Dear Colleagues,
I'm studying the optical limiting effect in organic material due to reverse saturation absorption. As we know, in reverse saturation absorption, the transmission coefficient decreases as the intensity increases, or the absorption coefficient increases as the intensity increases, resulting in power loss. So, when we increase the laser power to a threshold P0, there are two competing processes: the increase in input power and the power loss due to reverse saturation absorption. If these two processes are in equilibrium, the optical limit curve is horizontal (as in the attached pictures.) However, if the amount of lost power is greater than the increase in input power, the curve must go down at P0. Why in the paper on optical limiting don’t we see such cases?
Thank you and hoping for your insightful response.
The absorption coefficient of a material showing RSA will increase when the input optical fluence is increased. However, the processes underlying RSA (mostly excited state absorption in organic molecules) do not result in the absorption of more light than what is fed into it. Therefore, the scenario you envisage will not happen.
If you plot output transmission (i.e. output intensity/input intensity) as a function of input intensity then you will find that for low input intensity you have high (but flat) transmission curve and at higher input intensity (after a certain value of the input intensity, when NLO effect start occurring in the material) the curve will lowered down ( i think you are referring to this type of OL curve you have seen in published papers).
Dear Prof.Pathik Kumbhakar,
Thank you for your answer.
If we plot output power as a function of input power, are there any case in which the curve lower down instead of flat as showed in figs ?
The nonlinear effect that can be observed relates to General problems of nonlinear elements. The dependence of the nonlinear element of the output power on the input radiation power is determined by the properties of the material. This dependence is often approximated by the function Pout=Pin/(1+e*Pin). The coefficient e is called the saturation coefficient. Its value determines the curve.
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