MODEL FPI-05 This Fabry-Perot Interferometer, is commonly used in optics for measuring wavelengths of light, small displacements, and refractive index changes with very high precision, with this model Base Material: Heavy-duty metallic base with leveling feet for vibration isolation Construction: Precision optical mounts and micrometer screws m 5m Interferometer Mirrors type / mounting : 3cm in diameter, 0.