Lummer-Gehrcke plate

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The Lummer-Gehrcke plate , named after the German physicists Otto Lummer (1860–1925) and Ernst Gehrcke (1878–1960), is an optical filter that is used to generate narrow-band spectral lines .

Structure and functionality

The Lummer-Gehrcke plate consists of a plane-parallel "Lummer plate" made of glass or quartz and a Gehrcke attachment, a triangular prism, for coupling in light. In addition to this, another structure consisting of a plane-parallel plate with a beveled surface on one end face is referred to as a Lummer-Gehrcke plate.

The coupled light is reflected several times in the plane-parallel plate, slightly below the critical angle of total reflection. With each reflection, part of the light emerges grazingly from the plate at the upper and lower interfaces. The reflection close to total reflection ensures a high reflection coefficient and thus the possibility that a large number of rays can interfere with one another.

The parallel rays emerging on the upper and lower side are then bundled with a suitable lens arrangement and each interfere with one another (see also diffraction grating ). Two rays are obtained with a sharp spectral line, similar to a monochromatic source.

The disadvantage of the Lummer-Gehrcke plate is that a plane-parallel plate with a high degree of parallelism and surface flatness is required. These are difficult to manufacture and therefore expensive. Furthermore, with this rigid structure with constant plate thickness, the resolution cannot be varied. For these reasons, Lummer-Gehrcke plates are rarely used today and are being replaced by more flexible Fabry-Pérot interferometers .

Individual evidence

  1. ^ A b Herbert Daniel: Optics, thermodynamics, quanta: optics, thermodynamics, quanta . Walter de Gruyter, 1998, ISBN 978-3-11-080706-6 , p. 110 .
  2. ↑ Jan Scholz: 4.1.5 LUMMER-GEHRCKE plate. In: The F internship part 1. Winter semester 2000/2001. University of Giessen, July 1, 2003, accessed April 29, 2012 .
  3. ↑ Klaus Lüders, Robert Otto Pohl: Pohl's introduction to physics: Volume 2: Electricity and optics . Gabler Wissenschaftsverlage, 2010, ISBN 978-3-642-01627-1 , p. 325 .

Web links

  • Lorenz, Thomas: Internship report (PDF; 127 kB) with a very detailed derivation of the phase difference of the Lummer-Gehrcke plate in section 2.1, page 2ff