The performance of fiber-fed astronomical spectrographs is highly influenced by the properties of fibers. The near-field and far-field scrambling characteristics have a profound impact on the line spread function (LSF) of the spectra. Focal ratio degradation (FRD) influences the output beam size, thereby affecting the throughput, as well as the size of the collimator and dispersion elements. While previous research has indicated that these properties depend on the shape of the fiber core and showed that non-circular core fibers can yield uniform near-field scrambling, the result remains inconclusive for far-field. In this study, we investigate the near-field and far-field scrambling properties, along with the FRD, of 50-micron core fibers with different core geometries. We find that in addition to excellent near-field scrambling, octagonal-core fibers can also produce more uniform far-field output when compared to circular-core fibers. They also have less FRD effect when being fed with a f/3 beam.
The AMASE-P project presents a bold exploration into the potential utilization of state-of-the-art commercial photographic lenses and CMOS detectors as integral components in spectrograph designs, thereby offering a cost-effective solution for astronomy instrumentation. In this contribution, we present the current optical design of the telescope and spectrograph system, and present the expected performance of the design, including the point spread function, spectral resolution, throughput, and signal-to-noise ratios. We also present the design of a telecentric corrector for the Canon 400mm f/2.8 III telephoto lens, which is necessary for coupling it to optical fibers.
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