LaserInterferometer

A laser interferometer is a precision measurement instrument that uses the interference of coherent light to detect extremely small changes in optical path length. In a typical Michelson configuration, a laser beam is split by a beam splitter into two perpendicular arms, reflects off highly polished mirrors, and recombines. A path-length difference changes the relative phase and alters the interference pattern detected by a photodetector.

Common variants include Mach-Zehnder, Sagnac, and Fabry-Perot-based configurations that extend the effective path length. Modern high-sensitivity interferometers place the arms in vacuum, use long or folded cavities, and employ advanced vibration isolation and active stabilization to suppress environmental noise. Core components are the laser source, beam splitter, mirrors, photodetector, optical benches, and control systems that stabilize laser frequency, alignment, and arm length.

Sensitivity is limited by technical and quantum noise. Seismic and acoustic disturbances, thermal fluctuations, and laser intensity noise couple into the signal, while quantum shot noise and radiation pressure set fundamental limits. Techniques to mitigate noise include frequency and power stabilization, isolation systems, vacuum enclosures, and feedback control; in long-baseline detectors, recycling and arm-cavity locking schemes boost signal power and sensitivity.

Applications include precision metrology, surface profiling, and calibration tasks. The most notable use is gravitational-wave detection, with kilometer-scale instruments such as LIGO, Virgo, and KAGRA observing spacetime perturbations from cosmic sources. Interferometers also support fiber-optic sensing, rotation sensing with ring lasers, and industrial metrology. The technology has driven advances in laser stabilization, cavity design, and data-analysis methods for very small signals.