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Spectral narrowing of x-ray pulses for precision spectroscopy with nuclear resonances

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Science  28 Jul 2017:
Vol. 357, Issue 6349, pp. 375-378
DOI: 10.1126/science.aan3512
  • Fig. 1 Increasing the resonant x-ray brilliance.

    (A) The interaction of x-rays with a static target containing a narrow resonance usually imprints a resonant absorption dip onto the spectrum, accompanied by broadband electronic absorption (blue curve, compared to the gray normalized input spectrum). Here, we manipulate this interaction such that off-resonant photons are redistributed onto resonance. As a consequence, the resonant intensity of the x-rays is substantially enhanced while the undesired off-resonant background is reduced (red curve). (B) This manipulation is achieved by mechanically displacing the target immediately after excitation. With motion (red), a time-dependent phase is imprinted onto the scattered light (blue). This modifies the interference with the unscattered light (yellow), making it possible to tailor the spectrum of the resulting x-ray pulse.

  • Fig. 2 Experimental setup and results.

    (A) Short x-ray pulses (yellow) impinge on a 57Fe target (purple), which is displaced immediately after excitation by a piezo (gray). As a spectral analyzer, we used a 57Fe single-line absorber on a Doppler drive, which allowed us to adjust the detuning ΔD between target and analyzer via its velocity v. APD, avalanche photodiode. (B) Two approximately opposite piezo motions (red, blue) as function of time, reconstructed from the measurements. (C) Selection of spectra recorded as a function of ΔD. Data are shown for the two motions from (B) (blue, red) and for the target at rest (black); solid lines show theoretical fits. The two panels differ in the integration range over photon arrival times after the excitation. Photon shot-noise errors are within the marker size. (D) Reconstructed x-ray pulse spectra behind the piezo target. Without motion, two hyperfine absorption lines are obtained (black). With motion, the spectral intensity considerably exceeds the incident intensity on resonance [blue, red; colors as in (B) and (C)]. Gray shaded areas indicate regions out of which spectral intensity is redistributed onto resonance (indicated by dashed arrows).

  • Fig. 3 Cascading of two piezo stages.

    (A) Spectrum generated with two 57Fe targets on separate piezo stages (green) and the corresponding spectra for the respective single piezo stages (red, blue). (B) The two respective motional patterns redistribute spectral power from different off-resonant regions onto resonance [dashed arrows in (A)]. Thus, the combination of the two stages increases the resonant intensity beyond what is achieved with a single piezo (red, blue). (C) Measured spectrum for the two-piezo setup. The solid line shows the corresponding theoretical prediction. Photon shot-noise errors are within the marker size.

Supplementary Materials

  • Spectral narrowing of x-ray pulses for precision spectroscopy with nuclear resonances

    K. P. Heeg, A. Kaldun, C. Strohm, P. Reiser, C. Ott, R. Subramanian, D. Lentrodt, J. Haber, H.-C. Wille, S. Goerttler, R. Ruüffer, C. H. Keitel, R. Röhlsberger, T. Pfeifer, J. Evers

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Supplementary Text
    • Figs. S1 to S7
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