# Gauss FFT

Gauss FFT — MC Grating documentation for Modal Collinear and Modal Conical and Modal Crossed and Chandezon Collinear and Chandezon Conical and Chandezon…

Canonical: https://mcgrating.com/docs/common/gauss-fft.html


Written by Nikolay M. LyndinLast revised 2012-12-17

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).

***Gauss (FFT)***

The input result data are recalculated by parabola fit procedure to correspond to ***Number of FFT Points.*** This value effects on the angular resolution. An incident Gaussian beam has two intrinsic parameters: ***Waist Radius*** and ***Defocus*** and the external parameter is the incidence angle (***Fixed Beam Angle***) calculated with respect to the beam axis. The minimum ***Waist Radius*** depends on the input data angular scanning range: the larger range - the smaller possible *Waist Radius*. The maximum ***Waist Radius*** depends pro rata on ***Number of FFT Points***. The ***Defocus*** is the distance along beam axis from the crossing point with the cover interface and the waist position. If waist is placed in the cover the sign of defocus is negative otherwise the sign is positive. The user is able to get several structure responses from the incident Gaussian beam defined by the*** Output Type*** and ***Output (Reflection/Transmission)*** controls in the form of graph or table in editor window and in the format defined by the ***Output Decimal Digits*** and ***Output (Real; Imagine/Module; Phase)*** controls placed under the pagers area.

If the buttons ***Graph*** and ***Result Window*** are active this means that the result is already calculated otherwise it is necessary to press button ***Calculate*.**

This page contains the intrinsic checking of the input parameters on corresponding to the input data. This checking can be considered only as a guide and the user responsibility is to set reasonable parameters.

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).