Variable linear polarization from an X-ray undulator

Abstract

A new X-ray undulator has been designed and constructed which produces linearly polarized X-rays in which the plane of polarization can be oriented to a user selectable angle, from horizontal to vertical. Based on the Apple-II elliptically polarizing undulator (EPU), the undulator rotates the angle of the linear polarization by a simple longitudinal motion of the undulator magnets. Combined with the circular and elliptical polarization capabilities of the EPU operating in the standard mode, this new undulator produces soft X-ray radiation with versatile polarization control. This paper describes the magnetic structure of the device and presents an analysis of the magnetic ®eld with varying undulator parameters. The variable linear polarization capability is then exhibited by measuring the X-ray absorption spectrum of an oriented polytetra¯uoroethylene thin ®lm. This experiment, which measures the linear dichroism of the sample at two peaks near the C 1s absorption edge, demonstrates the continuous polarization rotation capabilities of the undulator.

Analysis of x-ray linear dichroism spectra for NiO thin films grown on vicinal Ag(001)

“…X-ray absorption spectrum (XAS) measurement was carried out at beamline 4.0.2 of the Advanced Light Source at the Lawrence Berkeley National Laboratory [20] which provides a 99±1% linear polarization of the emitted x-ray. The XAS was measured at different incident angle (θ) and polarization direction (φ), as shown in Fig. 1(a), where the incident angle (θ) is defined as the angle between the x-ray incident direction and the sample surface normal direction and the angle φ is defined as the angle between the polarization vector and the atomic step direction.…”

Molecular orientation in soft matter thin films studied by resonant soft x-ray reflectivity

“…Beamline 4.0.2 is optimized for magnetic spectroscopy 32 and provides a high flux of nearly 10 12 photons/second. It is equipped with an Apple-II Elliptical Polarizing undulator 33 for various X-ray polarizations including linear s and p and provides a free beam port that can accommodate mobile user instruments such as the UHV scattering chamber developed and operated by J. B. Kortright.…”

Angle-DependentNi2+X-Ray Magnetic Linear Dichroism: Interfacial Coupling Revisited

“…The Ni 2+ moments are coupled ferromagnetically in NiFe 2 O 4 and can be aligned in any direction by external magnetic fields while antiferromagnetic coupling is present in NiO. At T =298 K all three samples can be saturated magnetically along any in plane direction by external magnetic fields of 0.5 T. XA spectra were measured using the eight-pole resistive electromagnet [19] on beamline 4.0.2 at the Advanced Light Source (ALS) [20] providing (99±1)% linearly polarized x rays. All spectra were obtained in normal incidence at T =298 K in electron yield mode, in the presence of external fields of 0.55 T. The angular dependence of the XMLD signal across the Ni L 2,3 edges was determined by rotating the orientation of x ray polarization E and external magnetic field H relative to the crystalline axes, c.f., inset to Fig.…”