Toshiaki Kita

Mechanically ruled aberration-corrected concave gratings

Aberration-corrected concave gratings with curved and variable spacing grooves are ruled with a numerically controlled ruling engine. In the design of aberration-corrected concave gratings, mechanical methods allow more freedom to choose the amount of space variation than do holographic methods. A highly efficient visible-UV monochromator and a coma-type aberration-reduced Seya-Namioka monochromator have been designed and fabricated using mechanically ruled aberration-corrected concave gratings. The gratings can be used with VUV monochromators and spectrographs with improved image focusing properties.

Development of a flat-field grazing-incidence XUV spectrometer and its application in picosecond XUV spectroscopy

A new type of grazing-incidence spectrometer with a flat focal field is developed, and XUV spectroscopy in the extreme ultraviolet region ranging from 15 to 200 A is carried out. Soft x-ray line spectra emitted from picosecond laser plasmas of aluminum and iron targets are measured and good resolutions are obtained in the XUV region. The spectral regions of detection are extended to shorter wavelengths (15 A) using a finer spaced grating. Computational studies on x-ray spectra are also performed taking into account the transient characteristics of picosecond laser-produced plasmas; the importance of the transient treatment is clearly shown. This type of soft x-ray spectrometer should be useful for time-resolved picosecond soft x-ray spectroscopy.

Soft x-ray monochromator with a varied-space plane grating for synchrotron radiation: design and evaluation

A soft x-ray monochromator was developed for synchrotron radiation and installed at the Photon Factory in the National Laboratory for High Energy Physics. This monochromator consists of only two optical elements: a plane mirror and a varied-space plane grating with focusing properties. The 0.7-10-nm wavelength range can be covered with resolutions of 640 at 1.4 nm and 1200 at 5 nm. The output photon flux at wavelengths above 1 nm is ~10(10)-10(11) photons/s for a 100-mA beam current in the 1% spectral bandwidth.

VARIED LINE-SPACING PLANE GRATING MONOCHROMATOR FOR UNDULATOR BEAMLINE

A varied line‐spacing plane grating monochromator is installed at an undulator beamline BL‐19B of the Photon Factory. Small contribution of aberrations to image sizes at a focal plane of the varied line‐spacing plane grating is calculated with use of an optical path function. The largest resolving power obtained from a ray tracing is estimated to be 4600 at a photon energy of 1239.85 eV and 10 000 at 91.2 eV. Gas absorption spectra show the similar extent of resolution obtained by the ray tracing. A high brightness with a high resolution may be realized in this monochromator.

Mechanically Ruled Stigmatic Concave Gratings

Concave gratings that form stigmatic images in normal incidence spectrographs are analyzed and a new method of ruling stigmatic concave gratings has been developed. The ruling engine is numerically controlled for varying the groove spacings and is capable of ruling both straight and curved grooves. Three types of concave gratings, one conventional and two stigmatic have been ruled and the imaging properties of them are examined. From the results of the examination, the possibility of producing mechanically ruled stigmatic concave gratings with the freedom of choosing stigmatic wavelengths is proved.

Ruling engine using a piezoelectric device for large and high-groove density gratings.

A ruling engine for large and/or high-groove density gratings is developed. A hybrid driving method that uses a piezoelectric device and a screw-nut mechanism is adopted to achieve stop-and-go blank motion with a closed-loop control system. Several test gratings, including a ruled area of 300(width) x 200(groove length) mm(2), groove densities of 6000 and 10,000 grooves/mm, and a uniform and varied-line space, are ruled to confirm the basic functions of the ruling engine. A set of four spherical, varied-line-space gratings with central groove densities of 6000, 4550, 3450, and 2616 grooves/mm and a ruled area of 200 x 200 mm(2) is ruled for the orbital retrievable far and extreme ultraviolet spectrometer.

A Grazing Incidence Monochromator With A Varied-Space Plane Grating For Synchrotron Radiation

A grazing incidence monochromator to scan the 5 - 100 Å wavelength range of synchrotron radiation is designed by taking advantage of the focusing property of a varied-space plane grating ruled with a numerically controlled ruling engine. The plane grating monochromator uses only two plane surfaces for reflection optics so that high throughput in the soft x-ray region is expected.

Use of aberration-corrected concave gratings in optical demultiplexers.

A method of designing aberration-corrected concave gratings and their mounting for optical demultiplexers is described. An aberration-corrected concave grating for a demultiplexer has been designed and fabricated for use in a six-channel multiplex system in the 800-nm wavelength region. A coupling efficiency of 55% and signal cross talk of less than ~3 × 10−4 have been achieved experimentally.

Mechanically ruled diffraction gratings for synchrotron radiation

Abstract Improvements in the ruling, replication, and measurement of mechanically ruled diffraction gratings, are described, especially for synchrotron radiation applications. Profiles of extremely fine and shallow grooves are measured with a scanning electron microscope. Replica gratings can now be baked for high vacuum applications using a high-temperature durable epoxy as cement. The groove space variation technology is effective for reducing aberrations in concave grating monochromators. A grazing incidence monochromator without using collimating and focusing mirrors has been designed and fabricated for a soft X-ray beamline at the Photon Factory by utilizing the advantage of a varied-space plane grating with self-focusing properties.

Design of spherical varied line-space gratings for a high-resolution EUV spectrometer

A highly efficient EUV spectrograph is designed for high-resolution spectroscopic observation. The spectrograph is designed for point source astronomy in a 40-120 nm bandpass and is to be ORFEUS (Orbiting Retrievable Far and Extreme Ultraviolet Spectrometer), scheduled for launch as the first payload of a German space platform Astro-SPAS (Astronomy Shuttle Pallet Satellite). The design uses spherical varied line-space (SVLS) grating to minimize astigmatism, coma, and spherical aberration. The effectiveness and practical feasibility of the design is proved by an SVLS grating for visible use. The image focusing properties of the SVLS grating for ORFEUS are compared to those with toroidal uniform line-space (TULS) design. The SVLS design is superior to the TULS, theoretically in resolution and image concentration, but also practically with not only fabrication ease. Four SVLS gratings with nominal groove densities of 6000, 4550, 3450, and 2616 gr./mm, and a 200 mm x 200 mm ruled area have been ruled using a numerically controlled ruling engine for use in ORFEUS.