Focusing mirror

The dispersing element is a diffraction grating preferably used under conditions of grazing incidence (6 in Equation 3.9 about 89°) to improve the reflectance. The grating may also be concave to avoid the use of a focusing mirror. 

The experiment was performed following the procedure described in Sect. 4.4. Here we used a lens (/ = 2,400 mm) rather than a focusing mirror (/ = 5,000mm), and to determine the propagation effect Ipr0p(wq), a short gas cell (L = 15 mm) was adopted for HHG. The on-target intensity of the fundamental pulses was estimated to be Jir 2 x 1014 Wcm-2. 

Bloomer, A. C. and Arndt, U. W. (1999). Experiences and expectations of a novel X-ray microsource with focusing mirror. I. Acta Crystallogr. D 55,1672-1680. 

The curvature of a wavefront appears transformed into the curvature of a mirror surface shaped so that it would focus the total wavefront into the point of ohservation.The reason is that a focusing mirror reflects light in such a way that the total wavefront arrives to the focal point at one point of time. Thus, a small flat wavefront that passes by will appear tilted at 45°. A larger flat wavefront will not only appear tilted but will also be transformed into a paraboloid whose focal point is the point of observation. A spherical wavefront appears transformed into an ellipsoid, where one focal point is the point source of light (A) and the other is the point of observation (B). This configuration represents one of the ellipsoids of the holodiagram. 

We describe in the following sections how sub-pj-level high-order harmonic beams can be well-focused to a micron spot size, resulting in intensities of 1013—1014 W/cm2. Various focusing mirrors, as shown in Table 9.1 are tested and used in the focusing experiment. 

Table 9.1. Specifications of the focusing mirrors used in the experiment...

There are three accessories used to produce monochromatic radiation metal foil filters, crystal monochromators, and focusing mirrors. An element with atomic number Z can be used as a selective filter for radiation produced by an element of atomic number Z+ 1. For example, a nickel (Z=28) absorption filter, may be used to cut out the Cu KjS (Z=29 for Cu) radiation, leaving only Cu Ka radiation.Not all white radiation, however, is eliminated by this method. Alternatively a single-crystal monochromator may be used. An intense Bragg reflection from the monochromator crystal is used as the incident beam for X-ray diffraction studies. Focusing mirrors, designed to produce a beam that is not only monochromatic but also convergent, may be used. In this case the incident beam is doubly deflected by two perpendicular mirrors. 

Focusing mirror system Two bent metal mirrors that deflect the X-ray beam and produce a small intense beam with a narrow angular divergence, uniform beam profile and a low background intensity. They are useful for experiments involving crystals with large unit cells. 

Phillips, W. C., and Rayment, I. A systematic method for aligning double-focusing mirrors. Methods in Enzymology. 114, 316-329 (1985). 

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