The absorption of nanosecond laser pulses induces rapid thermo-elastic deformation in tissue. A sub-micrometer scale displacement occurs within a few microseconds after the pulse arrival. We investigate the thermo-elastic deformation using a 1.5 MHz phase-sensitive optical coherence tomography (OCT) system. An analysis of the results shows that the displacement is dominated by the optical absorption. By tuning the excitation wavelength, thermo-elastic displacement spectrum can be extracted, showing the similar features as optical absorption spectrum. By choosing proper excitation wavelength, targeted tissue type can be highlighted, which further enables a new imaging modality, so called thermo-elastic OCT.