为了提高如拉曼光谱仪和高分辨率成像光谱仪等微弱信号光谱仪的信噪比，应尽可能增大其相对孔径、增强其集光本领。Littrow-Offner型分光系统兼具Littrow型和Offner型分光系统的优点：结构简单紧凑、全部球面元件同心、固有初级像差小、可实现的相对孔径大和集光本领强。简要介绍该系统的结构与原理，并分析了该系统的成像特性。运用球面反射镜和衍射光栅的弧矢和子午成像公式，分析该系统的像散特性，给出波长范围内消像散的方法。引入弯月透镜来进一步消除系统中的固有像散，以拉曼光谱仪的分光系统为例，优化设计得到体积小、相对孔径大、分辨率高且成像质量优异的分光系统。

The light collection power and the relative aperture of weak-light spectrometers, such as Raman and hyperspectral spectrometers, are expected as high or big as possible, in order to improve their signal-to-noise ratio (SNR). Littrow-Offner spectroscopic mount has the advantages of both Offner and Littrow mounts, including its simplicity and compactness, concentricity of all spherical elements, low inherent aberration, realizable big relative aperture and high light collection. Such combined mount structure and principle are briefly introduced and then its imaging performance is investigated. Its astigmatic characteristic then is investigated, through application of the sagittal and meridian imaging formulas of spherical mirror and diffractive grating. The means to eliminate astigmatism in the wavelength range is suggested. Furthermore, the inherent astigmatism is corrected by introducing a meniscus singlet with negative astigmatism. In the case of Raman spectrometer, a compact spectroscopic optics with big relative aperture and resolution and excellent imaging quality is optimally designed.