves a coupled propagation-plus-trajectory model for 800 nm + 400 nm pulses focused into gas. Nonlinear propagation distorts the local waveform through Kerr and plasma defocusing; the altered field then drives electron trajectories whose recollision probability is corrected by the ionic Coulomb potential. Phase scans of the resulting net photocurrent show the THz maximum displaced by an additional 0.15–0.25 rad relative to propagation-only or Coulomb-only runs. The directional asymmetry of the momentum distribution narrows accordingly, directly reducing the radiated THz bandwidth.

Prior two-color THz literature treated propagation and atomic recollision as sequential or independent. The coupled treatment reveals that waveform distortion changes the recollision window, which in turn modifies local current density and back-action on propagation—an interaction missed by both hydrodynamic and pure TDSE approaches. This explains why experimental phase optima often deviate from simple two-step predictions.

The model is one-dimensional in propagation and uses a classical trajectory Monte Carlo ensemble; three-dimensional filamentation, ionization dynamics, and quantum interference remain omitted. Full validation therefore requires spatially resolved THz and electron-momentum measurements under controlled dispersion.

Next steps include extending the framework to circular or orthogonal polarizations and testing against measured THz spectra from 10–100 TW/cm² two-color filaments.