  Optical control of Dirac surface states (SS) in topological insulators (TI)
remains one of the most challenging problems governing their potential
applications in novel electronic and spintronic devices. Here, using
visible-range transient absorption spectroscopy exploiting ~340 nm (~3.65 eV)
pumping, we provide evidence for dynamic opening of a gap in Dirac SS of the
thin-film 3D TI Bi2Se3, which has been induced by the dynamic Rashba effect
occurring in the film bulk with increasing optical pumping power (photoexcited
carrier density). The observed effect appears through the transient absorption
band associated with inverse-bremsstrahlung-type free carrier absorption in the
gapped Dirac SS. We have also recognized experimental signatures of the
existence of the higher energy Dirac SS in the 3D TI Bi2Se3 (in addition to
those known as SS1 and SS2) with energies of ~2.7 and ~3.9 eV (SS3 and SS4). It
is evidenced that the dynamic gap opening has the same effect on the Dirac SS
occurring at any energy.
