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Description
The superradiant regime of free-electron lasers (FELs) provides a promising route toward the generation of ultrashort X-ray pulses, especially at the attosecond timescale. While previous studies have investigated the differences among various transverse modes during the FEL amplification process, this work focuses specifically on their behavior in the superradiant regime. Our study is based on the self-seeded FEL with orbital angular momentum (SSOAM) configuration, in which a seed pulse carrying different topological charges is introduced upstream of the FEL amplifier. We systematically analyze the evolution of different transverse modes under superradiant conditions, including the influence of detuning. Our results provide insights into the amplification mechanisms of different transverse modes in the superradiant regime and support the generation of high-peak-power, attosecond-scale OAM pulses, thus expanding the capabilities of XFELs in probing ultrafast electronic and structural dynamics.