J. R. Sandercock

Light scattering from surface and bulk thermal magnons in iron and nickel

We report on light scattering measurements on thin polycrystalline samples of iron and nickel. Both the surface and bulk magnons are observed. The measured magnon energies as a function of magnetic field, and of wavevector magnitude and direction, are in good agreement with the calculated values. The predicted exchange induced decay of the surface magnon is observed. In nickel the observed frequencies and linewidths are strongly strain dependent. Oxide layers have an almost negligible effect on the spin wave frequencies in both iron and nickel.

Active vibration isolation systems

Isolating a load from a source of vibrations includes detecting vibrations from that source, and controlling a displacement transducer stage with these detected vibrations through a feedforward loop. Isolation is increased with a resilient mount between the displacement transducer stage and the load. Residual movements of the load may be detected and the displacement transducer stage may additionally be controlled with these detected residual movements through a feedback loop.

Light scattering from thermal acoustic magnons in yttrium iron garnet

Abstract Brillouin scattering measurements on yttrium iron garnet (YIG) have revealed the scattering due to thermal acoustic magnons. The intensity and frequency shift of the magnon peaks as a function of applied magnetic field and incident light wavelength have been investigated and are discussed here within the framework of a simple light scattering theory.

Analysis of the light-scattering cross section for surface ripples on solids

A detailed theory of the scattering of light by acoustic surface ripples arising from both bulk and surface phonons in solids is given. The measured Brillouin spectra of Al, Ni, GaAs and GaP are presented. The experimental results are compared with theoretical predictions for the ripple scattering mechanism. This mechanism is dominant for Al and Ni, where there is good agreement between theory and experiment for the spectral distribution and angular dependence of the intensity, but poor agreement for the absolute cross section. The alternative scattering mechanism by way of the elasto-optic effect is shown to be important in GaAs and GaP, although in the latter the scattering from surface phonons is still apparently dominated by the ripple mechanism.

Surface Brillouin Scattering—Extending Surface Wave Measurements to 20 GHz

Brillouin light scattering is generally referred to as the inelastic scattering of an incident optical wave field by thermally excited elastic waves (elastic waves of thermal origin are usually called acoustic phonons) in a sample. This subject was first investigated early in the century by Brillouin(1) and Mandelshtam(2) in the case of scattering from transparent materials. Since the advent of the laser as a powerful source of monochromatic light, Brillouin scattering has received considerable interest for characterizing elastic and optoelastic bulk properties of materials.3,4 More recently with the introduction of high-contrast spectrometers,(5) scattering from opaque materials can be studied, thereby permitting considerable advances in the study of surface acoustic waves in solids. In the last decade, Brillouin scattering from surfaces, more often called surface Brillouin scattering (SBS), has been widely used to investigate elastic properties of thin films, interfaces, and layered materials.

Determination of magnetic and elastic properties of FeBO3 by light scattering

Brillouin back-scattering measurements on the weak ferromagnet FeBO3 (TN=348K) are reported in the temperature range 77-350K in magnetic field up to 6 kG for an incident wavelength of 514.5 nm. From the magnetic field and directional dependence of the magnon frequency, the Dzialoshinski-Moriya field HDM (1958, 1960) was obtained over the whole temperature range, and precise values were found for the three dominant exchange contributions. The full set of elastic constants is reported.

Light scattering from thermal magnons in iron and nickel

Light scattering measurements from thermal acoustic magnons have been performed for the first time in the metals iron and nickel. A three-pass-plus-two-pass tandem Fabry-Perot interferometer was used to analyze the backscattered light from the polycrystalline or single crystal samples. The magnetic field was parallel to the sample surface and perpendicular to the plane of incidence. Two modes can be observed: bulk magnons and surface magnons. The dependence of the frequency on the applied field for iron can be described by a magnetostatic dispersion relation for an insulating ferromagnet. In nickel the measured frequencies are considerably higher than predicted. Some of the problems arising from the metallic character of the samples are discussed.

Anti-vibration system

An object to be isolated from vibrations is supported by a structure having a curved surface which contacts the object. The support structure is in turn coupled to a resilient spring-like support frame which allows the structure to move in response to vibrations. Also contacting the support structure are three isolation elements which sense the vibration forces and produce forces to counter the vibrations.

Measurement of the near-surface crystallinity of silicon on sapphire by UV reflectance

Abstract An optical reflectance method has been developed for the fast, non-destructive and quantitative characterization of silicon films on sapphire substrates. Reflectance data have been correlated with the defect structure of the silicon films. A relationship has been found between circuit yield and performance and the quality of the starting material as determined by the reflectance method.

A light scattering study of the ferromagnet CrBr3

Abstract Measurements of light scattering from acoustic spin waves in CrBr3 in both the ferromagnetic and paramagnetic states are reported. The dispersion is shown to be adequately described in terms of a single anisotropy constant. Lifetime measurements are compared to those obtained by ferromagnetic resonance techniques. Anomalous effects arising from the very high magnetooptic coupling are discussed.