Masatada Yuri

Elliptical-polarization analyses of synchrotron radiation in the 5–80-eV region with a reflection polarimeter

Abstract The Stokes parameters, which completely represent the polarization state of light, have been measured in the 5–80-eV energy region for synchrotron-radiation beams on the VUV to soft X-ray beamlines at the Photon Factory. Various states of polarization were produced for the emerging beam by deflecting the incoming beam vertically with respect to the entrance slit of the monochromator with a premirror of the beamline. The resultant beam was polarization-analyzed using a polarimeter comprising two triple-reflection polarizers. Increasing the beam-deflection angle was found to result in a change in the polarization state from predominantly horizontal linear polarization to elliptical polarization. This procedure could be used both to produce and to verify circular polarization with | P c | ≳ 80% in the energy range 60–80 eV, which could be immediately applied to MCD experiments. Unpolarized light could clearly be distinguished from circularly polarized light. The unpolarized component was found to become larger with increasing energy on a soft X-ray beamline; this was shown to be mainly due to scattering by beamline optical elements.

Production and direct measurement of circularly polarized vacuum-ultraviolet light with multireflection optics

The conversion of linearly polarized synchrotron radiation to circular polarization has been successfully achieved beyond the LiF transmission cutoff in the vacuum ultraviolet by utilizing a triple‐reflection polarizer as a quarter‐wave retarder. The Stokes parameters of the emerging beam were directly measured at 30 eV with a reflection‐type polarimeter as a function of the rotation angle of the ‘‘circular polarizer’’ around the optical axis. The results show that a degree of circular polarization of up to ∼±82% was attained at ∼±25° rotation angles, respectively, between the incidence plane for the polarizer and the horizontal plane. This result is in good agreement with a calculation which took into account the independently measured Stokes parameters of the incoming beam.

Anisotropic Optical Spectra of α-Al2O3 Single Crystals in the Vacuum Ultraviolet Region. I. Spectra of Absorption Tail and Reflectivity

The spectra of absorption constant in the intrinsic absorption tail region of α-Al 2 O 3 single crystals at 297 K, 78 K and 10 K are presented for the electric fields of incident light parallel to the optic axis of α-Al 2 O 3 and normal to it. The absorption tail spectra obey the Urbach rule for each polarization, indicating that absorptions in the tail region result from the direct interband transitions. The optical anisotropy characterized by the Urbach rule is interpreted in terms of the bond length O 2- –Al 3+ participating in the absorption processes. The spectra of reflectivity are presented in the range of photon energies from 4.6 eV to 120 eV for electric fields parallel to and normal to it. Spectral positions of main maxima in the reflectivity spectra for each polarization are determined at 297 K and 10 K; the spin-orbit doublet of the Al 3+ L 2,3 is revealed at 78.67 eV and 79.12 eV for the first time in the case of α-Al 2 O 3 .

Anisotropic Optical Spectra of α-Al 2O 3 Single Crystals in the Vacuum Ultraviolet Region. II. Spectra of Optical Constants

The spectra of optical constants of α-Al 2 O 3 single crystals at 297 K and 10 K are presented over the range of photon energies from 6 eV to 120 eV for the electric fields of incident light parallel to optic axis and normal to it. The optical constants include the complex index of refraction, conductivity, complex dielectric constant, loss functions and effective number of electrons per unit cell. The spectra in E ≥ 78 eV are interpreted in terms of the interband transitions from the O 2p and 2s bands to the Al conduction bands and the free electron-like absorption of photons by the O 2p band electrons. The volume energy loss function has a prominent peak at E ∼26.4 eV for the plasma oscillation dominantly of the 2p electrons. The spectral features in E ≤78 eV resulting from electronic transitions from the Al L 2,3 levels are presented with the L 2,3 exciton doublet, e.g. , at 78.72 eV and 79.15 eV for e 2// .

Optical Spectra of Y3Al5O12 (YAG) Single Crystals in the Vacuum Ultraviolet Region

The reflectivity spectrum of Y 3 Al 5 O 12 (YAG) single crystals at 297 K is presented in the region of 6.734 eV ≤ E ≤116 eV. The spectra of optical constants derived from the reflectivity by the Kramers-Kronig analysis are tentatively interpreted in terms of the energy levels of the constituent atoms of YAG. Plasma resonance peaks are found at 23.3 8 eV and 36.2 0 eV in which the valence-band electrons and valence- as well as full-band electrons participate, respectively. The structure of absorption due to excitations of the electrons in the Al 3+ L 2,3 levels is found in the region of E ≥76 eV. The free electron-like absorption calculated by the Drude formula by use of the line shape parameters of the plasma resonance line is compared with the dielectric constant in the region of E ≥24 eV. The effective optical dielectric constant calculated from the optical constant e 2 is found to be in good agreement at 116 eV with the optical dielectric constant derived from the dispersion formula.

Optical Spectra of Y2O3 Single Crystals in the Vacuum Ultraviolet Region. II

The reflectivity spectrum of Y 2 O 3 single crystals at 297 K has been measured from 6 eV to 110 eV, and optical functions are derived by the Kramers-Kronig transformation. The plasma loss peaks are found at 14.2 3 eV and 38.40 eV. The spectrum of e 2 ( E ) is tentatively interpreted in terms of the energy levels of Y 2+ , Y 3+ and O 2- free ions. The spectral dependence of e 2 suggests that interband transitions will be exhausted in the neighbourhood of 50 eV. In the energy region of \(E\gtrsim 50\) eV occurs the spectrum due to the free electron-like absorption alone. The accuracy of the data is discussed by the effective optical dielectric constant. The spectral dependence of the free electron-like absorption is compared with that predicted by the Drude formula. The origin of the loss peak at 38.40 eV is discussed.

Elliptical‐polarization measurements in the vacuum ultraviolet and soft x‐ray regions with a reflection polarimeter

A complete polarization analysis has been successfully achieved for synchrotron radiation beams in the vacuum ultraviolet and soft x‐ray regions using a reflection polarimeter. The Stokes parameters, which provide a full description of the polarization state of light, were experimentally determined along with three polarizing quantities of the polarimeter. The present result indicates the possibility of a simultaneous determination of the optical constants of mirror materials through polarization analyses.

Polarization modulation spectroscopy for magnetic circular dichroism study using a polarizing undulator

We developed a polarization modulation spectroscopy in the extreme ultraviolet (XUV) region for magnetic circular dichroism (MCD) measurements. We used a polarizing undulator with crossed and retarded magnetic fields. It enables us to obtain radiation adjusting the polarization states arbitrarily and rapidly. The undulator is essential in our polarization modulation spectroscopy for MCD study in the XUV region.

Microscopic Imaging of Circular Dichroism Using a Polarizing Undulator

A new type of scanning microscope for observing circular dichroism (CD) images of samples was developed. As an illuminating light source, a polarizing undulator which generates right- and left-handed circularly polarized synchrotron radiations (SR) alternately, was used in the microscope. The SR from the polarizing undulator was focused to form a microbeam with a spot size of less than 1 µm, by axially symmetric mirrors. The sense of rotation of circular polarization of the undulator radiation was modulated with a frequency of about 2 Hz. Two-dimensional CD images of a thin film of d-10-camphorsulfonic acid, which is one of the standard samples used for measuring a CD spectrum, were obtained by this microscope.

COMPUTER SIMULATION STUDY OF UNDULATOR RADIATION

Calculations of the radiation from a four‐period polarizing undulator by use of the general radiation equation and numerical integration including the effects of electron‐beam emittance, energy spread, and finite observation distance are presented. Accurate electron‐beam profiles have been experimentally determined and modeled by the Monte Carlo method. Good agreement is found in spectral intensity between the measured and calculated spectra.