Mode locking is a technique used in lasers to generate short pulses of light (typically in the picosecond to femtosecond range) by forcing different longitudinal modes of the laser cavity to oscillate in phase. In a typical laser, multiple longitudinal modes (which are different frequencies of light that can oscillate in the cavity) can be present, but they may not be in sync with each other. This lack of synchronization results in a continuous wave output.
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