Ultrafast carrier relaxation dynamics in fluorescent carbon nanodots is investigated by femtosecond transient absorption spectra at different pH environments so as to understand the mechanism of fluorescence for the first time. Utilizing multi-wavelength global analysis to fit the measured signal via a sequential model, four different relaxation channels are found, which are attributed to electron-electron scattering and surface state trapping, optical phonon scattering, acoustic phonon scattering and electron–hole recombination respectively. The results reveal that the surface states are mainly composed of different oxygen-containing functional groups (epoxy, carbonyl and carboxyl) and carbon atoms on the edge of the carbon backbone and can effectively trap a large number of photo-excited electrons. The deprotonation of carboxyl groups at high pH will change the distribution of π electron cloud density between the carbon backbone and surface states and consequently, compared with the excited electrons in the acidic and neutral environments, those in the alkaline environment can be more easily trapped by the surface within 1 ps, thereby giving rise to stronger fluorescence emission.

Enhancement of laser-induced Fe plasma spectroscopy with dual-wavelength is investigated by using femtosecond double-pulse laser.

The current research confirms that substrate temperature plays a dominant role in improving the detection sensitivity of surface-enhanced laser-induced breakdown spectroscopy (SE-LIBS) technology. In the experiment, SE-LIBS is used to detect trace heavy metal elements in aqueous solutions. The influence of the substrate temperature on the spectral intensity of Pb and Cr is discussed. Calibration curves are constructed for Pb and Cr at different substrate temperatures. The corresponding limit of detection (LoD) is calculated. The LoDs of Pb and Cr decrease from 31.7 ng mL⁻¹ and 4.6 ng mL⁻¹ to 8.0 ng mL⁻¹ and 1.2 ng mL⁻¹ as the substrate temperature increases from 25 °C to 200 °C. Increasing the substrate temperature can further improve the analytical ability and detection sensitivity of SE-LIBS for detecting heavy metal elements. The study provides a feasible scheme for the detection of heavy metal elements in wastewater.

In this work, LIBS technology combined with the LASSO–LSSVM regression model was used to improve the detection ability of minor elements in Al–Cu–Mg–Fe–Ni aluminum alloy.

The influence of group-velocity-dispersion (GVD) effects on the propagation of femtosecond laser pulses in air at different pressures is investigated by numerically solving the extended nonlinear Schrödinger equation. It is observed that GVD has a great influence on the collapse distance $L_{\mathrm{c}}$ of the self-focusing short laser pulses when the pressure is relatively high (e.g., 10 atm), in which case the semiempirical formula describing the collapse distance of self-focusing laser pulse [Dawes and Marburger, Phys. Rev. 179, 862 (1969)] is no longer applicable, while GVD has little influence on the self-focusing process of longer laser pulses. Through the results of numerical simulations as well as analytical analysis, we find that the initial duration of the laser pulse is the main factor that determines the GVD effect on the propagation and the increase of the pressure and pulse compression during the propagation enhance this effect. The spectral data show that GVD also influences the spectrum broadening in high-pressure cases.