杂散光是光栅的重要技术指标,它直接影响光栅的信噪比,紫外波段的杂散光对光谱分析尤为不利。为了考察平面刻划光栅用于光谱仪器时产生的杂散光,采用标量衍射理论数值分析了杂散光产生的原因。数值模拟结果表明,紫外平面刻划光栅刻槽周期随机误差以及刻槽深度随机误差是杂散光的主要来源,而光栅杂散光对光栅表面小尺度随机粗糙度并不敏感。提出了平面光栅光谱仪出射狭缝相对宽度的概念,数值分析了仪器出射狭缝高度及出射狭缝相对宽度与杂散光强度的关系,从而分别为在光栅制作工艺中从根源上降低光栅杂散光以及在光栅应用过程中从使用方法上降低光栅杂散光提供了理论依据。最后,为了与采用滤光片法测得的光栅杂散光实验值进行比较,给出了理论求解杂散光总强度的求和公式,并对4个不同波长的杂散光进行了多次测量。结果表明,当刻槽周期随机误差、刻槽深度随机误差和表面随机粗糙度分别取0.8 nm、 0.5 nm和1.2 nm时,理论值和实验值的相对误差可控制在13%左右。

As one of important technical specifications of diffraction gratings, stray light directly affects Signal Noise Ratios(SNRs) of spectrometers; especially in spectrum analysis at UV spectral bands.In order to search the stray light from applications of ruled gratings in the spectrometers, this paper analyzes forming causes of the stray light in theory based on a scalar diffraction equation.The numerical simulation indicates that the random errors in the spacing of grating grooves and the random errors in the groove depths for UV ruled gratings are the main sources of the stray light, moreover, the small-scale random surface roughness affects the stray light slightly.Otherwise, it presents a concept of a relative width for the exit slit and establishes the relation between the height and relative width of exit slit and the intensity of the stray light,which provides a theoretical reference for reducing the stray light in the process of fabricating gratings essentially and repressing the stray light in practical applications.Finally, in order to compare theory results with experimental results measured by a filter method, an equation to solve the total stray light is presented to measure the stray light of four wavelengths by a UV spectrophotometer.It proves that the maximal relative error between theory results and experimental results is about 13%, when random errors in the groove periods, random errors in the groove depths and random surface roughness are 0.8 nm, 0.5 nm and 1.2 nm respectively.