飞秒激光在三维微细体系中的应用

飞秒激光的超快特性使其能以极低的脉冲能量获得超强光场,并且激光加照区淀积的能量能以通过热扩散途径逸出辐照区域,其与透明物质相互作用是通过双光子或多光子吸收过程实现,故作用区限域于焦点核心很小体积内,因而在三维微制备及生物医学领域有着独到优势。文章介绍了飞秒激光应用于微爆炸、高密度三维光学数据存储、直写光波导及三维光子晶体制备、生物医学工程等方面的最新进展。飞秒激光三维微制备技术在微电子、计算机、光通信、生物医学等高技术领域有着广阔的应用前景。     

Effect of relaxation rate on population distribution, EIT and refraction in Λ and V systems

In the three-level Λ-type and V-type systems, we find that the same pump-effect parameter R\left(=\dfrac{2|V_{c}|^{2}γ}{(ω_{ac}-ω_{c})^{2}+γ^{2}}\right) determines the population distributions, while the probe field leads to population fluctuations near the absorption peaks. With the increasing of the relaxation rate γ, the population distributions are shifted and their fluctuation amplitudes decrease. At the same time the electromagnetically induced transparency window becomes a broadened absorption peak, and the dispersion at the zero probe detuning changes from positive to negative. Large population fluctuation and non-fluctuation observed in different systems are attributed to the different relaxation rates.     

Long-range surface plasmon polaritons with subwavelength mode expansion in an asymmetrical system

Long-range surface plasmon polariton (LRSPP) modes in an asymmetrical system, in which the thin metal film is sandwiched between a semi-infinite substrate and a high permittivity polymer film with a finite thickness, are theoretically calculated and analyzed. Due to the high permittivity of the polymer film, at proper polymer film thicknesses, the index-matching condition of the dielectrics at both sides of the metal can be satisfied for supporting LRSPP modes, and the electromagnetic field above the metal can be localized well. It is found that these LRSPP modes have both long propagation lengths and subwavelength mode expansion above the metal at the optimal polymer film thicknesses. Furthermore, the requirements on the refractive index and the thickness of the polymer film to support LRSPP modes at the optimal thicknesses are found to be not critical.     

The dissociative ionization and Coulomb explosion of ethane by a femtosecond laser field

Femtosecond laser-induced dissociation and Coulomb explosion of polyatomic molecule C_2H_6 were systematically investigated using a time-of-flight mass spectrometer and a chirped pulse amplifier laser. With the laser intensity varying from 2.4×10^{15}W/cm^{2} to 1.2×10^{16}W/cm^2, strong molecular ions C_2H_n^+ (n=0－6) and atomic ions C^{m+} (m=1－3) signals were observed. The double-peak structure of atomic ions indicated the occurrence of Coulomb explosion. Compared with the nearly isotropic distribution of C^{+}, highly charged ions C^{m+} (m=2－3) exhibited a sharply anisotropic angular distribution, which was attributed to the geometric alignment.     

FIELD IONIZATION OF MOLECULES IN AN INTENSE LASER FIELD

In order to predict the field ionization probabilities, the accurate ab initio electrostatic potential of molecules has to be calculated. However, the calculation of the full ab initio electrostatic potential of molecules is complicated, even impossible for some larger molecules with low symmetry. Here, we present a semi-empirical model to treat the field ionization of molecules in an intense laser field. In this model, a modified Coulomb potential is used to take the place of the complicated ab initio electrostatic potential of molecules. The analytic equations of the Keldysh adiabatic parameter using the Coulomb potential and the modified Coulomb potential have first been given. Using our semi-empirical model, we have calculated the field ionization probabilities and the Keldysh adiabatic parameters of O₂, N₂, SO₂, C₂H₄, CH₃CN and C₆H₆ in an intense laser field. The results agree excellently with the calculations using the ab initio electrostatic potential of molecules. As the modified parameter for the Coulomb potential can be found from experimental measurements, the field ionization mechanism of molecules can be immediately predicted with our semi-empirical model.     

光自旋霍尔效应及面内光自旋分离

当宽度有限的实际光束反射和折射时,左旋光和右旋光成分会发生垂直于入射面的空间分离,这一新奇的光自旋霍尔效应近来引起了人们的广泛关注.文章介绍了光自旋霍尔效应的研究进展,特别关注了纳米量级分离的测量方面进展.作者还发现在入射面内也会出现光自旋分离现象,并对这一新现象进行了理论分析和实验研究,实验测量数据和理论计算结果非常符合.     

Bending Loss Calculation of a Dielectric-Loaded Surface Plasmon Polariton Waveguide Structure

Based on full 3D finite element method simulations, the transmission of a dielectric-loaded surface plasmon polariton waveguide （DLSPPW） based 1/4 circle is calculated for a 90° bend model and a 270° bend model, respectively. It is found that the 270° bend model gives almost pure bending loss while the 90° bend model contains additional coupling loss. The models are applied to deduce the loss and unloaded quality factor of DLSPPW based waveguide ring resonators （WRRs） and the results of the 270° bend model agree well with direct simulating results of the WRRs. Thus the 270° bend model gives a fast and simple way to calculate bending loss and it is helpful for WRR design because no wavelength scan is needed.     

Ge-Ga-Cd硫化物玻璃的超快三阶非线性光学性质与结构关系研究

本文采用飞秒时间分辨光学克尔门技术测量了GeS2-Ga2S3-CdS硫化物玻璃体系的超快三阶非线性光学响应，所用激光波长分别为820nm和640nm。?实验结果证明了GeS2-Ga2S3-CdS组分玻璃具有很大的飞秒超快三阶非线性光学响应，另外，其Kerr信号随摩尔组分的不同呈显著变化。通过拉曼光谱结构分析，探讨了此系列硫化物玻璃的三阶非线性光学性质与结构的关系，结果表明构成玻璃网络的四面体结构单元[GeS4]([GaS4])对其超快三阶光学非线性起重要作用。实验还表明了此硫化物玻璃体系的超快三阶非线性不符合半经验的Miller定律。     

Chirping-dependent ionization and dissociation of methane in an intense femtosecond laser field

We studied the ionization and dissociation of polyatomic molecule methane in an intense femtosecond laserfield with wavelength of 810 nm and intensities ranging from 1.4×10~(14)to 2.6×10~(15) W/cm~2 by massspeetroscopy.Abundant fragment inos were observed in addition to the strong parent ion.The effect offrequency chirp was investigated and it was found that the negatively chirped pulses dramatically enhancedthe dissociation probability,which might be used to control the dissociation pathways.