Extreme ultraviolet radiation with coherence time greater than 1 s

Abstract

Many atomic and molecular systems of fundamental interest possess resonance frequencies in the extreme ultraviolet where laser technology is limited and radiation sources have traditionally lacked long-term phase coherence. Recent breakthroughs in XUV frequency comb technology have demonstrated spectroscopy with unprecedented resolution at the MHz-level, but even higher resolutions are desired for future applications in precision measurement. By characterizing heterodyne beats between two XUV comb sources, we demonstrate the capability for sub-Hz spectral resolution. This corresponds to coherence times > 1 s at photon energies up to 20 eV, more than 6 orders of magnitude longer than previously reported. This work establishes the ability of creating highly phase stable radiation in the XUV with performance rivaling that of visible light. Further, by direct sampling of the phase of the XUV 1 arXiv:1404.3779v2 [physics.atom-ph]

Optical atomic clocks

“…In this approach, the frequency of the comb modes can be stabilized, controlled, and measured in the infrared spectral region, while the conversion of the original frequency comb into a sequence of odd harmonics makes the ensuing measurement precision available in the vacuum ultraviolet. This method has now permitted precision spectroscopy and frequency measurements of transitions in rare gases at extreme ultraviolet wavelengths around 50 nm (Kandula et al, 2010;Cingöz et al, 2012;Benko et al, 2014).…”

High-power ultrafast Yb:fiber laser frequency combs using commercially available components and basic fiber tools

“…1,2 They are now used for the calibration of astronomical spectrographs, 3 laser ranging, 4 high-order harmonic generation, 5 attosecond physics, 6,7 and direct frequency comb spectroscopy, 8,9 among other things. In our lab, for example, we have recently demonstrated a large improvement in the sensitivity of ultrafast optical spectroscopy using frequency comb methods.…”

Transition from perturbative to nonperturbative interaction in low-order-harmonic generation

“…[1])-On the other hand, low-order-harmonic generation (also, termed below-threshold harmonics) in the strong-field regime has received less attention. However, recent experiments [2][3][4] have demonstrated the potential to generate bright coherent low-order harmonics in the vacuum ultraviolet with photon energies below the threshold of the ionization potential of the target atom. These ultrafast sources have gained interest as tools for ultrafast spectroscopy of electron wave-packet dynamics in atoms and molecules [3] as well as for precision measurements [2,4].…”