Pulse post-compression after the grating compressor has provided a promising approach for shortening the pulse duration and further enhancing the peak power of super-intense and ultrashort lasers. Although the pulse post-compression technique features undisputed merits, there are still some problems hindering its implementation, especially the small-scale self-focusing (SSSF) effect. A novel method, combining an asymmetric four-grating compressor (AFGC) with the pulse post-compression, is numerically demonstrated to improve the spatial uniformity of laser beams and hence to suppress SSSF during the beam propagation in nonlinear materials. Compared with conventional methods (such as beam self-filtering, spatial filters, etc.), this method is simple and economical, as it does not require additional components or a long spatial propagation distance.

The numerical investigations of this novel pulse post-compression scheme were presented in High Power Laser Science and Engineering, vol. 12, Issue 4 (Pan S, Wu F, Zhao Y, Hu J, Zhang Z, Xu Y, et al. A novel small-scale self-focusing suppression method for post-compression in high peak power lasers [J]. High Power Laser Science and Engineering, 2024, 12(4): 04000e49).

The results indicate that the beam smoothing of AFGC can significantly decrease the gain of spatial noise during the beam propagation in nonlinear materials. As a result, AFGC is beneficial to the suppression of SSSF in the pulse post-compression process, and meanwhile, the shortening of pulse duration from 30 fs to sub-10fs can be achieved. This work proves that this novel method should be very meaningful to promote the practical applications of pulse post-compression in high peak power lasers.

Graphic description: Setup of the post-compression in high peak power lasers with a standard compressor (G₁, G₂, G₃ and G₄, L₁ = L₂) and an AFGC (G^'₁, G₂, G₃ and G^'₄, L₁ ≠ L₂).