计量线高次谐波的定量研究

Quantitative research on higher order harmonics in metrology beamline

采用自制的840/mm金膜自支撑透射光栅和美国IRD公司的AXUV100G光电二极管探测器,定量研究了光谱辐射标准和计量光束线在5-140 nm波段的高次谐波。研究了Al、Si3N4和Zr滤片在不同能量范围对高次谐波的抑制作用,给出了实验数据和曲线。实验结果显示:在5-15 nm波段,不用任何滤片高次谐波的信号强度<7%;在5-34 nm波段,适当的选用Al、Si3N4和Zr滤片可有效地抑制高次谐波,将高次谐波占基波的积分信号强度比例控制在<14%,经探测器的量子效率修正后高次谐波的百分比在6.5%以内。在经过MgF2窗滤波的115-140 nm波段,高次谐波的衍射峰几乎完全被抑制。这一研究为软X射线和极紫外的光谱计量、探测器定标和光学元件性能测试奠定了基础。

The synchrotron radiation spectra of spherical grating monochromator （SGM） working in soft X-ray and VUV region are often contaminated by significant amount of higher order harmonics, They cannot be suppressed completely by suitable filters. Higher order contributions in the spectral radiation standard and metrology beamline were researched using transmission grating （made in house） and IRD AXUV100G （USA） photodiode detector. The exit beam was dispersed with the transmission grating behind exit slit of the monochromator, and the contributions of the different orders were analyzed. The higher order distributions were quantitatively determined for three gratings in line densities of 1800, 600 and 200 1/mm. It is shown that in wavelength between 5-15 nm the contributions of the higher orders to the detector signal are restricted to less than 7 % even without filters; In wavelength region between 5 nm and 34 nm the contributions of the higher orders to the detector signal are less than 14% with proper Al, Si3N4 and Zr filters; after modified by quantum efficiency of the detector, the higher order contributions are restricted to less than 6.5 %. The research also shows that higher orders are almost totally suppressed by MgF2 filter when the wavelength between 115-140 nm.