Improving attosecond pulse reflection by large angle incidence for a periodic multilayer mirror in the extreme ultraviolet region

The improvement of attosecond pulse reflection by large angle incidence for a periodic multilayer mirror in the extreme ultraviolet region has been discussed. Numerical simulations of both spectral and temporal reflection characteristics of periodic multilayer mirrors under various incident angles have been analyzed and compared. It was found that the periodic multilayer mirror under a larger incidence angle can provide not only higher integrated reflectivity but also a broader reflection band with negligible dispersion, making it possible to obtain better a reflected pulse that has a higher pulse reflection efficiency and shorter pulse duration for attosecond pulse reflection. In addition, by increasing the incident angle, the promotion of attosecond pulse reflection capability has been proven for periodic multilayer mirrors with arbitrary layers.     

Effects of dispersion and filtering induced by periodic multilayer mirrors reflection on attosecond pulses

Using temporal and spectral methods,the effects of dispersion and filtering induced by Mo/Si multilayer mirrors reflection on incident attosecond pulses were studied.First,two temporal parameters,the pulse broadening factor,and the energy loss factor,were defined to evaluate the effects of dispersion and filtering.Then,by analyzing these temporal parameters,we investigated and compared the dispersion and filtering effects on attosecond pulses.In addition,we explored the origins of pulse broadening and energy loss by analyzing the spectral and temporal characteristics of periodic Mo/Si multilayer mirrors.The results indicate that the filtering effect induced by Mo/Si multilayer mirrors reflection is the dominant reason for pulse broadening and energy loss.     

Reflecting single attosecond pulse by periodic Mo/Si multilayer mirrors with different layers

The reflecting of single attosecond pulse from a periodic Mo/Si multilayer was investigated. With changing the number of bi-layers, the periodic multilayer showed greatly different spectral and temporal responses of the attosecond pulse reflection, which has been discussed in detail in this paper. The capability of attosecond pulse reflection of the periodic multilayers with different bi-layer numbers has been evaluated using suitable temporal parameters. In addition, the condition for obtaining high-efficiency reflected pulses has been analyzed by comparing the pulse responses of the periodic multilayer with different layers. The transfer-matrix method together with the fast Fourier transform has been used in our simulation.     

Reflecting a single attosecond pulse by using periodic Mo/Si multilayer mirrors with different layers

The reflecting of a single attosecond pulse from a periodic Mo/Si multilayer was investigated. By changing the number of bi-layers, the periodic multilayer showed greatly different spectral and temporal responses of the attosecond pulse reflection, which has been discussed in detail in this paper. The capability of attosecond pulse reflection of the periodic multilayers with different bi-layer numbers has been evaluated using suitable temporal parameters. In addition, the condition for obtaining high-efficiency reflected pulses has been analyzed by comparing the pulse responses of the periodic multilayer with different layers. The transfer-matrix method together with the fast Fourier transform has been used in our simulation.     

Metrologies for the phase characterization of attosecond extreme ultraviolet optics

Extreme ultraviolet (EUV) optics play a key role in attosecond science since only with higher photon energies is it possible to achieve the wide spectral bandwidth required for ultrashort pulses. Multilayer EUV mirrors have been proposed and are being developed to temporally shape (compress) attosecond pulses. To fully characterize a multilayer optic for pulse applications requires not only knowledge of the reflectivity, as a function of photon energy, but also the reflected phase of the mirror. We develop the metrologies to determine the reflected phase of an EUV multilayer mirror using the photoelectric effect. The proposed method allows one to determine the optic's impulse response and hence its pulse characteristics.     

4.48 nm正入射软X射线激光用Cr/C多层膜高反射镜的研制

针对4.48nm类镍钽软X射线激光及其应用实验,设计制备了工作于这一波长的近正入射多层膜高反射镜。选择Cr/C为制备4.48nm高反射多层膜的材料对,通过优化设计,确定了多层膜的周期、周期数以及两种材料的厚度比。模拟了多层膜非理想界面对高反射多层膜性能的影响。采用直流磁控溅射方法在超光滑硅基片上实现了200周期Cr/C多层膜高反射镜的制备。利用X射线衍射仪测量了多层膜结构,在德国BessyⅡ同步辐射上测量了在工作波长处多层膜反射率,测量的峰值反射率达7.5%。对衍射仪测量的掠入射反射曲线和同步辐射测量的反射率曲线分别进行拟合,得到的粗糙度和厚度比的结果相近。测试结果表明,所制备的Cr/C多层膜样品结构良好,在指定工作波长处有较高的反射峰,达到了设计要求。     

Reflective phase shift measurement of the Mo/Si multilayer mirror in extreme ultraviolet region

The reflective phase shift of multilayer mirror is one important property required in EUV lithography and attosecond pulses experiments. The reflective phase shift of the periodic Mo/Si multilayer mirror was characterized by combining the reflectivity with total electron yield signal at the synchrotron radiation in Hefei. The multilayer was fabricated using direct current magnetic sputtering method. Using the wavelet transform approach, the period and each layer thickness were obtained, the small angle X-ray reflective data from X-ray diffractometer were fitted using these data as the mutilayer's initial structure. The TEY signal of the multilayer is coincided with the surface electron field of the multilayer. A thick Si layer was used to eliminate the effect of the multilayer's surface layer on the TEY signal. The retrieved difference in reflected phase from the incident phase was obtained combining the reflectivity with the total electron yield signal and it is similar with the calculated phase shift of the multilayer.     

LCOS投影PBS分束器膜系设计

给出了一种全新的膜系设计方法,该方法与目前常用的偏振分束器PBS分光镜所采用的多组膜堆周期膜系的设计方法有着本质上的区别。全新的PBS膜系的设计引入一种有序对偶递变方法,它是基于周期性有序地变换成递变非周期性设计,目的是扰动针对45入射布鲁斯特角的敏感。采用了两种折射率材料光学厚度的递变,在SF75系列玻璃棱镜内部入射光能满足45角(5～6)变化、P偏振态的透射率平均不低于70%、S偏振态的反射率不高于99.6%的光学特征指标,而且偏振截止带的带宽可以扩展到400 nm～700 nm。简化了工艺难度,大幅度缩减镀膜时间,降低了投影显示器件制造成本,并提高了光学特征指标。     

磁控溅射法制备极紫外6.8~11.0 nm波段Mo/B4C横向梯度多层膜

用直流磁控溅射法结合掩模板控制膜厚的方法在Si衬底上制备了工作于6.8~11.0 nm波段的[Mo/B₄C]₆₀横向梯度多层膜。利用X射线掠入射反射测试以及同步辐射反射率测试对梯度多层膜的结构及性能进行了测试。X射线掠入射反射测试结果表明,多层膜周期厚度沿着长轴方向从4.39 nm逐渐增加到7.82 nm,周期厚度平均梯度为0.054 nm/mm。对横向梯度多层膜沿长轴方向每隔5 mm进行了一次同步辐射反射率测试,结果显示,横向梯度多层膜在45°入射角下的反射率约为10%,反射峰的半高全宽介于0.13 nm到0.31 nm之间。     

用于几keV能点动态成像诊断的KB-KBA混合型光学系统设计

围绕激光ICF研究中几keV能点的动态成像诊断需求,提出了具有大视场、高空间分辨、高集光效率和谱分辨特性的新型KB-KBA混合型光学结构。该结构以子午方向上两块单层膜球面镜校正像差,实现大视场内的高空间分辨;在弧矢方向上用一块多层膜球面镜聚焦,以保证较高的集光效率和谱分辨能力。该结构克服了传统单层膜和周期膜KBA结构在几keV能点动态成像诊断中存在的集光效率低,强度不均匀和有效视场受限等不足。针对2.5 keV和4.3 keV两个能点,给出了光学初始结构和膜系的设计,建立了考虑膜系反射性质的光线追迹模型。模拟结果表明,该KB-KBA混合型结构在子午方向1.4 mm视场内空间分辨均优于5μm,有效集光效率优于2×10~(-7)sr,可以满足动态成像诊断的需求。     

等效腔法研究低损介质镜的反射特性

利用多光束干涉原理的等效腔模型对四分之一波长多层介质镜进行了研究。证明在反射镜中心频率ωo附近，形为ρ(ω)exp[iψ(ω)]的反射系数中的ρ(ω)等于ρ(ω)，ψ(ω)与频率成正比。求得了在介质具有微弱吸收情况下，吸收引起的四分之一波长镜反射下降和反射时延的表达式，研究了反射率下降以及反射时延与膜层数目的奇偶性的关系。在此基础上还引入了一个具有一定普适性的权重因子，通过这个权重因子可以定量描述镜子中各层对多层介质镜反射率下降、反射时延等重要特性的影响。     

Reflection of atto-and femtosecond X-ray pulses from aperiodic multilayer mirror

The reflection of femto-and attosecond soft and hard X-ray pulses from multilayer structures (MSs) was investigated. The conditions are formulated under which the pulse shape and duration barely change upon reflection. The MSs are optimized for the reflection of extremely short pulses, and the possibility of compressing chirped pulses is considered. It is shown that the power reflection coefficient can be appreciably larger than unity. The aperiodic MSs capable of effectively reflecting pulses containing no more than three wave periods are calculated.     

High-dispersive mirror for pulse stretcher in femtosecond fiber laser amplification system

We present a high-dispersive multilayer mirror for pulse stretching in a femtosecond fiber laser amplification system. The designed mirror contains 54 layers with a total physical thickness of 7.3 μm, which can provide a positive group delay dispersion (GDD) of 600 fs² and a high reflectance over 99.9% from 1010 to 1070 nm. The samples were prepared by dual ion beam sputtering. The measured transmittance matches well with the theoretical result. The GDD characteristics of samples were tested by home-made white light interferometer. The measured GDD is higher than the design results, an average GDD of +722 fs² from 1010 nm to 1070 nm. The mirrors were employed in a Yb-doped large-mode-area photonic crystal fiber amplification system. An input pulse compressed by the gratings with autocorrelation function of 83 fs is obtained with a stretched FWHM of 1.29 ps after 28 bounces between the dispersive mirrors. The results show that the multilayer dispersive mirror could be an effective and promising technique for pulse stretching in femtosecond amplification systems.     

Figure Error Correction by Reflection Wavefront Control of Cu K<Subscript>α</Subscript> Grazing Incidence Multilayer Mirrors

Reflection phase and amplitude of grazing incidence multilayer mirrors for CuK_α radiation have been studied theoretically to evaluate phase correction effects of multilayer surface milling, which revealed good possibilities of correcting mirror substrate figure errors for focusing and imaging application. The mirror multilayers composed of base materials of Cu and Ni were studied in combination with Al, Be, C, Mg and Si for high reflectivity at a grazing angle of 3° incidence. The theoretical surface milling of Cu/Al multilayers of a period thickness of 1.478 nm provides phase correction of 1.7° per period, which corresponds to an accurate correction of substrate figure errors at a rate of 0.007 nm per period. Thus, the milling after the multilayer fabrication, compared to the milling before the multilayer fabrication, enables far more accurate phase correction with 200 times finer control.     

一种微米级高度台阶镜面条纹反射的三维测量系统

提出了一种检测微米级高度衍射台阶结构的条纹反射三维检测方法.对条纹反射光路的理论分析表明,合理选择入射光线角度和液晶屏放置角度以及液晶屏像素尺寸等系统参数,条纹反射系统能够分辨微米乃至亚微米级的镜面台阶.实际构建了一套微米级台阶镜面条纹反射测量实验装置;采用四步相移法进行条纹相位解算,运用移动屏幕方法确定反射光线方程,结合三角交汇原理,对待测台阶镜面进行三维重构.实际测量了名义值为5μm和10μm的台阶镜面,测量结果不确定度在0.5μm内,和商业仪器测量结果的偏差<0.5μm,证明了设计方法的可行性.本文结果对于包含衍射台阶结构的光学元件三维测量研究具有一定的借鉴意义.     

Phase characterization of the reflection on an extreme UV multilayer: comparison between attosecond metrology and standing wave measurements

We characterize the phase shift induced by reflection on a multilayer mirror in the extreme UV range (80-93?eV) using two techniques: one based on high order harmonic generation and attosecond metrology (reconstruction of attosecond beating by interference of two-photon transitions), and a second based on synchrotron radiation and measurements of standing waves (total electron yield). We find an excellent agreement between the results from the two measurements and a flat group delay shift (±40?as) over the main reflectivity peak of the mirror.     

在19.5 nm处高反在30.4 nm处抑制的双功能薄膜

 研究了极紫外波段的双功能光学元件。采用周期膜叠加的思想,运用遗传方法优化设计了在19.5 nm处高反,在30.4 nm处抑制的双功能多层膜。采用磁控溅射技术制备了多层膜,利用X射线衍射仪测试了多层膜的结构,在国家同步辐射实验室测试了双功能多层膜的反射特性。结果表明：制备出的双功能膜性能与设计相符,在入射角13°,19.5 nm处的反射率达到33.3%,接近传统的19.5 nm周期高反膜的反射率,并且在30.4 nm附近将反射率由1.1%降到9.6×10^-4。     

脉冲激光入射下介质薄膜双频互相关散射截面及功率展宽

 结合特殊的镀金聚酯薄膜表面的粗糙度和半球反射率,依据基尔霍夫近似及粗糙面脉冲散射互相关函数,数值计算了脉冲激光（1.06 μm）在不同入射角照射下该材料薄膜双频互相关散射截面随相干带宽频差和散射角的变化情况。并给出δ脉冲和高斯脉冲波入射下,其散射功率随时间和散射角的波形分布。计算结果表明：该薄膜材料激光双频互相关散射截面在镜反射方向有最大的散射峰值,在非镜反射方向上,其散射值随相干带宽频差的增大迅速减小,当窄脉冲垂直入射时,粗糙面散射功率展宽现象明显。     

A multilayer x-ray mirror in the form of an ellipsoid of revolution

Laboratory technology for the preparation of multilayer mirrors in the form of an ellipsoid of revolution for the hard x-ray wavelength range (λ = 0.1 nm) has been developed on the basis of the replica method. A prototype mirror in the form of a sector of an ellipsoid of revolution is prepared. Its shape and reflection characteristics are studied.     

The parametric doppler effect upon oblique radiation incidence in quartz glass

Frequency and reflection angle of probe radiation from a refractive-index inhomogeneity induced by an intense pumping pulse in quartz glass and moving with a relativistic velocity are calculated. Conditions under which the normal component of the wave vector of the reflected wave is directed to the opposite or to the same direction as the same component for the incident wave are determined. Comparison with the case of radiation reflection from a relativistic mirror in vacuum is performed. Conditions of the appearance of the Vavilov-Cherenkov radiation from a relativistic refractive-index inhomogeneity induced in the medium by an intense laser pulse are discussed.