User Sequence in QUADOA® Optical CAD
A User Sequence in QUADOA® Optical CAD lets you define exactly which surfaces the rays meet, in which order, and what happens at each of them. Unlike the Auto Sequence, which always runs top to bottom through the Optical Design Editor, a User Sequence can reflect at any surface, pass a surface several times or follow a branch of a multi-path system. Several User Sequences in one model, as in the Linnik interferometer example, are the basis of multi-sequential ray tracing.
Key points
- Create one with right-click → Convert to User Sequence or New User Sequence.
- The Surface List defines the order of surfaces; rays are traced top to bottom.
- Each entry selects a surface by its Identifier (and Surface Nr. for surfaces inside elements).
- The Surface Action is Transmission or Reflection.
- Per surface you can also choose the diffraction order and the polarization element.
- Converting back to an Auto Sequence deletes the custom surface list.
Terms used in this article
- Surface List
- The ordered list of surfaces of a User Sequence.
- Surface Action
- What happens at a surface: transmission or reflection.
- Reflect On
- The material assumed behind a surface when reflecting; set automatically for lenses, set by the user for custom elements.
Why use a User Sequence?
In a Linnik interferometer from the examples folder, the light takes several paths: some rays are reflected at a beam splitter surface, others transmitted. Each path is one User Sequence, and all of them are listed in the System Setup Editor under Sequences. Because the optical system and the ray paths are defined separately, a surface can be traced as often as needed without copying it.
How to create a User Sequence
- Open the System Setup Editor and expand Sequences.
- Right-click the Auto Sequence and choose Convert To User Sequence, or select it and click To User Sequence in the Sequence tab. A new, empty one is created with New User Sequence.
- Expand the new Surface List. It contains all surfaces with the identifiers from the Optical Design Editor.
How the surface list works
| Parameter | Meaning |
|---|---|
| Identifier | The surface, or the element the surface belongs to |
| Surface Nr. | The surface inside the element (1 = first); not needed for stand-alone surfaces |
| Surface Action | Transmission or Reflection (not available for the first and last surface) |
| Diffraction Order | Diffraction order at surfaces with a phase function; some phases, such as the 2D grating, have a second order |
| Jones Matrix | Which polarization element of the surface is applied in this sequence |
| Reflect On | Material behind the surface for reflections; automatic for lenses, set manually for custom elements |
Add surfaces with a right-click → Add Surface, the Insert key or the Add Surface button in the Sequence tab. Reorder them by drag and drop; delete them with the Delete key. The stop surface can also be set directly in the list.
Note: Converting a User Sequence back to an Auto Sequence resets the path to the default and deletes the custom surface list.
Example: a double reflection between two surfaces
The system has four surfaces: Source, Surface 2, Surface 3 and Imaging Surface. The light should be reflected at Surface 3 back to Surface 2, reflected again, and then pass Surface 3 to the image.
- Convert the Auto Sequence to a User Sequence.
- In the surface list, set the Surface Action of Surface 3 to Reflection.
- Add a surface, drag it above the Imaging Surface, select Surface 2 as identifier and set its action to Reflection.
- Add another surface above the Imaging Surface, select Surface 3 and set it to Transmission.
The resulting path is Source → Surface 2 → Surface 3 (reflection) → Surface 2 (reflection) → Surface 3 (transmission) → Imaging Surface.
Video tutorial: User Sequences
This 3-minute video converts an Auto Sequence into a User Sequence and adds a double reflection.
Video length: 3:15 min · Also on YouTube: User Sequence in QUADOA® Optical CAD: Defining Custom Ray Paths
Frequently asked questions
Right-click the Auto Sequence in the System Setup Editor and choose Convert To User Sequence, or create a new one with New User Sequence in the Sequence tab.
In the surface list of the User Sequence, set the Surface Action of that surface to Reflection.
Yes. Add the surface to the surface list again at the desired position; the surface itself is defined only once in the Optical Design Editor.
The custom surface list and surface actions are deleted and the default top-to-bottom path is used.