Fiber-fed Echelle Tayfçeker optical design and analyse

This study includes optical designs of two Fiber-Fed Echelle Spectrographs (FES), which differ from each other in terms of cross-dispersers, and optical analyzes of the spectra (orders) obtained from these designs. Optical analyzes were performed by interpreting the results obtained from the Spot Diagram, Footprint Diagram and Encircled Energy Diagram in the Zemax optical design program. Designed for the RTT150 telescope, this spectrophotometer system is defined as Fiber-Fed, since the beam focused in the Cassegrain focal plane is carried to the spectrometer by fiber. TÜBİTAK National Observatory located at Bakirlitepe mountain in Antalya has 1.5 m diameter telescope called The Russia-Turkey Telescope (RTT150). RTT150 has two focal planes, Cassegrain and Coude. Two spectrographs produced specifically for the RTT150 are used at these focal planes. The spectrograph used at the Cassegrain focal plane are called TUG Faint Object Spectrograph and Camera (TFOSC) and the other is Coude Eechelle Spectrograph (CES). The CES Spectrograph has R= 40000 resolving power and thus it is called a high resolution spectrograph. In this respect, it offers researchers the opportunity to obtain high-resolution spectral data. However, due to some disadvantages of the current CES spectrograph, the study in the thesis contains a concept spectrograph optical design that is considered as a substitute for it. Prism was used as cross-disperser for the first spectrograph type. In this design, two symmetric N-F2 glass type prisms which have 42 degree apex angles were used. In the other design, grism was used as cross-disperser. Different from the traditional types, the grism used in this study was created by placing a volume-phase holographic grating between two symmetrical thin prisms, which are N-BK7 glass types with 8 degree apex angles. The working wavelength range is determined as 390-900 nm for both spectrographs. m=113 order and its center wavelength 501,148 nm were taken into account for prisms cross-disperser optical design and optimization process. m=89 and its central wavelength 636,256 nm for grism cross-disperser optical design and optimization process. If the order and its center wavelength used for the grism cross-disperser spectrograph were preferred to use for the prism cross-disperser spectrograph, then a larger camera diameter would be needed. Therefore, it was preferred to use a higher order and lower wavelength for the prism cross-disperser optical design and optimization process. A camera with a focal length of 200 mm and a focal ratio of f/2 was used for the both designs. A CCD detector with a pixel size of 13,5x13,5 microns was used to determine optical parameters of the camera and analyze its image quality on the focal plane. In the analysis made after the tolerance process for both spectrographs, it was seen that the RMS and geometric spectrum image thickness values of the m=113 central order in the prism cross-disperser spectrograph were between 2,3-2,8 pixels and 5,8-7,6 pixels, respectively. In addition, the distance between the central order and its adjacent orders was measured as 17 pixels. When a similar study was performed for the grism cross-disperser spectrograph, it was seen that the RMS and geometric spectral image thickness values of the m=89 central order were in the range of 2,3-2,45 pixels and 5,7-8,1 pixels, respectively. the distance between the central order and its adjacent orders was measured as 25 pixels. It can be said that the distance between the orders increases towards the ultraviolet wavelength, and decreases towards the near-infrared wavelength in the design in which prisms are used as cross-disperser. The opposite situation is observed in the design in which grism is used as cross-disperser. Finally, when all spectrum obtained from both spectrographs is analyzed, it can be said that spectrum line tilt is more than the spectrograph in which prism is used as cross-disperser.