Interferometric

Interferometric refers to methods and instruments that rely on optical (or other wave) interference to measure properties of a system. Interferometry compares the phase of waves that have traveled along different paths, and from the resulting interference pattern one can infer path-length differences, refractive-index changes, or surface contours with high precision. Although commonly used with light, interferometry also applies to sound, electrons, and other coherent waves.

At its core, a wave is split into two or more paths by a beamsplitter. The beams are reflected and then recombined, producing constructive or destructive interference depending on the relative phase. The detected signal, usually an intensity or fringe visibility, is mapped to a path-length difference ΔL via the phase φ = (2π/λ)ΔL for monochromatic light. White-light interferometry uses a broad spectrum, yielding short coherence length and localized fringes that indicate a height difference.

Interferometric techniques are used in metrology (measuring surface flatness, thickness, and refractive index), spectroscopy, and vibration sensing. In astronomy, interferometry achieves higher angular resolution by combining light from separate telescopes. In gravitational-wave physics, large Michelson interferometers detect minute spacetime strains; ring-laser gyroscopes and fiber-based interferometers enable rotation sensing and precise phase measurements.

Common interferometers include the Michelson (two arms with a beam splitter), Mach-Zehnder (distinct input and output arms for samples), Fabry-Pérot cavities (two mirrors with multiple reflections), and the Sagnac interferometer (beam loop for rotation sensing).

Key challenges include sensitivity to mechanical vibration, thermal drift, and air turbulence; high precision often requires vibration isolation, vacuum enclosures, and laser stabilization. Alignment and optical quality of components are critical to fringe contrast.