[[EM.Tempo]] requires a finite plane wave incidence surface to calculate the excitation. When you create a plane wave source, a plane wave box is created as part of its definition. A trident symbol on the box shows the propagation vector as well as the E-field and H-field polarization vectors. The time domain plane wave excitation is calculated on the surface of this box and injected into the computational domain. The plane wave box is displayed in the project workspace as a purple wireframe box enclosing the structure. Initially, the radio button '''Size: Default''' is selected. With this option, the boundaries of the excitation box always have a distance of three cells from the bounding box of the geometry and cannot be changed. The radio button '''Size: Custom''' allows you to set the excitation box manually. The values for the coordinates of '''Corner 1''' and '''Corner 2''' can now be changed. Corner 1 is the front lower left corner and Corner 2 is the rear upper right corner of the box. The box has to be defined in the world coordinate system (WCS).
[[EM.Tempo]] gives you an option to illuminate objects with a focused beam instead of a uniform plane wave. The focused beam is a Gaussian beam, which is a solution of the paraxial approximation to the Helmholtz equation. The fundamental Gaussian beam is rotationally-symmetric about its propagation axis, and its transverse field distribution follows a Gaussian function profile. The critical parameter is the beam radius w<sub>0</sub>; it is the point where the field drops by 1/e from its value at the center. The beam opens up into a cone along the propagation direction, with a cone angle of tan θ = λ<sub>0</sub>/(π.ω<sub>0</sub>) (λ<sub>0</sub> is the free-space wavelength).
Â
Similar to the plane wave source, a Gaussian beam is define by spherical angles of incidence Theta and Phi in degrees. You can also set the '''Polarization''' of the Gaussian Beam and choose from the three options: '''TM<sub>z</sub>''', '''TE<sub>z</sub>''' and '''User Defined'''. A default Excitation Box three cells away from the bounding box of the geometry is initially suggested, i.e. the radio button '''Size: Default''' is selected by default. The radio button '''Size: Custom''' allows you to set the excitation box manually by modifying the coordinates of '''Corner 1''' (front lower left) and '''Corner 2''' (back upper right) of the box in the world coordinate system (WCS). The Gaussian beam box is displayed in the project workspace as a green wireframe box enclosing the structure. A translucent green circle normal to the direction propagation shows the footprint of Gaussian beam at its focal (waist) point.
Â
Unlike plane waves, a Gaussian beam is a localized field. Therefore, you need to specify the '''Beam Properties'''. This includes the coordinates of the beam's '''Focus''', which is the beam's waist center in the world coordinate system as well as the beam's '''Radius''' in project units.
Â
[[Image:Info_icon.png|40px]] Click here to learn more about '''[[Common_Excitation_Source_Types_in_EM.Cube#Plane_Wave_Sources | Plane Wave Sources]]'''.