Surface Properties

Surface Properties

Surface properties define the absorptance, BRDF, BTDF, specular reflectance and transmittance at a surface. In TracePro, surface properties are identified by name and catalog, and are stored in a database.

For detailed descriptions of the components of surface properties such as BRDF and BTDF. For more information about “BSDF”, see page 7.15.

Using the Surface Property Database

A database filled with predefined surface properties exists as a resource in TracePro. You can add your own surface properties using the Surface Property editor. The editor is a separate window. Once you are in the Surface Property window, you can return to the model window by selecting it from the Window menu.

To edit the records in the Surface Property Database, select Define|Edit Property Data|Surface Properties.

•The Surface Property Editor lets you modify the data type, description, and data entries of existing user-defined properties.

•The editor is a spreadsheet-style window that displays a row of data for each incident angle, wavelength and temperature.

•Data can be entered for multiple wavelengths, temperatures, and angles of incidence. TracePro performs a linear interpolation between wavelengths, temperatures, and angles during a raytrace for tabular data.

•The name and catalog of the surface property is applied to model data and provides a reference for looking up the data from the TracePro property database.

•Surface properties can be entered using several types of data. See Table 3.10, “Surface Property Types,” on page 3.25.

•Scattering, or BSDF data, may be entered for surfaces based on any of several scattering models. Scattering for transmission (BTDF) and reflection (BRDF) is entered in the data table for each temperature, wavelength, and angle of the surface property. For more information about “BSDF”, see page 7.15.

Using the Surface Property Editor

Select Define|Edit Properties|Surface Properties to open the editor window.

The surface property editor has several entries as described in the sections that follow. Notably, under a single name, you can enter properties for multiple temperatures, wavelengths and angles of incidence.

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3.23

Defining Properties

TABLE 3.9. Fields used in the Surface Property Information Panel

Catalog	Name of property catalog selected from dropdown list.
Name	Select a name from the Name: dropdown list or enter the name of a surface
	property not included in the data. The name of the surface property serves as
	its reference in all parts of TracePro. If the name you type matches the name
	of a coating in the database, its data displays in the spreadsheet part of the
	Surface Property Editor. When you add a new surface property, you are first
	prompted for its name, because this is the minimum amount of data needed to
	define a surface property.
Description	The description is optional. It provides a place to describe a surface property
	more fully than you can using the name.
Type	Choose from the following dropdown list: Fresnel, Table, Stack, Grating, Aniso-
	tropic or Coating DLL. As you define a new property, the type ‘Table’ is dis-
	played by default and the field ‘Solve For’ is activated to await a selection of
	values to calculate. See Table 3.10, “Surface Property Types,” on page 3.25.
Scatter	This displays the scatter model used by the property. The scatter model is
	selected when the property is created by a selection in the Add Property dia-
	log.
Retroreflec-	Place a check in this check box to give a surface the property of retroreflec-
tion	tance instead of transmittance. When you define a new surface property, the
	Retroreflector box is unchecked by default. To create a surface property that
	models a surface as being retroreflecting, check the Retroreflector box [Note:
	Retroreflector is not available with Grating type]. If you place a check in the
	Retroreflector check box, the columns for Specular Transmittance and BTDF
	change to Specular Retroreflectance and BRRDF (Bidirectional Retroreflec-
	tance Distribution Function). That lets you enter the specular retroreflection
	coefficient as well as scattering that is referenced to the retroreflection direc-
	tion. No transmission is allowed for a retroreflecting surface.Beware that the
	BRRDF is really a contributor to the total BRDF of the surface property. The
	real total BRDF of the surface is equal to the sum of the TracePro BRDF and
	BRRDF.
Polarization	Place a check mark in this check box to display polarization terms. This adds
Standard	columns for S and P polarization, and Phase data for the specular components
	of the property.
Expert
Stack	The Stack drop down list provides a selection of available Thin Film Stack def-
Standard	initions. This is shown for Stack type surface properties. You need to define a
	stack using the Stack Editor before it can be used with a surface property. See
Expert	“Thin Film Stacks” on page 3.42.
Spacing	For Grating surface properties, a Spacing entry is displayed to provide the
Standard	grating spacing of the property.
Expert

Side 1/2 Mate- Used for Direction-sensitive properties. This defines the Material to be applied

rial Property	to each side of the property. The Property values are entered in a Side 1 and
Standard	Side 2 panel to define the behavior of the surface depending on which side is
	struck by the ray.
Expert
DLL Name	For Coating DLL surface types, a DLL Name and Browse button is displayed
Expert	to provide the path and file name of the used defined coating DLL. See “User
	Defined Surface Properties” on page 7.25.

3.24	TracePro 5.0 User’s Manual

Surface Properties

The following table describes the types of surface properties supported by TracePro.

TABLE 3.10. Surface Property Types

	Fresnel	The Fresnel type assumes that no coating is applied to the surface and that
		TracePro uses the material property data of the object(s) on either side of the
		surface to calculate Fresnel reflection and transmission. Scatter data may be
		included. See “Calculation of Fresnel coefficients during raytrace” on
		page 7.23 for further discussion on this topic.
	Table	The Table type stores data in tabular form for various incident angles, wave-
		lengths and temperatures. The reflectance and transmittance may be entered
		with or without polarization terms. Scatter terms may be included and the data
		can use the Solve For functions. Typically tabular data comes from measure-
		ments.
	Stack	The Stack type calculates the specular data using a thin film stack and the
	Standard	material property data of the objects on either side of the surface. Polarization
		effects are included in the stack calculation. Scatter data may be added in tab-
	Expert	ular form in the Grid Panel. See “Thin Film Stacks” on page 3.42.
	Grating	The Grating type is like the Table type, except that the specular reflection and
	Standard	transmission entries are calculated from reflected and transmitted grating effi-
		ciencies, entered in the Grid Panel of the editor. Rays are split for each of the
	Expert	defined grating orders. Scatter data may be included and the data can use the
		Solve For functions. Grating parameters can also be imported from GSolver1.
		Since the Grating type allows for the entry of azimuthal angles, anisotropic
		gratings can be defined.
	Direction	This type allows surface properties that will have different behavior depending
	Sensitive	on which side is struck by the ray. Each side of the property has a Material
	Standard	Property assigned and includes an input tab to define the property values for
		the respective surface side designated as Side 1 and Side 2. See “Direction-
	Expert	Sensitive Properties” on page 3.27. Since the Direction Sensitive type allows
		for the entry of azimuthal angles, anisotropic surfaces can be defined.
	Anisotropic	The Anisotropic type is entered in tabular format and includes one or more azi-
	Standard	muthal angles for each incident angle, wavelength and temperature. Scatter
		data may be included and the data can use the Solve For functions. See
	Expert	“Anisotropic Surface Properties” on page 7.23.
	Coating DLL	This type uses a user supplied DLL to calculate the specular components of
	Expert	the property. Scatter data may be included in the Grid Panel. See “User
		Defined Surface Properties” on page 7.25.

1.GSolver (http://www.gsolver.com/gsprod.html) is a diffraction grating design and analysis software program produced by Grating Solver Development Co. GSolver now includes an option to export a TracePro grating type surface property which can then be imported into TracePro. See “Importing a Surface Property” on page 3.29.

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3.25

Defining Properties

FIGURE 3.12 - The Surface Property Editor

Using Solve for

Solve for: uses values on the editor spreadsheet to find the value specified in the Solve for: dropdown list. To be correct, the values must conform to the law of conservation of energy—absorptance, specular reflectance, specular transmittance, integrated BRDF, and integrated BTDF must total 1. TracePro will not allow you to save a property that does not conserve energy.

‘Solve For’ is available for Table, Anisotropic and Grating type properties only. If the Type: field is set to “Table”, “Anisotropic” or “Grating”, then the Solve for: field is active.

With Table and Anisotropic types, select Solve for: to derive one of the following values:

•Absorptance

•Specular reflectance

•Specular transmittance

•BRDF

•BTDF (or BRRDF)

With Grating type, select Solve for: to derive one of the following values:

•Absorptance

•BRDF

•BTDF

Note that NONE is also available on the Solve for: dropdown list. If you select NONE and type in values that do not compute, you cannot close the editor. It prompts you with a message. If absorptance is set to 0.3 and all other values are

3.26	TracePro 5.0 User’s Manual