Precision Laser Spectroscopy in the Extreme Ultraviolet

Abstract

Techniques for the production of short wavelengths in the extreme ultraviolet wavelength range are described, spanning low‐order harmonic generation in the perturbative regime for narrow bandwidth XUV production to the plateau‐regime with the three‐step collisional model for the generation of high harmonics with broadband ultrafast pulses. In addition, the intermediate regime is discussed for pulses of 300 ps duration, as well as the regime of harmonic conversion based on continuous wave lasers aiming at the production of coherent Lyman‐α radiation. Applications of XUV sources in the frequency domain typically rely on the production of XUV‐light from narrowband Fourier‐transform‐limited pulses for recording high‐resolution spectra. Alternatively, harmonically upconverted pulses of ultrashort duration (with inter‐pulse coherence) can be used for spectroscopic studies in the time and frequency domain (such as direct frequency comb spectroscopy techniques). Examples of both approaches for atomic and molecular spectroscopy are discussed at some length. For precision metrology on atomic systems, a focus is put on the Lamb shift determination in the He ground state. In the realm of molecular spectroscopy, predissociation phenomena in the nitrogen molecule are highlighted, with relevance for dissociation processes occurring in the upper layers of the Earth atmosphere. Similar predissociation phenomena in carbon monoxide are also treated in some detail, in this case with relevance for the chemistry in interstellar clouds. Precision XUV spectroscopy of molecular hydrogen is discussed as well, as it relates to the possibility of detecting a variation of the proton–electron mass ratio on a cosmological time scale. In the last section, applications of direct frequency comb spectroscopic techniques at short wavelengths are explained and prospects are given for using these techniques at extreme ultraviolet wavelengths.

Sub-Doppler two-photon spectroscopy of 33 Rydberg levels in atomic xenon excited at 205–213 nm: diverse isotopic and hyperfine structure

“…Wavelength-conversion methods to generate narrowband coherent tunable nanosecond-pulsed UV radiation (and, after χ (3) -type nonlinear-optical upconversion in noble-gas atoms [23,24], radiation in the vacuum-and extreme-UV regions) have traditionally depended on pulsed dye laser oscillators/amplifiers [6,8,10,[22][23][24][25], but higherperformance all-solid-state systems have evolved over the last few years [7,9,21,19,23,26].…”

Quantum-beat photoelectron-imaging spectroscopy of Xe in the VUV

“…For an extended discussion of recent developments in precision laser spectroscopies in the VUV and XUV, see ref. [27]. For short pulses, limitations on frequency resolution are placed, effectively, only by the temporal sampling parameters of the measurements.…”

“…[26] for a summary); for further general discussion of VUV laser spectroscopies in both time and frequency domain precision spectroscopy experiments see, e.g., ref. [27].…”

Line shape of amplitude or frequency-modulated spectral profiles including resonator distortions

“…We may mention here the highly accurate determinations of the ionization and bond dissociation energies of molecular hydrogen with submegahertz accuracy [4], the search for a time dependence of the fundamental constants of physics [5], the search for parity violation in chiral molecules [6,7], or fundamental questions related to the spectroscopy of atomic hydrogen [8]. While the quest for high precision concerns all spectral ranges from radiofrequency [9] to microwave and submillimeter wave spectroscopy toward XUV spectroscopy [10][11][12][13][14], microwave and gigahertz spectroscopy in the millimeter and submillimeter range has been traditionally a field of very high precision. High-precision analyses of gigahertz spectra have been discussed repeatedly for some decades, proposing a variety of techniques often in conjunction with the prototype molecules carbon monoxide (CO), carbon oxide sulfide (OCS), and others [15][16][17][18][19][20].…”