Fluence is a term used in various scientific and technical disciplines to describe the amount of something per unit area. The specific meaning of fluence can vary depending on the context in which it is used.
Here are a couple of common definitions:
Radiation physics/medicine: In the field of radiation physics and medicine, fluence refers to the total amount of radiation (such as photons or particles) that passes through a unit area. It is often expressed in terms of energy per unit area and is used to quantify the exposure to radiation.
Optics: In optics, fluence refers to the amount of radiant energy (light) per unit area that falls onto a surface. It is commonly used when discussing the intensity or energy distribution of laser beams.
In both cases, fluence provides a measure of the "dose" or amount of something with respect to the area over which it is distributed. The units for fluence will depend on the specific quantity being measured, such as joules per square meter (J/m²) for radiant energy in optics or gray for absorbed dose in radiation physics.