  We report on the coherent phonon spectroscopy of polymorphic
$\mathrm{MoTe_2}$ single crystals using a femtosecond-pulsed laser to
investigate the relationship between structural phase transitions and
photo-thermal effects induced by high-density laser excitation. Even when a
femtosecond pulsed laser was used, which generally induces fewer heat
accumulation effects than the case for a CW laser, tellurium segregation was
observed in coherent phonon spectra with increasing excitation density, while
no structural phase transition among polymorphs of $\mathrm{MoTe_2}$ was
observed. The use of higher photon-energy excitation, however, was found to
suppress tellurium segregation.
