Generation of sub-half-cycle ultrafast pulses in a flat-slit-confined optical field
Phys. Rev. A 113, 053515 – Published 12 May, 2026
DOI: https://doi.org/10.1103/wjxh-p9sn
Abstract
Compressing an ultrafast optical pulse down to a subcycle scale is an essential approach to improving temporal resolution in light-matter interaction. Considering that temporal far-field approaches have a half-cycle limit in generating subcycle pulses, recently we have proposed to break this limit in the temporal near field, and generate sub-half-cycle pulses via inverse Compton scattering in a sub-half-wavelength spatially confined optical driving field, which is generated in a line slit constructed by two sapphire hexagonal waveguides. While in principle one can generate an ultrafast optical pulse with pulse width narrower than 0.1 cycle, the practical fabrication of sapphire hexagonal waveguides and the line-slit-confinement structure is highly challenging. Here, we propose to replace the line slit with a flat slit constructed with two sapphire square waveguides, which can not only simplify the fabrication of the field-confining structure, but also evidently increase the single-pulse energy of the yielded sub-half-cycle pulse. For example, using a 0.4-THz 1-ps optical driving field and a 1-fs 3-MeV 0.1-nC electron bunch, a 0.12-cycle 5.1-fs-width midinfrared femtosecond pulse can be obtained, while the single-pulse energy is increased from 3.3 to 5.2 pJ, due to the increased fraction of the driving-field energy in the flat slit.
