ABSTRACT
The desirable imaging locations of the flat-field holographic concave gratings should be in a plane. And the object can be imaged perfectly by the grating when the tangential focal curve and sagittal focal curve both superpose the intersection of the image plane and dispersion plane. But actually, the defocus can not be eliminated over the entire wavelength range, while the astigmatism vanishes when the grating parameters satisfy some conditions. An optimization method for broad-band flat-field holographic concave gratings with absolute astigmatism correction was proposed. The ray tracing software ZEMAX was used for investigating the imaging properties of the grating. And we made a comparison between spectral performance of gratings designed by this new method and that by conventional method, respectively. The results indicated that the spectral performance of gratings designed by using the absolute astigmatism correction method can be as good as gratings designed with the conventional method. And the focusing performance in the sagittal direction is much better, so that the S/N ratio can be greatly improved.
Subject(s)
Holography , Software , AstigmatismABSTRACT
The spectral resolution of the spectrometer will be seriously deteriorated by radius error which is inevitable in the flat-field holographic concave grating fabrication. In order to give theoretical guidance to the design and assembly of the spectrometers, the geometric ray-tracing method was used to calculate and analyze the variation of the spectral image width with different radius error. It was discovered that in a wide range of the radius error, the position of the tangential focal curve moves forward or backward as the radius changes, while the shape of the tangential focal curve remains almost unchanged. As is shown through the calculation, the radius error can be compensated by adjustment of the detector's position or entrance slit distance. The simulation results indicate that with proper modification of the using structure, the grating can have a spectral resolution as good as the designed results.
