Fig. 4: Fitting analyses of high- and low- frequency components of reflectivity changes.

a The square of the electric-field waveform EMIR(t) of the mid-infrared (MIR) pulse with the maximum electric-field amplitude, EMIR, of 6.1 MV cm−1. b Time characteristics of the high-frequency component ΔRHF(t)/R (open circles). The red line shows the fitting curves. The purple and pink solid lines represent the components of the fitting curve corresponding to HPF{F(t)} and HPF{G(t)} in Eq. (1), respectively. HPF is an operator that extracts high-frequency components. F(t) and G(t) are functions defined by Eq. (2) and Eq. (3), respectively. c Time characteristics of the low-frequency components ΔRLF(t)/R(open circles) and the fitting curves (red line). The blue, orange and green solid lines represent the components of the fitting curve corresponding to the first, the third, and the second terms (LPF{b0[F(t)]}, oscillation A, and oscillation B) in Eq. (6), respectively. LPF shows an operator that extracts a low-frequency component.