可调谐集成光学Ti:LiNbO3光波导定向耦合滤波器

波分复用技术是当今光纤通信系统中的关键技术之一。具有增加光纤通信系统容量的巨大潜力,集成光学复用技术对于单模光纤通信系统特别重要本文给出了一种集成光学复用器件的设计和制作,这种集成光学滤波器是在之切LiNbO₃衬底上用非对称钛扩散条波导定向耦合器构成,它适于1.32μm和1.55μm波长耦合滤波。为了使单模光纤和条波导有效耦合,我们研制出了硅V型槽,并给出了一种光纤与波导的连接结构。提供了一种切实可行的途径。     

High-order harmonic generation of CO_2 with different vibrational modes in an intense laser field

We apply the strong-field Lewenstein model to demonstrate the high-order harmonic generation of CO_2 with three vibrational modes(balance vibration,bending vibration,and stretching vibration) driven by an intense laser field.The results show that the intensity of harmonic spectra is sensitive to molecular vibrational modes,and the high harmonic efficiency with stretching vibrational mode is the strongest.The underlying physical mechanism of the harmonic emission can be well explained by the corresponding ionization yield and the time-frequency analysis.Finally,we demonstrate the attosecond pulse generation with different vibrational modes and an isolated attosecond pulse with a duration of about 112 as is generated.     

Effect of elliptical polarizations on nonsequential double ionization in two-color elliptically polarized laser fields

Using the classical ensemble model, we investigate the nonsequential double ionization(NSDI) of Ar and Mg in the two-color elliptically polarized laser pulse for different elliptical polarizations. Numerical results show that for Ar atoms the NSDI yield increases as the ellipticity increases, which is different from the case of Mg atoms. Moreover, the correlated behavior in the correlated electron momentum along the x direction and ion momentum distributions of Ar atoms are influenced by the ellipticity. By statistical analysis of different times, we can conclude that the ellipticity may be responsible for the NSDI processes. The correlated momenta distributions along the x direction at the recollision time are demonstrated and the results show that the travelling time and ellipticity can affect the emitted directions of both electrons.     

Spectral redshift of high-order harmonics by adding a weak pulse in the falling part of the trapezoidal laser pulse

We investigate the spectral redshift of high-order harmonics of the H_2~+(D_2~+) molecule by numerically solving the non-Born–Oppenheimer time-dependent Schr ¨odinger equation(TDSE). The results show that the spectral redshift of highorder harmonics can be observed by adding a weak pulse in the falling part of the trapezoidal laser pulses. Comparing with the H_2~+ molecule, the shift of high-order harmonic generation(HHG) spectrum for the D_2~+ molecule is more obvious.We employ the spatial distribution in HHG and time-frequency analysis to illustrate the physical mechanism of the spectral redshift of high-order harmonics.     

Controlling the contributions to high-order harmonic generation from different nuclei of N_2 with an orthogonally polarized two-color laser field

The generation of high-order harmonic and the attosecond pulse of the N2 molecule with an orthogonally polarized two-color laser field are investigated by the strong-field Lewenstein model.We show that the control of contributions to high-order harmonic generation(HHG) from different nuclei is realized by properly selecting the relative phase.When the relative phase is chosen to be φ= 0.4π,the contribution to HHG from one nucleus is much more than that from another.Interference between two nuclei can be suppressed greatly; a supercontinuum spectrum of HHG appears from 40 e V to125 e V.The underlying physical mechanism is well explained by the time–frequency analysis and the semi-classical threestep model with a finite initial transverse velocity.By superposing several orders of harmonics,an isolated attosecond pulse with a duration of 80 as can be generated.     

Carrier envelope phase effect on the spatial distribution of high-order harmonic generation in asymmetric molecule

The spatial distribution in high-order harmonic generation(HHG) from the asymmetric diatomic molecule He H~(2+) is investigated by numerically solving the non-Born–Oppenheimer time-dependent Schr?dinger equation(TDSE). The spatial distribution of the HHG spectra shows that there is little contribution in HHG around the geometric center of two nuclei(z = 1.17 a.u.) and the equilibrium internuclear position of the H nucleus(z = 3.11 a.u.). We demonstrate the carrier envelope phase(CEP) effect on the spatial distribution of HHG in a few-cycle laser pulse. The HHG process is investigated by the time evolution of the electronic density distribution. The time–frequency analysis of HHG from two nuclei in HeH~(2+) is presented to further explain the underlying physical mechanism.     

Two-center interference in high-harmonic generation of H_2~+ in a combination of a mid-infrared laser field and a terahertz field

We theoretically investigate the two-center interference in high-order harmonics generated from the H_2~+ in a combination of a mid-infrared laser and a terahertz field by numerically solving the time-dependent Schr ¨odinger equation(TDSE).The interference minima in high-order harmonic generation(HHG) are effectively suppressed when a THz field is added.The contribution to HHG from the two separate nuclei is used to demonstrate the locating order of the harmonic minima.Furthermore, we also investigate the emission time of harmonics. The results show that the intensity of the short path around 60 thorder after adding a THz field is stronger than that in the mid-infrared laser field, which further illustrates the suppression of the interference minima in HHG.