Nonlinear beam matching to gas-filled multipass cells

Gas-filled multipass cells are an appealing alternative to capillaries to implement nonlinear temporal compression of high energy femtosecond lasers. Here, we provide an analytic expression for stationary beam coupling to multipass cells that takes into account nonlinear propagation. This allows a constant beam size on the mirrors and at the cell waist, thereby making the optical design more accurate, for example to avoid optical damage or significant ionization. The analysis is validated using spatio-temporal numerical simulations of the propagation in a near-concentric configuration. This is particularly important for multipass cells that are operated in a highly nonlinear regime, which is the current trend since it allows a lower number of roundtrips, relaxing the constraint on mirror coatings performance. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Automated summary

Gas-filled multipass cells offer an attractive option for implementing nonlinear temporal compression of high energy femtosecond lasers. By providing an analytic expression for stationary beam coupling to multipass cells considering nonlinear propagation, it is possible to maintain a constant beam size on the mirrors and at the cell waist, improving the accuracy of optical design to avoid damage or ionization. This analysis is validated through spatio-temporal numerical simulations in a near-concentric configuration, which is particularly important for operation in a highly nonlinear regime to reduce the number of round trips and relax constraints on mirror coatings performance.