The Sampled Coating type accepts user-entered data for relative reflectivity, transmissivity, and phase change for one or more specified wavelengths. These coefficients do not depend on the angle of incidence. To include angular variation, use the General Sampled Coating type. The reflection and transmission coefficients cannot sum to greater than one (R + T <= 1 ). Once a coating has been defined, the coating type cannot be changed.
The Sampled Coating can be created in the following ways: •Open a new coating dialog and select "Sampled Coating" as the coating type.
Transmission and reflection coefficient values can be automatically filled in using the commands "Set T = 1 - R (one row)", "Set R = 1 - T (one row)", "Set T = 1 - R (entire table)", "Set R = 1 - T (entire table)" from the list menu made available by right mouse clicking in the spreadsheet area. A single row is identified by each unique wavelength entry.
It is not necessary to use the system wavelengths in the coating definition. If more than one wavelength is entered in the coating definition, FRED performs a linear interpolation to calculate the reflection and transmission coefficients between adjacent wavelengths. If the wavelength being traced is outside the range specified in the coating dialog, then the coefficients are equal to those of the next highest or lowest wavelength in the range, as appropriate.
It is important to note that the the linear interpolation occurs in amplitude coefficient space, not in reflected/transmitted power coefficient space (what the user enters in the dialog). For a majority of cases where the density of sampled values is reasonable, the difference in the resulting interpolated values between the two spaces will be negligible. The effect of this interpolation space can be noticed if the user plots the coating performance and observes that adjacent sampled values are not connected by a straight line.
Wavelengths can be added, inserted or deleted from the coating definition by right mouse clicking in the coating spreadsheet area and selecting "Add wavelength", "Insert wavelength" or "Append Wavelength" from the list menu. Additionally, a wavelength entry can be added for each source wavelength by right mouse clicking in the spreadsheet area and selecting "Append all source wavelengths" from the list menu.
Coating data can be entered using the Digitization tool by right mouse clicking in the coating spreadsheet area and selecting either "Digitize reflection curve" or "Digitize transmission curve" from the list menu. There is no limit to the number of data points that can be digitized. The reflection/transmission curve must be a bitmap file.
Loading coating data from file Sampled Coating data can be read from a properly formatted text file by right mouse clicking in the coating spreadsheet area and selecting "Replace data with File Data" from the list menu. In the text file two header lines are followed by the coating data where the first header line reads "type sampledcoating" and the second header line reads "format type", with type being one of three type designations; 1) wave_pow, 2) wave_pow_pow, and 3) wave_pow_pha_pow_pha. The data formats corresponding to each type designation are: 1) wavelength and reflectance (two columns), 2) wavelength, reflectance, transmittance (three columns) or 3) wavelength, reflectance, phase, transmittance, phase (five columns). Examples of each format are shown below:
Type 1 - wavelength & reflectance
Type 2 - wavelength, reflectance, transmittance
Type 3 - wavelength, reflectance, phase, transmittance, phase
Exporting coating data to a file All wavelength, coefficient, and phase data can be exported to an ASCII text file by right mouse clicking in the coating spreadsheet area and selecting "Export Data to a File" from the list menu. This opens a dialog showing the file list of the current working directory, which can be changed using the conventional Windows interface. The file type must be ASCII text, but the extension is not important (*.txt or *.dat will work fine). The exported data format is exactly as shown in the coating dialog.
Coatings and raytrace controls Coatings are use in conjunction with the Raytrace Controls to determine ray propagation. •To continue propagating a reflected ray, both the Raytrace Control and the Coating must allow the reflection. •To continue propagating a transmitted ray, both the Raytrace Control and the Coating must allow the transmission. •Scattered rays are subject to the same limitations. Currently, an absorbing surface cannot generate scattered rays.
Copying to a new FRED document Copies between FRED models will always transfer new material and coating information.
Coatings - General Sampled Coating Coatings - Polarizer / Waveplate Coating Coatings - Quarter Wave Single Layer Coatings - Thin Film Layered Coating
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