Steady state simulation. Modeling emission.

Is there any way to do a steady state simulation in this software? If I want to see the real population of the each level, I would be able to predict the emission intensity.

The possibilities for predicting the amount of emitted light depend on whether 1) you are using a CW laser and looking at steady state emission or 2) you are using a pulsed laser and are looking for the number of emitted photons from a single pulse. 1) For steady state simulations: Use the 'box' shaped pulse that has a flat top.  For the pulse width (FWHM), pick a pulse width that is longer than the longest relaxation time for the ion.  This will allow the ions to come to approximately a steady state near the end of the pulse.  Note that for a 'box' pulse, the internal program variable T0 will be 1/2 of the pulse width FWHM.  In Numerical Setup, you may pick the 'Temporal Domain' as 2 times T0 (instead of 5) .  Also note that the center of the pulse is at 0, so the temporal domain of 2*T0 actually goes from -T0 to +T0.  After doing a simulation, compare the energy level populations near the end of the pulse. 2) For a single short laser pulse: Look at the time dependence of the population of the emitting state by running the program with Post-Simulation.  Pick a post-simulation time long enough to see the full decay.  In Plot Creator, generate a 2D plot of the kinetics of the population density at the center of the pulse (rho = 0).  Select the resulting plot with the mouse, right click on the plot and then select the option 'Integral'.  Using 'Integral', you may integrate the area under the curve of population versus time.  The area is proportional to the number of electrons that relax from that state.  If there is more than one relaxation pathway from that state, you will need to multiple the area under the curve by a factor equal to (rate of emission from the energy level)/(sum of all rates from the energy level) to get the fraction of electrons that emit photons.

Modeling reversible saturable absorber (RSA).

Can SimphoSOFT model a reversible saturable absorber? Where can I define a saturation intensity parameter I0?

SimphoSOFT is capable of simulating reversible saturation absorption. However, it does not require a user to specify a value for saturation intensity I0 as the program takes care of saturable absorption automatically by explicitly modeling ground state depletion. Introducing the saturation intensity I0 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 intensity-dependent absorption rate A. [CONVENTIONAL MODEL : with saturation intensity I0] ∂I  / ∂z = − A(I,z) I^2 A(I,z) =  α/(1+I/I0) 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 N0(z,t) I(z,t)^2 ∂N0(z,t)  / ∂t = − α N0(z,t) I(z,t)^2 /2 h ω0 – k10 (N-N0) What is important is that a user provides a “intrinsic” value for the two-photon absorption cross-section. 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.

Dissipative medium

Does SimphoSOFT model dissipative medium?

SimphoSOFT allows defining linear absorption coefficient which can simulate dissipative medium. Absorption coefficient can be defined for each wavelength presented in the workspace.