Short mid-infrared watt-level all-fiber nonlinear pulse compressor above 100-MHz pulse repetition rate

We firstly report a 2-μm all-fiber nonlinear pulse compressor based on two pieces of normal dispersion fiber(NDF),which enables a high-power scaling ability of watt-level and a high pulse compression ratio of 13.7.With the NDFbased all-fiber nonlinear pulse compressor,the 450-fs laser pulses with a repetition rate of 101.4 MHz are compressed to 35.1 fs,corresponding to a 5.2 optical oscillation cycle at the 2-μm wavelength region.The output average power reaches 1.28 W,which is believed to be the highest value never achieved from the previous 2-μm all-fiber nonlinear pulse compressors with a high pulse repetition rate above 100 MHz.The dynamic evolution of the ultrafast pulse inside the all-fiber nonlinear pulse compressor is numerically analyzed,matching well with the experimental results.

High thermoelectric properties with low thermal conductivity due to the porous structure induced by the dendritic branching in n-type PbS

PbS-based thermoelectric materials have attracted extensive attention in recent years for the advantages of earth abundancy and low cost,which is considered to be a substitute for traditional PbTe material.However,their high thermal conductivity restricts its development.Hence,in order to improve their thermoelectric performance from reducing the thermal conductivity,a kind of dendritic PbS with controlled crystal grain and morphology are obtained by solution synthesis.By adjusting the amount of surfactant(CTAB),the specific formation process of dendrites is regulated.After sintering,the dendritic PbS nanoparticles are easy to form porous structure due to the overlapping and staggered arrangement of dendritic branches.For comparison,we also prepare a kind of regular octahedral PbS and a dense packing arrangement is formed because of the integrity of the octahedral structure.DFT-based Boltzmann transport equation is used to prove the crucial role of porous structure in scattering phonon.Finally,a maximum zT=1.0 at 773 K in n-type PbS is obtained,which still keep a high-speed growth and is expected to get higher zT value in a higher temperature region.Our work may shed light to other thermoelectric materials from the formation of porous structure to reduce the thermal conductivity.

Mid-infrared Q-switch performance of ZrC

Zirconium carbide(ZrC)with layered structure and nanoparticle morphology was prepared by sonication in an ethyl alcohol solvent.The morphology and saturable absorption properties of the ZrC were systematically analyzed.By using ZrC nanoparticle coated substrates as saturable absorbers,stable Q-switched 3μm Er:Lu_(2)O_(3) lasers were realized.Pulse durations of 50 ns with pulse energies of 20μJ and peak power of 0.4 kW are the shortest obtained with novel-material-based Q-switched lasers in the 3μm wavelength range.

Thermoelectric properties of solution-synthesized n-type Bi2Te3 nanocomposites modulated by Se： An experimental and theoretical study

We report the investigation of the thermoelectric properties of large-scale solution-synthesized Bi2Te3 nanocomposites prepared from nanowires hot- pressed into bulk pellets. A third element, Se, is introduced to tune the carrier concentration of the nanocomposites. Due to the Se doping, the thermoelectric figure of merit （ZT） of the nanocomposites is significantly enhanced due to the increased power factor and reduced thermal conductivity. We also find that thermal transport in our hot-pressed pellets is anisotropic, which results in different thermal conductivities along the in-plane and cross-plane directions. Theoretical calculations for both electronic and thermal transport are carried out to establish fundamental understanding of the material system and provide directions for further ZT optimization with adjustments to carrier concentration and mobility.