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.

Neutral atoms have been observed to survive intense laser pulses in high Rydberg states with surprisingly large probability. Only with this Rydberg-state excitation (RSE) included is the picture of intense-laser-atom interaction complete. Various mechanisms have been proposed to explain the underlying physics. However, neither one can explain all the features observed in experiments and in time-dependent Schrödinger equation (TDSE) simulations. Here we propose a fully quantum-mechanical model based on the strong-field approximation (SFA). It well reproduces the intensity dependence of RSE obtained by the TDSE, which exhibits a series of modulated peaks. They are due to recapture of the liberated electron and the fact that the pertinent probability strongly depends on the position and the parity of the Rydberg state. We also present measurements of RSE in xenon at 800 nm, which display the peak structure consistent with the calculations.

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.