Phase-matching mechanism for high-photon-energy harmonics of a long trajectory driven by a midinfrared laser

High-order harmonics were generated with neon gas by using 12-fs midinfrared laser pulses with stabilized carrier-envelope phase (CEP). At some specific CEP, a broad supercontinuum of the extreme ultraviolet spectrum can be obtained. Two distinct continuous spectral regimes are found by numerical simulation, which come from two adjacent half cycles of the laser pulse. A phase-matching mechanism for high-photon-energy harmonics of a long trajectory driven by a midinfrared laser pulse is found.