High purity x-ray polarimetry Ingo Uschmann B. Marx, K. Schulze, S. Hoefer, R. Loetzsch, T. Kämpfer, O. Wehrhan, H. Marschner, E. Förster, M. Kaluza, H. Gies, G. Paulus, T. Stöhlker Helmholtz-Institut Jena, Helmholtzweg 5, Institut für Optik und Quantenelektronik, Friedrich-Schiller- Universität, Jena C. Detlefs, T. Roth, J. Härtwig, ESRF R. Röhlsberger, H.C. Wille, K. Schlage, DESY -PETRA III W. Wagner, FZD Dresden Petawatt-Lasers at Hard X-ray Light Sources, Dresden,

Content 1.History and Motivation 2.Method and Realization 3.Experimental Results 4.Summary and Outlook

First polarization experiment with x-rays 1906 J. Barkla X-ray scattering 1917 Nobel prize

First observation of optical activity in the x-ray range kW X-ray tube Cu K  Presicion of 5 arcmin (1.4 mrad) after 24 hours accumulation M. Hart, A.R.D. Rodrigues, 1981

Faraday effect in the x-ray range 1991 Source synchrotron: Divergence: 200 µrad Error of rotation: rad Sensitivity: 70 µrad Polarization ratio: 2 x M. Hart P. Siddons et al., RSI, 1991 X-ray polarimetry at Synchrotrons is today a standard method for study of magnetic Materials and resonant nuclear scattering 1997 R. Roehlsberger, T. Toellner, polarization purity of ~4x10 -8

Motivation of further development of x-ray polarizers Observation of vacuum birefringence At photon energies small compared to the electron mass electrons and positrons will not generally produced as real particles. But: Euler and Heisenberg: „ … 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“ 1936 T. Heinzl et al Strong electric field induced phase shift of a electromagnetic wave in birefrigent vacuum:  = 4  /15 z 0 / I o /I c k, for I 0 =10 22 W/cm 2 and = 1 A … ellipticity ~ (  ) 2 ~  - Sommerfelds fine structure constant z 0  interaction length  - wavelength Io –electric laser field Ic = 1.3 x V/m critical field for pair production in constant electric field

Proposed QED-experiment with high Power Laser This challenging experiment consist of three subprojects 1- development of X-ray polarimetry 2- development of the X-ray source 3- development of the Petawatt laser

Basics for x-ray polarizer dynamical theory of x-ray diffraction with perfect crystals Ewalds sphere for the two beam case K0K0 KhKh G Polarisation state depends on the scattering angle 2  Integrated reflectivity R i  ~ 1 for  - polarization R i  ~ cos (2  ) for  – polarization K o incident beam K h diffracted beam G reciprocal lattice vector  Bragg angle 

Reflection curves for sigma- and pi- component at 10° Bragg angle

Reflection curves for sigma- and pi- component at 47° Bragg angle

Generation of linear polarization state of x-rays 1.X-ray diffraction of x-rays at an Bragg angle close to 45° 2.Borrmann effect in the transmission case germanium 220, thickness t=1 mm, Cu K  Normal absorption µt = 34.17, exp(-µt)=1.5x sigmaµ e  =1.3, exp(-µ e  t)=0.272 piµ e  =11.9, exp(-µ e  t)=6.5x Channel cut by using multiple reflection 4. Using transmitted x-rays of a collimated X-ray beam, Bragg reflected by a crystal

Energy dependent rocking curves for Bragg angles at 45°, only sigma component

Linear polarization by Bragg reflection close to  B =45° Integrated reflectivity R i  ~ 1 n for  - polarization R i  ~ cos n (2  ) for  – polarization n=1 n=2 n=4 n-number of bounces

Efficiencies of 4-, 6-,and 8- bounces channel-cut crystals

High purity x-ray polarimetry Best value before: 4x10 -8, at 14.4 keV and a Bragg angle of 45.1°, R.Roehlsberger et al., NIM 1997

1. Simulation of multiple diffraction, which disturbs the polarisation degree.

2. Simulation of multiple diffraction, which disturbs the polarisation degree. Additional reflection Umweganregung

1. Simulation of multiple diffraction, which disturbs the polarisation degree. It can be suppressed by well selected and precise crystal orientation. All reflection calculated: Silicon crystal, =0.19 nm, 6.9 keV 400 reflection used

1. Simulation of multiple diffraction, which disturbs the polarisation degree. All reflection calculated: silicon crystal, =0.055 nm, 22 keV, 888 reflection used

The first Jena X-ray polarimeter 4 reflection channel cut

The first Jena X-ray polarimeter Jena, summer 2009

Si 333 reflection, Cu K ,  B = 47.43°, 4 symmetric reflection at each channel cut, Time for the 90° curve took 3 days. Rocking curves for different analyzer positions Determined purity: 3.9x10 -4, Limitation by X-ray tube (Brilliance and Bragg angle) First polarization purity measurement – X-ray tube

Brilliance of present x-ray sources Undulator parameters: … photons/s/eV Source size: 30 µm x 300 µm Divergence: 42 µrad, 16.9 µrad Authier, Dynamical theory of x-ray diffraction

x-ray beam size at the polarimeter: horizontal: 1.5 mm vertical beam size. 0.5 mm horizontal rms e--divergence: 10.3 µrad vertical rms e--divergence: 2.9 µrad X-ray hutch Storage ring Experimental campaign at ID 06 at ESRF: December 2009 Undulator radiation: Alternative two undulators are available for 3…10 keV and 10 keV … (30 keV): Highest photon flux is available at 10 keV (second undulator): ~10 15 photons/s Energy band width: ~ 10 eV Polarisation degree: > 99%, horizontal rms e--divergence: 10.3 µrad Photons after the Silicon 111 monochromator (band width ~1 eV): ~10 14 photons/s Photons after the first polarizer: ~10 12 photons/s Photons after the second polarizer (parallel position): ~10 10 photons/s

Experimental campaign at ID 06 at ESRF - Polarizer

Experimental campaign at ID 06 at ESRF - Analyzer

Rocking curves at parallel - and cross position ESRF winter 2009 B. Marx et al., Opt. Commun., 284 (2011), pp. 915

Polarization purity measured at 6457 eV, Si reflection channel cut B. Marx et al., Opt. Commun., 284 (2011), pp. 915

Polarization purity measured at different photon energies Si 444 E ph =11183 eV Si 800 E ph =12914 eV B. Marx et al., Opt. Commun., 284 (2011), pp. 915

Polarization purity measured at different crystal azimuth Si 800 E ph =12914 eV

Application: phase variation of x-rays by diffraction

High Purity X-ray Polarimetry Sensitive phase determination by the X-ray polarimeter ESRF Sept. 2010

Experimental campaign at ID 01 at PETRA III: August 2011 Polarization purity of the undulator at ID01: 4.4x10 -4 Beam diameter 3 mm x 3 mm

Summary -We measured a polarization purity of -The detection of ellipticity of the order of becomes possible -for Laser pump-X-ray probe the synchrotron of third generation has to long pulses and high repetition rate -alternative source – x-ray laser -The polarisation purity can still be improved by more sophisticated methods 1. tilted channel cuts 2. asymmetric reflection 3. suppression of multiple reflections and thermal diffuse scattering crystals with lower Z, diamond crystal cooling -The new extremly sensitive method, presently not existing will be able to detect newly weak polarisation effects in the x-ray regime Cotton-Mouton effect Fararday effect 2.4 x at 6457 eV 6.2 x at eV

Outlook 1. Experiments at LCLS: next step to the QED experiment: Synchrotron: 350 MHz repetition, photons per pulse, pulse duration: 100 ps LCLS: 10 Hz repetition, photons per pulse, pulse duration: 70 fs weak effects becomes visible in single x-ray pulses!!! ??? Nonlinear effects might destroy the purity??? 2. High purity polarimeter as optical shutter similar to optical polarimeter by using fast processes, i.e. optical phonons or piezzo effect 3. Optical pump laser: 1. high intensity, pulse duration ~ like XFEL 2. small focus size 1…3 µm, 3. high temporal average of energy, rep. rate like XFEL