Narrow-band tunable extreme-ultraviolet laser source for lifetime measurements and precision spectroscopy

A narrow-band, extreme-ultraviolet laser source is developed that has continuous tunability in the range 96–97.5 nm and a bandwidth below 250 MHz. The versatility of the radiation source is demonstrated in two applications. Accurate values for lifetimes of highly excited molecular quantum states are determined from line-broadening measurements in three electronic states of CO: $W^1\prod ,$ $v=0$ state (${\prod }_f$ components, $J=1–3$), $\tau =130\pm 10 \mathrm{ps};$ $L^1\prod ,$ $v=0$ state (${\prod }_f$ components, $J=1–6$), $\tau =1.0\pm 0.3 \mathrm{ns};$ and $K^1{\sum }^{+},$ $v=0$ state $(J=0–3),$ $\tau =54\pm 5 \mathrm{ps}.$ The application of the source in metrology in the extreme-ultraviolet domain is demonstrated by the highly accurate, absolute calibration of narrow resonances in CO. These molecular lines can be used for future reference standards at these short wavelengths. From accurately determined minute frequency shifts near the accidentally predissociated $J_f=7$ level of the $L^1\prod ,$ $v=0$ state the perturber state is characterized as a yet unidentified Rydberg state with an origin at $103 266.92 {\mathrm{cm}}^{-1}.$ It is demonstrated that molecular spectroscopy in the extreme-ultraviolet domain at megahertz precision is possible.