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What Is Q-Switching?

Andrew Kirmayer
Andrew Kirmayer

A laser that incorporates Q-switching operates with pulses of light energy rather than a continuous beam. The intensity of each pulse is extremely high in comparison to a beam that is emitted constantly. Also known as giant pulse formation, the process creates repeated pulses when the laser is fired. A Q-switch laser has an internal device that directly affects the performance of the laser’s optical resonator, changing its quality factor, or Q factor. By assessing this variable, laser operators can know how much light feedback occurs between the laser’s gain medium and resonator, to control short, powerful bursts of laser energy.

In Q-switching, energy builds up in the laser’s gain medium before it is released. Feedback from the laser resonator is prevented at this stage, and energy is stored in the gain medium until a level of saturation is reached. Combined with optical amplification, this process increases the light intensity so quickly that the stored energy is released and used up almost immediately.

Scientist with beakers
Scientist with beakers

Inside the laser, a Q-switch can be a mechanical shutter, a spinning mirror, or an optical modulator. It can also be in the form of a saturable absorber material as in the case of a passive Q-switching laser. The Q-switching lasers of this type can also incorporate a crystal or a semiconductor saturable absorber mirror. A Q-switch laser generally pulses light in bursts of two nanoseconds at a time. The intensity of the pulse depends on the energy storage capacity of the gain medium, and the system’s ability to prevent spontaneous emissions prior to the maximum energy buildup.

Fiber lasers and lasers that utilize crystals and glass can all use Q-switching. Depending on the type of laser and its ability to distribute energy, the ability of the Q-switch can vary. Certain laser characteristics or combinations of them may lead an engineer to adjust the pulse repetition rate according to the required energy level. The duration of the pulse generated by the switching device may also need to be configured, which can be done manually with an active Q-switching laser.

Applications for Q-switching lasers include metal cutting by a manufacturing company or localized dental work where quick, high intensity laser bursts are beneficial. In laser marking, the Q-switch must be turned on and off at specific intervals that vary based on the work being done. Lasers are also Q-switched in medical applications such as plastic surgery and tattoo removal.

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      Scientist with beakers