X射线激光及等离子体物理研究中的X光光学进展

近十年来,X射线技术的发展很快,用途日益扩展。激光核聚变、X光激光及激光等离子体研究的发展对X光光学提出了新的要求。X光诊断技术也在激光等离子体、X激光以及激光核聚变研究中处于重要地位。本文分别介绍X射线光谱和XUV诊断光学技术、X光成像系统、编码成像、X激光腔反射镜等方面的X光光学进展。     

软X射线探测器

西安光机所自1984年开始,共研制了不同型的五台软X射线条纹相机;1987年开始,研制了软X光分幅相机。这些仪器,已在激光核聚变研究、激光等离子体诊断、核试验及爆轰物理研究等领域,作为有效的测试工具。本文介绍了我们的有关研究工作和X线条纹相机、分幅相机的主要性能。     

X射线光学专栏导读

<正>伴随着衍射极限同步辐射光源、X射线自由电子激光装置、高温高密度等离子体、强场物理、极紫外光刻和X射线成像天文学的发展,X射线光学不断从一个台阶走向另一个新的台阶。X射线光学是一门快速发展的学科领域,其不仅与现代前沿科学研究密不可分,更离不开现代超高精度微纳加工与检测技术的大力支撑。X射线光学研究的困难和复杂性不仅体现在米量级非球面深亚纳米精度光学元件的制作与检验上,还表现在纳米尺度结构的超高精度制作上,更体现在反射、衍射与折射元件并重的多种聚焦与成像系统的选择     

软X射线投影光刻原理装置的设计

首先介绍了投影光刻技术发展的历程、趋势和软X射线投影光刻技术的特性,其次介绍了软X射线投影光刻原理装置的研制工作.该装置由激光等离子体光源、掠入射椭球聚光镜、透射掩模、镀有多层膜的Schwarzchild微缩投影物镜、涂有光刻胶的硅片及相应的真空系统组成.0.1倍的Schwarzchild微缩投影物镜具有小于0.2μm的分辨率.     

椭圆型晶体谱仪谱测量的解谱

描述了椭圆型晶体谱仪配X射线CCD相机的X射线谱测量系统(EBCS-XCCD),研究了CCD相机记录信号的解谱处理方法,推出了对实测原始谱曲线辨认或标识值的计算公式及激光等离子体辐射X射线在某一波长光谱强度的公式,使之应用在激光打靶产生的等离子体源辐射X射线谱的回推,辨认出了激光等离子体X射线源能谱,并与文献[1]的结果进行了比较,结果基本一致.测试结果证实了解谱方法的可行性,表明X射线CCD相机适用于椭圆型晶体谱仪的光谱测量记录.在已知晶体的积分反射率、滤片透射率和CCD探测效率的条件下,可以获得X射线源光谱强度,为下一步诊断激光等离子体的电子温度和离子密度的空间分布轮廓和进一步细化X射线激光研究奠定了基础.     

新型低能X光机

本文报导我们研制成功的DNX-Ⅰ型双光束低能单色X光机。该机输出强度5×10~5光子数/秒、cm~2、在0.28～8.9keV能段中八种固定的单色X光。目前已应用到磁约束核聚变、惯性约束核聚变、激光等离子体物理和空间天文等领域的低能X光探测仪器的标定上。     

激光焊接过程中小孔行为对光、声的影响

利用错边试样的激光焊接实验来研究小孔行为对等离子体光、声辐射信号的影响。发现等离子体光辐射强度仅受被焊材料蒸发量的影响。而等离子体声信号的强度以及光、声信号的频谱分布都受到小孔行为的制约,在不能出现小孔的情况下,等离子体失去了周期性行为。     

Xe液体微滴靶激光等离子体光源实验

基于Xe的惰性和在13~14 nm波段高的辐射强度,Xe被认为是极紫外投影光刻(EUVL)潜在的靶材,为此设计和研制了一台液体微滴喷射靶激光等离子体(LPP)极紫外光源。详细地研究了Xe液体微滴喷射靶的光谱辐射特性、在13.4 nm的激光-EUV转换效率、辐射稳定性及碎屑产生状况。实验结果表明,Xe在13.4 nm的最高转换效率可以达到0.75%/2πsr/2%bw,辐射稳定性±4%(1σ),在激光打靶10⁵次后无碎屑产生。     

椭圆型晶体谱仪谱测量的解谱研究

对椭圆型晶体谱仪配X射线CCD相机的X射线谱测量系统（EBCS-XCCD）进行了简要描述,研究了CCD相机记录信号的解谱处理方法,推出了对实测原始谱曲线辨认或标识值的计算公式及激光等离子体X射线源在某一波长光谱强度的公式,使之应用在激光打靶产生的等离子体源辐射X射线谱的回推,辨认出了激光等离子体X射线源能谱,并与文献[1]的结果进行了比较,结果基本一致。这一事实有力地佐证了解谱方法的可行性,也表明X射线CCD相机是适宜于椭圆型晶体谱仪的光谱测量记录。在已知晶体的积分反射率、滤片透射率和CCD探测效率的条件下,还可以获得X射线源光谱强度,可为下一步诊断激光等离子体的电子温度和离子密度的空间分布轮廓和进一步细化X激光研究奠定了更深厚的基础。     

激光等离子体软X射线光源的一种诊断方法

激光等离子体软X射线光源是脉冲式光源,对这类光源的光谱诊断有几种方法.文章介绍了一种新的、实用的测量激光等离子体软X射线光源光谱的方法.此方法以低噪声的通道电子倍增器探测来自光源的ns量级的脉冲光信号,并由低噪声、响应快的电荷灵敏前置放大器进一步将其放大,前放的输出电荷与输入的脉冲信号的峰值成正比.使用这种方法测量了铜靶激光等离子体光源和氧、氪气体靶激光等离子体软X射线源在8～30nm波段的光谱.     

用热解石墨晶体作色散和聚焦光学元件的激光等离子体源的超快X射线光谱仪

由于激光等离子X射线源的光子通量显著低于同步辐射源的光子通量且射线为所有方向的各向同性辐射,所以,很需要具有大的集光立体角和高的积分反射率的光学元件,用热解石墨(PG)晶体作色散和聚焦元件可满足上述要求。由于PG晶体为嵌镶结构,所以可给出很高的积分反射率,而PG薄膜还可安装在任意形状的模具上构成任意形状的光学元件。此外,特殊形状的嵌镶聚焦使这些晶体甚至在弯曲的情况下,也可作为高分辨率X射线光学元件。基于上述元件特性,可以设计出有高集光效率的色散光学元件,用于激光等离子体源超快X射线光谱检测。文中描述了PG弯晶在一台改型的von HAMOS光谱仪中的应用,使用这台光谱仪,测量了飞秒激光器产生等离子体发射的X射线的光谱分布。讨论了产生的X射线在时间分辨扩展X射线吸收精细结构(EXAFS)分析中的应用。实验表明,通过优化晶体特性和光谱仪几何设置,可以实现对过渡金属K边的高分辨率EXAFS测量。     

Rising the signal-to-noise ratio in X-ray spectra of femtosecond laser-produced plasmas using the “mean-median” algorithm

As femtosecond laser pulses increase in intensity and decrease in duration, interaction between the focused laser radiation and a substance is followed by a sharp increase in the intensity of fast-electron, ion, and electromagnetic noise generation. In turn, the noise signals of X-ray detectors grow in amplitude and the signal-to-noise ratio in recording X-ray spectra of multiply charged ions approaches unity. A significant excess of the noise level over the useful signal is observed in plasmas generated by laser pulses with a power density of ≥10¹⁷ W/cm². The most powerful effect of the above factors is exerted on X-ray spectra recorded by such electromagnetic equipment as CCD-based detectors, photoelectron amplifiers, etc. A new “mean-median” algorithm is described, with which it is possible to considerably increase the signal-to-noise ratio of CCD detectors used to measure X-ray spectra of femtosecond laser-produced plasma.     

Overview of diagnostic system in the experimental advanced superconducting tokamak

The first plasma was achieved in the experimental advanced superconducting tokamak (EAST) on September 26, 2006. Single-and double-null diverter plasma discharges were also achieved successfully in the EAST in January 2007. The plasma diagnostics for the first EAST plasma study have been developed as follows: a vertical one-channel far-infrared hydrogen cyanide (HCN) laser interferometer for measuring the line average density, a ten-channel soft X-ray array for intensity measurement, a 16-channel heterodyne electric cyclotron emission for measuring the profile of the electron temperature, an eight channel XUV bolometer array to measure plasma radiation losses, a three-channel hard X-ray array for intensity measurement, an electromagnetic measurement system, a 35-channel H _α radiation array, 20 triple probes for diverter plasma, a one-channel visible bremsstrahlung emission, an impurity optical spectrum measurement system, and two optical spectroscopic multichannel analyzers. The first experimental results of the diagnostic system and the plan of what is to come are summarized in this paper. The text was submitted by the authors in English.     

Absolute calibration of X-ray optical elements and detectors at a wavelength of 46.9 nm

The results are presented of the absolute calibration of X-ray optical elements (diffraction gratings and Sc/Si multilayers) and detectors (an УΦ-4 photographic film and a vacuum X-ray diode) used in diagnostic devices to study generation of X-ray laser radiation in an argon plasma of a capillary discharge (λ = 46.9 nm). The measurements have been performed at the soft X-ray and vacuum UV station of the VEPP-4 storage ring at the Siberian International Center of Synchrotron Radiation. An absolutely calibrated AXUV 100G photodiode has been used as a reference detector. The relative error of calibration is 10%. The measured reflectances of the multilayer mirrors and gratings are in good agreement (within the limits of errors) with the results of their calibration at the RKK-1-100 X-ray calibration facility.     

Development of Debris-free Laser Plasma Sources for EUV Lithography in CIOMP

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Recording the time dependence of the electron temperature and absolute yield of continuous and line X-rays from flat Au targets irradiated on the Iskra-5 facility

Two techniques for recording the absolute yield of continuous X rays in the spectral range > 1 keV and M-series line X rays from flat Au targets irradiated with one channel of the Iskra-5 facility are described. In the first and second methods, radiation is detected with a KAP-crystal-based spectrograph and an X-ray streak camera with a 50-ps time resolution, respectively. Both techniques allow obtainment of absolute values of the yields of continuous and line X-ray radiations from laser plasma that coincide within the measurement accuracy. The time-dependent plasma electron temperature is measured with an X-ray streak camera.     

Digital in-line X-ray holography with zone plates

Single pulse imaging with radiation provided by free-electron laser sources is a promising approach towards X-ray microscopy, which is expected to provide high resolution images of biological samples unaffected by radiation damage. One fully coherent imaging technique for this purpose is digital in-line holography. Key to its successful application is the creation of X-ray point sources with high photon flux. In this study we applied zone plates to create such point sources with synchrotron radiation provided by the storage ring BESSY II. The obtained, divergent light cone is applied to holographic microscopy of biological objects such as critical point dried Navicula perminuta diatoms and human cells using photons with an energy of 250 eV. Compared to conventional experiments employing pinholes, exposure times are reduced by two orders of magnitude.     

高强度脉冲软X光源

本文介绍清华大学电机工程系研制的一种高强度软X光源,这种光源是由喷气式Z箍缩等离子体产生的。阐述了Z箍缩装置的工作原理,研究了装置的运行参数(如充电电压、充气密度等)对软X射线发射的影响。用热电堆测量了X射线的产额。并介绍了用无窗XRD(X射线二极管)测量脉冲x射线的初步结果:光源处的X射线总能量超过100J,发射时间约100ns,其功率达10⁹W以上。     

X-ray microscopy of plant cells by using LiF crystal as a detector

A lithium fluoride (LiF) crystal has been utilized as a new soft X-ray detector to image different biological samples at a high spatial resolution. This new type of image detector for X-ray microscopy has many interesting properties: high resolution (nanometer scale), permanent storage of images, the ability to clear the image and reuse the LiF crystal, and high contrast with greater dynamic range. Cells of the unicellular green algae Chlamydomonas dysosmos and Chlorella sorokiniana, and pollen grains of Olea europea have been used as biological materials for imaging. The biological samples were imaged on LiF crystals by using the soft X-ray contact microscopy and contact micro-radiography techniques. The laser plasma soft X-ray source was generated using a Nd:YAG/Glass laser focused on a solid target. The X-ray energy range for image acquisition was in the water-window spectral range for single shot contact microscopy of very thin biological samples (single cells) and around 1 keV for multishots microradiography. The main aim of this article is to highlight the possibility of using a LiF crystal as a detector for the biological imaging using soft X-ray radiation and to demonstrate its ability to visualize the microstructure within living cells.     

双色激光产生太赫兹辐射的调控机理研究

采用双色激光在气体介质中诱导产生太赫兹波的数值模拟方法,深入分析了各种激光参数对双色激光场产生太赫兹波的影响,目的是优化参数以实现太赫兹波辐射能量的最大化。模拟计算表明,双色激光的波长、相对相位、激光脉冲宽度等对瞬态电流和太赫兹能量都有调控作用,并且具有不同的规律性。此外,还通过分析激光电场、电子密度、光电流等相关因素,对双色激光场产生太赫兹波的物理机理进行了解释。该研究为在不同激光激发条件下提高太赫兹波辐射强度,提供了详尽的参数优化分析和理论支持,对后续大幅增强太赫兹辐射效率具有重要意义。