Focus on Special Features

Electric Field Intensity

The computation of the electric field intensity (EFI) can yield valuable information about the performance of thin film coatings. In general, the coating designer wants to either

• minimize laser damage by reducing the EFI or
• maximize the EFI so that energy is absorbed in a particular layer

The plot below shows the EFI (at 550 nm) of the 19-layer quarter-wave stack H(LH)^9 shown in the reflector example.

Here M and S refer to the incident medium and the substrate. There is a peak in the EFI at the interface between layers 18 and 19, which can be particularly bad. Using optimization, the design can be modified to reduce this problem:

Note that (1) the high-index layers (which tend to be more absorbing) have been made thinner near the incident medium and (2) the peak EFI is inside the low-index layers.