New VPH based GRISMs for AFOSC

AFOSC is a versatile instrument mounted at the Copernico 1.82 meter telescope in Asiago (Italy) and it is equipped with a suite of dispersing elements covering the optical range. Two innovative dispersing elements in GRISM configuration are designed in order to boost the observing performances. One GRISM works in the Ha and it is characterized by a resolving power of 3600. Its peak diffraction efficiency reaches 90% and it remains high in the spectral window. The other GRISM is a multiorder element that allows for the recording of a low-resolution spectrum in the 0.35 - 1.00 um in a single exposure, by projecting two diffraction orders on the detector. The VPHG is optimized in both first and second orders and a combination of two prisms (forming an Amici prism) is used to achieve the cross-dispersion. The diffraction efficiency of the VPHG is well balanced across the spectral range with >80% of peak efficiency in the lst order and >60% in the 2nd.