Simulating THz generation for powering compact X-ray sources

Compact x-ray sources can be made compact by using THz electromagnetic waves to power scaled down accelerating structures. An efficient method of generating the THz is via optical rectification using tilted pulse fronts in a nonlinear optical crystal such as Lithium Niobate. A phenomenological simulation code for the THz generation by an optical pump pulse impinging on a lithium niobate crystal is presented. linear and nonlinear optical parameters serving as inputs are obtained from the literature. A realistic optical system delivering the pump pulse to the crystal is modelled, and optical rectification is achieved in a 2D model. The simulation model is validated by comparison with an experiment consisting of a 4.2 mJ, 1030 micron, 650 fs pump pulse incident on a 5.6% MgO doped LiNO₃ crystal. There is reasonable agreement between simulation and experiment. At a pump fluence of 500 J/m², THz is extracted with 0.6% efficiency at 300 K and 1.2% efficiency at 100 K. Optimisation of the extracted efficiency using the simulation is explored.