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Photonics Dictionary

mode beating

In optics, "mode beating" refers to an interference phenomenon that can occur in laser systems with multiple longitudinal modes. Longitudinal modes are specific electromagnetic field patterns that can exist within the resonant cavity of a laser.

When a laser emits light, it may support multiple longitudinal modes, each corresponding to a different resonance condition within the laser cavity. These modes can have slightly different frequencies or wavelengths. Mode beating occurs when these different modes interfere with each other, leading to intensity fluctuations or variations in the output of the laser.

The interference arises because the modes have different frequencies, and their superposition can result in constructive or destructive interference, causing the laser output to exhibit intensity variations over time. This phenomenon is particularly noticeable in lasers with a narrow linewidth, where the separation between adjacent modes is smaller.

Mode beating can have practical implications in applications where a stable and uniform laser output is crucial, such as in precision measurements or certain types of spectroscopy. Techniques like mode-locking or linewidth reduction may be employed to control or minimize mode beating in laser systems.
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