A device that confines light in a closed path to enhance optical interactions.An optical resonator is a device that confines light in a closed path, typically between mirrors, allowing it to bounce back and forth and build up intensity through constructive interference. Resonators are fundamental to lasers, where they provide the feedback needed for light amplification, and to optical cavities used in precision measurement, quantum optics, and sensing. They enable enhanced light–matter interactions by trapping photons for many round trips, effectively increasing the interaction length by orders of magnitude.
The concept of an optical resonator dates back to the early 20th century with Fabry–Pérot interferometers, developed by Charles Fabry and Alfred Pérot in 1897. The application to lasers was realized in the 1950s–1960s, with the first working laser by Theodore Maiman in 1960 using a simple resonator.
Light circulating in a resonator forms standing waves at specific frequencies determined by the cavity length and mirror reflectivity. When the round-trip phase shift is a multiple of 2π, the cavity is on resonance and light builds up coherently. The quality factor Q measures how long photons persist in the cavity, with high-Q cavities confining light for microseconds or longer, enabling extremely sensitive measurements of frequency shifts, absorption, or mechanical motion.
Optical resonators are used in laser technology, gravitational wave detectors like LIGO, optical frequency combs, and cavity quantum electrodynamics experiments for quantum computing and communication.
The LIGO gravitational wave detectors use Fabry–Pérot resonators with mirrors that are so reflective that light bounces back and forth about 280 times, effectively extending the detector's arm length from 4 km to over 1,100 km.
| F | variable | form factor value — form factor |
| k | variable | momentum transfer — momento kilogram metre per second |
| Λ | constante | energy scale above which new physics or compositeness becomes relevant — cutoff scale = varies kilogram metre per second |
