Diffraction Gratings

The diffraction gratings developed by Hitachi have been used in various application areas and are now highly evaluated as the world's foremost element. Hitachi's highly reputed precision-ruling engine has now been combined with laser interferometric technology. This permits arranging the groves to a nanometer precision! Our burnishing technique, with use of a diamond tool, enables forming excellent grooves, making surfaces far smoother than vacuum evaporated metal surfaces.

Features

• From X-ray to Infrared, gratings can now be designed to meet specific requirements.
• The ruling engine equipped with a highly sensitive laser interferometer is able to rule grating grooves with ultra-high accuracy and realizes high-resolution spectroscopic instruments.
• Grating grooves having two or more different blaze angles can be combined on a single diffraction grating. This structure allows for broader wavelength coverage.
• Coma-type aberration-corrected concave grating for high resolution Seya-Namioka monochromator.

Plane, Concave, or CUSTOM-designed diffraction gratings with a choice of blank material and coating:

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These gratings are available in North America and Europe.

Overview

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 1.7µ 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

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Specifications

Overview

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.

Reference

T. Harada and T. Kita, "Mechanically ruled aberration-corrected concave gratings", Appl. Opt. 19, 3987-3993(1980).

Options

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

• Equally-Spaced Straight-Groove Concave Gratings (PDF format, 54kBytes)

Aberration-Corrected Concave Gratings

• For Seya-Namioka Monochromators (Coma Type) (PDF format, 79kBytes)

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 (PDF format, 79kBytes)

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 (PDF format, 100kBytes)

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 (PDF format, 90kBytes)

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.

Overview

Diffraction gratings of special specifications can also be manufactured on request.

Material

Pyrex glass is used as a standard material. Hitachi is also prepared to use materials other than Pyrex glass when specified.

Coating

Diffraction gratings are coated with aluminum (Al) as a standard. Hitachi will coat the gratings with gold (Au) and platinum (Pt) as special specifications.

Diffraction gratings with Part No. 001-0450 and 001-0437 exceptionally are coated with gold (Au) as a standard.

Overcoating

Diffraction gratings are overcoated with magnesium fluoride

(MgF₂) or lithium fluoride (LiF) as special specifications.

Dimensions

Diffraction gratings are manufactured to dimensions other than specified in this catalog. They can also be shaped round.

Certificate

For certifying the groove profile, an electron micrograph can be provided together with the manufactured diffraction grating at the expense of the customer.