| ECE532 Biomedical Optics
© 1998
Steven L. Jacques, Scott A. Prahl
Oregon Graduate Institute |

# Time-resolved Monte Carlo

## Relative concentration and fluence rate

In time-resolved Monte Carlo simulations, we record the time-resolved spatial distribution of photons expressed as either an energy concentration (C [J/cm^{3}]) or an instantaneous fluence rate (F [W/cm^{2}]) relative to the impulse energy (U_{o} [J]) of the source at time zero:

If one wishes to do bookkeeping of C as [photons cm^{-3}] or F as [photons cm^{-2} s^{-1}], then one simply multiplies the Monte Carlo result, C/U_{o} or F/U_{o}, by the value of one's source expressed as number of photons, for example, a 1-J impulse at 532 nm wavelength:

U_{o} = (1 J) / ( hc/λ )

= (1 J) / ( (6.626x10^{-34} Js)(2.998x10^{8} m/s) / (532x10^{-9} m) )

= 2.7x10^{18} photons.

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