nJ

The nanojoule, symbol nJ, is an SI unit of energy equal to 10^-9 joules. It is formed from the joule with the nano- prefix, which denotes a factor of one billionth.

The nanojoule is a convenient scale for describing small energies in nanoscience, photonics, and microelectronics. For context, 1 joule equals about 6.242×10^18 electronvolts (eV), so 1 nJ is roughly 6.24×10^9 eV (about 6.24 GeV). In terms of photons, a 2 eV photon carries about 3.204×10^-19 J, so one nanojoule corresponds to roughly 3.1×10^9 such photons. In unit conversions, 1 nJ equals 1000 pic joules (pJ) and 0.001 microjoules (µJ).

Usage and examples include describing energy per pulse in ultrafast laser systems, small energy storage in nanoscale devices, and energy budgets in microelectronic components. The nanojoule is small enough to be meaningful for single or few-photon interactions in some regimes, yet large enough to be measured with common laboratory equipment.

Other interpretations of the abbreviation nJ exist in different contexts, but in the SI system the nanojoule is the standard meaning. When encountered, the intended meaning is typically clear from the scientific domain or accompanying units.