Pulse Repetition Rate
The pulse repetition rate (or pulse repetition frequency) frep of a regular train of pulses is defined as the number of emitted pulses per second, or more precisely the inverse temporal pulse spacing.
- Typical mode-locked solid-state lasers emit with pulse repetition rates between 50 MHz and a few gigahertz, but in extreme cases < 10 MHz or > 100 GHz are possible. In most cases, there is a single pulse circulating in such a laser, so that the pulse repetition rate is the inverse round-trip time in the laser resonator.
- Q switching of solid-state lasers typically allows repetition rates from below 1 Hz to the order of 100 kHz. For active Q switching, the pulse repetition rate is determined by an external drive signal, while for passive Q switching its depends on the magnitude of loss modulation, the pump power and various other parameters.
- Gain switching of semiconductor lasers can provide repetition rates from below 1 Hz to many megahertz.
- Attosecond pulse trains of finite length can be generated via high harmonic generation with repetition rates of hundreds of terahertz. Here, the pulse repetition rate is twice the optical frequency of the pump light.
The article on pulse trains for methods of multiplying or dividing the pulse repetition rate.
For burst mode lasers, there are two different repetition rates: the pulse repetition rate within each burst and the much lower repetition rate of the bursts.
If a pulse train is regular and the pulses are mutually coherent, the optical spectrum of the pulse train is a frequency comb, where the spacing of the lines is determined by the pulse repetition rate.
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