Herein, coherent phonon spectroscopy of polymorphic MoTe 2 single crystals using a femtosecond‐pulsed laser is used to investigate the relationship between structural phase transitions and photo‐thermal effects induced by high‐density laser excitation. Even when a femtosecond‐pulsed laser is used, which generally induces fewer heat accumulation effects than the case for a continuous‐wave (CW) laser, tellurium segregation is observed in coherent phonon spectra with increasing excitation density, while no structural phase transition among the polymorphs of MoTe 2 is observed. The use of higher photon‐energy excitation, however, is found to suppress tellurium segregation.