Spectrally narrow X-ray pulses by manipulating Mössbauer resonance

A research group led by Professor Jorg Evers (Max Planck Institute for Nuclear Physics, Heidelberg, Germany) has recently reported a method for narrowing the spectral width of X-ray pulses by the use of subluminal light propagation. So far, in visible light, slow group velocity such as 17 m/sec has been observed in low temperature sodium gas at 435 nK (see, L. V. Hau et al., Nature, 397, 594 (1999)). The authors intend a similar effect in X-ray wavelength photons by manipulating the optical response of the 14.4 keV Mössbauer resonance of ⁵⁷Fe nuclei. The method combines coherent control, as well as cooperative and cavity enhancements of light-matter interaction in a single setup. It was found that the reduced group velocity of the obtained X-ray pulses is lower than 10^-4 of the speed of the light. For more information, see the paper, "Tunable Subluminal Propagation of Narrow-band X-Ray Pulses", K. P. Heeg et al., Phys. Rev. Lett. 114, 203601 (2015).