# General Parameters

General Parameters — MC Grating documentation for Modal Collinear and Modal Conical. General Method allows choosing the method of calculation TMM or FMM.…

Canonical: https://mcgrating.com/docs/modal/general.html


Written by Nikolay M. LyndinLast revised 2016-06-10

This documentation was written for releases up to 2018 and is being revised. Some dialogs have changed since. If something does not match what you see, write to [mc@mcgrating.com](mailto:mc@mcgrating.com).

**General**

- ***Method*** allows choosing the method of calculation TMM or FMM.
- ***Number of Modes*** defines the number of eigen modes of lamellar layers (truncation order). This value should be adequate to the number of appropriate Rayleigh diffraction orders in every layer. There is a possibility of automatic fixing of this problem (see page ***Options***).
 The Rayleigh diffracted orders index is calculated in positive direction of *X* axis.
- ***Wavelength***, measurement unit is *nm*.
- Grating ***Period***, measurement unit is *nm*.

- ***Polarization. ***In the collinear mount for the** *TE (s)*** polarization the electric field vector is parallel the *X-Y* plane and for the ***TM (p)*** polarization the magnetic field vector is parallel the *X-Y* plane.

- In the conical mount the polarization state is defined by two electric field vectors ***Es*** and ***Ep*.** The wave vector ***k*** of the incident wave and these electric field vectors are mutually orthogonal. Vector ***Es*** is parallel the *X-Y* plane and vector ***Ep*** is parallel the incidence plane. Amplitudes of these vectors are defined by the ***State*** polarization angle and the phase difference between them is defined by the ***Phase*** angle.
 Angles measurement unit is *degrees*.
 Under exactly normal incidence it is impossible to define the incidence plane unambiguously. In this case depending on a coordinate system the software uses the following rules.
 - For the Plane base coordinate system a plane of AngleI changing is considered as the incident plane.
 - For the Grating base coordinate system a X-Z plane is considered as the incident plane.

- ***Incidence Angles,*** the angles definition is explained in the ***Structure Geometry*** picture. In the conical mount version the incident wave orientation is defined by two angles (definition depends on ***Coordinate System***). Theirs meaning are obvious from the pictures presented at the same page.
 Measurement unit is *degrees*.** **
- ***Method*** defines the calculation method True Modes or Fourier Modes.

From the in-application help of Modal Collinear and Modal Conical, documented through 2018. If you publish results computed with MC Grating, see [how to cite it](https://mcgrating.com/references.html#cite).