= Attosecond physics
{wiki}
<Attosecond physics> resolves changes on the scale of $10^{-18}$ <seconds>, especially <Electron> dynamics. Its central trick is to convert a short optical event into an experimentally accessible <energy> or <phase> change. A broad <optical spectrum> provides the ingredients for a short <optical pulse>; their <spectral phases> determine when those ingredients add constructively. <High harmonic generation> supplies the <optical spectrum>, while <RABBITT> and <attosecond streaking> supply complementary timing measurements. XUV denotes <extreme ultraviolet> radiation.
There are two separate timing problems: characterize the incident <optical pulse>, then infer the response of the target. A <photoelectron> measurement mixes the incident <spectral phase>, the target's transition response and the probing <electric field>. Recovering one requires constraints on the others. These methods measure distributions of <photoelectron> <energies> over repeated shots, rather than photographing a moving <atomic orbital>.
\Image[/attosecond-generation-and-electron-readout.png]
{title=Attosecond generation and electron timing use separate gas interactions}
{description=Original functional schematic, not a reproduction of a historical apparatus. The upper path generates and selects short-wavelength radiation; the lower path supplies a delayed reference <electric field>. The analyser converts <photoionization> into an <electron spectrometer> readout. The two lower panels distinguish weak-reference two-path <wave interference> from a classical <momentum>-shift idealization.}
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