Investigation of noise-like pulses from a net normal Yb-doped fiber laser based on a nonlinear polarization rotation mechanism.

We investigated the characteristics of noise-like pulses (NLPs) from a net normal dispersion Yb-doped fiber laser (YDFL) by using the grating pairs (GPs) inside the laser cavity as a dispersion compensation element. Without the insertion of the slit inside the laser cavity, the operation of the YDFL is at an NLP state with the double-scale intensity autocorrelation trace once the mode-locked pulses are generated. Through the dispersion delay line outside the laser cavity, the substantial temporal compression of the NLPs has been demonstrated. After inserting the slit between the GPs as a bandpass filter, the operation state of the YDFL can be switched between the NLPs and the dissipated solitons by means of a pump power. Besides, the NLPs can also transit to the bound solitons as the YDFL is operated within long and short wavelength regimes through the spatial shift of the slit.

Promoting ethylene epoxidation on gold nanoclusters: self and CO induced O2 activation.

We have investigated the epoxidation of ethylene heterogeneously catalyzed by small gold nanoclusters based on density functional theory calculations. A promising trimolecular Langmuir-Hinshelwood mechanism via co-adsorbed ethylene- and CO-assisted reaction is addressed which provides significant insights into the fundamental catalytic mechanism for ethylene oxidation on small Au nanoclusters. O2 activation is found to be a key step for accelerating ethylene oxidation. Especially, the coadsorbed neighboring CO is found to be more robust for promoting the activation of the O-O bond, resulting in the formation of epoxide and CO2 due to the barrierless process. The new CO-promoted oxidation mechanism has also been clarified by the ab initio MD simulations.