Can SimphoSOFT model a
reversible saturable absorber?
Where can I define a
saturation intensity parameter I_{0}?

SimphoSOFT is capable of simulating
reversible saturation absorption. However, it does not require a user to
specify a value for saturation intensity I_{0 }as the program takes care of
saturable absorption automatically by explicitly modeling ground state depletion.
Introducing the saturation intensity I_{0 }is
a way to avoid solving rate equations to the full extent. It shows the
intensity level at which the ground state will be depleted which will
drastically reduce absorbing power of the active material. Up to some extent,
one can just solve a propagation equation by using the intensitydependent
absorption rate A.
[CONVENTIONAL MODEL :
with saturation intensity I_{0}]
∂I / ∂z = − A(I,z) I^2
A(I,z) = α/(1+I/I_{0})
SimphoSOFT goes much further. It models
depletion of the ground state explicitly by calculating the dynamics of
population densities of all the energy levels. For example, if absorption
from the ground state to the first excited state is strong and the relaxation
is slow, the ground state will be depleted and the attenuation term in the
propagation equation will be decreased substantially, which will stop
absorption.
[SimphoSOFT MODEL]
∂I(z,t) / ∂z = − α N_{0}(z,t)
I(z,t)^2
∂N_{0}(z,t) / ∂t = − α N_{0}(z,t)
I(z,t)^2 /2 h ω_{0} – k_{10} (NN_{0})
What is important is that a user
provides a “intrinsic” value for the twophoton absorption crosssection.
To run this analysis in SimphoSOFT, one
needs to define data snapshots in Run Configuration / Output tab. One should
choose “Dyn popln dty” to output dynamics of population density at a desired
sample depth and the distance from the beam center.

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 SimphoSOFT Modeling features (3)
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Modeling reversible saturable absorber (RSA).
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