Frequency-domain field monitors collect the field profile in the frequency domain from simulation results across some spatial region within the simulation in the FDTD, varFDTD solvers.
Note: There are two very similar types of frequency domain field monitors: 'Frequency domain field profile' and 'Frequency domain field and power' monitors. These monitors are identical except for one advanced setting (the spatial interpolation setting). In most situations, we recommend using the 'field and power' monitor. This monitor 'snaps' to the nearest mesh cell, which minimizes the amount of interpolation required, generally leading to more accurate data. The 'profile' monitor does not snap to the nearest mesh cell. Instead, it records the data exactly where the monitor was located. This can be useful in a few situations, but the extra interpolation required can slightly reduce the accuracy of the data.
Tip: Computations requirements
Frequency domain field monitors can require large amounts of memory when recording data over a large spatial domain. When possible, use 1D or 2D rather than 3D monitors. Similarly, try to minimize the number of frequency points recorded. It is also possible to use spatial downsampling to record less spatial resolution. Finally, it is possible to control which field components are recorded on the Data to record tab. If you are only interested in the power flux, you can select the OUTPUT POWER and disable everything else.
Generally, frequency monitors don't have a large effect on the simulation time, except when recording a very large amount of data. To determine the effect on the simulation speed, simply disable the monitor and re-run the simulation.