RESUMO
Irradiation inside some transparent materials such as fused silica can induce nanograting structures at the focal area. Here, we investigate experimentally how the nanograting formation can be influenced by tuning the ionization property of the transparent material, which is achieved by irradiation inside a porous glass immersed in water doped with NaCl at variable concentrations. Our results show that the doping of NaCl not only reduces the threshold fluence of optical breakdown, but also leads to nanograting structures with shorter periods. These effects may be attributed to the enhanced photoionization in water doped with NaCl.
RESUMO
We theoretically investigate the selective enhancement of high-harmonic generation (HHG) in a small spectral range when an orthogonal-polarized two-color laser field interacts with aligned O(2) molecules. It is shown clearly that the enhanced narrow-bandwidth emission near the cutoff of the HHG spectrum can be effectively controlled by the molecular alignment angle, laser intensity and the relative phase of two-color laser fields. Furthermore, the strong dependence of narrow-bandwidth HHG on molecular alignment angle indicates that it encodes information about O(2) molecular orbitals, so it may be an alternative method for reconstruction of O(2) molecular orbitals.
Assuntos
Modelos Químicos , Oxigênio/química , Oxigênio/efeitos da radiação , Simulação por Computador , Lasers , Conformação Molecular , Espalhamento de RadiaçãoRESUMO
We investigate theoretically the enhancement of the low-order harmonic emission from a polar molecular medium. The results show that, by using a control laser field, the intensity of the spectral signals near fourth-order harmonics will increase over 25 times as a result of the four-wave mixing process. Moreover, the enhancement effects depend strongly on the carrier-envelope phase of the initial laser fields, which cannot be found in a symmetric system.