  We present nonlinear optical absorption properties of pulsed laser deposited
thin films of topological insulator (TI), Bi2Se3 on quartz substrate, using
open aperture Z - scan technique. The saturable intensity of as-deposited thin
films has been found remarkably improved by an order of magnitude compared to
the values reported earlier in the literature. Past results from the literature
are inconclusive in establishing whether the saturable absorption is coming
from surface states or the bulk. Specifically designed experiments with
magnetically doped TI samples allow us to attribute the saturable absorption
characteristic of TI to the bulk states. Detailed experimental procedures and
possible explanation of observed results have been discussed.
