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Pulse Characterization

Definition: the measurement of various properties of an optical pulse

More specific terms: pulse duration measurement, carrier–envelope frequency measurement

German: Pulscharakterisierung, Pulsvermessung

Categories: light detection and characterization, optical metrology, light pulses


How to cite the article; suggest additional literature

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Light pulses and regular optical pulse trains can be generated e.g. with Q-switched and mode-locked lasers. As important pulse parameters such as pulse duration and energy and also the aspects of interest can be very different, in the following we separately consider pulse characterization for Q-switched and mode-locked lasers.

Pulse Characterization for Q-switched Lasers

The pulse characterization for Q-switched lasers is relatively simple; it typically comprises the following aspects:

Pulse Characterization for Mode-locked Lasers


Complete Ultrashort Pulse Characterization

The characterization as outlined above is still somewhat incomplete. There are methods of complete pulse characterization [5], which reveal more details:

  • the electric field versus time or the complex spectrum (including spectral shape and spectral phase)
  • the precise pulse shape
  • the chirp of the pulses

For example, an ordinary intensity autocorrelator always delivers symmetric signal shapes concerning time, even if the pulses are asymmetric (e.g. with steep rise and a slower fall of power). The pulse duration calculated from an autocorrelation trace is often based on the assumption of a certain temporal pulse shape, which cannot be fully validated based on the obtained data. Such an autocorrelator can also not reveal any optical phase properties or a chirp.

The most prominent techniques for complete pulse characterization are

The results can be visualized in various ways, e.g. with graphs of time- or frequency-dependent functions, or with spectrograms.

Further possibly interesting details are:

Spatial Aspects

Note that apart from the temporal aspect, there is also the spatial aspect [15]. Both aspects are often approximately separated in the sense that the whole spatio-temporal profile of the electric field of a pulse can be specified as the product of two functions, one depending only on time and the other only on the spatial position. However, a significant coupling of temporal and spatial properties can occur in various situations. For example, pulses from Kerr lens mode-locked lasers often exhibit a time-dependent beam radius, which makes the complete characterization (and modeling) very challenging. Another spatio-temporal aspect is pulse front tilt, which is related to angular dispersion and can, e.g., result from a misaligned pulse compressor.


Accurate and reliable pulse characterization is essential for many applications. For example, if an ultrafast laser system does not work properly, e.g., due to misalignment of components, this can greatly affect the operation of a larger system. The problem can be located and fixed only if the pulse properties can be monitored. Therefore, an ultrafast laser system can often be considered as complete only if it comprises comprehensive pulse characterization equipment, which may substantially contribute to the overall cost.

Particularly careful pulse characterization may be required in the laser development, where various effects on the pulse formation need to be investigated.


The RP Photonics Buyer's Guide contains 31 suppliers for pulse characterization instruments. Among them:


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See also: light pulses, spectral phase, carrier–envelope offset, autocorrelators, frequency-resolved optical gating, spectral phase interferometry, streak cameras

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