Pulse Repetition Rate
Author: the photonics expert Dr. Rüdiger Paschotta (RP)
Acronym: PRF
Definition: the number of pulses emitted per second e.g. by a mode-locked or Q-switched laser
Alternative term: pulse repetition frequency
Categories:
- pulse properties
- carrier–envelope offset
- chirp
- pulse bandwidth
- pulse duration
- pulse energy
- pulse front tilt
- pulse repetition rate
- spectral phase
Related: pulse generation light pulses pulse trains frequency combs timing jitter
Units: Hz
Formula symbol: ($f_\textrm{rep}$)
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DOI: 10.61835/aep Cite the article: BibTex BibLaTex plain text HTML Link to this page! LinkedIn
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What is a Pulse Repetition Rate?
The pulse repetition rate (or pulse repetition frequency) ($f_\textrm{rep}$) of a regular train of pulses is defined as the number of emitted pulses per second, or more precisely the inverse temporal pulse spacing.
Depending on the technique of pulse generation (concerning light pulses), typical pulse repetition rates can be in different parameter regions:
- 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 it 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.
See 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.
The deviation from perfect periodicity of the optical power is called timing jitter .
Frequently Asked Questions
This FAQ section was generated with AI based on the article content and has been reviewed by the article’s author (RP).
What is the pulse repetition rate?
The pulse repetition rate, also called pulse repetition frequency, is the number of light pulses emitted per second in a regular pulse train. It is the inverse of the time interval between consecutive pulses.
What determines the repetition rate of a mode-locked laser?
In most mode-locked lasers, a single pulse circulates in the laser resonator. Therefore, the pulse repetition rate is the inverse of the resonator round-trip time.
How do typical repetition rates of Q-switched and mode-locked lasers compare?
Mode-locked lasers typically have much higher repetition rates, often from 50 MHz to several gigahertz. In contrast, Q-switched lasers usually operate at lower rates, from less than 1 Hz up to about 100 kHz.
What is the relationship between pulse repetition rate and a frequency comb?
If a pulse train is regular and the pulses are mutually coherent, its optical spectrum is a frequency comb. The frequency spacing between the comb lines is equal to the pulse repetition rate.
What is a burst mode laser in terms of repetition rates?
A burst mode laser emits bursts of pulses and is characterized by two different repetition rates: a high rate for the pulses within each burst and a much lower rate for the bursts themselves.
Suppliers
Sponsored content: The RP Photonics Buyer's Guide contains 21 suppliers for pulse pickers. Among them:
pulseSelect is an acousto-optic pulse picker, developed for the special demands of femtosecond laser technology. Pulse distortion is minimized by a low dispersive design and the use of reflective optics. High repetition rates and high contrast rates are achieved by using acousto-optical elements. The pulse repetition rate can be reduced by an adjustable internal frequency divider or by external triggering.
APE offers pulse pickers for either a wavelength range from 500 nm to 1600 nm or dual wavelength bands from 340 nm to 540 nm and from 680 nm to 1080 nm.
GWU’s UHG-PSK Series has been designed for ultrafast laser oscillators. It offers pulse picking with highest output powers and optimum contrast ratio. The system is suitable for femtosecond and picosecond pulses with high input powers, without requiring any attenuation. Integral pulse selecting from single shot to 40 MHz with adjustable contrast ratio is possible by a convenient software control. The UHG Pulse Selector is either available as standalone version or it can be integrated in our Harmonic Generator, where it is positioned before all harmonic stages to offer all features in a single compact housing.
UHG Pulse Selector features and benefits:
- modular design: standalone version or integrated in our Harmonic Generator
- high pulse picking efficiency
- adjustable contrast ratio
- suitable for high fs/ps power without any attenuation
- convenient and user-friendly software control
Based on proprietary technology, ALPHALAS offers most advanced pulse pickers for selecting single pulses from a train of picosecond or femtosecond optical trains. Large amplitudes of > 10 kV, pulse widths FWHM of 7 ... 10 ns and repetition rates up to 10 kHz in combination with a specially designed short-crystal Pockels cell are best suited for selecting individual pulses from various mode-locked lasers. Low jitter of < 40 ps and short delay of typically 30 ns guarantee a precise synchronization for perfect pulse selection.
The ModBox-OPP optical pulse picker allows to pick and optionally shape any sub-nanosecond pulse pattern or pulse sequence in an incoming pulse train. It acts as a fast gate with low insertion loss and high extinction from 30 dB to above 55 dB with high stability over time, and with user-adjustable optical pulse duration and optical pulse train repetition rate (when pre-scaler option is embedded).
SHIPS TODAY: Pulse Picker is a synchronization tool for driving external modulation devices such as EOMs, AOMs or SOAs in a pulse-picking mode of operation. It has been designed to work with low level electrical or optical input pulse power like typically the signal coming from a photodiode. It includes 3 pulse picking modes (frequency divider, external triggering & high frequency clock, burst shaping). The Pulse Picker board includes a software-adjustable input voltage level threshold and an (optional) photodiode. This board also includes a special AWG function synchronized with the input signal to perform burst shaping of mode-locked lasers.
NEW: A turn-key pulse-picker solution is now offered covering the full wavelength range between 700 and 1750 nm. It includes the synchronization board described above with our high performances AOMs and drivers.
See our detailed application note for Pulse Picker.
With the EKSMA Optics opto-electronic laser pulse picking system, femtosecond pulses can be picked from a pulse train at up to 2 MHz rate. The pulse picker UP2 and digital synchronization and delay pulse generator pMaster 4.2 can be synchronized with lasers operating at up to 100 MHz rate. The pulse picker MP1 can select pulses at up to 600 kHz repetition rate and be synchronized with lasers generating pulse trains with up to 60 MHz repetition rate.
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