## photon fluence rate, $$E_{\text{p,o}}$$

https://doi.org/10.1351/goldbook.P04635
Rate of photon fluence. Total number of photons (Np) incident from all directions on a small sphere divided by the cross-sectional area of the sphere and per time interval. SI unit is m-2 s-1. Same as photon spherical irradiance.
Notes:
1. Mathematical definition: $$E_{\text{p,o}} = \text{d}N_{\text{p}}/\left ( \text{d}t\, \text{d}S \right ) = \text{d}H_{\text{p,o}}/\text{d}t$$. If $$E_{\text{p,o}}$$ is constant over the time interval and the surface, $$E_{\text{p,o}} = N_{\text{p}}/t\, S$$. Equivalent definition: $$E_{\text{p,o}} = \int _{4\pi}L_{\text{p}}\text{d}\varOmega$$ with $$L_{\text{p}}$$ the @P04639@ and $$\varOmega$$ the solid @A00346@ of the beams passing through the given point on the surface.
2. It reduces to @P04637@ $$E_{\text{p}}$$ for a parallel and normally incident beam not scattered or reflected by the target or its surroundings.
3. This quantity can be used on a @C01019@ basis by dividing $$E_{\text{p,o}}$$ by the @A00543@, the symbol then being $$E_{n\text{,p,o}}$$, the name 'photon @FT07376-2@, amount basis', SI unit is $$\text{mol m}^{-2}\ \text{s}^{-1}$$; common unit is $$\text{einstein m}^{-2}\ \text{s}^{-1}$$.
Source:
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 395 (https://doi.org/10.1351/pac200779030293)