1 / 21

Magnetic neutron wave guides for optical devices

Magnetic neutron wave guides for optical devices. Frédéric OTT 1 , Sergey KOZHEVNIKOV 1,2 1 Laboratoire Léon Brillouin, CEA Saclay, France 2 Frank Laboratory of Neutron Physics, JINR, Dubna, Russia. Sergey KOZHEVNIKOV. Arrived: September 2004, LLB, postdoc

roary-kirk
Download Presentation

Magnetic neutron wave guides for optical devices

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Magnetic neutron wave guides for optical devices Frédéric OTT1, Sergey KOZHEVNIKOV1,2 1Laboratoire Léon Brillouin, CEA Saclay, France 2Frank Laboratory of Neutron Physics, JINR, Dubna, Russia

  2. Sergey KOZHEVNIKOV • Arrived: September 2004, LLB, postdoc • From: Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Dubna, Russia • PhD thesis “Investigation and application of spatial splitting of neutron beam in magnetic media”, Dubna, 2002 • Previous activities: Neutron depolarization in superconductors and magnetics Polarized neutron reflectometry Development of neutron polarization analysis on old SPN-1 reflectometer (Dubna) Testing of new REMUR reflectometer (Dubna) Development of SESANS on TOF spectrometer

  3. Outline • Magnetic wave-guides Neutron interaction with an modulated optical magnetic potential • Present state (understanding wave-guides) • Future work (simulation - RF Kerr)

  4. Modulated Magnetic Potential • Use of a magnetic modulation to dynamically vary the optical properties of a reflecting layer • Principle : • Magnetisation of the layer rotates at speed w • Optical potential : V(t) = U + u(t) Optical index Potential variations due to the rotation of the magnetisation Vacuum (incidence medium) Magnetic layer

  5. Principle • Change of momentum of the neutron when there is an exchange of a quantum (during a spin-flip) • Amount of “inelastic reflection” in grazing incidence (~ 0.5°) • a large fraction of the incident beam (between 10 and 30%) . • [1] A. Frank et al, Ann. Of the New York Ac. Sc. 755 (1995) 858.[2] R. Golub et al, Am. J. Phys. 62 (1994) 779. Incident beam specular reflection (NSF) “inelastic” reflection (SF)

  6. Potential applications • Control of the reflection angles and reflection by varying the frequency • Coherent separation of a beam (for interferometry) • Wavelength dispersion for a time of flight reflectometer for an energy analysis of a white beam. • Neutron switch in the case of a magnetic pulse • Solid flipper with tuneable parameters

  7. Samples • Large magnetisation • Low coercivity (Amorphous layers) • Permalloy – Co alloys • Single crystal layers • Low damping (Fe, a = 0.005) • Problem of the losses in the system • Insulating ferromagnetics (magnetic oxides) • Patterned layers

  8. Magnetic neutron wave guides for neutron optical devices • ILL Annual Report • F. Pfeiffer, V. Leiner, P. Høghøj, I. Anderson Optical index Soft magnetic layer Guiding layer (with low optical index) Pinned magnetic layer substrate

  9. Combination : dynamics and wave-guides • Magnetic traps Allows the neutron beam to freely enter the guide Acts like a guide

  10. Combination : dynamics and wave-guides • The modulation of the top magnetic layer should allow to trap neutron bunches inside the waveguide

  11. Work plan • Wave guides (Cu/Al/Cu) choice is suitable for x-ray AND neutrons • X-ray characterisation (in progress)and simulation wave-function (for x-rays and neutrons) • Neutron characterisation (1-10 Dec 2004)static magnetisation • Equipment for RF KERR has arrived • Set-up during winter – spring 2005

  12. Samples preparation • At the moment • Evaporation • Quality seems to good enough • Good flexibility and large choice of materials (mainly metals)

  13. Simulation of neutron wave-guides • SimulReflec available at http://www-llb.cea.fr/prism/programs/simulreflec/simulreflec.html Theta in =0.42 nm PRISMA reflectometer, LLB z Cu Al Cu Air Cu Ti Cu Air Cu Al Cu Air (75nm) (75nm) (50nm)

  14. Simulation • The potential well should not be too deep • Al is perfectly suitable for the guide material • Ti provides a contrast which is too largeThe first mode cannot be confined in the guide • The use of Al makes the structures easy to test with x-rays

  15. Simulation : to be done • Include the Spin-Flip signal in the modeling of magnetic guides • Include the interaction with a dynamically modulated magnetization

  16. X-rays characterization of a wave-guide structures • In the reflectivity signal the “signature” of the WG structure can be directly probed by the presence of absorption “resonances” in the specular reflectivity signal

  17. Neutron characterization of a wave-guide structure Qx Qz • Glass//Co(190mn)/Al(260nm)/Co(10nm) 2002, EROS, LLB The structure of the off-specular signal is the signature of the wave-guide effect. The off-specular signal is enhanced when the wave-function is localized.

  18. Neutron wave-guides • No absorption • BUT off-specular scattering can be observed if the roughness of the interfaces is large • Next month • Direct observation of the wave-guide signal • See Pfeiffer measurements

  19. Modelling (dynamics) • Anne de Virmes (to arrive during winter) • Modelling of magnetic systems in the RF – HF range

  20. RF Kerr setup project laser beam polarizer analyzer fast photodiode RF field exciter sample (thin magnetic film) lock-in radio frequency acquisition

  21. Conclusion • Project covers broad range of expertise (sample preparation and characterization, RF magnetization, Kerr, etc.) • X-ray sample characterization and simulations have been started • Neutron sample characterization is in the nearest future

More Related