The interactions of short pulse lasers with matter are interesting subjects not only in applications such as surface fabrication but also in physical phenomena for study. Optical short pulse lasers have abilities to occur the ablation phenomena accompanying the creation of high temperature, high pressure, and excited states of electrons. The picosecond soft x-ray laser (SXRL) pulse also has ability to occur the ablation. The SXRL having the wavelength of 13.9 nm and duration of 7 ps is one of attractive x-ray source for ablation study, because the ablation threshold obtained with the focused SXRL pulse is much smaller than those obtained with other lasers having longer durations and/or longer wavelengths. The low ablation threshold of a material for the SXRL beam has a possibility of efficient nanometer scale surface machining by an ablation. The ablation study will lead to the physical research and the direct surface machining. In addition, the wavelength of the SXRL is very close to the wavelength of the extreme ultraviolet (EUV) lithography system (λ = 13.5 nm). In the presentation, we report on development of the soft x-ray laser irradiation system. The irradiation system has an intensity monitor based on the Mo/Si multilayer beam splitter. This intensity monitor provides the irradiation energy onto sample surface. The SXRL has an ability to confirm the ablation threshold and to examine the damage property of EUV optical elements, which have the same specifications of those in the EUV lithography. And more, it is possible to evaluate the doses for sensitivity of resists.
Mo/Si multilayer mirror with 300-bilayers for EUV lithography is developed for the purpose of long-lifetime use in LPP EUV source. The multilayer mirrors are fabricated by a magnetron sputtering method and are characterized by coherence scanning interferometry, XRR and EUV reflectometer. The results show the excellent performance of 320 layer pair multilayer being useful for EUV multilayer mirror.
A multilayer coating mirror of Mo/Si is usually integrated into an EUV optics for space science, especially for He-II (30.4 nm) radiation, because it is highly stable under vacuum and atmosphere and achieves the fairly high reflectance of 15-20%. But space science community needs the coating of higher reflectance at 30.4 nm radiation for the future satellite missions. In this work, to develop a new multilayer mirror of He-II radiation, we report the design of a multilayer consisting of a pair of Mg and SiC, and its production, and aging change of the reflectance under the atmosphere and vacuum circumstance.
The development of hard X-ray focusing optics is widely recognized as
one of key technologies for future X-ray observatory missions such as
NeXT(Japan), Constellation-X(US) and possibly XEUS(Europe). We have developed hard X-ray telescope employing depth-graded multilayers, so-called supermirrors. Its benefit is to reflect hard X-rays by Bragg reflection at incidence angles larger than the critical angle of total external reflection. We are now continuously fabricating platinum-carbon(Pt/C) supermirror reflectors for hard X-ray observations. In this paper we focus on our development of the
hard X-ray telescope for the first balloon flight observation
(InFOCuS) and its results. InFOCuS is an international balloon-borne hard X-ray observation experiment initiated by NASA/GSFC. InFOCuS hard X-ray telescope have been jointly developed by Nagoya University and GSFC. The telescope is conical approximation of Wolter-I optics with 8m focal length and 40cm diameter. It consists of 255 nested ultra-thin reflector pairs with incidence angles of 0.10 to 0.36deg. Reflectors are coated with Pt/C supermirrors with periodic length of 2.9 to 10nm and bi-layer number of 25 to 60, depending on incidence angles. The effective area and imaging quality are expected as 100 cm2 at 30 keV and 2 arcmin in half power diameter, respectively. The InFOCuS experiment was launched on July 5, 2001, from National Scientific Balloon Facility in Texas, USA. We successfully observed Cyg X-1, chosen for a calibration target, in 20-40keV energy band. We are planning to carry out next flight for scientific observations as soon as additional telescopes, detectors, and upgraded gondola system are implemented.
We have been developing the high throughput hard X-ray telescope, using reflectors coated with the depth graded multilayer known as supermirror, which is considered to be a key technology for future satellite hard X-ray imaging missions. InFOC(mu) $S, the International Focusing Optics Collaboration for (mu) -Crab Sensitivity is the project of the balloon observation of a cosmic hard X-ray source with this type of hard X-ray telescope and CdZnTe pixel detector as a focal plane imager. For the fist InFOC(mu) S balloon experiment, we developed the hard X-ray telescope with outermost diameter of 40cm, focal length of 8m and energy band pass of 20-40 keV, for which Pt/C multilayer was used. From the pre-flight X-ray calibration, we confirmed its energy band and imaging capability of 2 arcmin HPD and 10 arcmin FOV of FWHM, and a effective area of 50 cm2 for 20-40 keV X-ray. We report the current status of our balloon borne experiment and performance of our hard X-ray telescope.
Mass production of replicated thin aluminum x-ray reflecting foils for the InFOC(mu) S (International Focusing Optics Collaboration for Micro-Crab Sensitivity) balloon payload is complete, and the full mirror has been assembled. InFOC(mu) S is an 8-meter focal length hard x-ray telescope scheduled for first launch in July 2001 and will be the first instrument to focus and image x-rays at high energies (20-40 keV) using multilayer-based reflectors. The individual reflecting elements are replicated thin aluminum foils, in a conical approximation Wolter-I system similar to those built for ASCA and ASTRO-E. These previous imaging systems achieved half-power-diameters of 3.5 and 1.7-2.1 arcminutes respectively. The InFOC(mu) S mirror is expected to have angular resolution similar to the ASTRO-E mirror. The reflecting foils for InFOC(mu) S, however, utilize a vertically graded Pt/C multilayer to provide broad-band high-energy focusing. We present the results of our pre-flight characterization of the full mirror, including imaging and sensitivity evaluations. If possible, we will include imaging results from the first flight of a multilayer-based high-energy focusing telescope.
We studied about new design of supermirror and inerfacial roughness for the X-ray telescope above 40 keV. We have developed hard X-ray telescope above 10 keV using platinum-carbon multilayer supermirror. In our balloon borne experiment, named InFOC(mu) S launched in this June, the supermirror expand the upper-limit of energy band of X-ray telescope up to 40 keV. We are trying to improve supermirror design to have energy band up to 70 keV. In previous design, the absorption of upper layers and lower-limit of layer thickness prevent us to extend the energy band. In this paper, we optimize design parameters of supermirror and use second Bragg peak, and we obtained high reflectivity up to 70 keV. We studied about interfacial roughness of platinum-carbon multilayer to design the supermirror, because the interfacial roughness is very serious problem such high energy region. In many cases, simple Debye-Waller factor can't represent measured reflectivity. We introduced two different roughness for Pt/C and C/Pt interfaces. This model well fit the data and make us possible to design the supermirrors.
We measured Pt/C multilayers and supermirrors with hard X-rays at synchrotron radiation facility SPring-8. These mirrors were fabricated for the hard X-ray telescope on board our balloon- borne experiment named InFOC(mu) S. The energy band of InFOC(mu) S telescope is from 20 to 40 keV, thus characterization of reflectors with hard X-rays above 20 keV is important. SPring-8 is one of the world's most powerful third-generation synchrotron radiation facility. We measured multilayers and several types of supermirrors. We also measured reflectivity of supermirrors on three different kind of substrates; float grass, gold replica foil and platinum replica foil. From the reflectivity measurements, performance of these supermirrors was found quite satisfactory for our telescope. Furthermore platinum replica foil substrate showed significantly better reflectivity than gold replica foil. Thus we chose platinum replica foil as a substrate for flight reflectors. Scattering measurements gave us important informations. Our preliminary analysis showed that the scattered power distribution can be explained as a convolution of structures in lateral and depth direction.
We have been developing high throughput X-ray telescope for hard X-ray region (20 - 40 keV) using Pt/C multilayer supermirrors for balloon borne experiment launched in 2001 June. The Walter type I telescope consists of about 2,000 supermirrors coated on very thin (150 micrometer) aluminum foils. We started mass production of the supermirror reflectors. Two different method is used for fabrication process. One is multilayer deposition on the platinum replica foil, and the other is direct replication of supermirror. The performance of the supermirrors are measured in X-ray beam line in Nagoya University and synchrotron radiation facility SPring-8. We obtained 30% reflectivity at 30 keV, corresponding to 0.35 nm interfacial roughness by Debye-Waller factor. The performance of multilayer supermirrors indicate that we can achieve about 100 cm2 effective area for a telescope.
High sensitivity hard X-ray data by means of focusing optics is crucially important to investigate active galaxies and cluster of galaxies. We have developed focusing telescopes with platinum-carbon multilayer coatings. The energy band is broadened by multilayers with graded periodic length, so called `Supermirrors'. We were successful to obtain hard X- ray images in the energy band from 25 to 40 keV with a demonstration model of telescope with 20 mirror shells of supermirrors. The flight model of supermirror telescope is now in production for balloon flight in the summer of 2000. The current status of the balloon mission and future application of supermirror technology is discussed.
It is important to enhance the reflectivity of multilayer supermirrors in 10-100 keV region used for hard x-ray optical systems. For this purpose design methods of multilayer supermirrors have been investigated at the grazing angle of 0.3 degrees by means of the x-ray etalon or phase matching configuration. It means that the 1st and higher order Bragg reflections emanated from different periodic lengths cooperatively enhance the reflectivity at energy bands concerned. The x-ray etalons method is useful for multi-band mirror with the band width of 5 keV or so, but becomes a bit difficult to make the energy band wider connecting gaps between isolated bands. Because heavy oscillation of reflectivity curve occurs due to adjacent destructive and constructive interference. The phase matching method is useful to get smooth reflectivity in the broad energy band and is possible to enhance the 2nd order Bragg reflection in higher energy region. We present the design of hard x-ray telescope sensitive in 25-40 keV region by means of multi-block supermirrors of Pt/C multilayers. The effective area was obtained to be more than 100 cm2.