  Simultaneous measurements of transient transmission and reflectivity were
performed in the unintentionally doped InN film to reveal ultrafast optical
bleaching and its recovery behavior under intense laser irradiation. The
optical bleaching is attributed to Pauli blocking due to the occupation of
photoexcited electrons at the probing energy level. The time constant for the
transition from the excitation state to the conduction band edge is $\sim$260
fs. The interplay between band filling and band gap renormalization caused by
electron-hole and electron-electron interactions gives rise to complex spectral
characteristics of transient reflectivity, from which the time constants of
photoexcited electron-hole direct recombination and band edge recombination are
extracted as $\sim$60 fs and 250$\sim$400 fs, respectively. Our results also
reveal that the electron-electron interaction suppresses band edge
recombination, and mitigates the recovery process. Our experiments highlight
the controllability of the band structure of semiconductors by intense laser
irradiation.
