Yoshihisa Harada

Design of holographic gratings recorded with aspheric wave-front recording optics for soft X-ray flat-field spectrographs

Abstract Holographic gratings recorded with aspheric wave fronts have been designed by means of the analytic design method so as to have the interchangeability with mechanically ruled varied-line-space (VLS) gratings that were designed for soft X-ray flat-field spectrographs. It is shown that aspheric wave-front recording optics makes it possible to produce large variations in the grating constant (e.g., more than 30% over a ruled area of 50 mm) required for flat-field spectrographs. The imaging properties of the holographic gratings thus designed are discussed from the viewpoint of interchangeability with mechanically ruled VLS gratings.

Holographic grating recorded using aspheric wavefronts for a Seya-Namioka monochromator

The geometric theory of the holographic grating is expanded to those recorded by use of aspheric wavefronts which can be easily made. General expressions are given for the groove function and the light path function. Additional terms in the groove function unique to this recording method suggest the possibility of sufficient compensation of coma aberration over conventional holographic gratings recorded with plane and spherical wavefronts. To confirm this advantage, we compared the imaging properties of a Seya-Namioka monochromator equipped with both types of grating, which were designed and fabricated by use of spherical and aspheric wavefronts. The experimental results confirm that our method enhances resolution and throughput of the monochromator.

New evaluation beamline for soft x-ray optical elements

An evaluation system capable of measuring the wavelength and angular characteristics of the absolute reflectivity (or diffraction efficiency) of soft x-ray optical elements has been designed and constructed. The system was installed on a beamline (BL-11) of the AURORA, a superconducting compact storage ring, at the Synchrotron Radiation Center, Ritsumeikan University. To cover a wavelength range of 0.5 nm<λ<25 nm, this system incorporates two types of Monk–Gillieson monochromators. One is a conventional type equipped with three varied-line-spacing gratings, allowing a choice of two included angles. The other is a new type that employs a scanning mechanism based on surface normal rotation. The outline of the system and some preliminary experimental data obtained in the course of test runs are described.

Performance of laminar-type holographic grating for a soft x-ray flat-field spectrograph in the 0.7–6 nm region

A laminar-type holographic grating having a groove density of 2400 lines/mm was designed and fabricated for use with a soft x-ray flat-field spectrograph covering the 0.7–6 nm region. The varied-line-spaced grating pattern was generated by use of an aspheric wave front recording system and the laminar-type grooves were formed by a reactive ion-etching method. The performance of the grating was evaluated by using a molybdenum K x-ray generator and a spectrograph with a charge coupled device imaging detector. Also, the absolute diffraction efficiencies of the zeroth, first, second, and third, spectral orders were measured by use of the reflectometers installed at Synchrotron Radiation Beamlines. The experimental results showed that the holographic grating indicated comparable spectral resolution and maximum first-order diffraction efficiency (>2%) at ∼2 nm with a replica grating made from a mechanically ruled varied-line-spacing grating. It also showed higher efficiency in the <1.0 nm region and lower level...

Varied-line-spacing laminar-type holographic grating for the standard soft x-ray flat-field spectrograph

An aspheric wave-front recording system was designed to produce a holographic grating for use in a standard soft X- ray flat field spectrograph interchangeable with a mechanically ruled varied-line-spacing (VLS) grating. The grating grooves recorded with the designed aspheric wave- front recording system were processed to form a laminar groove profile by means of reactive ion etching. Measurements done with synchrotron radiation and a laboratory X-ray source are reported for this laminar-type grating and a commercial grating replicated from a mechanically ruled VLS grating that was specifically designed and fabricated for the standard soft X-ray flat- field spectrography. The laminar-type holographic grating is found to have an absolute first-order efficiency of approximately 10% for wavelengths of approximately 4.5 - 12 nm. It is also shown that the holographic grating is effective in suppressing the higher orders and stray-light level for soft X-ray of 4.36 nm (C-K) and has a comparable spectral resolution to the replica VLS grating.

Comparison of mechanically ruled versus holographically varied line-spacing gratings for a soft-x-ray flat-field spectrograph

Recent progress in the design of aspheric wave-front recording systems has permitted the manufacture of holographic gratings with highly variable groove densities that are suitable for flat-field spectrographs. A holographic grating thus recorded was processed to produce a laminar profile by use of reactive-ion etching. Measurements are reported of the absolute diffraction efficiency of this grating and of a comparable mechanically ruled grating. It is found that the holographic grating is much more effective in suppressing the higher orders. The spectral resolution was determined by use of a carbon Kalpha x-ray generator and a spectrograph with an imaging detector. The spectral resolution of the holographic grating was approximately 3 times worse than that of the ruled grating.

New Blazed Holographic Grating Fabricated By Using An Aspherical Recording With An Ion-Etching Method

Basic equations of the holographic grating are expanded to those of a new holographic grating produced by recording the interference fringes of two aspherical beams. Aberration terms peculiar to this recording configuration show the possibility of the additional compensation of aberrations over the conventional holographic gratings recorded with plane or spherical beams. To confirm this advantage, we designed and fabricated some aberration-corrected blazed holographic gratings for use with a Seya-Namioka and a Czerny-Turner monochromators, and a polychromator suitable for an array detector. The experimental results indicated that the usefulness of our method to enhanse resolution and throughput of spectrometers.

New type of Monk-Gillieson monochromator capable of covering a 0.7- to 25-nm range

A new type of monochromators that incorporates two kinds of Monk-Gillieson monochromators has been designed and constructed for the purpose of realizing an evaluation beamline for characterizing soft X-ray optical elements in a wide wavelength range of 0.7-25 nm. One of the monochromators is a conventional type equipped with three varied-line-spacing plane gratings, allowing a choice of two inclusion angles. The other is a new type that employs a scanning mechanism based on Surface Normal Rotation (SNR). The SNR scheme provides high throughput at short wavelengths and simple scanning mechanism by means of a grating rotation about its normal. The monochromators is operated in the SNR and conventional modes over the ranges of 0.7-2.0 nm and 2.0-25 nm, respectively. The system was installed on a beamline of the AURORA, a superconducting compact storage ring, at the Synchrotron Radiation Center, Ritsumeikan University. In this paper we describe the optical and mechanical designs of the monochromators, and a practical method of wavelength calibration. Also experimental data are shown which demonstrate the performance and versatility of the new type of Monk-Gillieson monochromators.

A beam intensity monitor for the evaluation beamline for soft x-ray optical elements

Evaluation Beamline for Soft X-Ray Optical Elements (BL-11) at the SR Center of Ritsumeikan University has been operated to measure the wavelength and angular characteristics of soft x-ray optical components in a wavelength range of 0.65-25 nm using a reflecto-diffractometer (RD). The beam intensity monitor that has been equipped in BL-11 has observed the signal of the zero-th order light. For the purpose of more accurate evaluation of the performance of optical components, a new beam intensity monitor to measure the intensity of the first order light from the monochromator in BL-11 has been developed and installed in just front of RD. The strong positive correlation between the signal of the beam monitor and a detector equipped in the RD is shown. It is successful that the beam intensity of the first order light can be monitored in real time.