Mode structure of supercontinuum generated by ultrashort pulses in antiresonant hollow-core fibers

The mode structure of broadband radiation with the spectrum from 200 to 2500 nm, which is obtained in the process of soliton self-compression of a laser pulse in an antiresonant hollow-core fiber, has been analyzed. It has been demonstrated that the most energy-intensive infrared part of radiation from 1300 to 2500 nm, which forms a single-cycle pulse, is localized in the fundamental spatial mode $LP_{01}$. Under phase matching conditions in the visible part of the supercontinuum, the third harmonic is generated near 620 nm in high-order modes and tube modes. It has been shown that the third harmonic radiation at a wavelength of about 700 nm localized in the core of the fiber can be used to measure the phase of the field with respect to the envelope of ultrashort pulses at the output of the fiber.