Material Properties

Material Properties

The material property (of an object) in TracePro specifies the index of refraction and the bulk absorption. To use a material property, select the Define|Apply Properties dialog box, then select the tab labeled “Material.” See “Material Properties” on page 4.4.

Material Catalogs

Several catalogs of manufacturer data come with TracePro. You can also add your own catalogs and materials. These catalogs and materials will then appear as options within the Information Panel selections.

Material Property Database

A database exists containing predefined material catalogs and materials. You can choose among them or you can add or modify user-defined materials by using the Material Property editor.

You can add or modify materials in the Property Database by selecting

Define|Edit Property Data|Material Properties. This opens a new window in TracePro, not just a dialog box like many other features.

The Material Property editor allows you to modify the name, interpolation type, description, temperature and wavelength of certain materials. Some pre-defined material data supplied with TracePro is Read-Only and cannot be edited.

A spreadsheet-like window displays the index and absorption coefficients when interpolation is by interpolation formulae, or wavelengths and index values for tabular data. Absorption coefficient data may be entered as α in units of 1/mm, or k, which is dimensionless. See Equation 3.4 on page 3.8.

Selecting a catalog and entering a material name or selecting one from the list causes TracePro to display the data for that material in the editor window. You can add new materials and catalogs by using the respective Add buttons in the editor window Command Panel. Ten interpolation formulas are available for material property data. You must choose the interpolation type when using the Material Property editor. For example, Figure 3.3 on the next page shows the Formula tab for entering the coefficients for the Sellmeier interpolation method.

Note: The Properties editors are different from most features in TracePro because each one is a window rather than a dialog box. The menu bar displays a different set of options when you are in the editor window. If you are in the editor, you can return to the model window by selecting the model item from the Window menu.

TABLE 3.3. Fields used in the Material Property Information Panel

Catalog	Selects a Material property catalog.
Name	Material property name selection box. The name can be selected using the
	drop down arrow or by typing the name into the text box. If the name is found
	in the database its data will be displayed.
Description	The description contains notes about the Material Property.

TracePro 5.0 User’s Manual

3.5

Defining Properties

Interpolation Selects the interpolation method. Schott, Sellmeier, Extended Schott, Table and other interpolation methods are available. See “Material Property Interpolation” on page 7.7.

Type

Expert

The type of property is displayed next to the Interpolation method. The available types are Isotropic and Uniaxial. Isotropic properties have a single refractive index and Uniaxial properties are Birefringent. The type is set in the Add Property dialog when the property is originally defined.

FIGURE 3.3 - The Material Property Editor

Create a new material property

The steps listed below show the method to create a new property within Material Properties.

1.Select Define|Edit Property Data|Material Properties to open the Material Property editor.

2.Select a catalog, using the dropdown catalog list, into which your new material property is to be added. Add the material to an existing catalog or use the Add Catalog button to create your own.

3.Click the Add Property button, enter a name for your new property and click OK. For users of TracePro Expert also select if the material is isotropic (i.e., single refractive index) or uniaxial (i.e., birefringent).

4.Select the interpolation type. If not tabular data, click on the Formula tab at the bottom of the Grid Panel area and enter the values for that equation. There is more information on this subject in “Material Property Interpolation” on

page 7.7.

5.Click the Table tab and use the Add button to add absorption data or tabular index data at multiple wavelengths. This data is in spreadsheet-like format.

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Material Properties

6.You can edit the values that define the property simply by selecting a cell or field and entering your numbers. Be sure, however, that the Unlock Icon is displayed in the Toolbar.

7.Select File|Save or close the Material Property editor and answer yes to the question, “property data has changed, save data?” Your new property is available in the database for future use the next time you access your property.

Editing an existing material property

The steps listed below show the method to edit an existing property within Material Properties.

1.Select Define|Edit Property Data|Material Properties to open the Material Property editor.

2.Choose a catalog from the catalog dropdown list.

3.Choose the name of your property from the name dropdown list.

4.Click the Lock icon in the Toolbar to enable editing. You cannot make changes to a property that is Read Only. Pre-defined manufacturer properties cannot be edited unless you export them to text format, change their status to user defined, and re-import them into TracePro. See “Material Property Format” on page 7.84.

5.Edit the values that define a property by selecting a cell or field and entering your data.

6.Select File|Save or close the Material Property editor and answer yes to the prompt, “Property has changed, save data?” The edited property is now available in the database.

Exporting a material property

The steps listed below show the method to export a property within Material Properties.

1.Select Define|Edit Property Data|Material Properties to open the Material Property editor.

2.Choose a catalog from the dropdown list of catalogs.

3.Choose the name of your property from the dropdown list.

4.Use the File|Export Property command to create a text file that contains the information for the selected property. See “Material Property Format” on page 7.84. The exported file is a tab-delimited text file that can be opened with a spreadsheet program.

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3.7

Defining Properties

Importing a Material Property

The steps listed below show the method to import a property into Material

Properties.

1.Select Define|Edit Property Data|Material Properties to open the Material Property editor.

2.Use the File|Import Property command to import a text file (in the proper format) that contains the information for a material property. You will be prompted to enter the name and location of the text file. The property is saved upon importing.

Bulk Absorption

The units for the absorption coefficient are 1/mm. Rays that enter a material with non-zero absorption coefficient are attenuated according to Beers'-Lambert's law of transmission,

ΦT = Φ0e–αt ,

(3.1)

where ΦΤ and Φ0 are transmitted and incident flux, α is absorption coefficient, and

t is the thickness of material through which the ray travels. The flux absorbed by the material is then

ΦA = Φ0(1 – e–αt) .

(3.2)

Note: When entering bulk absorption for materials defined using the table interpolation type, remember that bulk absorption is in units of inverse millimeters. Table 3.4 illustrates use of Lambert’s law for two samples at 1 and 2 mm thickness.

TABLE 3.4. Bulk Absorption in Inverse Millimeters

Absorption	Transmission	Transmission
Coefficient	through 1 mm	through 2 mm
0.0001	0.9999	0.9998
0.001	0.999	0.998002
0.01	0.99005	0.980199
0.1	0.904837	0.818731
1	0.367879	0.135335

Note: Absorption data is saved in terms of α in the database. α is in units of inverse mm. You can also enter the data using the Extinction coefficient, k, which is a dimensionless quantity that comes from the complex index in Equation 3.3.

N = n + ik	(3.3)
k and α are related via the following:

α	4πk	(3.4)
	= --------- .
	λ

When converting k to and from α, you must be careful to use λ in millimeters.

3.8	TracePro 5.0 User’s Manual