In the standard blow-off model, a common heuristic model is used to predict tissue ablation,^{25} Beer’s law is assumed to govern energy deposition into calculus. In this model, deposited energy densities $Ed$ exceeding the ablation threshold energy density, $Eabl$, cause calculus removal. The threshold energy density is typically a constant^{25}^{,}^{26} related to the enthalpy of ablation for calculus. The absorption coefficient, $\mu a$, is assumed to remain constant during irradiation and scattering is assumed to be negligible. For the standard blow-off model, $Ed$ is given by Display Formula
$Ed=\u2212dFdz=\mu aF(z)=\mu aF0e\u2212\mu az,$(1)
where $F0$ is the incident fluence (in $J/cm2$) and $F(z)$ is the fluence at depth $z$. Ablation occurs over the etch depth $\delta SB$ if $\mu aF(z)>Eabl$. Beyond the etch depth, tissue is not ablated but merely heated since the deposited energy density is below the ablation threshold. The fluence at the etch depth is the ablation threshold fluence $Fth$ and for $F(z)>Fth$ the etch depth is found from Eq. (1) to be Display Formula$\delta SB=1\mu aln(F0Fth).$(2)