exahertz

Exahertz (symbol EHz) is the SI unit of frequency equal to 10^18 hertz. It is formed by applying the SI prefix exa- to hertz.

As a unit of frequency, one exahertz corresponds to one quintillion cycles per second. In terms of photon energy, E = hf, a photon with frequency of 1 EHz has energy around 4.14 keV, placing it in the soft X-ray region; its wavelength is about 0.3 nanometers.

Practical usage of exahertz is limited. The term is mainly used in physics contexts to describe electromagnetic radiation in the X-ray domain or in discussions of extremely high-energy photons. In electronics and communications, frequencies are far smaller, with common ranges in kilohertz to terahertz.

In SI, exa- denotes 10^18, so exahertz is six orders of magnitude higher than the terahertz range and sits well above visible-light frequencies, which lie in the hundreds of terahertz. Exahertz is thus a useful descriptive unit in high-energy physics and astronomy, but it is not a common measurement in routine laboratory equipment or industry.