Göbel Mirrors

Optics for 1D X-ray Diffractometry


Nowadays the most widespread optics for XRD are the so-called "Göbel Mirrors". The Göbel Mirror (GM) converts the X-ray beam coming from an X-ray tube into a parallel or focused beam and additionally monochromatizes it. The mirror consists of multilayers with laterally graded thickness, deposited with extreme accuracy onto a prefigured surface.

 

X-ray instruments equipped with a Göbel Mirror show dramatically improved performances in various types of measurements compared with instruments without a Göbel Mirror. A typical application for GM's is in X-ray Reflectometry (XRR). The graphic below shows a comparison between measurements with and without the use of a GM: the intensity achieved with a GM is more than 10 times higher.

 

XRR Measurement of a V-C multilayer sample with a Göbel Mirror and a comparable system without such optics.

It is possible to carry out measurements with X-ray Reflectometry in over 9 orders of magnitude. These results can usually be surpassed only by synchrotron X-ray sources.

A significant intensity gain was also achieved using our X-ray mirrors for measurements in High Resolution Diffractometry (HRXRD). This was made possible by the development of the so-called 3rd generation GM's. They consist of an ultra-precise prepolished parabolical form (with slope errors down to 1 arcsec rms) with an ultra-precise multilayer coating (pat. US 6226349). The intensity achieved by directing a beam from the 3rd Gen GM into channel-cuts was 16 times higher compared to a set-up without a GM.

 

3rd Generation for highest resolution


  • optics with slope errors of 1 arcsec
  • lowest divergence and best parallel beam
  • best monochromatization

 

Together with the standard Parallel Beam Göbel Mirror, Incoatec also produces both Convergent Beam as well as Divergent Beam Göbel Mirrors. In some applications, for example in powder diffractometry, a parallel beam is not always the best choice. Better results are achieved with a slightly divergent Göbel Mirror due to a maximization of intensity. The product range includes optics for various types of tubes. The table gives an overview of relevant data on our standard mirrors.

Data of the standard Incoatec Göbel Mirrors
Length 40 mm / 60 mm
Distance 90 mm / 100 mm / 150 mm
Wavelength Cr, Co, Cu, Mo
Beam divergence
(for 40 µm line focus tubes)		 0.5 mrad
Exit beam width 0.8 mm / 1.2 mm / 1.0 mm
Flux
(Cu tube 40 kV 40 mA)		 2...3 x 109 cps
Spectral purity > 99.8 %
Figure errors of the optic:
2nd generation
3rd generation
< 12 arcsec rms (bent wafer)
< 4 arcsec rms (prepolished form)

Customer-specific mirrors beyond these data are also possible.

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