Effect of sample temperature on femtosecond laser ablation of copper

We conduct an experimental study supported by theoretical analysis of single laser ablating copper to investigate the interactions between laser and material at different sample temperatures,and predict the changes of ablation morphology and lattice temperature.For investigating the effect of sample temperature on femtosecond laser processing,we conduct experiments on and simulate the thermal behavior of femtosecond laser irradiating copper by using a two-temperature model.The simulation results show that both electron peak temperature and the relaxation time needed to reach equilibrium increase as initial sample temperature rises.When the sample temperature rises from 300 K to 600 K,the maximum lattice temperature of the copper surface increases by about 6500 K under femtosecond laser irradiation,and the ablation depth increases by 20%.The simulated ablation depths follow the same general trend as the experimental values.This work provides some theoretical basis and technical support for developing femtosecond laser processing in the field of metal materials.

Ultrafast Dynamics of Defect-Assisted Carrier Capture in MoS2 Nanodots Investigated by Transient Absorption Spectroscopy

MoS2 nanodots are emerging as promising semiconductor materials for optoelectronic de-vices.However,most of the recent attention is focused on the fabrication of MoS2 nanodots,and the survey for exciton dynamics of MoS2 nanodots remains less explored.Herein,we use femtosecond transient absorption spectroscopy to investigate the carrier dynamics of MoS2 nanodots.Our results show that defect-assisted carrier recombination processes are well consistent with the observed dynamics.The photo-excited carriers are captured by defects with at least two different capture rates via Auger scattering.Four processes are deemed to take part in the carrier relaxation.After photoexcitation,carrier cooling occurs instantly within^0.5 ps.Then most of carriers are fast captured by the defects,and the corresponding time constant increases from^4.9 ps to^9.2 ps with increasing pump uence,which may be interpreted by saturation of the defect states.Next a small quantity of carriers is cap-tured by the other kinds of defects with a relatively slow carrier capture time within^65 ps.Finally,the remaining small fraction of carriers relaxes via direct interband electron-hole recombination within^1 ns.Our results may lead to deep insight into the fundamentals of carrier dynamics in MoS2 nanodots,paving the way for their further applications.

A Novel Low Air Pressure-Assisted Approach for the Construction of Cells-Decellularized Tendon Scaffold Complex

Objective The goal of this study was to develop a decellularized tendon scaffold(DTS)and repopulate it with adipose-derived stem cells(ADSCs)assisted by low air pressure(LP).Methods The porcine superficial flexor tendons were processed into the DTSs using a combination of physical,chemical,and enzymatic treatments.The effectiveness of decellularization was verified by histological analysis and DNA quantification.The properties of the DTSs were evaluated by quantitative analysis of biochemical characterization,porosimetry,in vitro biocompatibility assessment,and biomechanical testing.Subsequently,the ADSCs-DTS complexes were constructed via cell injection assisted by LP or under atmospheric pressure.The differences in cell distribution,biomechanical properties,and the total DNA content were compared by histological analysis,biomechanical testing,and DNA quantification,respectively.Results Histological analysis confirmed that no cells or condensed nuclear materials were retained within the DTSs with widened interfibrillar space.The decellularization treatment resulted in a significant decrease in the content of DNA and glycosaminoglycans,and a significant increase in the porosity.The DTSs were cytocompatible in vitro and did not show reduced collagen content and inferior biomechanical properties compared with the fresh-frozen tendons.The assistance of LP promoted the broader distribution of cells into the adjacent interfibrillar space and cell proliferation in DTSs.The biomechanical properties of the scaffolds were not significantly affected by the recellularization treatments.Conclusion A novel LP-assisted approach for the construction of cells-DTS complex was established,which could be a methodological foundation for further bioreactor and in vitro studies.

Combination of spark discharge and nanoparticle-enhanced laser-induced plasma spectroscopy

A combination of spark discharge and nanoparticle-enhanced laser-induced plasma spectroscopy is investigated.Depositing Au nanoparticles at the surface of a brass target can enhance the coupling of the target and the laser.More atoms in the brass sample are excited.As a secondary excitation source,spark discharge reheats the generated plasma,which further amplifies the enhancement results of nanoparticles.The spectral intensity with the spark discharge increases more obviously with nanoparticle concentration increasing than without the spark discharge.Also,plasma temperature and electron density are calculated by the Boltzmann plot and Stark broadening.The changes in the plasma temperature and electron density are consistent with the spectral emission changes.

Influence of polarization of laser beam on emission intensity of femtosecond laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy(LIBS)is an important technique which is widely used to analyze element composition.In order to improve the sensitivity of LIBS,much effort has been made to enhance the spectral intensity of LIBS by proposing a number of methods.In addition,we find that laser polarization has great influence on the emission intensity of femtosecond LIBS.By comparing the emission intensity of femtosecond LIBS in the circular polarization with that in the linear polarization,the spectral intensity in the case of circular polarization is stronger than that in the case of linear polarization.Moreover,this phenomenon is more obvious as laser energy increases.The polarization plays an important role in LIBS signal intensity.Based on the observation,the enhanced mechanism of the laser polarization for the spectral intensity is discussed in this paper,which will be helpful in spectral analysis and component analysis.