  High-energy, few-cycle laser pulses are essential for numerous applications
in the fields of ultrafast optics and strong-field physics, due to their
ultrafast temporal resolution and high peak intensity. In this work, different
from the traditional hollow-core fibers and multiple thin solid plates, we
represent the first demonstration of the octave-spanning supercontinuum
broadening by utilizing multiple ultrathin liquid films (MTLFs) as the
nonlinear media. The continuum covers a range from 380 to 1050 nm,
corresponding to a Fourier transform limit pulse width of 2.5 fs, when 35 fs
Ti:sapphire laser pulse is applied on the MTLFs. The output pulses are
compressed to 3.9 fs by employing chirped mirrors. Furthermore, a continuous
high-order harmonic spectrum up to the 33rd order is realized by subjecting the
compressed laser pulses to interact with Kr gas. The utilization of flowing
water films eliminates permanent optical damage and enables wider and stronger
spectrum broadening. Therefore, this MTLFs scheme provides new solutions for
the generation of highly efficient femtosecond supercontinuum and nonlinear
pulse compression, with potential applications in the fields of strong-field
physics and attosecond science.
