Comprehensive Numerical Modelling of a Low-Gain Optical Parametric Amplifier as a Front-End Contrast Enhancement Unit

TL;DR

This paper develops a detailed numerical model for a second harmonic generation optical parametric amplifier used to improve laser pulse contrast, accounting for various physical parameters and optimizing system configuration.

Contribution

It introduces a comprehensive simulation framework that considers all key parameters affecting the performance of the optical parametric amplification system.

Findings

Optimal crystal length and delay settings enhance efficiency.

Initial beam divergence impacts spectral and temporal pulse characteristics.

Chirped pulses benefit from specific delay adjustments for maximum gain.

Abstract

We present a comprehensive model for predicting the full performance of a second harmonic generationoptical parametric amplification system that aims at enhancing the temporal contrast of laser pulses. The model simultaneously takes into account all the main parameters at play in the system such as the group velocity mismatch, the beam divergence, the spectral content, the pump depletion, and the length of the nonlinear crystals. We monitor the influence of the initial parameters of the input pulse and the interdependence of the two related non-linear processes on the performance of the system and show its optimum configuration. The influence of the initial beam divergence on the spectral and the temporal characteristics of the generated pulse is discussed. In addition, we show that using a crystal slightly longer than the optimum length and introducing small delay between the seed and the pump ensures maximum efficiency and compensates for the spectral shift in the optical parametric amplification stage in case of chirped input pulse. As an example, calculations for bandwidth transform limited and chirped pulses of sub-picosecond duration in beta barium borate crystal are presented.