Coherent soft x‐rays in high resolution imaging

To illustrate the coherence problems in x‐ray imaging we examine −scanning x‐ray microscopy −holography, and soft x‐ray diffraction as illustrating examples. We show that only x‐rays from within the emittance xx’yy’<(2.44l)2 have the necessary spatial coherence to yield diffraction‐limited images. The degree of temporal coherence required depends on the nature of the imaging system, and the size of the specimen. In conventional x‐ray systems, spatial coherence is generated by collimation, while temporal coherence is achieved with monochromators. In these systems, then, one filters out a minute coherent fraction of an intense incoherent beam. Aside from the inefficiency of the procedure, there is a practical limitation of the temporal coherence length of about 103λ that one can generate this way in the soft x‐ray regime.A coherent source, with sufficient flux, and a large coherence‐length would open up new possibilities in soft x‐ray interferometry and holography. With beams of great brilliance, very high ...