A method and apparatus for detecting changes in the vibrational mode spectra and/or elasticity of a pellicle without reliance upon visual inspection are provided. Embodiments include providing a pellicle, a lower surface of the pellicle attached to a photomask; directing light from a light source onto an upper surface of the pellicle at an angle to the upper surface; causing a deflection of the pellicle concurrently with the light being directed onto the pellicle; detecting light reflected off of the deflected pellicle; and characterizing a vibrational mode of the pellicle based on the detection.