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The use of fast-modulated elliptically polarized soft x-rays in the detection of small polarization signals Cecilia S á

The use of fast-modulated elliptically polarized soft x-rays in the detection of small polarization signals Cecilia S á nchez-Hanke S. L. Hulbert and C-C. Kao National synchrotron light source (NSLS) Brookhaven National Laboratory (BNL).

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The use of fast-modulated elliptically polarized soft x-rays in the detection of small polarization signals Cecilia S á

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  1. The use of fast-modulated elliptically polarized soft x-rays in the detection of small polarization signals Cecilia Sánchez-Hanke S. L. Hulbert and C-C. Kao National synchrotron light source (NSLS) Brookhaven National Laboratory (BNL) supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886 SRI April 23-25 Baton Rouge

  2. Motivation to work with fast switching Introduction of EPW how it works (very fast) no big explanations but something about the stability shape of the polarization distribution Comparison with undulator Why is important high sensitivity Magnetism and small signals, well XMCD done already and not too much more to do.. now signals: induced magnetic moments, that have to be studied, Nanomagnets also small signals (unless studied in arrays) and together in scattering mode signals at interfaces and/or magnetic interfaces Phase sensitive detection XAS and MCD measured at the same time, saves time .. But at the same time is possible to correct for possible changes in the polarization ratio. X13A endstation (capabilities) measurements of the electron yield and photon yield. Scattering chamber on fast switching polarization, unique, because opens the possibilities for SRI April 23-25 Baton Rouge

  3. Motivation: small magnetic signals • The physics behind the small magnetic signals current at X13A limit is observation of polarization on Nitrogen in Fe-Nitrides on a 20nm thin film. • Nanomagnets (properties dependence on size) • Induced magnetic moments, mechanisms (properties depend on distance/size/elements/hybridization) • Devices with magnetic properties, with magnetic behavior on non magnetic element for example oxygen or nitrogen. Not only spectroscopy but also scattering. • Magnetic interfaces (Sujoys paper) publication… • Depth sensitivity depending on study with • Photon yield (Photodiode + APD) • Electron yield (Sample current + channeltron) Pic with HL of Nitrogen Pic with HL of Cu Baltimore 7-11 January January 7-11 Baltimore SRI April 23-25 Baton Rouge

  4. Cecilia: The main motivation to have fast switching, and switching as fast as possible is mainly because of the necessity of measuring small magnetic signals. Motivation • a) better signal to noise: • b) What other effect is possible to see? Magnetic moment interactions with dependence, highly diluted or small effects to be able to differenciates what is exclusively happening at the interfaces • Noise sources: • e- instabilities time frame • Electronic noise at the beamline better current amplifiers • Beamline stability problem, depending on the size of the beam and the feature that is going to be investigated Baltimore 7-11 January January 7-11 Baltimore SRI April 23-25 Baton Rouge

  5. EPW pic Circular- and Linearly polarized x-rays Fast switching polarization: fast inverting the current in electromagnets Beam-stability corrected respect to the other beamlines switching frequency 22 Hz testing 47Hz future faster up to 97 Hz • Signal from EPW directly into a photodiode, full intensity, • And 20 x 20 entrance and exit slit… • a) no chopper • b) with chopper • Signal that goes onto the sample • Polarization ratio (between left and right elliptically • polarized) • Dependence with the switching rate. • Dependence with beamposition SRI April 23-25 Baton Rouge

  6. EPW (X13 NSLS) Fast switching the polarization • In soft X-rays : insertion devices (two schemes) • a) switching in time • electromagnetic insertion device • EPW (NSLS, X13), CPU (APS Sector 4) • EPU’s , SPRING-8 or • mechanical switch • b) switching in space • 2 canted EPU’s • (BESSY-II, SLS) • (also require a chopper) SRI April 23-25 Baton Rouge

  7. Polarization and stability Δ pol. = 1% Polarization ratio @10 –3 Δ pol. = 0.001% Polarization ratio @ 10 –3 Y X I =Z Flux density Y t horizontal vertical Angle (mrad) Y SRI April 23-25 Baton Rouge

  8. Beam position and stability Flux density Angle (mrad) Degree of polarization (%) Angle (mrad) SRI April 23-25 Baton Rouge

  9. hard and soft x-rays Linear and circular Top / bottom Permanent magnets Left / right Electromagnets 22 Hz 47 Hz (in test) future 97 Hz Pic. Delivery of X-rays into X13A.

  10. Comparison with undulator delivery and polarization profile and stability test • Changes in time: tf switching frequency • more problems are continuous change in polarization ratio • t >> tf _ with long period change affects the comparison with different measurements • t ≥ tf t =1% tf affects the difference signal introducing noise • tf> t lower pass filters in lock-in SRI April 23-25 Baton Rouge

  11. Flux density vertical horizontal Angle (mrad) Cecilia: calculate the amount of beam we are having from EPW… in the horizontal and vertical and put that in shadow in the figure…. Beam position and stability SRI April 23-25 Baton Rouge

  12. Beam position and stability Flux density Angle (mrad) Degree of polarization (%) Angle (mrad) SRI April 23-25 Baton Rouge

  13. Experiment geometry Baltimore 7-11 January January 7-11 Baltimore SRI April 23-25 Baton Rouge

  14. to X13A EPW Mirror in place MGU EPW to X13B MGU Mirror out Outlook X13A beamline Examples • EPW and new mirror operation New mirror and beamline new alignment (August 2004) gain x 10 more intensity 50% of beamtime

  15. SRI April 23-25 Baton Rouge

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