Elastography is a method to image the biomechanical properties of tissues. The experimental setup has a 10 MHz ultrasound transducer (focal length of 5cm and a spot size of 0.3mm localized excitation and unfocused for wide-area excitation) which generates acoustic radiation force (ARF) to perturb the sample and the corresponding mechanical response is imaged with a spectral domain optical coherence tomography (SD-OCT) with a center wavelength of 800 nm and a bandwidth of 180 nm at a transverse optical resolution of 8[mu]m. The existing hypothesis which states that localized harmonic excitation in audio frequency regime has potential advantages in terms of a better mechanical resolution over wide area harmonic excitation is tested. Contrary to the hypothesis, experimental results demonstrates that wide area harmonic excitation has better mechanical resolution. Further the characterization of the frequency dependence of mechanical contrast establishes that mechanical contrast improves with increasing excitation frequency.