WIP: Implement two-photon absorption (TPA) support by jtravs · Pull Request #412 · LupoLab/Luna.jl

jtravs · 2026-02-24T13:44:06Z

Introduce TPA coefficients, spectral responses, and examples.

Copilot

Pull request overview

Adds initial two-photon absorption (TPA) capability to Luna by introducing a material β₂(ω) model, a frequency-domain nonlinear response path, plus tests/docs/examples demonstrating energy loss and spectral suppression.

Changes:

Add PhysData.β₂_TPA with empirical material parameters (TPA_params) for fused silica / MgF₂.
Introduce Nonlinear.SpectralResponse + Nonlinear.TPAResponse and route spectral responses through the Trans* pipelines in NonlinearRHS.
Extend prop_gnlse interface with n2/material + Aeff calling conventions to enable correctly scaled TPA; add tests and example scripts.

Reviewed changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
`src/PhysData.jl`	Adds empirical β₂(ω) TPA model and parameters.
`src/Nonlinear.jl`	Introduces `SpectralResponse` and `TPAResponse` implementation.
`src/NonlinearRHS.jl`	Routes `SpectralResponse` responses via ω-domain path for modal/mode-avg/free-space transforms.
`src/Interface.jl`	Adds `prop_gnlse_args` overloads using `n2/material + Aeff` and supports `tpa` kwarg with scaling.
`src/Luna.jl`	Changes default integrator `init_dz`.
`test/test_tpa.jl`	New test coverage for β₂_TPA values, TPAResponse conversion, and propagation loss/suppression.
`test/runtests.jl`	Adds inclusion of the new TPA testset.
`docs/src/model/nonlinear_responses.md`	Documents TPA as a spectral response and provides usage guidance.
`examples/simple_interface/gnlse_tpa.jl`	Simple-interface example showing TPA-induced spectral suppression.
`examples/low_level_interface/freespace/radial_env_tpa.jl`	Low-level radial free-space envelope example including TPA response.
`.gitignore`	Adds ignore patterns (notably `.DS_Store`).

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

Copilot · 2026-02-24T13:50:29Z

            error("unrecognised value for ramanmodel")
        end
    end
+    if !isnothing(tpa)


prop_gnlse_args(γ, ...) currently errors whenever tpa is not nothing, which includes tpa=false. That’s inconsistent with the documented meaning of tpa=false (= disabled) and makes it awkward to pass through user options. Consider only erroring when TPA is actually enabled (e.g. !isnothing(tpa) && tpa !== false).

Suggested change

if !isnothing(tpa)

if !isnothing(tpa) && tpa !== false

Copilot · 2026-02-24T13:50:30Z

+responses = (Nonlinear.Kerr_env(χ3), tpa)
+
+# Or via prop_gnlse interface
+prop_gnlse(γ, flength, βs; ..., tpa=β₂_ω)


The documented prop_gnlse(γ, flength, βs; ..., tpa=β₂_ω) usage conflicts with the implementation: TPA is rejected for the γ calling convention because Aeff is required for scaling. Update this example to use the prop_gnlse(flength, βs; n2/material, Aeff, tpa=...) convention instead.

Suggested change

prop_gnlse(γ, flength, βs; ..., tpa=β₂_ω)

prop_gnlse(flength, βs; n2=n2, material=:SiO2, Aeff=Aeff, tpa=β₂_ω)

Copilot · 2026-02-24T13:50:30Z

 function run(Eω, grid,
             linop, transform, FT, output;
-             min_dz=0, max_dz=grid.zmax/2, init_dz=1e-4, z0=0.0,
+             min_dz=0, max_dz=grid.zmax/2, init_dz=grid.zmax/4, z0=0.0,


Changing the default init_dz from a fixed value to grid.zmax/4 can make the first RK45 step extremely large for long propagations (potentially causing many rejected steps or poor initial error estimates). Consider keeping the previous small default (or using a capped heuristic like min(grid.zmax/4, 1e-4)).

Suggested change

min_dz=0, max_dz=grid.zmax/2, init_dz=grid.zmax/4, z0=0.0,

min_dz=0, max_dz=grid.zmax/2, init_dz=min(grid.zmax/4, 1e-4), z0=0.0,

Copilot · 2026-02-24T13:50:31Z

+λ, Iλtpa = Processing.getIω(output_tpa, :λ, flength)
+λ, Iλnotpa = Processing.getIω(output_notpa, :λ, flength)
+
+using PyPlot


using PyPlot is present twice (at the top and again before plotting). Remove the duplicate import to keep the example minimal.

Suggested change

using PyPlot

Copilot · 2026-02-24T13:50:31Z

+ω_below = 2π * PhysData.c / 300e-9   # below SiO₂ TPA edge (~299 nm)
+ω_above = 2π * PhysData.c / 220e-9   # well above TPA edge
+


This example sets material = :MgF2, but the inline comments here refer to the SiO₂ TPA edge. Please update the comment (and/or the chosen reference wavelengths) to match the selected material, so readers don’t infer the wrong absorption edge.

Copilot · 2026-02-24T13:50:31Z

+xlabel("Wavelength (nm)")
+ylabel("On-axis spectral Intensity (a.u.)")
+legend()
+title("Spectral suppression from TPA in SiO₂")


The plot title mentions “SiO₂”, but this script currently uses material = :MgF2. Update the title (or the material) so the example output is correctly labeled.

Suggested change

title("Spectral suppression from TPA in SiO₂")

title("Spectral suppression from TPA in MgF₂")

Copilot · 2026-02-24T13:50:31Z

+    haskey(TPA_params, material) || error(
+        "Unknown material for TPA: $material. Supported: $(keys(TPA_params))")


Error handling here is inconsistent with the rest of PhysData.jl: other material lookups throw DomainError(material, "Unknown material $material"), but β₂_TPA uses a generic error(...). Consider throwing DomainError (or ArgumentError) for consistency with the existing API.

Suggested change

haskey(TPA_params, material) || error(

"Unknown material for TPA: $material. Supported: $(keys(TPA_params))")

haskey(TPA_params, material) || throw(DomainError(

material,

"Unknown material for TPA: $material. Supported: $(keys(TPA_params))",

))

Copilot · 2026-02-24T13:50:32Z

+    # TPA should cause energy loss.
+    λ0 = 240e-9
+    τfwhm = 5e-15
+    energy = 20e-9  # 1 nJ


The comment says energy = 20e-9 corresponds to 1 nJ, but 20e-9 J is 20 nJ. Please correct the comment (or the value) so the test parameters are self-consistent.

Suggested change

energy = 20e-9 # 1 nJ

energy = 20e-9 # 20 nJ

Copilot · 2026-02-24T13:50:32Z

+function (tpa::TPAResponse)(out_ω, F_E2E_ω, ρ)
+    @inbounds for i in eachindex(out_ω)
+        out_ω[i] += ρ * tpa.coeff_ω[i] * F_E2E_ω[i]
+    end
+end


TPAResponse's call overload uses @inbounds while indexing tpa.coeff_ω[i] and F_E2E_ω[i] without any length checks. If a user constructs TPAResponse(coeff_ω) with a mismatched length, this can lead to out-of-bounds memory access (potentially a crash). Add a DimensionMismatch/@assert check up-front (or drop @inbounds) to guarantee all arrays have the same length before the loop.

jtravs added 8 commits February 24, 2026 11:57

Add TPA coefficients to PhysData

a022be5

spectral TPA implementation

64ff9cd

Add spectral nonlinear responses

5af5c9a

fix initial step size

df83f9d

radial example for TPA

7d44d9f

add tests

74f6949

Add some quick docs

e81c13d

update prop_gnlse for TPA support

8f26a2b

Copilot AI review requested due to automatic review settings February 24, 2026 13:44

Copilot started reviewing on behalf of jtravs February 24, 2026 13:44 View session

Copilot AI reviewed Feb 24, 2026

View reviewed changes

jtravs requested a review from chrisbrahms February 24, 2026 13:51

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

WIP: Implement two-photon absorption (TPA) support#412

WIP: Implement two-photon absorption (TPA) support#412
jtravs wants to merge 8 commits into
LupoLab:masterfrom
jtravs:TPA

jtravs commented Feb 24, 2026

Uh oh!

Copilot AI left a comment

Uh oh!

Copilot AI Feb 24, 2026

Uh oh!

Copilot AI Feb 24, 2026

Uh oh!

Copilot AI Feb 24, 2026

Uh oh!

Copilot AI Feb 24, 2026

Uh oh!

Copilot AI Feb 24, 2026

Uh oh!

Copilot AI Feb 24, 2026

Uh oh!

Copilot AI Feb 24, 2026

Uh oh!

Copilot AI Feb 24, 2026

Uh oh!

Copilot AI Feb 24, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

	prop_gnlse(γ, flength, βs; ..., tpa=β₂_ω)
	prop_gnlse(flength, βs; n2=n2, material=:SiO2, Aeff=Aeff, tpa=β₂_ω)

	min_dz=0, max_dz=grid.zmax/2, init_dz=grid.zmax/4, z0=0.0,
	min_dz=0, max_dz=grid.zmax/2, init_dz=min(grid.zmax/4, 1e-4), z0=0.0,

		ω_below = 2π * PhysData.c / 300e-9 # below SiO₂ TPA edge (~299 nm)
		ω_above = 2π * PhysData.c / 220e-9 # well above TPA edge

	title("Spectral suppression from TPA in SiO₂")
	title("Spectral suppression from TPA in MgF₂")

		haskey(TPA_params, material) \|\| error(
		"Unknown material for TPA: $material. Supported: $(keys(TPA_params))")

-    haskey(TPA_params, material) || error(
-        "Unknown material for TPA: $material. Supported: $(keys(TPA_params))")
+    haskey(TPA_params, material) || throw(DomainError(
+        material,
+        "Unknown material for TPA: $material. Supported: $(keys(TPA_params))",
+    ))

Conversation

jtravs commented Feb 24, 2026

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Copilot AI Feb 24, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Feb 24, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Feb 24, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Feb 24, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Feb 24, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Feb 24, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Feb 24, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Feb 24, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Feb 24, 2026

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants