nanojoule

Nanojoule (nJ) is the SI unit of energy equal to 10^-9 joule. It is used to express very small amounts of energy in fields dealing with nanoscale phenomena and precision measurements. Because it is a modest fraction of a joule, the nanojoule is convenient for describing energetic processes that are larger than picojoules but smaller than microjoules.

One nanojoule equals 0.000000001 joule, and one joule equals 1 × 10^9 nanojoules. In terms of electron volts, 1 nJ is approximately 6.24 × 10^9 eV (about 6.24 GeV). In photonics, a visible photon around 500 nm carries about 3.98 × 10^-19 J, so 1 nJ corresponds to roughly 2.5 × 10^9 photons at that wavelength.

Applications of the nanjoule occur in nanotechnology and micro/nano-scale experiments, including energy budgeting for MEMS and nanoscale calorimetry, calibration of laser-pulse energies, and measurement of energy deposition in biological or electronic systems. The nanojoule helps quantify small energy changes without resorting to larger units, and is often used alongside other submultiples such as picojoules and microjoules.

See also: Joule, Electronvolt.