Soft X-ray Bunching Lens Characteristics

The basic purpose of the X-ray lens is to obtain maximum density of the X-ray radiation at the focus of the system. The X-ray transmission property of capillary is the basis for designing X-ray lens. In order to design the X-ray lens to obtain a sufficiently high concentration of X-ray radiation, the transmission character of X-ray through bending capillary is theoretically studied, experiments are carried out to measure the transmission coefficient and the parameters of the X-ray lens are optimized. As a result, the X-ray lens was made in our laboratory and experiments are carried out to study the focusing property of the new lens with the help of laser plasma as the source of soft X-ray radiation.Based on the theory of X-ray transmission through capillary, a ray-tracing method is suggested in this paper. A corresponding computer program is worked out to calculate the transmission efficiency and intensity distribution through a curve capillary. It is shown that the transmission efficiency reduces as capillary diameter increases, and increases as capillary curvature increases. The transmission efficiency generally reduces as the photo energy increases, which curve goes evenly in the "water window' and drops sharply to K-absorption line of oxygen.The experimental results of measuring transmission efficiency within the energy range from 50eV to 1.5keV for a variety type of capillaries are presented, including different materials, different inner radius, different bent radius. It is shown that the transmission efficiency of curved capillary decreases as the X-ray energy increases, increases with the inner diameter of capillary, decreases as the bend radius of curved capillary increases. As a result, capillary manufactured of glass DM308 with inner diameter 0.45mm and outer diameter 0.60mm is the best choice for soft X-ray lens.The X-ray lens made at our laboratory consists of 1387 glass capillaries with an outer diameter of 0.6 mm, and a channel diameter of 0.45mm. The radiation capture angle is 28.9°. The focal distance is 50mm. The total lens length is 400mm. The capillaries are made of glass DM308.The focal spot diameter is about 2mm, where the maximum density of X-ray radiation 1.3 × 10~5W/cm~2 can be obtained by laser plasma. 0.8‰ of the maximum power of the source can be obtained at the output of the system, thus the transmission coefficient of the system is 4.7% and the density at the focal spot during focusing increases by a factor of 825. That result shows that at a distance of 500mm from the isotropic source the lens under consideration will give the same radiation density as that of an isotropic source without lens produces at the distance of 17.8mm. As to the total energy of the X-ray radiation, the focusing characters are as follow: 1.3‰ of the total energy of the radiation can be obtained at the output of system, the transmission coefficient is 7.4%, the density at the focal spot during focusing increases by a factor of 1297 and the same distance where the same density can be obtained without lens is about 14.2mm.