Case Study 17: Galvo F-Theta Laser Scanner

Goal

This case study walks through the built-in Galvo F-Theta Laser Scanner layout as a scanner design workflow:

• load the common layout preset;

• read the Gaussian laser source, beam-expander, galvo mirror, F-theta lens, and scan-plane rows as one folded scene;

• understand the galvo scan-overlay angle convention;

• inspect detector power and branch-field snapshots at the scan plane;

• separate integrated scanner debugging from standalone F-theta lens prescription validation.

The static snapshots in this tutorial are generated from the common layouts with:

python -m KrakenOS.UI.render_layout_snapshot --layout "Galvo F-Theta Laser Scanner" --mode 2d --output docs/source/_static/tutorials/galvo_f_theta_laser_scanner/01_folded_layout_yz.png --dpi 150
python -m KrakenOS.UI.render_layout_snapshot --layout "Galvo F-Theta Laser Scanner" --mode detector_map --output docs/source/_static/tutorials/galvo_f_theta_laser_scanner/02_detector_map.png --dpi 150
python -m KrakenOS.UI.render_layout_snapshot --layout "Galvo F-Theta Laser Scanner" --mode branch_field --output docs/source/_static/tutorials/galvo_f_theta_laser_scanner/03_branch_field.png --dpi 150
python -m KrakenOS.UI.render_layout_snapshot --layout "F-Theta Lens 50mm Figure 8" --mode 2d --output docs/source/_static/tutorials/galvo_f_theta_laser_scanner/04_standalone_f_theta_lens.png --dpi 150

Validate the page, assets, and current common-layout angle convention with:

python -m KrakenOS.UI.validate_galvo_f_theta_case_study

Load The Preset

1. Start the UI with python -m KrakenOS.UI.layout_editor.

2. Choose Layouts -> Sources / Illumination -> Galvo F-Theta Laser Scanner.

3. Confirm these left-panel settings:

Source model       = Gaussian beam
GB input mode      = Diameter + divergence
GB diameter [mm]   = 1.0
GB full div [mrad] = 2.0
GB M2              = 1.1
Wavelength [um]    = 0.65
Trace mode         = Folded Preview
Folded reach       = Display compatibility
Ray Count          = 9

The source is a physical Gaussian source, not an abstract field sample. The scanner scene then sends representative rays through a two-lens beam expander, reflects them from the galvo mirror, and traces the folded leg through the F-theta lens to the scan plane. Display compatibility is deliberately explicit here: the folded display path is allowed to provide detector reach for this legacy folded scanner preview, while the exported ray records still mark that terminal source as folded-display provenance.

The scanner is a scene workflow. The beam expander, mirror, F-theta lens, and scan plane are physical entities along one traced path.

Read The Rows

The preset table is intentionally explicit. The row groups are:

Group	Rows	Purpose
Laser source	Object	Defines the Gaussian launch plane and source direction.
Beam expander L1	two refractive rows	Negative lens that starts the expansion.
Beam expander L2	two refractive rows	Positive lens that recollimates the beam near the galvo/stop.
Galvo mirror	one Mirror row	A 45 deg fold. Its TiltX overlay draws scan positions.
F-theta Figure 8 lens	eight refractive rows	The 50 mm, 40 deg full-field prescription transcribed from attachment/F-theta.pdf Figure 8. The source K9 glass label is mapped to bundled CDGM H-K9L.
Scan plane	Image	Flat scan/focus plane used by detector and branch-field analyses.

Click Update. The YZ view should show the beam propagating along +Z, folding downward at the galvo mirror, then passing through the F-theta lens to the scan/focus plane.

The green center bundle is the nominal 45 deg galvo pose. The orange and red bundles are the preset scan-overlay poses.

Use The Galvo Scan Overlay

The mirror row’s TiltX cell is a mirror-slant value. It is not the F-theta field angle. In the current common layout, the nominal fold is:

Galvo mirror TiltX = 45

To draw a conservative -10, 0, +10 deg optical scan overlay, enter:

TiltX = 40,45,50

The equivalent range syntax is:

TiltX = 40:50:5

Around the nominal 45 deg fold, the reflected optical scan is approximately twice the mirror slant change. For the nominal full Figure 8 -20, 0, +20 deg optical scan, use:

TiltX = 35,45,55

The middle value remains the nominal row value. The full list is stored as display/path metadata and draws additional folded rays without duplicating prescription rows.

The table value is mirror slant. The reflected beam angle changes by about twice the slant change from the nominal fold.

Check The Scan Plane

Use detector analysis to verify that traced power reaches the scan/focus plane:

1. Keep the preset loaded.

2. Click Detector or render the detector_map snapshot.

3. Inspect the map annotation: it should name the Flat scan/focus plane and report nonzero accumulated power.

The default preset uses only nine representative rays, so the detector map is intentionally sparse. Increase Ray Count and detector bins when you need a smoother engineering map.

Use branch-field analysis when you want the coherent field grid rather than a ray-hit power histogram:

Branch field promotes the detector samples into an intensity/phase grid and reports the branch-local Gaussian-q fit on the scan plane.

Validate The F-Theta Lens Alone

If the integrated scanner spot is not where you expect, do not start by editing the fold mirror or beam expander blindly. First isolate the lens prescription:

1. Load Layouts -> Components -> F-Theta Lens 50mm Figure 8.

2. Keep Object Mode = Infinity.

3. Keep Field Type = Angle and Field Value = 20.0.

4. Click Update.

The standalone lens layout removes the Gaussian source, beam expander, and fold mirror. Use it to verify the lens prescription before debugging the integrated scanner bench.

After the standalone lens is correct, return to the scanner and adjust the upstream bench in this order:

1. Gaussian source diameter, divergence, and M2.

2. Beam-expander spacing and lens powers.

3. Galvo TiltX nominal fold and overlay values.

4. Scan plane location or detector size.

Why This Is Non-Sequential-First

This case uses Folded Preview because the scanner is not a simple axial ordered lens train. The source, mirror, lens, scan plane, and path metadata are scene entities. The YZ/XZ/XY panes are projections of traced 3D data, and the detector/branch-field analyses read the selected terminal surface rather than running a separate 2D simulation.

For new scene work, prefer Non-Sequential Preview or Auto with physical sources and detector surfaces. Keep Folded reach = Trace events unless the layout is intentionally using folded-display detector reach as a compatibility preview.

The standalone F-theta lens remains a valid sequential special case. Use it for classic lens-prescription checks. Use the integrated galvo scanner when the question includes the physical source, beam expander, fold mirror, scan overlay, detector, or path metadata.

Common Checks

Use these quick checks when the scanner view looks wrong:

Symptom	Check
The spot misses the scan plane	Validate the standalone F-theta layout first, then check beam-expander collimation at the galvo/entrance stop.
Scan overlay looks mirrored	Confirm whether the current layout uses a positive 45 deg fold. For this preset, use 40,45,50 or 35,45,55.
Detector map is blocky	Increase Ray Count and detector bins. The preset has only nine rays.
XZ or XY appears collapsed	The preset is mostly a YZ folded bench. XZ and XY are still valid projections, but most geometry lies in the YZ plane.
Wavefront comparison does not match a Zemax screenshot	Use F-Theta Lens 50mm Wavefront 0 Deg for the on-axis wavefront reference. The integrated scanner includes a finite Gaussian source and folded mirror, so it is not the same validation problem.

What This Proves

The case study exercises the North Star workflow:

• the scanner is loaded as a scene with physical source and folded path metadata;

• 2D views are projections of the traced scene;

• detector and branch-field results report on the selected scan plane;

• the sequential F-theta lens is still available as an ordered-prescription special case when that is the actual analysis question.