Ultrafast Self-Induced X-Ray Transparency and Loss of Magnetic Diffraction

Z. Chen, D. J. Higley, M. Beye, M. Hantschmann, V. Mehta, O. Hellwig, A. Mitra, S. Bonetti, M. Bucher, S. Carron, T. Chase, E. Jal, R. Kukreja, T. Liu, A. H. Reid, G. L. Dakovski, A. Föhlisch, W. F. Schlotter, H. A. Dürr, and J. Stöhr

Phys. Rev. Lett. 121, 137403 – Published 28 September 2018

Abstract

Using ultrafast $≃ 2.5 fs$ and $≃ 25 fs$ self-amplified spontaneous emission pulses of increasing intensity and a novel experimental scheme, we report the concurrent increase of stimulated emission in the forward direction and loss of out-of-beam diffraction contrast for a $Co / Pd$ multilayer sample. The experimental results are quantitatively accounted for by a statistical description of the pulses in conjunction with the optical Bloch equations. The dependence of the stimulated sample response on the incident intensity, coherence time, and energy jitter of the employed pulses reveals the importance of increased control of x-ray free electron laser radiation.

Received 17 May 2018

DOI:https://doi.org/10.1103/PhysRevLett.121.137403

Physics Subject Headings (PhySH)

Electronic structure Light-matter interaction Magneto-optical effect

Magnetic multilayers

Coherent control X-ray absorption spectroscopy X-ray diffraction

Condensed Matter, Materials & Applied PhysicsAtomic, Molecular & Optical

Authors & Affiliations

Z. Chen¹, D. J. Higley², M. Beye³, M. Hantschmann⁴, V. Mehta⁵, O. Hellwig^6,7, A. Mitra^8,9, S. Bonetti¹⁰, M. Bucher⁸, S. Carron⁸, T. Chase¹¹, E. Jal⁸, R. Kukreja¹², T. Liu¹, A. H. Reid⁸, G. L. Dakovski⁸, A. Föhlisch⁴, W. F. Schlotter⁸, H. A. Dürr^8,13, and J. Stöhr^14,*

¹Department of Physics, Stanford University, Stanford, California 94305, USA
²Department of Applied Physics, Stanford University, Stanford, California 94305, USA
³Department of Photon Science, DESY, Notkestraße 85, D-22607 Hamburg, Germany
⁴Department of Materials and Energy Science, Helmholtz Zentrum Berlin, D-14109 Berlin, Germany
⁵San Jose Research Center, HGST a Western Digital company, San Jose, California 95135, USA
⁶Institute of Physics, Technische Universität Chemnitz, D-09107 Chemnitz, Germany
⁷Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany
⁸SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
⁹Department of Physics, University of Warwick, CV4 7AL Coventry, United Kingdom
¹⁰Department of Physics, Stockholm University, S-10691 Stockholm, Sweden
¹¹Department of Applied Physics, Stanford University, Stanford, California 94305, USA
¹²Department of Materials Science and Engineering, University of California Davis, Davis, California 95616, USA
¹³Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
¹⁴SLAC National Accelerator Laboratory and Department of Photon Science, Stanford, California 94035, USA

^*stohr@stanford.edu

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 121, Iss. 13 — 28 September 2018

Reuse & Permissions

Access Options

Article Available via CHORUS

Download Accepted Manuscript

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Experimental geometry for simultaneous pulse-by-pulse measurements of the transmitted and diffracted response of a $Co / Pd$ thin film. Incident SASE pulses of $\sim 2.5 fs$ or $\sim 25 fs$ length are focused onto the sample plane and split by the sharp edge of a mirror, with one half propagating through a $Co / Pd / SiN$ sample in a picture frame and the other through a pure SiN reference film for normalization purposes. The horizontal magnetic stripe domains in $Co / Pd$ produce strong first and third order Bragg diffraction peaks on a pnCCD detector [11]. The spatially separated undiffracted beams are allowed to propagate into a downstream spectrometer. A grating disperses the two offset beams onto a yttrium aluminum garnet (YAG) fluorescence screen, yielding separate single-shot sample and reference spectra around the Co $L_{3}$ resonance. The shown spectra and diffraction images are real data averaged over several pulses.
Reuse & Permissions
Figure 2
Normalized transmission signal $S = C (S^{'} - 1) + 1$ defined in the text for three different incident intensities around the Co $L_{3}$ resonance for a $Co / Pd$ multilayer sample. Each spectrum represents an averaged spectrum across multiple shots in a certain fluence range. With increasing intensity the absorption peak (clearly visible at lower intensities) is suppressed and has vanished at the highest intensity of $1600 mJ / {cm}^{2} / fs$ , revealing x-ray transparency.
Reuse & Permissions
Figure 3
Top: Experimentally observed change in the transmitted intensity as a function of incident intensity (solid blue circles and line). Each data point is an average over multiple shots. The open blue circles correspond to the simulated shot-by-shot response using the stimulated forward scattering model discussed in the text. Bottom: Observed shot-by-shot out-of-beam diffracted intensity due to magnetic domains (solid red circles) plotted on a log scale to emphasize the large statistical noise due to the used SASE pulses. Simulated data are shown as open red circles. The shown experimental and simulated data consist of an equal number of single-shot pulses of 2.5 fs and 25 fs duration.
Reuse & Permissions
Figure 4
Simulations juxtaposed with experimental data for various beam parameters. Top: Simulations and data for 2.5 fs SASE pulses, with a representative simulated pulse plotted in the inset. Bottom: Simulations and data for 25 fs SASE pulses with (blue) and without (red) monochromatization, with representative simulated pulses for both cases plotted in the insets. The response of the longer 25 fs SASE pulses follows the same mean value as the response of the shorter 2.5 fs pulses, but with lower standard deviation by a factor of $\approx \sqrt{10}$ , consistent with our independent SASE spike assumption. Monochromatized data utilizing 50 fs pulses are taken from Ref. [10].
Reuse & Permissions
Figure 5
Summary results of the observed transmission (blue) and magnetic diffraction (red) contrast relative to the flat conventional spontaneous response as a function of incident intensity.
Reuse & Permissions

Physical Review Letters