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Light-induced deprotonation of molecules is an important process in photochemical reactions. Here, we theoretically investigate the tunneling deprotonation of H 2 + and its asymmetric isotopologues driven by circularly polarized THz laser pulses. The quasi-static picture shows that the field-dressed potential barrier is significantly lowered for the deprotonation channel when the mass asymmetry of the diatomic molecule increases. Our numerical simulations demonstrate that when the mass symmetry breaks, the tunneling deprotonation is significantly enhanced and the proton tunneling becomes the dominant dissociation channel in the THz driving fields. In addition, the simulated nuclear momentum distributions show that the emission of the proton is directed by the effective vector potential for the deprotonation channel and, meanwhile, the angular distribution of the emitting proton is affected by the alignment and rotation of the molecule induced by the rotating field. [ABSTRACT FROM AUTHOR]

We experimentally study two-body Coulomb explosions of CO2, O2, and CH3Cl molecules in intense femtosecond laser pulses. We observe an obvious variation in the ionic angular distribution of the fragments with respect to the kinetic energy releases (KERs). Using a classical model based on ab initio potential energy curves, we find that the dependence of the ionic angular distribution on the KER is relevant to the fact that the accurate potential energy deviates significantly from the value determined by applying the Coulomb interaction approximation at a relatively small internuclear distance of the molecule. We show that the KER-dependent ionic angular distribution provides an effective way to determine the critical internuclear distance at which the Coulomb interaction approximation holds or breaks down without relying on the knowledge of the accurate potential energy curves. [ABSTRACT FROM AUTHOR]

Mode selecting plays a vital role in the field of optoelectronics, such as optical communication, signal processing, on-chip light manipulation, mode conversion, and frequency synthesis. In this work, flexible selection and enhancement of the frequency modes in an unidirectional coupled Su–Schrieffer–Heeger (SSH) frequency lattice are obtained with Floquet exceptional points (EPs) and chiral Zener tunneling (ZT). The unidirectional coupled non-Hermitian SSH frequency lattices are synthesized by a double-ring system with complex dynamical modulations. Under an effective direct current (dc) force induced by the phase-mismatching of the modulations, the two Floquet bands of the non-Hermitian frequency lattices are degenerated and the Floquet EPs arise. Therefore, the unidirectional and irreversible frequency mode conversion takes place, which is the chiral ZT. Moreover, through perturbation analysis and numerical simulations, we prove that the frequency modes of the two-band system can be selected and enhanced by a multi-photon resonance dc force. [ABSTRACT FROM AUTHOR]

We extend the functionality of nonlinear photonic crystals by fabricating a structure combining a few individual optical transformations in second harmonic generation. In particular, we employed all-optical spontaneous polarization reversal in ferroelectrics to create nonlinear holograms with curved fork-like spatial modulation of nonlinearity for the generation of second harmonic optical vortices. The curved fork-like structure represents a combination of a standard vortex harmonic generator (fork structure) and an axicon, thereby allowing us to realize the second harmonic "perfect vortices" whose diameter remains constant independently of their topological charge. [ABSTRACT FROM AUTHOR]

Experiments involving laser produced tin plasma have been carried out using a CO2 laser with an energy of 800 mJ/pulse and a full width at half maximum (FWHM) of 80 ns in vacuum. Time-integrated extreme ultraviolet spectral measurement showed that the peak of the extreme ultraviolet lithography spectrum was located at 13.5 nm and the spectrum profile's FWHM of the unresolved transition arrays was 1.1 nm. Plasma parameters of the electron temperature and density measurements in both axial and radial directions at later times had been obtained from a two-dimensional time and space resolved image spectra analysis. The axial spatial distribution of the electron density showed a 1/d2.6 decrease profile, and the radial spatial distribution of the electron density showed a 1/r1.1 profile, in which d is the axial distance from the target surface and r is the radial distance. The electron density was found to maintain symmetry across the radial distance at all delay times. Near the plasma plume center, the electron temperature Te varied slightly with increasing axial or radial distance, which was related to collisional decoupling and reheating of the ionized species in the plasma at distances longer than 3 to 4 mm. The space averaged electron temperature was measured in the range of 3.4-1.0 eV, and the space averaged electron density was measured in the range of 2.0 × 1017 to 2.2 × 1016 cm-3, as the time delay varied from 1.6 μs to 3.6 μs with respect to the pulse discharge. Time evolutions of the plasma temperature and density were found to have an apparent rise at a delay time of 2.4 μs in the corresponding time of the laser pulse tail peak. This suggests that plasma parameters and extreme ultraviolet emission intensity can be controlled by a double pulse combined laser. [ABSTRACT FROM AUTHOR]

Using the classical ensemble method, we have investigated double ionization (DI) of diatomic molecules driven by circularly polarized laser pulses with different internuclear distances (R). The results show that the DI mechanism changes from sequential double ionization (SDI) to nonsequential double ionization (NSDI) as the internuclear distance increases. In SDI range, the structure of the electron momentum distribution changes seriously as R increases, which indicates the sensitive dependence of the release times of the two electrons on R. For NSDI, because of the circular polarization, the ionization of the second electron is not through the well-known recollision process but through a process where the first electron ionizes over the inner potential barrier of the molecule, moves directly towards the other nucleus, and kicks out the second electron. [ABSTRACT FROM AUTHOR]

The optical nonlinearity of hybrid structures composed of CdTe quantum dots and periodical particle array of gold is studied using Z-scan method. The optical nonlinearity is dramatically affected by the interaction between exciton in CdTe quantum dots and surface plasmons in Au periodical particle array. When the Au surface plasmon is tuned to be in resonance with the exciton transition in CdTe quantum dots, the largest nonlinear refractive index and the smallest two-photon absorption coefficient, n2 = -0.53 cm2/GW and β = 25 cm/GW, which are about 8 times larger and 50 times smaller than that of bare CdTe quantum dots, can be achieved. [ABSTRACT FROM AUTHOR]

We report the two-photon absorption induced lasing performance in a single CdS microwire under the excitation of a femtosecond pulse laser with a wavelength of 800 nm. Sharp lasing peaks are centered at 523 nm with an average linewidth of 0.4 nm, indicating a high quality factor of 1300. The lasing emission is highly dependent on the polarization direction of the excitation light and the optimized lasing threshold is estimated to be 3.3 mJ/cm2 as the polarization direction is parallel to the microwire axis. Furthermore, the polarization-dependent lasing effect is confirmed by performing the finite-difference time-domain method. [ABSTRACT FROM AUTHOR]