Parametric down-conversion is a quantum-optical process in which a 'pump' photon splits spontaneously into two (the 'signal' and 'idler') in a nonlinear optical medium. Recently, Professor T. Ishikawa (RIKEN, Harima, Japan) and his colleagues reported their experiments with X-ray photons. They have visualized three-dimensionally the local optical response of diamond at wavelengths between 103 and 206 Å with a resolution as fine as 0.54 Å. This corresponds to a resolution from λ/190 to λ/380, an order of magnitude that is the best ever achieved. For more information, see the paper, "Visualizing the local optical response to extreme-ultraviolet radiation with a resolution of λ/380", K. Tamasaku et al., Nature Physics 7, 705 (2011).
