Showing papers on "Circular polarization published in 1996"

Circular Dichroism and Circular Polarization of Photoluminescence of Highly Ordered Poly{3,4-di[(S)-2-methylbutoxy]thiophene}

Abstract: Conformationally disordered poly{3,4-di[(S)-2-methylbutoxy]thiophene} is prepd via monomer polymn by anhyd FeCl3 Optically active ordered polymer is prepd by cooling of the polymer to -30 Deg In the aggregated phases a splitting of the excited state into two exciton levels occurs

Net Circular Polarization in Magnetic Spectral Lines Produced by Velocity Gradients: Some Analytical Results

Abstract: The net circular polarization in a spectral line due to the combined effect of magnetic fields and velocity gradients is analyzed for a few schematic situations. In some particular cases, its dependence on the magnetic field, velocity field and line parameters can be expressed analytically.

Polarization holographic gratings in side-chain azobenzene polyesters with linear and circular photoanisotropy.

Abstract: We investigate thin phase polarization holographic gratings recorded with two waves with orthogonal linear polarizations in materials in which illumination with linearly/circularly polarized light gives rise to linear/circular birefringence. The theoretical analysis shows that the presence of circular photoanisotropy changes significantly the diffraction characteristics of the gratings. The intensities of the waves diffracted in the +1 and −1 orders of diffraction and their ratio depend substantially on the reconstructing-wave polarization. Experiments with films of side-chain liquid-crystalline azobenzene polyester that is a photoanisotropic material of the considered type confirm the unusual polarization properties. It is shown that polarization holography may be used for real-time simultaneous measurement of photoinduced linear and circular birefringence.

Phase difference plate and circularly polarizing plate

Abstract: PROBLEM TO BE SOLVED: To obtain a phase difference plate which has decreased phase differences by wavelengths and has the excellent consistency thereof by sticking a quarter-wave plate and a halfwave plate to each other in the state of intersecting their respective optical axes. SOLUTION: This phase difference plate is formed by sticking the quarter- wave plate (a double refractive film of which the phase difference of the double refractive light is a quarter wave) 13 and the halfwave plate (a double refractive film of which the phase difference of the double refractive light is a half wave) 11 to each other in the state of intersecting the respective optical axes at a preset angle. The halfwave plate 11 and the quarter-wave plate 13 are formed by subjecting high-polymer films to stretching treatments. In such a case, a polycarbonate material which is often used as a wavelength material is selected. This phase difference plate is designed to function as the quarter-wave plate improved in the wavelength dispersion characteristic when linearly polarized light of a perpendicular direction (0 deg. direction) is made incident from the halfwave plate 11 side. The phase difference plate is thus capable of converting the light to nearly perfectly circularly polarized light regardless of wavelengths in a range of visible light.

Spin-Polarized Photoelectron Spectroscopy

Abstract: Besides mass and charge, electrons also possess a spin. By detecting the direction of the spin of photoemitted electrons one can gain important information about the photoexcitation process and the properties of the sample under investigation. There are two modes in which a PE experiment can produce a spin polarization of the photoemitted electron. One can use unpolarized light to excite polarized electrons in a sample, which is a good way to investigate, e.g., magnetic materials, and one can employ circularly polarized light to excite transitions between states that are split by spin-orbit interactions, thereby obtaining spin-polarized electrons in the final state. This second method is useful for producing beams of polarized electrons, which can then be used for other experiments. Unfortunately, the measurement of spiry polarization is a non-trivial problem and there are relatively few laboratories that can employ this very elegant method. Therefore, we shall simply outline the principles of such experiments whilst referring the reader to the excellent reviews [10.1–10.6] for further details.

Polarization of Astronomical Maser Radiation. III. Arbitrary Zeeman Splitting and Anisotropic Pumping

Abstract: General solutions of the maser polarization problem are presented for arbitrary absorption coefficients. The results are used to calculate polarization for masers permeated by magnetic fields with arbitrary values of \xB, the ratio of Zeeman splitting to Doppler linewidth, and for anisotropic pumping. The $\xb \to 0$ limit of the magnetic solution reproduces the linear polarization derived in previous studies, which were always conducted at this unphysical limit. While terms of higher order in \xb\ have a negligible effect on the magnitude of $q$, they produce some major new results. In particular, the linear polarization is accompanied by circular polarization, proportional to \xb. Because \xb\ is proportional to the transition wavelength, the circular polarization of SiO masers should decrease with rotation quantum number, as observed. In the absence of theory for $\xb < 1$, previous estimates of magnetic fields from detected maser circular polarization had to rely on conjectures in this case and generally need to be revised downward. The fields in SiO masers are \about\ 2--10 G and were overestimated by a factor of 8. The OH maser regions around supergiants have fields of \about\ 0.1--0.5 mG, which were overestimated by factors of 10--100. The fields were properly estimated for OH/IR masers ($\la$ 0.1 mG) and \H2O masers in star-forming regions (\about\ 15--50 mG). Spurious solutions that required stability analysis for their removal in all previous studies are never reproduced here; in particular, there are no stationary physical solutions for propagation at $\sin^2\theta < \third$, where $\theta$ is the angle from the direction of the magnetic field, so such radiation is unpolarized. These spurious solutions can be identified as the \xb\ = 0 limits of non-physical solutions and they never arise at finite

Longitudinal and transverse effects of nonspecular reflection

Abstract: A rigorous spectral analysis is given for the nonspecular reflection of a three-dimensional Gaussian beam at a dielectric isotropic planar structure. For the first time all independent nonspecular effects are derived in a self-consistent manner for the three-dimensional case. It is shown that the longitudinal nonspecular effects in the incidence plane, that is, the lateral and focal shifts of the beam waist position, the angular rotation of the reflected-beam axis, and the modifications of the beam waist width and complex amplitude, have their direct analogies in the plane transverse to the incidence and interface planes that gives transverse nonspecular effects. Moreover, the existence of the other, not yet reported, effect of nonspecular modification of the beam polarization is also proved. A role for TM and TE polarizations in reflected-beam formation is indicated. The results show that, up to the symmetric second-order terms in approximation of Fresnel coefficients, each of the longitudinal and transverse beam factors independently preserves its shape under reflection at the expense of changes of the beam reference frame, width, amplitude, and polarization parameters.

Formation of arc-shaped Alfvén waves and rotational discontinuities from oblique linearly polarized wave trains

Abstract: The forms of Alfvenic fluctuations in the solar wind sometimes possess nearly constant magnetic intensities but have an approximate arc rather than circular polarization. They are also associated with layers of abrupt field rotation called rotational discontinuities (RDs) where the field changes direction by < 180°. Ion-sense and electron-sense rotations are observed in approximately equal numbers. To explore the origin of this form, we conduct a one-and-one-half-dimensional hybrid numerical simulation study of the evolution of obliquely propagating, low-frequency (≪ion cyclotron) Alfven wave trains. Starting from a linearly polarized wave train, an approximate arc polarization evolves rapidly where the magnetic field moves to and fro on a less than semicircular arc. Large-amplitude (|δB|/B ∼ 1) wave trains steepen and produce RDs which always rotate the field by < 180° with no preference for ion or electron sense of rotation. These properties correspond to those of Alfvenic fluctuations in the solar wind, and our model is the first which offers an explanation of the observed arc-shaped waves and imbedded RDs. At early times, a large density signal is also generated. For large plasma β, the signal rapidly damps, and the waveform varies little with time. For small plasma β, the generated constant-B Alfven wave is parametrically unstable and causes the density signal to grow further before the instability saturates. The wave train and density signal beat strongly giving a periodic time variation of the wave amplitude and waveform. Ion heating from steepening, RD formation, relaxation to constant B, and parametric processes occurs mainly parallel to the background magnetic field and cannot explain the perpendicular heating of ions observed in the solar wind.

Estimation of Ice Hydrometeor Types and Shapes from Radar Polarization Measurements

Abstract: An approach to distinguish between various types of ice hydrometeors and to estimate their shapes using radar polarization measurements is discussed. It is shown that elevation angle dependencies of radar depolarization ratios can be used to distinguish between planar crystals, columnar crystals, and aggregates in reasonably homogeneous stratiform clouds. Absolute values of these ratios depend on the reflectivity-weighted mean particle aspect ratio in the polarization plane. Circular depolarization ratios depend on this ratio, and linear depolarization ratios depend on this ratio and particle orientation in the polarization plane. The use of nearly circular elliptical polarization provides a means of measuring depolarization for low reflectivity scatterers when the circular polarization fails due to low signal level in one of the receiving channels. Modeling of radar backscattering was applied to the elliptical depolarization ratios as measured by the Ka-band radar developed at the NOAA Environme...

Comparison of linearly and circularly polarized probes of second-order optical activity of chiral surfaces

Abstract: We compare two nonlinear‐optical techniques for measuring chirality of isotropic surfaces. One technique measures the difference in the efficiency of surface second‐harmonic generation between the cases of left‐hand and right‐hand circularly polarized fundamental light and the other measures the difference in the efficiency between the cases of fundamental light linearly polarized −45° and +45° with respect to the p‐polarized direction. A nonzero difference in either case indicates chirality, where no difference should be measured for an isotropic achiral surface. We examine the complementariness of these two techniques theoretically and experimentally. In experiments utilizing thin films of a chiral poly(isocyanide), we measure the second‐harmonic response as a function of the state of polarization of the fundamental light when manipulated by both quarter and half waveplates. We extract the circular and linear differences from these more complete measurements and find the largest circular and linear diff...

Inverse Faraday effect and propagation of circularly polarized intense laser beams in plasmas.

Abstract: The magnetic field generation through inverse Faraday effect and its effects on the propagation of a circularly polarized light wave are studied in a self-consistent way for relativistic intensities. The following results are presented. (i) The magnetic field is produced by two sources, the circular motion of single electrons which produces plasma magnetization, and the inhomogeneity of both the electron density and light intensity which produces nonzero currents in the azimuthal direction. The magnetic field is calculated for various profiles of electron density and light intensity. (ii) For the case of a plane wave in a homogeneous plasma, the cutoff frequency is calculated as a function of light intensity, which is different from that without consideration of magnetic field generation. An ultra-intense magnetic field as large as hundreds of MG is obtainable in an overdense plasma where the wave can propagate owing to the induced transparency. (iii) The evolution equations for a laser beam of finite width are derived. Due to magnetic field generation, the critical power for self-focusing of the laser beam is reduced by a factor of (1+${\mathrm{\ensuremath{\omega}}}_{\mathit{p}}^{2}$/${\mathrm{\ensuremath{\omega}}}^{2}$${)}^{\mathrm{\ensuremath{-}}1}$; the magnetic field tends to reduce the effect of the electron cavitation resulting from the transverse ponderomotive force. \textcopyright{} 1996 The American Physical Society.

Experimental Evidence for Circular Dichroism in the Double Photoionization of Helium

Abstract: Circular dichroism in the double photoionization of He by circularly polarized light has been observed in an angle resolved coincidence experiment at 93.5 eV photon energy. The use of a transmission multilayer, which acts as a quarter-wave plate for the linearly polarized incident light, together with time-of-flight spectrometers, which enable simultaneous detection of all electron pairs, has made the measurements possible. The results show strong dependence of the dichroism on the relative emission angles and the energy sharing between the ejected electrons in good agreement with our numerical calculations.

Apparatus for observing a surface using polarized light

Abstract: An observation apparatus of the present comprises (i) a light source for generating light; (ii) a separating optical system which splits the light from the light source into two different polarized light beams; (iii) a condenser optical system which converges the two polarized light beams from the separating optical system so as to respectively form light spots on two different positions on a sample object; (iv) a polarization selecting means which has a predetermined analyzer angle and selects a specific polarized light component from composite light made of the two polarized light beams by way of the sample object; (v) light detecting means which detects the polarized light component selected by the polarization selecting means; and (vi) phase difference adjustment means which adjusts a phase difference between the two polarized light beams by way of the sample object and guides composite light composed of the two polarized light beams as circularly polarized light to the polarization selecting means, when the sample object does not modulate both phase and amplitude of the light incident thereon. Accordingly, this observation apparatus can detect a phase difference generated between the two light components respectively emitted from both side of a level difference on the sample object.

Diffuse and coherent backscattering by discrete random media—I. Radar reflectivity, polarization ratios, and enhancement factors for a half-space of polydisperse, nonabsorbing and absorbing spherical particles

Abstract: It has been demonstrated recently that diffuse, incoherent multiple scattering of electromagnetic waves by media composed of randomly positioned, discrete scattering particles is always accompanied by coherent backscattering and may explain intriguing opposition phenomena observed for some solar system bodies, in particular peculiar characteristics of radar returns from icy satellite surfaces. In this paper, we study theoretically photometric and polarization characteristics of diffuse and coherent backscattering by discrete random media. The cyclical component of the Stokes reflection matrix at exactly the backscattering direction is expressed in terms of the ladder component, and the ladder component is accurately computed by numerically solving the vector radiative transfer equation. We give formulas expressing the radar reflectivity, radar linear and circular polarization ratios, and backscattering enhancement factors in the elements of the Stokes reflection matrix and describe in detail the computational technique used. Assuming that the scattering medium is homogeneous and semi-infinite and that scattering particles are polydisperse spheres, we report the results of a comprehensive theoretical survey of the dependence of the photometric and polarization characteristics of the radar return on the illumination zenith angle and on the particle effective size parameter and real and imaginary parts of the refractive index.

Ar ursae majoris: the first high-field magnetic cataclysmic variable

Abstract: We identify the luminous soft X-ray source AR UMa as a magnetic cataclysmic variable containing a white dwarf with the highest field yet detected in an accreting binary. IUE and optical spectroscopy, optical photometry, and circular polarimetry and spectropolarimetry define remarkably distinct accretion states of this binary. Circular polarization is nearly absent in the high state, but the low state exhibits values which vary between 2% and 5% on the orbital period of 1.932 hr. The UV continuum contains a broad absorption feature near 1300 A, while optical spectropolarimetry during the low state reveals a number of strongly polarized dips. These are interpreted as Zeeman components of hydrogen Lyα and another atmospheric species, possibly He I, in a photospheric magnetic field of ~ 230 MG.The radial velocity curve of the low-state optical emission lines shares the period of the optical photometry and polarimetry and is phased appropriately for an origin on the irradiated secondary star. While the high state exhibits prominent UV line emission typical of the magnetic variables, the strength of the UV continuum does not vary appreciably with a change in accretion state. This, combined with the high soft X-ray luminosity and lack of circular polarization, indicates that accretion occurs largely in the form of dense filaments which avoid a standoff shock and thermalize their kinetic energy below the white dwarf photosphere. We suggest that these phenomena may play a role in the apparent lack of high-field systems with easily detectable circular polarization during high-accretion states.

Optical quadrature interferometry utilizing polarization to obtain in-phase and quadrature information

Abstract: An optical quadrature interferometer is presented. The optical quadrature interferometer uses a different state of polarization in each of two arms of the interferometer. A light beam is split into two beams by a beamsplitter, each beam directed to a respective arm of the interferometer. In one arm, the measurement arm, the light beam is directed through a linear polarizer and a quarter wave plate to produce circularly polarized light, and then to a target being measured. In the other arm, the to reference arm, the light beam is not subject to any change in polarization. After the light beams have traversed their respective arms, the light beams are combined by a recombining beamsplitter. As such, upon the beams of each arm being recombined, a polarizing element is used to separate the combined light beam into two separate fields which are in quadrature with each other. An image processing algorithm can then obtain the in-phase and quadrature components of the signal in order to construct an image of the target based on the magnitude and phase of the recombined light beam.

New aspects of second-harmonic optical activity from chiral surfaces and interfaces

Abstract: New expressions are developed within the electric dipole approximation for the four Stokes parameters characterizing the polarization properties of coherent second-harmonic radiation generated from chiral isotropic surfaces in reflection. These are employed to derive, in addition to the three well-known incident circular polarization second-harmonic opticalactivity (SHOA) observables, thirteen new basic observables for the detection of surface SHOA which involve second-harmonic intensity difference measurements using right and left circular, and + 45 and - 45 linear, polarization modulation in the incident and second-harmonic radiation and in both simultaneously. Because of their dependence on a fully electric dipole allowed tensor these circular and linear intensity differences and the corresponding intensity sums have the same order of magnitude, so that all the dimensionless surface SHOA effects they generate are of the order of unity. The circular intensity differences (CIDs) depend on the imaginary p...

Polarization of specular reflection and near-specular scattering by a rough surface

Abstract: Polarization of specular reflection and near-specular scattering (NSS) by a randomly rough surface is investigated by the use of a Mueller matrix formulation. The collective effect by a rough surface on the average specular field results in reflectance loss and polarization, which can be explained by an effective medium theory. Effects of random NSS can be represented by a scattering matrix that is partially coherent and polarized. The incoherent and unpolarized part of scattering causes depolarization, and the coherent and polarized parts of scattering change the apparent polarization properties of specular reflection. Results of a simulation and least-squares fit of ellipsometric data to the models including the NSS effect, for a black anodized aluminum sample, are presented. Simultaneous least-squares fits for both ellipsometric data and reflectance data at multiple angles of incidence at three different wavelengths gave approximately the same rms roughness, which agrees with the profilometric values reported previously.

Fiber optic interferometric circuit and magnetic field sensor

Abstract: A number of optical interferometric sensor configurations are provided. The interferometric sensors include a polarization maintaining optic fiber forming either a loop or linear optical path. Circularly polarized light propagate along the optical path and pass through a field-sensitive sensing medium. A differential phase shift induced in the light waves by a magnetic field is then detected by a photodetector and associated signal processing electronics.

A Circularly Polarized Omnidirectional Antenna

Abstract: A circularly polarized omnidirectional antenna consisting of a vertical sleeve dipole and three pairs of tilted parasitic elements set around it is proposed. The antenna has a simple structure and no feeding network for radiating circular polarization. The authors describe the idea of the proposed antenna, some experimental approaches and the evaluation of the antenna by using the moment method.

Spectral analysis of the nonlinear relativistic Doppler shift in ultrahigh intensity Compton scattering

Abstract: The relativistic dynamics of an electron subjected to the classical electromagnetic field of an ultrashort laser pulse is studied theoretically at arbitrary intensities. Frequency modulation effects associated with the nonlinear relativistic Doppler shift induced on the backscattered radiation are analyzed in detail. For circular polarization, an exact analytical expression for the full nonlinear spectrum is derived. For linear polarization, it is found that the scattering of coherent light by a single electron describing a well-behaved trajectory can yield anharmonic spectra when the laser ponderomotive force strongly modulates the electron{close_quote}s proper time. At ultrahigh intensities, these nonlinear relativistic spectra exhibit complex structures. In addition, the temporal laser pulse shapes best suited to generate narrow Compton backscattered spectral lines at ultrahigh intensities are discussed. {copyright} {ital 1996 The American Physical Society.}

Time-resolved measurements of the polarization state of four-wave mixing signals from GaAs multiple quantum wells

Abstract: The complete polarization state of the degenerate four-wave mixing signal from a GaAs/AlxGa1-xAs multiple quantum well is determined by time resolution of all four of its Stokes parameters as a function of the relative angle between the two linear input polarizations. The degree of ellipticity and the orientation of the polarization ellipse are both observed to vary dramatically in time, and the temporal evolution is found to depend strongly on the orientation of the input polarizations. These time-resolved results are shown to be consistent with previous measurements of the time-integrated Stokes parameters and to provide new constraints for physical models. The results are shown to be qualitatively consistent with a phenomenological model requiring the inclusion of both many-body interactions and biexcitonic effects.

Diffraction analysis of photoanisotropic holography: an anisotropic saturation model

Abstract: The photoisomerization of a highly anisotropic dye molecule depends not only on the intensity but also on the polarization state of the acting light with respect to the molecular axis. Polarization-dependent isomerization of uniformly oriented distributions of anisotropic dye molecules produces an orientational distribution of photoexcited states. Saturation occurs when all the molecules aligned in a particular orientation are isomerized so further photoexcitation cannot occur. This anisotropic saturation occurs first in the direction aligned with the incident polarization. We investigate this anisotropic saturation behavior and present a theoretical model that incorporates intensity saturation for describing holographic diffraction in dynamic photoanisotropic organic materials. Numerical simulations of diffraction versus intensity and polarization are provided and compared with the experimental results.

Band-gap structure for periodic chiral media

Abstract: We study electromagnetic wave interactions in periodic chiral media through an examination of the band-gap structure derived from a coupled-mode solution. For oblique incidence the singly periodic chiral medium possesses three separate fundamental Bragg conditions, which lead to a richer band-gap structure than that observed for its achiral counterpart. We examine these fundamental Bragg conditions in three characteristic domains defined as the subchiral, chiral, and superchiral regions. The conditions defining each region and the band-gap characteristics are presented. The chiral band-gap structure suggests that periodic chiral media may be useful as filters, polarization mode converters, mode discriminators, and multiplexers for circularly polarized waves. It also demonstrates the increased degrees of freedom for the design of distributed-feedback or Bragg-reflection devices.

Energetic electrons in strong-field ionization

Abstract: A strong-field theory is extended to the description of energetic photoelectron spectra. Experimental spectra are accurately described for both linear and circular polarizations, subject only to a single adjustment of reported peak laser intensities. Examined are single and (sequential) double ionization of helium, to energies of about 1 keV. An approximation of the spectrum as a Maxwellian distribution yields a temperature dependent on the spectrometer viewing angle. Final-state Coulomb effects in circular polarization are examined.

Wave propagation in a guiding structure: one step beyond the paraxial approximation

Abstract: Propagation of electromagnetic waves is considered for a medium with (x, y)-dependent locally isotropic dielectric and magnetic susceptibilities ∊ik = ∊(x, y)δik and μik = μ(x, y)δik, i.e., for a waveguide. In the paraxial approximation the polarization is disconnected from the propagation. We have developed a self-consistent theory of the postparaxial corrections. It allows, in particular, for the description of intrafiber geometrical rotation of polarization and its inverse phenomenon, the optical Magnus effect, which are both determined by the profile of refractive index n=∊μ only and constitute spin–orbit interaction of a photon. The birefringence splitting of linearly polarized modes or meridional rays on the other hand, turns out to be dependent on the gradients of impedance ρ=μ/∊, the quadrupole part of spin–orbit interaction. An important point of the theory is a transformation of field variables such that the z-propagation operator becomes Hermitian, in analogy with the transitions from a full relativistic Dirac equation to the Schrodinger–Pauli equation with spin–orbital corrections. A theoretical explanation is given for the phenomenon previously observed in experiment: preservation of circular polarization by an axially symmetric step-profile multimode fiber and depolarization of an input linearly polarized wave by the same fiber.

Circular polarization dichromatic optical element and apparatus therefor and liquid crystal polymer

Abstract: PROBLEM TO BE SOLVED: To obtain a circular polarization dichromatic optical element which is thin and light and is hardly changed in an orientation state, such as pitch, at a practicable use temp. by providing this optical element with a solidified layer of a liquid crystal polymer consisting of a cholesteric liquid crystal phase subjected to a grandjean orientation. SOLUTION: The circular polarization dichromatic optical element having the solidified layer of the liquid crystal polymer consisting of the cholesteric liquid crystal phase subjected to the grandjean orientation is formed. A liquid crystal display device constituted by using such optical element for back light system has the back light system 4, the optical element 1, a phase difference layer 2 for linearly polarizing the circularly polarized light and a light source 3. Further, the device has liquid crystal polymer solidified layer 11, 12, 13 forming the optical elements of a lamination type, a light source holder 31, light diffusion plates 41, 44, a light emitting layer 42, reflection layers 43, 46, a housing space 45 and a phase difference plate 7 for compensation. Light is made incident on a liquid crystal cell 6 via the optical element 1 and the phase difference layer 2 for polarizing the circularly polarized light to the linearly polarized light. COPYRIGHT: (C)1997,JPO

Circular Dichroism Instrumentation

Abstract: Circular dichroism (CD) measures the difference in absorption between the two rotations of circularly polarized light by an asymmetric molecule. Most biological molecules are asymmetric, and their measured CD is sensitive to their conformation. In the case of biological polymers, CD is the method of choice for monitoring secondary structure. The technique is nondestructive, requires only a small amount of material, and can be applied to molecules in solution.

The optical activity of an artificial non-magnetic uniaxial chiral crystal at microwave frequencies

Abstract: Constitutive relations which include electric quadrupole terms, in addition to electric and magnetic dipole terms, are used to predict the circular birefringence experienced by an electromagnetic wave propagating in an artificial uniaxial chiral crystal which is non-magnetic. The formulation is independent of the origin chosen for the computation of the multipole moments. Numerical values are presented, in the long wavelength regime, for the rotatory dispersion as a result of circular birefringence. It is shown that in this regime the rotatory dispersion has a quadratic frequency dependence, in accordance with the Drude model. The polarizability tensors which determine circular birefringence are computed from the multipole moments of a single structure. It is quantitatively demonstrated that neglect of the electric quadrupole contribution would lead to a serious error in the predicted value for the rotation angle of the polarization plane in the case of a uniaxial crystal. In fact, the contribution of the electric quadrupole moments to optical activity is comparable to that of the magnetic dipole moments. The geometry, dimensions and spacing of the chiral element were chosen for relative ease of fabrication of the crystal, and to allow experimentation at frequencies where microwave instrumentation is readily available. Hence it was possible to subject the numerical prediction of the expected rotatory dispersion, and the effect of the electric quadrupole contribution, to experimental investigation. This was done with good agreement.