Magneto-Rayleigh-Taylor instability in compressible Z-pinch liner plasmas

In this paper, the characteristics of magneto-Rayleigh-Taylor(MRT) instability of liner plasmas in Mag LIF is theoretically investigated. A three-region slab model, based on ideal MHD equations, is used to derive the dispersion relation of MRT instability. The effect of compressibility on the development of MRT instability is specially examined. It is shown that the growth rate of MRT instability in compressible condition is generally lower than that in incompressible condition in the presence of magnetic field. In the case of zero magnetic field, the growth rate in compressible assumption is approximately the same as that in incompressible assumption. Generally, MRT instability in(x, y) plane can be remarkably mitigated due to the presence of magnetic field especially for short-wavelength perturbations. Perturbations may be nearly completely mitigated when the magnetic field is increased to over 1000 T during liner implosions. The feedthrough of MRT instability in liner outer surface on inner surface is also discussed.     

Change in the relief of a target surface treated by compression plasma flows

The change in the surface relief of a steel-3 target (GOST 380) treated by compression plasma flows is experimentally studied. The energy density absorbed by the target varies in the range of 10–35 J/cm² and the pulse duration is 100 μs. It is shown experimentally and numerically that the development of KelvinHelmholtz instability strongly affects the formation of the target surface treated with compression plasma flows: a large-scale wave-like relief with characteristic sizes of 200 × 1000 μm is formed on the target surface and, as a result, the roughness of the surface increases. However, the microrelief at the scale of individual elements is smoothed to a maximum roughness of about 0.5 μm.     

Stimulated Raman conversion of radiation from a YAG:Nd laser with wavelengths of 1.319, 1.338, and 1.357 µm in a barium nitrate crystal

We have studied stimulated Raman (SRS) conversion to the first Stokes component of multimode (M₂ = 8) radiation from a YAG:Nd laser with lasing wavelengths of 1.319 μm, 1.338 μm, and 1.357 μm in a barium nitrate crystal. We have obtained pulses of converted radiation with energies up to 120 mJ. We have achieved conversion efficiencies greater than 40% for each of the three Raman laser wavelengths of 1.530 μm, 1.556 μm, and 1.582 μm with divergence of the beams of converted radiation close to the diffraction-limited value (M₂ < 1.5). __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 330–334, May–June, 2006.     

深振幅Al调制靶的化学腐蚀制备工艺研究

 介绍了用于惯性约束聚变分解实验的铝调制靶的制备。以半导体光刻工艺结合化学腐蚀工艺在铝箔表面引入周期为50 μm的条槽图形，研究腐蚀条件对腐蚀速率的影响;采用光学显微镜、扫描电镜和台阶仪对图形形貌和样品表面成分进行测量和分析，获得厚度在32 μm左右、腐蚀深度达到20 μm的铝调制靶。     

Radiation characteristics and implosion dynamics of tungsten wire array Z-pinches on the YANG accelerator

We investigated the radiation characteristics and implosion dynamics of low-wire-number cylindrical tungsten wire array Z-pinches on the YANG accelerator with a peak current 0.8-1.1 MA and a rising time ～ 90 ns.The arrays are made up of(8-32)×5 μm wires 6/10 mm in diameter and 15 mm in height.The highest X-ray power obtained in the experiments was about 0.37 TW with the total radiation energy ～ 13 kJ and the energy conversion efficiency ～ 9%(24×5 μm wires,6 mm in diameter).Most of the X-ray emissions from tungsten Z-pinch plasmas were distributed in the spectral band of 100-600 eV,peaked at 250 and 375 eV.The dominant wavelengths of the wire ablation and the magneto-Rayleigh-Taylor instability were found and analyzed through measuring the time-gated self-emission and laser interferometric images.Through analyzing the implosion trajectories obtained by an optical streak camera,the run-in velocities of the Z-pinch plasmas at the end of the implosion phase were determined to be about(1.3-2.1)×10 7 cm/s.     

Germanium microsphere high-Q resonator

In this Letter, the fabrication and characterization of a microsphere resonator from the semiconductor germanium is demonstrated. Whispering gallery modes are excited in a 46 μm diameter germanium microsphere resonator using evanescent coupling from a tapered silica optical fiber with a waist diameter of 2 μm. Resonances with Q factors as high as 3.8×10(4) at wavelengths near 2 μm are observed. Because of their ultrahigh optical nonlinearities and extremely broad transparency window, germanium microsphere resonators offer the potential for optical processing devices, in particular at long wavelengths, such as around 2 μm.     

Field compressing magnetothermal instability in laser plasmas

The mechanism for a new instability in magnetized plasmas is presented and a dispersion relation derived. Unstable behavior is shown to result purely from transport processes-feedback between the Nernst effect and the Righi-Leduc heat-flow phenomena in particular-neither hydrodynamic motion nor density gradients are required. Calculations based on a recent nanosecond laser gas-jet experiment [D. H. Froula, Phys. Rev. Lett. 98, 135001 (2007)] predict growth of magnetic field and temperature perturbations with typical wavelengths of order 50 μm and characteristic growth times of ～0.1 ns. The instability yields propagating magnetothermal waves whose direction depends on the magnitude of the Hall parameter.     

等效球模型模拟冰晶云反射的误差分析

用射线光学理论计算了具有一定尺度分布的六角冰晶粒子在可见和近红外光谱区一系列波长上(0.2～5μm)的单次散射特性.利用米氏(Mie)理论,计算了与六角冰晶具有相同截面积的球形粒子的单次散射特性.根据辐射传输理论,应用累加法,分别计算了由冰晶粒子和等效球形粒子构成的卷层云的多次散射特性,计算结果表明当入射波长λ≈3.0 μm时,等效球Mie理论可以很好地用于计算卷层云的反射特性,但是当λ＜2.8μm时,尤其在可见光区,将引起显著的误差.最后提出了计算冰云光学特性的两种方案.     

基于敦煌场地定标的FY-3 MERSI反射太阳波段在轨响应变化分析

鉴于中分辨率光谱成像仪不能实现反射太阳波段的星上绝对辐射定标,提出了基于地表方向模型、矢量辐射传输模型6SV并联合MODTRAN吸收透过率校正的敦煌场替代定标新方法,4年的同步定标结果表明,除了水汽吸收中心波段之外,定标不确定度小于5%,而多数波段优于3%。以Aqua MODIS为辐射基准的大气顶辐射计算试验表明,正演与卫星观测间的平均偏差在波长<1 μm的窗区波段小于3%,波长>1 μm的小于5%(除了2.1 μm波段);此外,经场地定标的MERSI 表观反射率与MODIS具有很好的一致性。基于多年的场地定标结果发现：可采用二次多项式拟合定标系数的时间变化,进而实现逐天的定标更新;波长<0.6 μm的波段衰变较大,波段8(0.41 μm)入轨第一年的衰变率约为14%;在轨初期衰变最大,一年后趋缓,两年后部分波长>0.6 μm的波段出现响应增加现象。     

长周期光纤光栅谐振波长的特性研究

研究了长周期光纤光栅谐振波长与光纤参数及光栅周期的变化关系,发现高阶包层模与低阶包层模具有完全不同的特点,在各种参数变化时两者的谐振波长向相反的方向移动。通过实际制作周期分别为１００μｍ和４００μｍ的光栅证实了这种差别。得到了一些有益于长周期光栅设计和制作和结论。     

Non-collinear phase matched 4-wave mixing of CO2 and NH3 laser radiation in germanium

4-wave mixing has been demonstrated in room temperature germanium using a TEA CO₂ laser (9.3 μm) and an optically pumped NH₃ laser (12.8 μm) as radiation sources. Non-collinear phase matched emission near 7 μm has been observed with a mixing efficiency close to the calculated value. The extension of this mixing process to generate wavelengths in the important region near 16 μm is discussed.     

Linear spatial displacement of spectral components in the light reflected from multilayer structures

Based on an analogy with thin-film dispersion compensators used in femtosecond lasers, a linear dependence of the spatial displacement of reflected beams with different wavelengths is obtained at the output surface of a one-dimensional metal-dielectric multilayer at oblique incidence of a wave packet with λ₀ = 1.5 μm with a view to application in compact demultiplexers of optical communication systems.     

一种输出三波长超短光脉冲的激光源

利用对撞脉冲锁模非稳腔Ｎｄ：ＹＡＧ激光器，采用ＫＴＰ非线性晶体作腔外倍频，结合受激拉曼散射技术，在一台锁模激光器同时得到１．０６μｍ，０．５３μｍ，０．６３μｍ超短光脉冲的输出。     

Specific features of the reflection of infrared radiation by crystalline dielectrics in a magnetic field

Magnetic-field-induced variations in the reflection spectra R(λ) of the crystalline dielectrics Al₂O₃, LiF, and MgO in the infrared band (λ = 2.5–25 μm) are investigated. It is found that the reflection spectra exhibit specific features in the neighborhood of wavelengths corresponding to the excitation of optical phonon modes in the above-mentioned crystals and that a magnetic field causes an appreciable variation in the reflectivity at these wavelengths. To qualitatively describe the effect of a magnetic field on the reflection of light, the magnetoreflection spectra ΔR/R are investigated. The spectra ΔR/R exhibit sharp peaks in the neighborhood of wavelengths at which the materials under investigation are characterized by minimal reflectivity. The values of ΔR/R for p-polarized infrared radiation in a magnetic field of about 12 kOe amount to about 0.5% for Al₂O₃ at λ ≈ 9.6 μm, 7% for LiF at λ ≈ 11.1 μm, and 0.07% for MgO at λ ≈ 11.7 μm.     

金属网栅法布里珀罗干涉仪测量太赫兹波波长

设计并制作了用于测量波长大于150 μm(频率低于2 THz)的太赫兹波波长的金属网栅法布里珀罗干涉仪(FPI)。采用光电子微纳制造工艺制作了五组周期不大于40 μm,线宽不大于10 μm的有衬底方形金属网栅,利用太赫兹时域光谱技术测量了金属网栅的太赫兹波段光电特性,得到了各组金属网栅在感兴趣频段的反射率和金属网栅FPI的反射精细度,结果表明所制作的金属网栅FPI均可用于测量波长大于150 μm的太赫兹波。实验搭建金属网栅FPI扫描测量了212 μm的太赫兹波波长,与理论结果吻合。研究了金属网栅FPI对太赫兹波偏振方向的依赖性以及对FPI腔镜平行度的要求,结果表明,方形金属网栅FPI对正入射太赫兹波偏振方向不敏感,而对FPI腔镜平行度很敏感。     

脉冲激光辐照硅材料引起表面波纹的特性研究

叙述了激光与材料相互作用过程中引起相干受激光散射的机制,以及形成材料表面波纹的特性。在激光波长1．06μm、能量15mJ、光斑直径2mm、脉冲半峰全宽约10ns和入射方向为布儒斯特角的条件下,进行了脉冲激光辐照硅材料形成表面波纹的实验研究。在脉冲激光辐照硅材料表面功率密度略大于材料损伤阈值的条件下,发现了硅材料表面形成的平行等间距直线条纹结构。用光学显微镜和原子力显微镜分别测量了被辐照硅材料表面的波纹形貌特征。在假设硅材料表面波纹的产生与声波在材料中的传播速度有关的条件下,由声波传播速度和激光辐照硅材料的脉冲宽度较好地解释了材料表面形成条纹的宽度．并认为在形成表面波纹的过程中,热应力起主要作用。     

Mechanism of the formation and evolution of periodic surface relief nanostructures under the scanning laser-induced inelastic photodeformation of semiconductors

A defect-deformational (DD) mechanism is proposed for the self-organization of laser-induced point defects (vacancies and interstitials) under low-threshold (far from the melting point) local (10–100 μm) light-induced heating with the scanning periodic pulsed laser irradiation of a semiconductor resulting in an inelastic deformation of micron-sized regions of Ge. A linear theory of DD instability is developed within the model of a biaxially stressed defective film. This model describes the main experimental data on the formation of two-and one-dimensional periodic nanostructures on a semiconductor surface relief.     

Ejection of uniform micrometer-sized droplets from Faraday waves on a millimeter-sized water drop

This Letter reports the first observation and theoretical analysis of a new phenomenon: one large spherical water drop ejecting simultaneously a very large number of monodisperse microdroplets. An ultrasonic nozzle with multiple-Fourier horns in resonance enables controlled excitation of megahertz Faraday waves on the free water surface. The temporal instability of such waves leads to the ejection of 3.5-4.4 μm monodisperse droplets at a high rate (>4.0×10(7) droplets/sec). This is in stark contrast to the Rayleigh-Plateau instability, which ejects one droplet at a time.     

A study of the spectral emissions in laser-irradiated microdot targets at 0.53 and 0.27 μm wavelengths with micron resolution

Using a knife-edge technique, we have determined the spatial extension of H-like and He-like emissions and the time-integrated axial electron density profile in laser-irradiated aluminium microdot targets at 0.53 and 0.25 μm wavelengths with about 3 μm resolution.     

Fabrication of a mid-IR wire-grid polarizer by direct imprinting on chalcogenide glass

A mid-IR wire-grid polarizer with a 500 nm pitch was fabricated on a low toxic chalcogenide glass (Sb-Ge-Sn-S system) by the thermal imprinting of periodic grating followed by the thermal evaporation of Al metal. After imprinting, deposition of Al on the grating at an oblique angle produced a wire-grid polarizer. The fabricated polarizer showed polarization with TM transmittance greater than 60% at 5-9 μm wavelengths and an extinction ratio greater than 20 dB at 3.5-11 μm wavelengths. This polarizer with a high extinction ratio can be fabricated more simply and less expensively than conventional IR polarizers.