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Gratings with 10,000 grooves per millimeter

Hitachi’s highly reputed, precision ruling engine has now been combined with laser interferometric technology. This permits arranging the grooves to nanometer precision. Furthermore, a burnishing technique, making use of a diamond tool enables forming excellent grooves whose surfaces are far smoother than vacuum evaporated metal surfaces heretofore considered as the smoothest mirror surface. All these features serve to provide a highly efficient diffraction grating with minimum stray light in UV-VIS region as well as in the soft X-ray and vacuum UV regions. The accurate blaze angle and the regularly arranged groove-to-groove spacings can be observed clearly by scanning electron micrograph. This precision is shown in the figure to below.

Varied-space gratings

The figure below shows a photograph of varied space grooves taken by using a scanning electron microscope. The spacing varies from 0.3 to 1.7 µm in 50 nm increments.



Hitachi's new engine is capable of ruling varied-space grooves moreflexibly than the conventional engines. Common applications do not requiremuch varied spacing and do not require adjustment of tool loading. When a large space variation, such as shown above, is required, tool loading also need be adjusted.

A wide variety of high performance, mechanically-ruled diffraction gratings

• The ruling engine equipped with a highly sensitive laser interferometer is able to rule grating grooves with ultrahigh accuracy, and realizes high resolution spectroscopic instruments.
• Burnishing process, by using a diamond tool, serves to form triangularly shaped echelette grooves whose surfaces are extremely smooth yielding minimum stray light.
• The grooves, having an exact blaze angle, can be formed by selecting an appropriate diamond tool and measuring the groove profiles with a scanning electron microscope and/or an atomic force microscope. These processes allow the grating to provide a highly efficient diffraction efficiency in the designed wavelength region.
• Grating grooves having 2 or more different blaze angles can be combined on a single diffraction grating. This structure allows for broader wavelength coverage.
• A variety of diffraction gratings with variable spaced grooves and shapes are manufactured.

This graph shows the efficiency of 1st-order diffraction light for each wavelength. Select a diffraction grating having an optimum blaze wave-length taking into account the energy distribution of the light source and the wavelength sensitivity of the detector to be used.