Types of Calculations Performed by MULTILAYER
The incident beam on the multilayer stack is plane and monochromatic, with vacuum wavelength l, a- direction of incidence given by the angles q (polar) and f (azimuthal), and a user-defined state of polarization. Once the multilayer stack and the incident beam parameters are specified, the user is asked whether he/she wants to vary any of the parameters. If the answer is "No," the reflection and transmission coefficients of the stack for the particular wavelength, angle of incidence, and polarization state of the beam are calculated and saved in SESSION.DAT. The program then terminates.
The user who decides to vary some of the parameters will be given the option to specify a range of variation for each and everyone of the parameters. For example the wavelength can vary in the interval [l1, l2]. The value chosen previously for this parameter determines one end of the interval, and the user can set the other end by specifying a second value for l. For instance, if l of the beam is initially declared as 500nm, the user can now enter a value of 800nm and cause the range of wavelengths from 500nm to 800nm to be scanned. By not entering any value at all (i.e., by pressing the RETURN key) the user fixes the wavelength at its initial value, thus keeping it constant during the calculations.
It is possible to vary more than one parameter at a time. For example, one can choose to vary the wavelength, the angle of incidence, the index of refraction of the substrate, and the thickness of one or more layers, all at the same time. It should be borne in mind that all the selected variables vary together. So, the user decides which parameters are interdependent and must vary simultaneously. For example, if several layers of the stack are made of the same material, then their refractive indices can be made to vary simultaneously to study the effect of deposition environment on the optical properties of the stack.
At the end, when all the variables have been identified, the program asks for the number of steps to take between the minimum and the maximum of the specified range. Any number of steps between 1 and 1000 is allowed. Results of these calculations are recorded in SESSION.DAT. In addition, ASCII files are created for all the variables and all the reflection/transmission coefficients, so the user can port them to a graphic routine and plot the variation of the multilayer characteristics with the changing values of selected parameters.
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