High-temporal-contrast stretcher design based on an asymmetric Offner triplet

A new stretcher design based on an asymmetric Offner triplet is proposed for better pulse contrast performance while maintaining excellent imaging performance of the conventional Offner stretcher. The contrast degradation due to the intermediate focusing on the secondary mirror in a symmetric Offner stretcher is avoided in the asymmetric Offner, where the intermediate focus is shifted away from the secondary mirror surface. The effect of beam propagation on contrast is analyzed with respect to the location of the phase screen that introduces spatiospectral coupling, as well as the location of the detection plane. It is found that a larger optical distance from the phase screen to the detection plane improves the contrast. The contrast performances of spherical and cylindrical Offner stretchers and the asymmetrical spherical Offner stretcher are compared using 3D ray tracing and beam propagation calculation within ±20 ps. The new stretcher shows the best contrast compared with the other two while minimizing spatiotemporal distortion of the pulse.