Therefore, according to Eqs. ( 2) and ( 3), the coma effect can be conditionally removed only at some specifically designed wavelength positions restricted within a relatively narrow spectral region.Ĭontinuous researches are being made to make the feasibility and precision of spectrometers be improved in many different configurations and applications 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32. Where m is the order of the grating diffraction and g is specified by the density of grooves of the grating (lines per mm). In the C–T configuration, the astigmatic aberrations, called the coma effect is an intrinsic issue that makes the spectral image out of focus at the focal plane of the diffracted light reflected from the mirror 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18. 1, is the most common configuration for spectroscopic analyses 1. To date, the typical Czerny–Turner (C–T) configuration 3, which consists of two spherical mirrors and a plane grating as shown in Fig. Moreover, these problems, which induce substantial measurement errors in a wide spectral range due to the strongly correlated restriction of the optical element arrangement in the system design, are difficult to solve.

In optical systems, especially in high-precision optical instruments, astigmatic aberrations affect seriously the performance of the system. Since the beginning of last century, many studies had been reported trying to solve the issue of astigmatic aberrations that occur as a result of reflection or refraction at a spherical surface, shifting the incident light beam obliquely off of the homocentric axis 2. Super-high resolution optical spectrometers are significantly important for a wide range of applications in biochemical analysis, remote sensing, astronomy, and etc.

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