The resonator's quality factor, Q, is held low with a Pockels cell, acousto-optic modulator or saturable absorber while the pump builds inversion far above normal threshold. Switching Q high releases the stored energy in a single giant pulse, typically 5 to 100 ns long with peak powers of kilowatts to megawatts. Media with long upper-state lifetimes, such as Nd:YAG at about 230 µs, store the most energy.
Q-switching at 10 kHz the pulses are 12 ns, drop to 1 kHz and they get shorter with way more energy, so check the fluence on the doubler first.
Do not mix it up with
- Mode locking: Mode locking gives picosecond or femtosecond pulses at MHz rates; Q-switching gives nanosecond pulses at Hz to kHz rates.
Related terms
Pockels cell
An electro-optic crystal that changes a beam's polarization when high voltage is applied, used as a fast optical switch.
Saturable absorber
A material whose absorption drops at high intensity, used to start and sustain Q-switching or mode locking passively.
Population inversion
The condition where more atoms occupy the upper laser level than the lower one, which a medium needs to give gain.
Peak power
The highest instantaneous power reached during a laser pulse, roughly pulse energy divided by pulse duration.
Double pulsing
A fault where a pulsed laser emits two pulses where it should emit one, from too much gain or bad switch timing.