We have used the dichroic table coating that we created successfully at two wavelengths, 0.400 mm and 0.525 mm. What about the performance of this coating at other wavelengths?

Open the Wavelength Data dialog and add wavelengths to extend our sampling spectrum as shown:

Open the menu option, “Analysis » Coatings » Transmission vs. Wavelength”. Change the settings of this analysis to show the coating performance of our dichroic coating at an angle of incidence of 45 degrees:

Here is the resulting plot:

As you can see, ZEMAX is modeling the transition region in a linear fashion while, in reality, the transition region adjusts from high transmission to low transmission in a very non-linear fashion. In this case, the transition region is modeled linearly due to the limited amount of data that we used to define the SWP table coating. For table coatings, the transmission and reflection for wavelength values between wavelengths defined in the table (i.e. wavelengths between 0.400 mm and 0.525 mm) are determined via linear interpolation. In other words, as the wavelength increases from 0.400 mm, the transmission drops in a linear fashion until it reaches 0 at 0.525 mm. If we wanted to model the transition region more accurately, we would just have to add the transmission and reflection coefficients for additional wavelengths between 0.400 mm and 0.525 mm in our table coating definition.

Notice that for wavelengths outside of the range of wavelengths defined in the table coating (i.e. wavelengths shorter than 0.400 mm as well as wavelengths longer than 0.525 mm), the transmission remains constant in these regions. For wavelengths that fall outside of the range of wavelengths defined in the table coating, no extrapolation is done. ZEMAX will simply use the transmission and reflection coefficients for the nearest defined wavelength. Thus, we would have to add the transmission and reflection coefficients for the additional wavelengths to expand the wavelength band of our table coating accurately.

For the dichroic beam splitter that we have been modeling, the angle of incidence of all rays incidence on the dichroic coating is 45 degrees given the orientation of our plate beam splitter as well as the fact that our source is collimated. How would sources that are not collimated (i.e. with rays that have angles of incidence on the beam splitter other than 45 degrees) be handled?

Open the menu option, “Analysis » Coatings » Transmission vs. Angle”. Change the settings to show the performance of our dichroic coating:

Here is the resulting transmission vs. angle curve:

Notice that the coating performance is the same across all angles of incidence. While, in reality, this is highly unlikely, it is the case with our SWP coating because we only defined one angle of incidence in our table. The rules defined above for wavelength data apply in the same fashion for angle of incidence data. So, to more accurately model the angle of incidence dependence of our dichroic coating, we would have to add the transmission and reflection coefficients for additional angles of incidence.

Similarly, all of the plots generated by ZEMAX suggest that the performance for S and P polarization states is the same. In reality, the amount of transmission and reflection for a dichroic coating is not just dependent upon wavelength and angle of incidence, but also polarization state. When defining our SWP table coating, we chose not to define different transmission and reflection coefficients for the S and P polarization states though we certainly could have.