We report the spectrum of nitric oxide (NO) in the ultraviolet (UV) (225.4–227.0 nm) region based on cavity ringdown spectroscopy (CRDS). A cavity ringdown system, which consisted of a tunable UV laser source and a vacuum-pumped ringdown cavity, was constructed to measure NO at room temperature and atmospheric or reduced pressure. The measured spectra were validated using LIFBase simulations. The absorption cross-section of NO at the strongest absorption peak at 226.255 nm was measured to be 7.64 × 10−18 cm2 molecule−1. Using the measured mirror reflectivity of 99.55% at 226.255 nm, the detection limit of NO was determined to be 7.4 ppb (parts per billion) based on the standard 3-σ criteria. The stability and reproducibility of this CRDS system were also tested. Furthermore, exhaled gas samples from 203 human subjects (105 healthy people and 98 lung cancer patients) were measured using the system. Results demonstrated that the cavity ringdown spectroscopy in the deep-UV region has potential for breath NO test.

The effects of alkali and alkaline earth metals on the spatial distribution of electron number densities (n,) in an inductively coupled plasma have been studied. An optical fibre probe was used to sample the spatial position of the plasma and the photodiode array spectrometer to detect the HP line. The resultant lateral profiles were subjected to an Abel inversion. An on-line intelligent background correction method was used to correct the background under the HP line, whose full width at half maximum was then calculated automatically. Graphs of three-dimensional spatial distributions of n, in the presence of K, Na and Ca are compared with that of water. At an observation height of 7.2 mm above the load coil, the n, increased with decreasing ionization potentials of the elements. At an observation height of 9.6 mm, no measurable increase of n, is observed except for K.

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