Solving nonlinear problem using parameter sweep

Hi, everyone!

I am struggling to solve some nonlinear optical problem (the material has 3rd-order nonlinear optical response to the electrical-magnetic field) using Comsol RF-frequency domain module. But when the nonlinear become significant enough, the calculation can not converge.
I heard that the problem may be solved by using parameter sweep and adding the nonlinear parameter gradually, but I am not sure the right way to do that, I have set

Study 1 > Solver Configurations > Dependent Variables: Initial Values of Variables Solved For / Not Solved For > Method: Initial Expression, Solution: Solver 1

Is that enough? Under the "Mehtod" tab there is another choice as " Solution" , what's the difference with "Initial Expression"? which one should I choose? Under the "Solution" tab there is also another choice as "Parametric 1", what's the difference then?

Is there any thing else I should do? Does anyone has suggestions about how to correctly solve such nonlinear problem?

Thank you!

Best regards!
Zhiqi