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.
References
1. T. Harada, M. Itou, T. Kita, ”A grazing incidence monochromator with a varied-space plane grating for synchrotron radiation”, Proc. Soc. Photo-Opt. Instrum. Eng. 503, 114(1984)
2. T. Harada, T. Kita, M. Itou and H. Taira, ”Mechanically Ruled Diffraction Gratings for Synchrotron Radiation”, Nucl. Instrum. Methods A 246, 272(1986)
3. T. Harada, H. Taira, T. Kita, M. Itou , ”Groove profile measurement of diffraction gratings using scanning electron microscope”, in Application and Theory of Periodic Structures, Diffraction Gratings, and Moire Phenomena Ⅲ, J. M. Lerner, ed. , Proc. Soc. Photo-Opt. Instrum. Eng. 815,118-123(1987)
4. M. Itou, T. Harada and T. Kita, ”Soft x-ray monochromator with a varied-space plane grating for synchrotron radiation：designand evaluation”, Appl. Opt. 28, 146-153(1989)
5. T. Kita and H. Harada, ”Rulimg engine using a piezoelectric device for large and high-groove density gratings”, Appl. Opt. 31, 1399-1406(1992)
6. M. Fujisawa, A. Harasawa, A. Agui, M. Watanabe, A. Kakizaki, S. Shin, and T. Ishii, T. Kita, T. Harada, Y. Saitoh, and S. Suga, "Varied line-spacing plane grating monochromator for undulator beamline", Rev. Sci. Instrum. 67(2), Februsry 1996
