Many of the scattering models inheriting BRDF_Model provide bidirectional transmittance distribution function (BTDF)(type set to 1), bidirectional reflection distribution function (BRDF) for reflection from the substrate side (type set to 2), and/or BTDF from the substrate side (type set to 3). However, they calculate that quantity inside the material, not taking into account refraction and transmission into and out of the material. The model Transmit_BRDF_Model provides an interface that allows one to calculate the scatter by any of those models, but evaluated outside of the material, assuming that the material has parallel faces. The model takes another model as a parameter and requires that the optical properties of the substrate be non-absorbing. It connects the internal angles to the external angles by Snell's law, accounts for the transmittance through the bottom interface (taking into account any films on that interface), and accounts for the change in the projected solid angle as the light passes through the interface. Note that with type set to 0, the model is evaluated in reflection, and no refraction or transmission effects are needed.
Parameters:
| Parameter | Data Type | Description | Default |
|---|---|---|---|
| lambda | double | Wavelength of the light
in vacuum [µm]. (Inherited from BRDF_Model). Note: This parameter overrides the same parameter in model. |
0.532 |
| type | int |
Indicates whether the light is incident from above the
substrate or from within the substrate and whether the
scattering is evaluated in reflection or transmission.
The choices are: 0 : Light is incident from the above the substrate, and scattering is evaluated in reflection. 1 : Light is incident from the above the substrate, and scattering is evaluated in transmission. 2 : Light is incident from the within the substrate, and scattering is evaluated in reflection. 3 : Light is incident from the within the substrate, and scattering is evaluated in transmission. For 1, 2, and 3, the substrate must be non-absorbing. Transmit_BRDF_Model supports all types, provided the model pointed to by model supports it. (Inherited from BRDF_Model). |
0 |
| substrate | dielectric_function | The
optical constants of the substrate, expressed as a
complex number (n,k) or, optionally, as a function of
wavelength. (Inherited from BRDF_Model). Note 1: This parameter overrides the same parameter in model. Note 2: The material must be nonabsorbing. The default must be changed. |
(4.05,0.05) |
| model | BRDF_Model_Ptr | The scattering model. |
Microroughness_BRDF_Model |
| films | StackModel_Ptr | Description of the stack of films deposited on the bottom surface | No_StackModel |
See also:
SCATMECH Home, Conventions, BRDF_Model
Include file:
#include "transmit.h"
Source code:
transmit.cpp
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Current SCATMECH version: 7.22 (April 2021)