Effect of distances between lens and sample surface on laser-induced breakdown spectroscopy with spatial confinement

Spatial confinement can significantly enhance the spectral intensity of laser-induced plasma in air. It is attributed to the compression of plasma plume by the reflected shockwave. In addition,optical emission spectroscopy of laser-induced plasma can also be affected by the distance between lens and sample surface. In order to obtain the optimized spectral intensity, the distance must be considered. In this work, spatially confined laser-induced silicon plasma by using a Nd：YAG nanosecond laser at different distances between lens and sample surface was investigated.The laser energies were 12 mJ, 16 mJ, 20 mJ, and 24 mJ. All experiments were carried out in an atmospheric environment. The results indicated that the intensity of Si（I） 390.55 nm line firstly rose and then dropped with the increase of lens-to-sample distance. Moreover, the spectral peak intensity with spatial confinement was higher than that without spatial confinement. The enhancement ratio was approximately 2 when laser energy was 24 mJ.

Interface engineering of tungsten carbide/phosphide heterostructures anchored on N,P-codoped carbon for high-efficiency hydrogen evolution reaction

The development of inexpensive and efficient Pt-free electrocatalysts for the hydrogen evolution reaction(HER)is greatly crucial for water electrolysis.Tungsten carbide(WC)exhibiting a Pt-like electronic structure represents an attractive alternative,although its overall performance is limited by the strong W-H bond that impedes hydrogen desorption.Here,we employed an in-situ interface engineering strategy to construct high-performance and cost effective electrocatalysts comprising WC/tungsten phosphide(WP)heterostructures that were anchored on N,P-codoped carbon(WC/WP@NPC)via a one-step pyrolysis of a melamine polyphosphate/WO_(3) hybrid in an inert atmosphere.Owing to the crystal structure compatibility and electron-rich property of WP,it optimizes the electronic structure and hydrogen adsorption configuration of WC,thus significantly weakening the W-H bond with a thermoneutral Gibbs free energy of hydrogen adsorption(ΔG_(H^(*)))of−0.05 eV.Additionally,NPC ensures fast electron transport and structural stability of the WC/WP@NPC ternary architecture.These synergistically lead to outstanding HER performances of the catalyst in acidic and alkaline media.Our finding offers a new strategy for designing Pt-alternative electrocatalysts with outstanding electrochemical performances for high-efficiency water splitting and other applications.

All-fiber pulsed laser Doppler vibrometer development based on time-domain chopping techniques

A 1550 nm all-fiber pulsed laser Doppler vibrometer (LDV) based on time-domain chopping techniques is developed to overcome demodulation failures caused by multipath interference. The system adopts an adjustable configuration on pulse duration and pulse repetition frequency according to the distance. An experiment is carried out at a 25 m standoff with pulse duration of 80 ns, single pulse energy of 0.4 nJ, and pulse repetition frequency of 1 MHz. A waveform and spectrogram of the demodulated voice show that the pulsed LDV system has a good performance in long-range voice listening.