Figure 7

Layout of focusing optics using ellipsoidal mirrors. (a) Focusing optical system with a large N.A. X-rays from the light source (f₁) are reflected by two ellipsoidal focusing mirrors (M_e1 and M_e2) that face each other. Then, the reflected X-rays are two-dimensionally focused at one focal point (f₂). This optics can be designed to have a small diffraction-limited focus size compared with the focusing optics that uses a single ellipsoidal mirror, as a result of the large N.A. For example, N.A. is 0.0207, which is calculated from a convergence angle (2θ _m ) of 41.5 mrad, when the ellipsoidal focusing mirrors designed in the present work are used. The diffraction-limited focus size (δ) can be roughly estimated in the present case using the well-known formula⁵⁹ δ = 0.61 × λ/N.A., where λ is the wavelength of light. Therefore, δ is calculated as 5.2 and 1.8 nm (FWHM) when λ is 0.177 nm (7 keV) in the case of the total reflection mirrors and 0.062 nm (20 keV) in the case of multilayer mirrors, respectively. (b) Upstream optics for the (a) optical system to produce two divergent beams. The X-rays from the primary light source (f₀) are reflected and divided into two beams by the two plane surfaces (S_p1 and S_p2) with different incident angles. Then, the two beams are two-dimensionally focused at point f₁ by the two ellipsoidal surfaces (S_e1 and S_e2) and become two divergent beams. The two-step focusing optics with the (b) upstream and (a) downstream optics can be designed using common focus f₁ as a secondary light source for the (a) optical system. However, the intensities in the core region of the incident beam are lost when one large incident beam illuminates the two ellipsoidal mirrors (M_e1 and M_e2) in (a) the optical system. This event can be avoided using (b) the optical system with two divergent beams. In addition, the two-step focusing optics can have a large demagnification ratio, which is essential for nanofocusing optics.