mJcm2

mJ/cm^2, or millijoules per square centimeter, is a unit of radiant energy per unit area used to express fluence or energy density delivered to a surface. It is common in fields dealing with laser-material interactions, photopolymerization, UV exposure, and related photonic processes. Fluence describes how much energy is incident on a given area, independent of how quickly it arrives.

Conversions and relationships: 1 mJ/cm^2 equals 10 J/m^2. Conversely, 1 J/m^2 equals 0.1 mJ/cm^2. Fluence is related to irradiance (power per unit area) and exposure time by the equation F = I × t, where I is irradiance (in mW/cm^2 or W/m^2) and t is time in seconds. For example, a laser delivering 50 mW per square centimeter for 2 seconds yields a fluence of 100 mJ/cm^2.

Measurement and instrumentation: Fluence is measured with energy meters or power meters that include calibrated sensors, often using photodiodes or thermal detectors. In some setups, integrating spheres or calibrated detectors are used to capture total energy over an illuminated area.

Applications and considerations: Fluence thresholds determine material responses such as polymer curing, photochemical reactions, surface modification, or ablation. Different materials and wavelengths require different fluence levels to achieve desired effects, and excessive fluence can cause damage or unintended changes. Because mJ/cm^2 is a surface-restricted measure, it is most meaningful when the illumination is uniform over the target area, or when spatial fluence distribution is accounted for in the analysis.