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Pulse Energy

Definition: energy of an optical pulse

German: Pulsenergie

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

Units: J

Formula symbol: <$E_\textrm{p}$>


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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.

See also: light pulses, pulse characterization, optical energy meters

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