浸入式光栅谱线特性

摘要

Immersion gratings are typically used in the infrared spectral band in which optical materials with high refractive index.Some issues inevitably arise due to their special operating mode.And they are critical to the application of immersion gratings.This study investigated the relations between the lengths of the long-and short-wave of normal gratings.For the features of the relevance of the refractive index with wavelength,the short-wave infrared spectral band (1.5 ～ 2.5 μm) was taken as an example to analyze the change characteristics of spectral line location and spectral resolution of immersion gratings.Results showed that when immersion gratings were adopted,significant differences were observed in the distribution of spectral lines as compared with normal gratings,and "trapezoidal" spectral lines tilted.For short-wave infrared spectral lines,the inclination of the "trapezoidal" spectral lines became more apparent due to larger changes in the refractive index of the medium.When Littrow conditions were registered with long-wave length (2.5 μm),the spectral line tilted toward the short-wave end.When registration was done with short-wave length (1.5 μm),the spectral line tilted toward the long-wave end,and the Littrow wavelength drifted away from the central wavelength.The refractive index had a few changes at the thermal infrared spectral band.The tilt of "trapezoidal" spectral lines was smaller and more similar to that of normal gratings.The spectral resolution of immersion gratings varied due to changes in the refractive index.At the same order,the wavelength increased,and resolution increased;between various orders,the order decreased,and the resolution decreased.Meanwhile,considering that the high-order resolution was larger than the low-order's,the ratio of the lengths of spectral lines at various orders no longer meet the relation of normal gratings.%浸入式光栅常应用于光学材料折射率较高的红外谱段.其特殊的工作模式会产生一系列普通反射式光栅不需面临的问题,而它们对于浸入式光栅的应用却十分重要.论文推导了普通光栅长波端与短波端谱线长度的关系.针对折射率与波长相关的特点,以短波红外(1.5～2.5 μm)为例,分析其谱线位置分布及光谱分辨率变化特性.结果表明,浸入式光栅谱线分布相较于普通光栅有明显差异,“梯形”谱线会发生倾斜.在折射率变化较大的短波红外谱段,“梯形”谱线倾斜程度较明显.在以长波(2.5 μm)配准Littrow条件时,谱线向短波端倾斜,以短波(1.5 μm)配准时向长波端倾斜,且Littrow波长均漂离中心波长.由于折射率在热红外谱段变化较小,“梯形”谱线倾斜较小,更接近普通光栅情况.浸入式光栅的光谱分辨率随折射率变化而改变,同级中,波长增大分辨率增大;各级间,级数减小分辨率减小.同时,由于高级次(短波)分辨率大于低级次(长波),因此各级谱线长度之比不再满足普通光栅中的比例关系.