Theoretical comparison of spatiotemporal contrasts of pulsed beams in unfocusing, 1D-focusing, and 2D-focusing fields and enhancement of the on-axis temporal contrast at the focus

Abstract

With the rapid development of ultra-intense femtosecond lasers, the measurement and then the improvement of the temporal contrast (ratio of signal to noise) become more and more important, which have already aroused wide concern. Recently, due to the technical limit, the temporal contrast usually is measured in the unfocusing or 1D-focusing field; however, such lasers are utilized in the 2D-focusing field for relativistic or even higher intensities. Herein, we theoretically compared the spatiotemporal contrasts of pulsed beams in the unfocusing, 1D-focusing, and 2D-focusing fields while common temporal and spatiotemporal distortions are being considered. The result shows the near-field spatiotemporal distortion of a pulsed beam would degrade its spatiotemporal contrast at the focus, however, which cannot be detected in the unfocusing field. Meanwhile, different from the traditional view, the on-axis temporal contrast at the focus can be enhanced by introducing a suitable slowly varying spatiotemporal coupling in the near field, e.g., a suitable low spatial frequency deformation at the second or the third grating in the compressor.