Femtosecond laser ablation (FLA) has been playing a prominent role in precision fabrication of material because of its circumvention of thermal effect and extremely high spatial resolution. Molecular dynamics modeling, as a powerful tool to study the mechanism of femtosecond laser ablation, still lacks the connection between its simulation results and experimental observations at present. Here we combine a single-shot chirped spectral mapping ultrafast photography (CSMUP) technique in experiment and a three-dimensional two-temperature model-based molecular dynamics (3D TTM-MD) method in theory to jointly investigate the FLA process of bulky gold. Our experimental and simulated results show quite high consistency in time-resolved morphologic dynamics. According to the highly accurate simulations, the FLA process of gold at the high laser fluence is dominated by the phase explosion, which shows drastic vaporized cluster eruption and pressure dynamics, while the FLA process at the low laser fluence mainly results from the photomechanical spallation, which shows moderate temperature and pressure dynamics. This study reveals the ultrafast dynamics of gold with different ablation schemes, which has a guiding significance for the applications of FLA on various kinds of materials.

The spatial, temporal, and spectral information in optical imaging play a crucial role in exploring the unknown world and unencrypting natural mysteries. However, the existing optical imaging techniques can only acquire the spatiotemporal or spatiospectral information of the object with the single-shot method. Here, we develop a hyperspectrally compressed ultrafast photography (HCUP) that can simultaneously record the spatial, temporal, and spectral information of the object. In our HCUP, the spatial resolution is $1.26\mathrm{lp}/\mathrm{mm}$ in the horizontal direction and $1.41\mathrm{lp}/\mathrm{mm}$ in the vertical direction, the temporal frame interval is 2 ps, and the spectral frame interval is 1.72 nm. Moreover, HCUP operates with receive-only and single-shot modes, and therefore it overcomes the technical limitation of active illumination and can measure the nonrepetitive or irreversible transient events. Using our HCUP, we successfully measure the spatiotemporal-spatiospectral intensity evolution of the chirped picosecond laser pulse and the photoluminescence dynamics. This Letter extends the optical imaging from three- to four-dimensional information, which has an important scientific significance in both fundamental research and applied science.

The compressed ultrafast photography (CUP) technique, providing the fastest receive-only camera so far, has shown to be a well-established tool to capture the ultrafast dynamical scene. This technique is based on random codes to encode and decode the ultrafast dynamical scene by a compressed sensing algorithm. The choice of random codes significantly affects the image reconstruction quality. Therefore, it is important to optimize the encoding codes. Here, we develop a new scheme to obtain the optimized codes by combining a genetic algorithm (GA) into the CUP technique. First, we measure the dynamical scene by the CUP system with random codes and obtain the dynamical scene image at each moment. Second, we use these reconstructed dynamical scene images as the optimization target and optimize the encoding codes based on the GA. Finally, we utilize the optimized codes to recapture the dynamical scene and improve the image reconstruction quality. We validate our optimization scheme by the numerical simulation of a moving double-semielliptical spot and the experimental demonstration of a time- and space-evolving pulsed laser spot.

We propose a scheme to achieve the field-free molecular orientation around the half rotational periods with the combination of single- and dual-color laser pulses. We show that the molecular orientation can be obtained and controlled by precisely controlling the time delay between the two laser pulses. Furthermore, we discuss the effect of the laser intensity and pulse duration of the single-color laser pulse on the molecular orientation created by the dual-color laser pulse, and show that the molecular orientation depends on the change in the alignment degree between the odd and even rotational wave-packet contributions created by the single-color laser pulse.

Depleted UCL in NaYF₄:Yb³⁺,Tm³⁺ UCNPs upon simultaneous excitation at 980 nm and 1550 nm is attributed to the STED process.