Blazed grating

Blazed grating (of English. Sparkle to blaze = ), also known as Echelettegitter ( according to French échelle = ladder ) are special optical lattice. They are optimized so that the diffraction efficiency for a given diffraction order is at a maximum. To this end, as much intensity is concentrated in a desired diffraction order, in the other systems (in particular the zeroth ), however, minimized. Since this can be achieved exactly for only one wavelength is always specified for which the grating blaze wavelength optimized ( " blazed " ) is. In addition to the blazed wavelength, and the diffraction order of the blaze angle is the third characteristic variable of a blaze grating.

Blaze angle

Like all optical lattice have also blazed grating constant grating line spacing, which determines the strength of the lattice caused by the wavelength splitting. However, the individual grating lines have a triangular saw-tooth shape in cross-section, whereby a step structure. The steps are inclined by the so-called Blaze angle to the grating surface. According levels Normal and grating normal are also angularly.

The blaze angle is optimized so that the efficiency for the wavelength of the light used in the desired diffraction order is at a maximum. This clearly means, that is chosen so that the diffracted at the grid beam and a reflected beam to be deflected against the step in the same direction. In general blaze grating are manufactured in the so-called Littrow arrangement.

Littrow configuration

In the Littrow arrangement, the blaze angle is selected such that the angle of the diffracted beam corresponding to the angle of incidence. A reflection grating, this means that the diffracted beam is reflected back in the direction of the incident beam (blue beam in the picture). The beams are then perpendicular to the stage, ie parallel to the normal levels. This applies in Littrow configuration.

, The diffraction angle of the grating are not affected by the stepped structure. They will continue to be determined by the line spacing and can be prepared by the grating equation:

With:

For the Littrow arrangement thereof, which can be prepared by dissolving after the blaze angle calculated for any combination of diffraction, wavelength and line spacing:

Geblazedes transmission grating

Blazed grating can also be implemented as a transmission grating. Here, the blaze angle is selected such that the desired diffraction order, which coincides with the diffracted by the grating medium light beam.

Echelle

The Blaze grids includes the echelle grating. It is characterized by a particularly large blaze angle (> 45 ° ), whereby the light is no longer true on the long, but on the short leg of the geblazeden grid lines. Echelle gratings are usually made with a larger lattice spacing, but optimized for higher diffraction orders.