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Anne L'Huillier develops experimental and theoretical methods based on high harmonic generation in gases. The generated extreme ultraviolet light contains many harmonics of the driving laser frequency; their relative spectral phases determine whether they combine into short optical pulses. Her research connects that generation problem with attosecond measurements of electron dynamics following photoionization. The central link is between a controlled optical waveform and the timing information carried by emitted electrons.^[ref]

A physicist who researches high harmonic generation and ultrafast electron dynamics.^[ref]

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.

C. Manus coauthored an experiment converting $1064$-nm laser radiation into high odd harmonics in rare gases. In argon, the spectrum reached the $33$rd harmonic at $32.2$ nm, demonstrating a route to extreme ultraviolet radiation.^[ref]

Extreme ultraviolet denotes short-wavelength ultraviolet between longer-wavelength ultraviolet and X-rays; precise band boundaries depend on convention. Its photons have sufficient energy to cause strong optical absorption in many materials that transmit visible light.

This makes beam transport an apparatus problem: an ordinary air path or visible-light window can absorb the beam, and suitable reflective optics can be more useful than an ordinary transmitting optical lens. Before interpreting a weak detector signal, compare a blocked-beam reading with the open-beam reading and account for wavelength-dependent detector quantum efficiency.

G. Mainfray coauthored an experiment converting $1064$-nm laser radiation into high odd harmonics in rare gases. In argon, the spectrum reached the $33$rd harmonic at $32.2$ nm, demonstrating a route to extreme ultraviolet radiation.^[ref]

L. A. Lompre coauthored an experiment converting $1064$-nm laser radiation into high odd harmonics in rare gases. In argon, the spectrum reached the $33$rd harmonic at $32.2$ nm, demonstrating a route to extreme ultraviolet radiation.^[ref]

M. Ferray coauthored an experiment converting $1064$-nm laser radiation into high odd harmonics in rare gases. In argon, the spectrum reached the $33$rd harmonic at $32.2$ nm, demonstrating a route to extreme ultraviolet radiation.^[ref]

Use multilayer reflective optics and a reflective patterned mask. Near the usual extreme ultraviolet wavelength of 13.5 nm, ordinary lenses and thick transmissive masks absorb too strongly. Multilayer mirrors focus and project the image, while an absorber pattern on a multilayer-coated mask defines the exposed regions.

The optical path operates in vacuum to avoid absorption by air. The key distinction is reflective mask projection, rather than a transparent chromium-on-glass mask or a scanned electron probe.

Use electron lenses and a digitally scanned, blanked electron beam; no physical mask is required for direct writing. Electromagnetic lenses focus the charged-particle beam, deflectors place it, and the pattern generator controls position and dose. Electrostatic elements can also form part of electron optics, but these are not refractive glass lenses.

The extreme ultraviolet mask mentioned in the problem is the object being manufactured by this maskless write process, rather than a mask placed in the electron path.

The resist is positive tone, because the written regions are the regions removed during development. A suitable example is poly(methyl methacrylate), conventionally PMMA, used in its ordinary positive-tone electron-beam exposure regime. Electron-induced chain scission reduces its molar mass and increases its solubility in the developer.

The fact that this writing step fabricates an extreme ultraviolet mask does not make the resist an EUV-exposed resist: the exposure process being classified here is the electron-beam mask-writing step.

X. F. Li coauthored an experiment converting $1064$-nm laser radiation into high odd harmonics in rare gases. In argon, the spectrum reached the $33$rd harmonic at $32.2$ nm, demonstrating a route to extreme ultraviolet radiation.^[ref]