Gaussian beam excitation

7. Gaussian beam excitation

Illumination with a plane wave well approximates these physical cases where a spot size of the illuminating wave is larger than the scattering object’s dimensions. There are, however, numerous cases where the actual finite size of the spot must be considered and may be smaller than the object’s dimensions. This happens in measurements and scatterometry techniques.

Solutions to the Maxwell equations in free space that provide finite spots are Gaussian beams. The so-called 3D Gaussian beam propagating along a particular dimension focuses in the other two dimensions around a point called a neck centre, creating a Gaussian-shaped spot of size called a neck diameter; it then de-focuses beyond the neck. The so-called 2D Gaussian beam propagates along one dimension, focuses in the second dimension, and remains invariant along the third.

Both types of Gaussian beams are supported in QW-3D starting with version 6.0. They are generated at the same boxes as previously the plane wave. The choice of the illuminating wave is made at the I/O Ports Parameters level and described in Section UG 2.6.4, together with examples of application.