12 -- A user element in Python: a programmable pulse shaper¶

{"type": "user", "callback": "@dazzler", "params": {...}} hands the main beam's spectrum to a function you register (uf.run(..., elements={"dazzler": dazzler}) or Run.element("dazzler", fn)), and continues with the spectrum it returns. The function also gets the frequency axis, the carrier, the time axis and the element's params, so one callback serves many elements.

python docs/examples/GettingStarted/user-element/dazzler.py

The script measures the dispersion of 25 mm of SF11 plus 1 m of air with the engine itself (summary["totals"]["systemGddS2"], "systemTodS3"), then puts the shaper in front of the glass with the opposite phase:

accumulated dispersion: GDD = 4711 fs^2, TOD = 3111 fs^3
no shaper             : FWHM   522.8 fs (TL  25.0 fs), energy 1.000 nJ
shaper (GDD + TOD)    : FWHM    25.0 fs (TL  25.0 fs), energy 1.000 nJ
shaper + 40 nm window : FWHM    46.2 fs (TL  46.2 fs), energy 0.775 nJ

The energy the window removes is booked as "user" in the element's energy budget. The same callback works from C# (registry.RegisterCallback("dazzler", (ElementCallback)(ctx => ...))) and from C/C++ (uf_run_set_element_callback); see docs/active-elements.md.