Pulse Energy
Author: the photonics expert Dr. Rüdiger Paschotta (RP)
Definition: energy of an optical pulse
Categories:
Units: J
Formula symbol: <$E_\textrm{p}$>
DOI: 10.61835/40a Cite the article: BibTex plain textHTML Link to this page LinkedIn
The pulse energy <$E_\textrm{p}$> is simply the total optical energy content of a pulse, i.e., the integral of its optical power over time.
The pulse energy together with the pulse duration is often used to estimate the peak power of pulses. Conversely, temporal integration of the optical power results in the pulse energy.
Typical pulse energies from Q-switched lasers range from microjoules to millijoules, and for large systems to multiple joules or even kilojoules.
Mode-locked lasers achieve much lower pulse energies (picojoules, nanojoules or sometimes several microjoules) due to their high pulse repetition rates and sometimes due to limiting nonlinear effects in the laser resonator.
Much higher energies of ultrashort pulses can be achieved by amplifying pulses at a lower repetition rate, as obtained e.g. with a pulse picker or a regenerative amplifier.
Measurement of Pulse Energies
Direct Measurement
For pulses with not too high pulse repetition rate, e.g. from a Q-switched laser, the pulse energy may be directly measured e.g. with a pyroelectric detector.
Pulse Energy from Average Power and Repetition Rate
For regular pulse trains with high repetition rate, the (usually low) pulse energy is often calculated by dividing the average power (measured e.g. with a power meter) by the pulse repetition rate. This is a valid procedure provided that the energy emitted between the pulses is negligible. However, there are cases where, e.g., a mode-locked laser emits a pulse train together with a low-level background emission. Even if the background power level is far below the peak power, the background can significantly contribute to the average power. If, e.g., a photodetector has an insufficient dynamic range for testing this, it can be useful to test the conversion efficiency of a frequency doubler in a carefully controlled situation in the low-conversion regime.
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Suppliers
The RP Photonics Buyer's Guide contains 11 suppliers for pyroelectric detectors. Among them:
Gentec Electro-Optics

Gentec Electro-Optics offers a selection of pyroelectric measurement heads for measuring high-energy laser pulses with up to 3.9 J, and various compatible displays and PC interfaces. There are also pyroelectric power detectors. Discrete pyroelectric thermal detectors are also available.
AMS Technologies

AMS Technologies carries a broad variety of both digital and analog pyroelectric IR detectors (PIR), in single-, dual and quad element configurations, ideal for motion detection or gas detection in many application areas:
- single-element PIRs in TO-5 metal housing, analog or digital, single- or dual-channel, thermally compensated, for gas detection
- dual-element PIRs in TO-5, low-profile TO-39, or LCC SMD housings, analog or digital, for horizontal-mount motion detection devices, also over long distances
- four-element PIRs in TO-5 metal housing, analog or digital, single or dual output, for ceiling-mount short-, mid- and long-distance motion detection devices
- low-power digital dual- and four-element PIRs in TO-5 or LCC SMD housings, for battery-operated short-, mid- and long-distance motion detection
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