Focus on: Electric Field Intensity

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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.

Plot of EFI

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:

Plot of modified EFI

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.
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