In this Letter, temporal self-modifying behavior of amplitude modulation pulse propagation characteristics in multiphoton absorbers is presented by solving the underlying theoretical model coupling the propagation equation with the rate equations. The characteristics of the output temporal shapes are of primary concern and are discussed in detail. Amplitude modulation suppressing effects of multiphoton absorbers are numerically demonstrated; they have not been reported previously, to our knowledge. By taking a time resolved absorption coefficients, the corresponding physical mechanism is explicitly interpreted.

The influence of air turbulence on the transverse wandering of a single femtosecond laser filament is studied by numerical simulation. The results show that the average transverse displacement of the single filament δr is proportional to the square root of turbulent structure constant and the relations between δr and the propagation distance can be fit by a power function. In addition, by using an axicon as a focusing optics, the wandering of a single filament is suggested to be stronger than the free-propagation case.

The visible and near-UV emission spectroscopy of methane (CH4) induced by a femtosecond intense laser field (800 nm, 40 fs, 1014 W/cm2) is studied. By measuring the decay profiles of the neutral fragment product CH (A2Δ→X2Π), two reaction pathways, i.e., the electron-ion recombination through e +CH4+ and the direct disintegration of CH4+ are found to be responsible for populating the electronic excited states of the neutral fragment product CH, which gives rise to the photoemissions. Our results provide complementary information on previous understanding of the strong-field-induced photoemission mechanism of CH4 through neutral dissociation of superexcited states.

Intense-laser-induced above-threshold ionization of a bound electron into continuum states with low energy is investigated in the context of the strong-field approximation that allows for one act of rescattering of the revisiting electron. The quantum orbits for forward and backward scattering are evaluated and generalized to arbitrary scattering angles. The velocity map of the liberated electron exhibits the well-known low-energy structure as well as other features off the polarization axis.

In this Letter, we focus on the theoretical analysis of the relativistic energy and angular distributions of the ejected photoelectrons during the relativistic tunnel ionization of atoms by intense, circularly polarized light. We make a small modification of the general analytical expressions for these distributions. The role of the initial momentum, the ponderomotive potential, and the Stark shift are considered. We also present the maximal angle of electron emission.

We report photoelectron energy spectra and angular distributions for ionization with elastic scattering in ultrastrong laser fields. Noble gas species with Hartree–Fock scattering potentials show a reduction in elastic rescattering with the increasing energy of ultrastrong fields and when the Lorentz deflection of the photoelectron exceeds its wave function spread. The relativistic extension of a three-step recollision model is well-suited to the ultrastrong intensity regime (>1017 W/cm2) that lies between traditional strong fields and extreme relativistic interactions.

Investigations are performed to explore high-repetition-rate femtosecond laser ablation effects on the physical and chemical properties of poly(methyl methacrylate) (PMMA). A scanning electron microscopy (SEM) is used to characterize the morphology change in the laser-ablated regions. The infrared and Raman spectroscopy reveals that the fundamental structure of the PMMA is altered after laser ablation. We demonstrate the cumulative heating is much greater during high-repetition-rate femtosecond laser ablation, supporting a photothermal depolymerization mechanism during the ablation process.

Ablation dynamics of tungsten irradiated with a 70 fs laser pulse is investigated with X-ray interferometry and X-ray imaging using a 13.9 nm soft X-ray laser of 7 ps pulse duration. The evolution of high-density ablation front of tungsten (i.e., W) is presented. The ablation front expands to ～120 nm above the original target surface at 160 ps after femtosecond-laser irradiation with an expansion speed of approximately 750 m/s. These results will provide important data for understanding ablation properties of W, which is a candidate material of the first wall of magnetic confinement fusion reactors.