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Fastie-Ebert configuration

Fastie Ebert

The Fastie-Ebert configuration is a rather simple and inexpensive configuration. A spectrometer in this configuration consists of a single large spherical mirror and one plane diffraction grating

The entrance slit is placed in the focal plane of the spherical mirror. Light passing through the entrance slit will be reflected to form a parallel beam, directed towards the plane grating. At the grating the light is dispersed, and ‘reflected’ back towards the mirror. This reflected, or dispersed parallel beam, will again be collimated and form an image, or several coloured images of the entrance slit. The exit slit, again situated in the focal plan of the spherical mirror, serves to select one of the these coloured images, allowing a photo detector to measured the trasmitted light intensity, spectral intensity.

The opening angel q  or rather 2qis an important parameter of the Fastie-Ebert configuration. It determined by the distance between entrance and exit slit, and the focal length (radius) of the spherical mirror. The larger this angle, the more the spherical mirror is used in an off axis configuration, which detoriates the optical quality of the system.

Fastie-Ebert instruments are inexpensive and commonly used design, but exhibit some limitation in their ability to maintain image quality, due to system aberrations such as spherical aberration, coma, astigmatism, and a curved focal field. These aberrations are rather strong due to the off-axis operation of the system .

First published on the web: 19.11.2006

Authors of the latest version: Aranka Derzsi and Giovanni Lotito. The text is based on a lecture given by Thomas Nelis at the first Gladnet training course in Antwerp Sept. 2007