Measurement on the linewidth of a home-build XUV comb using frequency comb spectroscopy with molecule

Optical frequency comb in the vacuum ultraviolet (VUV)/extreme ultraviolet (XUV) region has attracted a great deal of attention, as it provides coherent VUV/XUV radiation source with a rather narrow bandwidth, facilitating precise spectroscopic measurements in the short wavelength regime. In this study, we report on the linewidth measurement of a home-built VUV comb centered at 148 nm using direct frequency comb spectroscopy with NO 2 . The measurement reveals that the upper bound of our comb linewidth is less than 28 MHz. Fitting the whole trace with different repetition rates shows that the center frequency of the excitation is 2 021.25 ± 0.24 THz (∼148.32 nm). Thus, we assigned this excitation to the transition from the 6a 1 orbital ( ν 1 ′ =0, ν 2 ′ =0) to the 3p σ u orbital ( ν 1 ′ =3, ν 2 ′ =8) in NO 2 . Our work demonstrates that VUV combs are potentially powerful tools for precision spectroscopic measurements in the short wavelength regime.