Spatiotemporal filtering of high harmonics in solids

We study the macroscopic spatial and temporal properties of harmonic radiation generated by a model solid in the interaction with an intense, focused laser beam. We show that different temporal contributions to the harmonic yield can be separated in the spatial domain because they lead to radiation with different divergences, similar to what is observed in gas-phase harmonic generation. We show that applying a spatial filter in the far field results in a temporal separation of the two contributions upon refocusing, which yields spatially collimated harmonics, a spectrum with well-resolved peaks, and a subcycle time profile of the harmonic radiation with only one burst per half-cycle.