  We investigate the ultrafast transient absorption spectrum of Bi2Se3
topological insulator. Bi2Se3 single crystal is grown through conventional
solid-state reaction routevia self-flux method. The structural properties have
been studied in terms of high-resolution Powder X-ray Diffraction (PXRD).
Detailed Rietveld analysis of PXRD of the crystal showed that sample is
crystallized in the rhombohedral crystal structure with a space group of R-3m,
and the lattice parameters are a=b=4.14A and c=28.7010A. Scanning Electron
Microscopy (SEM) result shows perfectly crystalline structure with layered type
morphology which evidenced from surface XRD. Energy Dispersive Spectroscopy
(EDS) analysis determined quantitative amounts of the constituent atoms, found
to be very close to their stoichiometric ratio. Further the fluence dependent
nonlinear behaviour is studied by means of ultrafast transient absorption
spectroscopy. The ultrafast spectroscopy also predicts the capability of this
single crystal to generate Terahertz (THz) radiations (T-rays).
