1. A pulse of electromagnetic energy. 2. The electromagnetic radiation from a nuclear detonation caused by Compton recoil electrons and photoelectrons from the photons that (a) are scattered in the materials of the nuclear device and (b) are distributed in the medium surrounding the detonation. Common abbreviationEMP.Note 1: The electric and magnetic fields resulting from electromagnetic pulses (EMPs) may couple with electrical/electronic systems to produce damaging electric current and voltage surges. In fiber optic links, fiber optic loops, and fiber optic nets, except for their electronic components, there is no direct coupling in the sense of induced electrical currents, but they are vulnerable to a high-level electromagnetic pulse (EMP) that causes the optical fibers to lose transparency for a brief period, of the order of seconds, after which transparency usually returns to a sufficient level to provide for optical pulse transmission. The duration of recovery time and the extent of loss of transparency depends on the severity, i.e., the intensity, of the EMP. Note 2: Electromagnetic pulses (EMPs) may be caused by nonnuclear means. 3. A wideband, high-intensity, short-duration burst of electromagnetic energy. Note: In the case of a nuclear detonation, the resulting electromagnetic pulse (EMP) consists of a continuous frequency spectrum, with most of the energy distributed throughout the lower frequencies between three hertz (3 Hz) and 30 kHz. See also coupling,  frequency spectrum,  high-altitude electromagnetic pulse,  intensity,  pulse,  fiber optic link,  fiber optic loop,  fiber optic net,  hardened,  magnetic field,  optical fiber,  optical pulse,  photon,  radiation-hardened optical fiber,  transmission,  transparency,  transparent,  wideband. 4. A pulse of electromagnetic energy that may be guided, such as (a) an optical pulse in an optical fiber or a slab dielectric waveguide, or (b) unguided, such as a gamma-ray pulse from a nuclear detonation in the atmosphere. Note: The electromagnetic pulse may be a pulse in a pulse train obtained from the digital modulation of an electromagnetic wave, such as a lightwave, a radio wave, or a microwave. See also digital modulation,  lightwave,  microwave,  optical fiber,  optical pulse,  pulse,  pulse train,  radio wave,  slab dielectric waveguide,  waveguide.