ESRF-EBS-NRS Workshop, Grenoble, 11 - 13 March 2019 Sharpening spectral resolution and polarization purity of hard x-rays at the ESRF-EBS Ralf Röhlsberger Deutsches Elektronen-Synchrotron DESY, Hamburg
Outline (1) Structure and dynamics of complex materials on mesoscopic length scales (2) Vibrational spectroscopy with µ eV resolution (3) Enabling technology: High purity polarimetry (4) Applications of high purity polarimetry Revealing anisotropies in condensed matter • Spinwave spectroscopy • (5) Outlook: High-energy polarimetry | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 2
The quest for x-rays with Energy Length A ´complex´ system Time ultrasmall emittance: 10 µ m Understanding dynamics Milli- peV seconds on mesoscopic length scales 1 µ m Emergence Mesocosmos Micro- neV 100 nm seconds Self-Organization 10 nm Nano- µ eV seconds Composites 1 nm Pico- meV seconds A ´simple´ system 0.1 nm (atom, molecule) Femto- eV seconds | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 3
Vibrational dynamics on mesoscopic length scales (1 nm – 100 nm) Nanocomposites Artificially structured materials Photonic and phononic crystals | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 4
Dynamics of artificially structured materials Dynamical properties are modified due periodic variation of elastic properties Phononic crystal This allows to tailor the vibrational properties of new 10 materials by adjusting their structure Energy ( µ eV) à Nanocomposites 5 (e.g. metal/polymer, amorphous/crystalline) Vibrational excitations play an 0 important role for energy dissipation upon friction T. Gorishnyy et al., Phys. Rev. Lett. 94, 115501 (2005) | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 5
| Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 6
Enabling Technology: High-purity Polarimetry Crossed polarizers for hard X-rays Collaboration with I. Uschmann, Anisotropy G. Paulus et al., FSU + HI Jena à optical activity Si Polarization Purity Efficient selection of s à p scattering δ = # $ /# & = 10 )*+ … 10 )- • Detection of very weak anisotropies • (linear, circular) B. Marx et al., Opt. Commun. (2011) 4-bounce polarizer for 14.4 keV (B. Marx et al.) Phys. Rev. Lett. (2013) H. Bernhardt et al., Appl. Phys. Lett (2016) | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 7
Optical activity in (nuclear ) f n ( ω ) resonant scattering Magnetic hyperfine interaction f n ( ω ) Electric hyperfine interaction | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 8
High-resolution inelastic scattering with µ eV-resolution APD Spectrometer principle array sample analyzer Si(840) 10 µ m 57 Fe Rotating mirror, coated polarizer Analyzer with 57 Fe, for Doppler shifting Energy scan by transverse displacement of disk 20 µ m f = 20000 rpm 2 cm Scanning ∆ E = ± 1 meV Spectrometer throughput range Polarizer and spectral resolution δ E = 2 µ eV Energy are determined by the band width source parameters ! F ~ 10 7 ph/s Photon flux | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 9
ESRF-EBS Source Parameters 4 m undulator (18 mm period, k = 2) à Improvements at ID18 mostly due to the small horizontal source size | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 10
Polarimetry at ultralow-emittance storage rings Small source size + collimation à small horizontal beam cross section and small divergence Refractive collimator point source plane wave CRL A. Q. R. Baron et al., Appl. Phys. Lett. 74, 1492 (1999) Collimation down to 1 µ rad seems feasible at the ESRF-EBS Values < 1 µ rad in combination with asymmetric Bragg reflections | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 11
The quest for ultrahigh purities: Polarization of the Vacuum Z. Physik 98, 714 (1936) „ … even in situations where the photon energy is not sufficient for matter production, its virtual possibility will result in a � polarization of vacuum � and hence in an alteration of Maxwell � s equations“ à vacuum becomes birefringent Photon-photon scattering | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 12
Detection of Vacuum Birefringence: Probing the quantum vacuum Ellipticity high-power laser z 0 I 0 Δ φ = 4 α 15 I C λ a fine structure constant z 0 interaction length l probe wavelength x-ray beam I 0 electric laser field I C critical field for pair polarizer analyzer production = 4.4 x 10 29 W/cm 2 for I 0 = 10 22 W/cm 2 and l = 1 Å à ellipticity < 10 -12 expected à Purities d ~ 10 -12 required T. Heinzl, R. Sauerbrey et al., Opt. Commun. 267, 318 (2006) | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 13
| Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 14
Fundamental limitations of the polarization purity (a) Multiple wave diffraction s à p polarization transfer limits the purity for multiple reflections (b) Beam divergence For a Gaussian beam with H/V divergencies s H and s V : Polarization purity d ~ 10 -12 for s V , s H ~ 1 µ rad | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 15
Charge anisotropy in a iron spin crossover (SCO) compound Collaboration with L. Scherthan, J. Wolny, V. Schünemann (TU Kaiserslautern) [Fe(PM-BiA) 2 (NCS) 2 ] SCO complex with a strong EFG at the position of the Fe atom T > 170 K Molecular packing, monoclinic phase High-spin Low-spin | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 16
Change of EFG orientation upon spin-crossover [Fe(PM-BiA) 2 (NCS) 2 ] results of DFT calculations high-spin low-spin | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 17
Nuclear resonance polarimetry of an SCO complex T = 220 K, high-spin Rotation angle c I = I πσ ( t ) ∝ (sin χ ⋅ cos χ ) 2 250 experimental data simulation c 200 150 counts 100 50 0 -135 -120 -105 -90 -75 -60 -45 -30 -15 0 c (°) | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 18
Nuclear resonance polarimetry of an SCO complex T = 220 K, high-spin Rotation angle j 250 j =0° 200 150 100 50 0 j =45° 150 100 50 0 75 j =65° 50 25 -40 counts c -Scan 0 75 theory j =80° 50 25 -60 0 75 c MIN (°) j =90° 50 -80 25 0 75 j = - 90° 50 -100 25 0 20 40 60 80 100 0 -160 -140 -120 -100 -80 -60 -40 -20 0 j (°) c (°) | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 19
Results: Electric field gradient in the high-spin state DFT calculations Measured data | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 20
Nuclear resonance polarimetry of an SCO complex Experimental results: Temperature dependence 1000 j = 80° T =120 K T = 120 K T= 120 K Significant contribution from Room temperature Raumtemperatur high-spin phase 100 Impulse counts T = 120 K 10 T = 220 K 1 -160 -140 -120 -100 -80 -60 -40 -20 0 c (°) à Change of EFG orientation Evaluation reveals: due to the SCO 78 % low-spin, 22 % high-spin (oriented !) Diploma thesis Lena Scherthan, Uni Kaiserslautern (2016) | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 21
Probing Anisotropies in Condensed Matter via Polarimetry Static Anisotropies Analyzer plane à Polarization rotation a B B, dE/dz L Sample W d k 0 k 0 Polarizer plane Dynamic Anisotropies (b) à Polarization precession (a) Probing charge anisotropies in Probing spin excitations in magnetic correlated materials materials à Adressing selected orbitals à PRL 112, 117205 (2014) via resonant x-rays | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019 Page 22
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