Saturation parameter ($s=I/I_{\mathrm{sat}}$)

For a specified optical transition, the on-resonance saturation parameter is the light intensity divided by the saturation intensity. The independent-beam Doppler cooling force model assumes weak total excitation and defines $s$ separately for each beam.

The saturation intensity is the characteristic light intensity used to normalize the on-resonance saturation parameter of a specified optical transition. Its value depends on the transition and the stated illumination convention.