Abstract
During amplification in a noncollinear optical parametric amplifier the spatial and temporal coordinates of the amplified field are inherently coupled. These couplings or distortions can limit the peak intensity, among other things. In this work, a numerical study of the spatiotemporal distortions in BBO-based noncollinear optical parametric chirped-pulse amplifiers (NOPCPAs) is presented for a wide range of parameters and for different amplification conditions. It is shown that for Gaussian pump beams, gain saturation introduces strong distortions and high conversion efficiency always comes at the price of strong spatiotemporal couplings which drastically reduce the peak intensity even when pulse fronts of the pump and the signal are matched. However, high conversion efficiencies with minimum spatiotemporal distortions can still be achieved with flat-top pump beam profiles.
Highlights
Over the past two decades, optical parametric amplification has become an attractive technique to generate ultrashort, tunable pulses over a broad wavelength range from the visible to the mid-infrared [1,2,3]
Single stage and double stage amplifiers have been modelled under different amplification conditions and the spatiotemporal distortions in the amplified signal pulses have been characterized
As long as the amplifier is not saturated, the distortions at the output that are confined to the walk-off plane, are almost linear, and can be characterized by well-known parameters such as the pulse-front tilt angle, and constant spatial chirp and angular dispersion values
Summary
Over the past two decades, optical parametric amplification has become an attractive technique to generate ultrashort, tunable pulses over a broad wavelength range from the visible to the mid-infrared [1,2,3]. A detailed numerical study of spatiotemporal distortions in noncollinear optical parametric chirped-pulse amplifiers (NOPCPAs) is presented, utilizing threedimensional (3D) simulations. The aim of our study is to characterize the spatiotemporal properties of the amplified field and to find guidelines for optimum amplifier design It is investigated how spatiotemporal distortions in the amplified beam depend on experimental conditions such as noncollinear angle, pump beam size, phasematching geometry, pulse front matching, and distortions in the seed beam and how they are related to gain saturation and back conversion. The impacts of spectral shaping of the signal pulse and spatial shaping of the pump beam are analyzed in saturated amplifiers It is discussed how spatiotemporal distortions from a first amplification stage influence a second amplification stage. A series of recommendations for the optimal design of a BBO-based NOPCPA are given based on the simulation results
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