X-ray and optical wave mixing

• Published in: Nature (London) 2012-08, Vol.488 (7413), p.603-608
• Main Authors: Glover, T. E., Fritz, D. M., Cammarata, M., Allison, T. K., Coh, Sinisa, Feldkamp, J. M., Lemke, H., Zhu, D., Feng, Y., Coffee, R. N., Fuchs, M., Ghimire, S., Chen, J., Shwartz, S., Reis, D. A., Harris, S. E., Hastings, J. B.
• Format: Article
• Language: English
• Subjects: 639/766/25; 639/766/36; 639/766/400; 639/766/400/1106; Biochemistry, Molecular Biology; Biophysics; Efficiency; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Humanities and Social Sciences; Life Sciences; multidisciplinary; Nonlinear optics; Optics; Phase conjugation, optical mixing; photorefractive and kerr effects; Physics; Science; Science (multidisciplinary); Semiconductors; X-rays
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature11340

Light–matter interactions are ubiquitous, and underpin a wide range of basic research fields and applied technologies. Although optical interactions have been intensively studied, their microscopic details are often poorly understood and have so far not been directly measurable. X-ray and optical wave mixing was proposed nearly half a century ago as an atomic-scale probe of optical interactions but has not yet been observed owing to a lack of sufficiently intense X-ray sources. Here we use an X-ray laser to demonstrate X-ray and optical sum-frequency generation. The underlying nonlinearity is a reciprocal-space probe of the optically induced charges and associated microscopic fields that arise in an illuminated material. To within the experimental errors, the measured efficiency is consistent with first-principles calculations of microscopic optical polarization in diamond. The ability to probe optical interactions on the atomic scale offers new opportunities in both basic and applied areas of science. A free-electron laser provides a sufficiently intense source of X-rays to allow X-ray and optical wave mixing, here demonstrated by measuring the induced charge density and associated microscopic fields in single-crystal diamond. Now X-rays and light do mix Interactions between light and matter are central to many areas of science, but the microscopic details of how light can change matter remain unclear because of observational difficulties. These details can be probed by mixing X-rays and optical waves, an X-ray-scattering process that was proposed nearly half a century ago, but was beyond the technology of the time. Now, with the advent of free-electron lasers, X-rays of sufficient intensity have become available. In this week's Nature , Ernie Glover et al ., working with the Linac Coherent Light Source, report X-ray and optical mixing (or sum-frequency generation) in diamond. The new capability may enable direct visualization of the making and breaking of chemical bonds.