Qswitching

Q-switching is a laser technique used to generate short, high-intensity optical pulses by manipulating the cavity quality factor (Q). In a Q-switched laser, energy is stored in the gain medium while the cavity remains highly lossy or the intracavity gain is suppressed. When the cavity Q is rapidly lowered (or the loss is released), the stored energy is released in a short, intense pulse.

Implementation can be passive or active. Active Q-switching uses an external fast modulator, such as a Pockels cell or an acousto-optic modulator, controlled by electronics to switch the cavity between high- and low-loss states. Passive Q-switching relies on a saturable absorber inside the cavity that is lossy at low intensity and becomes transparent as the intracavity power rises, enabling a pulse. Some designs employ both approaches or saturable absorber mirrors to tailor performance.

Pulse characteristics typically include durations in the nanosecond range (from a few nanoseconds to tens of nanoseconds) with high peak powers, often kilowatts to megawatts, depending on the gain medium and pump conditions. Repetition rates can range from a few hertz to tens of kilohertz. Common lossy media include Nd:YAG and ruby crystals, producing wavelengths such as 1064 nm (and 532 nm when frequency-doubled) and 694 nm, respectively.

Applications span materials processing, laser ranging and LIDAR, micromachining, engraving, and certain medical or cosmetic procedures. Q-switched lasers deliver high peak power with relatively simple timing compared with mode-locked systems, though they typically produce longer pulses and may exhibit greater timing jitter and beam-quality trade-offs.

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