  The quasi-two-dimensional nickel chalcogenides $TlNi_2Se_2$ is a newly
discovered superconductor. We have performed optical spectroscopy study on
$TlNi_2Se_2$ single crystals over a broad frequency range at various
temperatures. The overall optical reflectance spectra are similar to those
observed in its isostructure $BaNi_2As_2$. Both the suppression in $R(\omega)$
and the peaklike feature in $\sigma_1(\omega)$ suggest the progressive
formation of a pseudogap feature in the midinfrared range with decreasing
temperatures, which might be originated from the dynamic local fluctuation of
charge-density-wave (CDW) instability. We propose that the CDW instability in
$TlNi_2Se_2$ is driven by the saddle points mechanism, due to the existence of
van Hove singularity very close to the Fermi energy.
