Shenghai Wu

First international comparison of femtosecond laser combs at the International Bureau of Weights and Measures

The first international comparison of femtosecond laser combs has been carried out at the International Bureau of Weights and Measures (BIPM). Three comb systems were involved: BIPM-C1 and BIPM-C2 from the BIPM and ECNU-C1 from the East China Normal University (ECNU). The agreement among the three combs was found to be on the subhertz level in the vicinity of 563 THz. A frequency difference measurement scheme was demonstrated that is suitable for general comb comparisons.

Study on the (1, 2) and (2, 3) bands in the comet-tail system of 12C16O+ by optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy

Optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy was employed to observe the absorption spectra of the (1, 2) and (2, 3) bands of the comet-tail (A2 Πi—X2Σ+) system of CO+ in the visible region. A rotational analysis was performed to obtain more precise molecular constants for the four involved vibrational levels. Moreover, accurate RKR potentials and the Franck-Condon factors are given for these four vibronic levels. This calclulation reveals that v = 0, 5, 10 vibrational levels in the A state will be perturbed by the v = 10, 14, 18 levels in the × state, respectively, and the v = 9 level might be weakly perturbed by the v = 17 level.

The absorption spectra of H2O+ and D2O+ in the visible and near infrared region

The absorption spectra of the electronic transition of H2O+ and D2O+ are investigated in the visible region from 16 400 to 17 600 cm−1 and in the near infrared region from 12 200 to 14 000 cm−1 using optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy (OH-MR-VMS). Three subbands including 111 spectral lines of H2O+ and seven subbands including 209 spectral lines of D2O+ are observed and analysed, among which four subbands, Σ (0,9,0)−(0,0,0), Δ (0,9,0)–(0,0,0), Π (0,8,0)–(0,0,0) and Π (0,10,0)–(0,0,0) of D2O+ in the near infrared region are studied for the first time. Holding the molecular constants of the lower state fixed at the published values, a set of molecular constants and rotational energy terms for each observed vibronic level of the upper state are obtained.

Band (5, 0) in the Red System A2ΠI - X2Σ+ of CN Studied by Optical Heterodyne Magnetic Rotation Enhanced Concentration Modulation Spectroscopy

We study the CN radical using optical heterodyne magnetic rotation enhanced concentration modulation spectroscopy in the visible region. The radical has been produced in the ac glow discharge of acetonitrile with helium as the carrier gas. The (5, 0) band of the red system A(2)Pi(I) - X(2)Sigma(+) in the range 17450-17830cm(-1) has been observed and rotationally analysed. We determine a set of precise molecular constants for the v = 5 vibrational level of CN in the A(2)Pi(I) state.

Measurement of the absorption spectrum of H2O+ in the visible region

Together with the 74 lines belonging to (0,9,0)-(0,0,0) band, the high-resolution absorption spectrum of H2O+ Ã2A1 - X2B1 system was observed in the visible region of 16680–17300 cm−1 using optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy for the first time, which verifies the high sensitivity and high signal to noise ratio (S/N) of this technique.