ABSTRACT
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 NO2. 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 (â¼148.32 nm). Thus, we assigned this excitation to the transition from the 6a1 orbital (ν1'=0, ν2'=0) to the 3pσu orbital (ν1'=3, ν2'=8) in NO2. Our work demonstrates that VUV combs are potentially powerful tools for precision spectroscopic measurements in the short wavelength regime.
ABSTRACT
OBJECTIVE: To investigate the sleep structure in patients with vascular cognitive impairment-no dementia (VCI-ND) and its differences from that of normal individuals. METHODS: The whole night sleep record of 20 patients with VCI-ND were monitored by 32-head video-taped polysomnographic system, and the results were compared with the data of 20 normal subjects. RESULTS: Compared with normal subjects, patients with VCI-ND showed significantly reduced total sleep duration, increased waking times, increased stage 1 sleep, decreased stage 2 sleep, decreased stage 3 sleep, decreased rapid eye movement stage (REM) and reduced sleep efficiency. CONCLUSION: Increased light sleep as well as decreased slow-wave stage 3-4 sleep and decreased REM stage may be a specific electroneurophysiologic marker for VCI-ND, but large-sampled multi-centered randomized controlled trial is necessary to test the validity of these features as specific markers for screening and early diagnostic purposes.
