Masato Koike

Plane gratings for high-resolution grazing-incidence monochromators: holographic grating versus mechanically ruled varied-line-spacing grating

Comparative studies have been made on the holographic plane grating and the ruled varied-line-spacing (VLS) plane grating designed for two kinds of objective Monk-Gillieson type high-resolution grazing incidence monochromator, I and II. The ray-traced performance of monochromator types I and II on a synchrotron radiation beam line was evaluated in terms of resolving power and spectral purity by the introduction of new concepts of effective Gaussian line and purity profiles. The resolving power defined on the basis of the effective Gaussian profile is consistent with the spectral purity of the beam emerging from the exit slit and is more realistic as compared with those defined in the conventional manner, especially when spectral images have asymmetric profiles. It is concluded that holographic plane gratings recorded with a spherical and an aspheric wave front are capable of providing high resolution with high spectral purity and are fully interchangeable with the corresponding ruled VLS plane gratings. This interchangeability provides more flexibility for users in choosing a proper grating for a high-resolution grazing incidence monochromator of the Monk-Gillieson type.

Development of a pumping laser system for x-ray laser research

A two-beam chirped-pulse-amplification Nd:glass laser system dedicated to x-ray laser research is described. Each beam provides an output energy of 20 J with a typical pulse duration of 1.3 ps. A prepulse of variable duration is generated by use of a novel, to our knowledge, optical system. A reflection optical system, comprised of an off-axis parabolic mirror and a spherical mirror, produces a line focus with 6-mm length and 165-microm width without chromatic aberration. By use of this pumping laser system, the nickel-like silver x-ray laser at a wavelength of 13.9 nm has been demonstrated.

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.

Performance of a reflection-type polarizer by use of muscovite mica crystal in the soft x-ray region of 1keV

To develop the polarizer functioning in the soft x-ray region of 1keV, the polarization performance of muscovite mica has been investigated theoretically with a simulation code based on dynamical theory. As the result of calculation, muscovite mica is found to be a promising candidate as a reflection-type polarizer with the reflectivity for s polarization of 0.03 at approximately 0.9keV at the angle of incidence of 45°. In order to verify the polarization performance of muscovite mica experimentally, a symmetric Bragg reflection measurement of muscovite mica(002) was carried out using a linearly polarized undulator radiation. As a result, the maximum reflectivity for s polarization and the extinction ratio of muscovite mica were approximately 0.018 and 200 at 878eV, respectively. This result indicates that muscovite mica works as a practical polarizer in the soft x-ray region.

Dispersive x-ray absorption spectroscopy with gratings above 2 keV

Laminar gratings can be used to perform x-ray absorption measurements dispersively in energy, thereby making an efficient use of the available x-ray intensity. To examine the performance of a laminar grating in diffracting short wavelength x rays, efficiency measurements of a 600l∕mm grating were performed over the photon energy range from 3 to 8 keV. A peak efficiency of 5.8% was observed without surface normal rotation (SNR); with a SNR of 60° a maximum efficiency of 14.1% was measured. The measured grating efficiencies are in good qualitative agreement with values calculated by a code based on the Neviere theory. By considering both the peak efficiency and the diffracted bandwidth, a gain of 97 is obtained for the 600l∕mm grating with a SNR of 60° in comparison with a germanium (111) crystal. Sufficient energy resolution for extended x-ray absorption fine structure experiments can be achieved by a grating at short wavelengths.

Grazing-incidence Monk-Gillieson monochromator based on surface normal rotation of a varied-line-spacing grating.

A geometric theory of a grazing-incidence varied-line-spacing plane-grating monochromator system whose scanning is made by a simple grating rotation about the grating normal has been developed for designing Monk-Gillieson monochromators capable of covering an energy range of 0.6-2.5 keV. Analytic expressions are given for the grating equations, focal conditions, dispersion, spectral image shape, and optimization of groove parameters. On the basis of the theory, two monochromator systems have been designed: system I for moderate resolution and system II for relatively high resolution. The validity of the analytic formulas and the expected performance of the designed systems have been evaluated by means of ray tracing. The results show that the analytic formulas are sufficiently accurate for practical applications and that systems I and II would provide resolving power of approximately 1450-600 and 7500-2000, respectively, in the wavelength region of 0.5-2.0 nm.

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.

Application of hybrid design method to VUV double-element optical systems equipped with holographic gratings recorded with aspheric wavefronts

A design method, called the hybrid design method, is applied to the design of(1) a zero-dispersion and constant-devialion type doub1egrating predisperser system for a VUV high-resolulion off-plane Eagle spectrometer which utilizes a high-order spectrum and (2) a wide-aperture Wadsworth4ype VtJV imagng spectrograph which consists of aspheric mirror and grating. The gralings of these systems are holographic gralings recorded with aspheric wave fronts. The results Obtained show the effectiveness of the hybrid design method and the versatile applicability ofa holographic grating recorded with asphenc wave fronts.