Stigmatic imaging of spectra by using an aberration-corrected concave diffraction grating
The variable spacing and curved groove ruling technology, developed solely by Hitachi, eliminates the aberrations inherent to the conventional concave diffraction gratings. This greatly enhances the spectral image focusing properties of concave gratings. The Hitachi aberration corrected concave diffraction gratings include high resolution, reduced astigmatism, compact size, etc., which can be selected in accordance with the function of the equipment to which they are applied.
Mercury line spectra
The conventional concave grating images the spectra emitted from a pinhole into vertical straight lines, while the newly developed aberration-corrected concave grating images the spectrum in the form of a point.
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Abberation correction by using the concave diffraction grating with varied-space grooves.
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Abberation correction by using the concave diffraction grating with curved grooves. |
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Conventional (equally-spaced, straight grooves) concave diffraction grating.
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Reference
T. Harada and T. Kita, ”Mechanically ruled aberration-corrected concave gratings”, Appl. Opt. 19, 3987-3993(1980).
From X-rays to Infrared! Gratings can now be designed to meet specific requirements
The diffraction gratings that are capable of analyzing a variety of radiations ranging from soft X-rays to far infrared are now expanding their application areas as optical elements, indispensable for spectroscopy.
Conventional Concave Gratings
Aberration-Corrected Concave Gratings
- For Seya-Namioka Monochromators (Coma Type)
These gratings eliminate the coma-type aberration of the Seya-Namioka monochromator, which has been most widely used in monochromators with concave gratings that provide high resolution. Hitachi is manufacturing a wide variety of aberration-corrected gratings for Seya-Namioka monochromator which cover a wavelength range from the vacuum ultraviolet to the near infrared region.
- For Compact, High-Efficiency Monochromators
These gratings are designed for normal incidence mounting. They reduce aberrations and at the same time increase the efficiency of light intensity. As a result, a high quality of image focusing of the concave grating is available.
- For Flat-Field Spectrographs - Normal Incidence
Variable space grooves enable flat-field image focusing of concave grating spectrograph. The spectrograph permits simultaneous measurement of multi-wavelength spectra when combined with a linear array detector. These gratings are optimized for normal-incidence optical system (for VIS-UV ray).
- For Flat-Field Spectrographs - Grazing Incidence
Highly dispersive concave gratings for grazing-incidence mounting are available, especially for synchrotron radiation and extreme ultraviolet applications. These gratings are very effective for the application of soft X-rays whose reflectance is extremely low on a metal surface.
