Showing papers on "Kerr effect published in 1990"

Molecular vibrational and rotational motion in static and dynamic electric fields

Abstract: For many years the effects of a static or dynamic electric field upon electronic motion in a molecule have been studied. These effects have been described in terms of multipolar electronic polarizabilities and higher-order hyperpolarizabilities. Much less attention, however, has been paid to the effects of an electric field upon vibrational and rotational motion. It is the aim of this review to consider, in some detail, these effects. As in the electronic work, they too will be described in terms of polarizabilities and hyperpolarizabilities (the latter being particularly important for the study of nonlinear optics). The theory will be developed so as to bring together the different methods that have been used in various calculations. Examples drawn from the recent literature will be discussed and it will be seen that in many cases vibrational and rotational changes with an electric field are as important as electronic ones, if not more so. Examples of experimental work relevant to this review include research on the Kerr effect, electric-field-induced second-harmonic generation, and third-harmonic generation.

Mechanisms of quadratic electro-optic modulation of dye-doped polymer systems

Abstract: We present the experimental and theoretical considerations needed to determine the mechanisms of quadratic electro-optic modulation in dye-doped polymer systems. The modulation is observed in thin dye-doped polymer films and the quadratic Kerr coefficient is determined by using a modified Mach–Zehnder interferometric technique. The theory of several nonlinear mechanisms is developed and applied to representative systems to determine the various contributions. The fast, virtual electronic mechanism is shown to be the largest contribution, as inferred from the measured frequency dispersion of the quadratic electro-optic effect. This quick interferometric method is also shown to be useful for determining nonlinear-optical structure–property relationships.

Detecting two magnetization components by the magneto‐optical Kerr effect

Abstract: A novel technique was detecting two orthogonal in‐plane magnetization components is presented. This technique utilizes the magneto‐optical Kerr effects to sense the two components. These components of magnetization are parallel and perpendicular to the plane of incidence of the light beam. The ability to sense two components, individually or simultaneously, is a result of the disparity in the longitudinal and transverse Kerr effects. Based on the Frensel reflection coefficients of these two effects, an anlysis is presented describing this dual component sensitivity. The physical conditions are given for simultaneous and individual detection of the two in‐plane magnetization components. To substantiate this analysis, magneto‐optical measurements are made on single‐crystal Fe films. The results are discussed in the context of dual component sensitivity.

Experimental probe for thin-film magnetism in p(1×1) Pd and V on Ag(100)

Abstract: We report high-sensitivity experiments utilizing the magneto-optic Kerr effect which probe for ferromagnetism in ultrathin epitaxial films of Pd and V on Ag(100) substrates. Our experiments fail to detect unambiguous manifestations of ferromagnetism in these two thin-film systems.

Film thickness dependence of magneto‐optical and magnetic properties in Co/Pt and Co/Pd multilayers

Abstract: Co/Pt and Co/Pd multilayers were prepared by two source dc‐magnetron sputtering. It was found that magneto‐optical and magnetic properties of the multilayers were affected by total film thickness. Kerr rotation angle of the films was remarkably enhanced at the film thickness below several hundred angstroms. The theoretical calculation clarified that the increase of Kerr rotation was due to optical interference and multiple reflection. The shape of Kerr loop also depends upon the film thickness and a perfect squareness is attained only at the ultrathin region. The improvement in the squareness of Kerr loop can be explained by the change in the domain structure from a stripe domain to a single domain. These behaviors at the ultrathin region in the multilayers are suitable for new magneto‐optical recording media.

Large Kerr effects in transparent encapsulated liquid crystals

Abstract: The encapsulation of liquid crystals in a polymer matrix produces a material with interesting and potentially useful optical properties. The earliest efforts generated a dispersed phase whose dimensions were comparable to optical wavelengths and therefore afforded materials which were highly scattering. These materials have already been found useful for display applications. We have found that when these materials are fabricated so that the dimensions of the dispersed phase are substantially smaller than the incident radiation wavelengths, the material is far less scattering. dc Kerr measurements on these liquid‐crystal composites yield quite large values, ranging as high as 30 000 times CS2 This activity is shown to be a strong function of the liquid‐crystal loading and the temperature.

Quantum confinement mediated enhancement of optical kerr effect in CdS x Se 1−x semiconductor microcrystallites

Abstract: We first discuss theoretically the enhancement of the optical nonlinearity due to quantum confinement in semiconductor-doped glasses. This quantum confinement mediated enhancement also pertains to the figure of merit x (3)/α, in which case it is due to a decrease in the spectral width rather than in an increase of the matrix elements. We then report on frequency and size-dependent measurements which confirm the theoretically expected enhancement due to quantum confinement.

Determination of electric field distribution in oil using the Kerr-effect technique after application of DC voltage

Abstract: A technique based on the Kerr electrooptic effect is used for the measurement of electric field strength in dielectric liquids such as transformer oil. An elliptically polarized laser beam is used as incident light and the applied DC voltage is modulated with an AC voltage. Using this technique, low-level electric fields are measured in liquids with small Kerr constants using a short electrode length. The change of electric field distribution with respect to time after application of a DC step voltage and the nonuniformity of the electric field in water-saturated transformer oil are also studied. The electric field in water-saturated transformer oil is shown to be distorted, and the charge density is shown to be about 1 nC/cm/sup 3/ when the applied step DC voltage is 2 kV. However, electric field distribution is found to be uniform in dry transformer oil, dry silicone oil, and water-saturated silicone oil. >

Chapter 2 Magneto-optical spectroscopy of f-electron systems

Abstract: Publisher Summary This chapter discusses the spectroscopic aspect of magneto-optics with the goal to relate the experimentally determined magneto–optical spectra to electronic transitions and provides directions for searching for improved magneto–optical materials. The analysis of the magneto–optical activity of a substance is generally carried out in two stages: first, the measured quantities like the Kerr rotation and ellipticity are related to the dielectric tensor or the conductivity tensor. In a second step, these functions are then interpreted in terms of band-structure features or may even be calculated directly from relativistic and spin-polarized band-structure calculations. The chapter reviews Faraday spectra and polar magneto-optical Kerr effect spectra, and a few times, Voigt effect and equatorial and longitudinal Kerr effect spectra. In the Faraday configuration, for which the field direction is parallel to the light propagation direction, the linearly polarized wave can be decomposed into a right- and a left-hand circularly polarized wave. The rotation of the plane of polarization indicates a phase shift between the two partial waves. The Faraday rotation is, therefore, a magnetic circular birefringence.

Limitations in long haul IM/DD optical fibre systems caused by chromatic dispersion and nonlinear Kerr effect

Abstract: The power penalty induced by dispersion, Kerr nonlinearity and attenuation is numerically investigated for long haul IM/DD systems with cascaded optical amplifiers. We demonstrate that the eye opening is critically dependant on the input mean power.

Transverse modulation instability of copropagating optical beams in nonlinear Kerr media

Abstract: Two optical beams, copropagating in a Kerr medium, interact with each other through cross-phase modulation. Such nonlinear beam coupling leads to a transverse modulation instability that is evident as spatial modulation of the beam profiles. A linear-stability analysis in the plane-wave approximation predicts the range of spatial frequencies over which modulation can occur. The case of self-defocusing media is particularly interesting, since modulation instability occurs only when both beams are present simultaneously. Numerical simulations are used to study how modulation instability can occur for finite-size beams. In particular, the mutual coupling of two copropagating Gaussian beams is studied in detail.

Kerr effect of two-medium layered systems

Abstract: Detailed and practical expressions are given for the magneto‐optical Kerr effect (MOKE) for various configurations of two media. One is a magneto‐optic (MO) one, and the other is a nonmagnetic (NM) medium. For a system of two thick media with a single interface, with a first‐order approximation in MOKE term Q, the Kerr function is determined by the product of a MOKE term Q and an optical term η. A second type of system includes a thin MO (or NM) layer deposited on a thick NM (or MO) substrate. For a MO/(NM‐substrate) configuration, the Kerr function is related to the Kerr effects from the air/MO and MO/NM interfaces, and to the Faraday effects of the MO layer, as well as to interference effects. The enhancement factor can be expected to be large by proper choice of materials. For a NM/(MO‐substrate) configuration, the total Kerr function is related to the Kerr effect from the NM/MO interface and can be enhanced by interference. The enhancement factor is expected to be less than one if the NM layer is stro...

A novel nonlinear optical effect: Stimulated Raman–Kerr scattering in a benzene liquid‐core fiber

Abstract: By using a long interaction length (250 cm) provided by a liquid (benzene)‐core multimode hollow fiber, we have observed a novel superbroadening stimulated scattering added to the first‐ and second‐order Stokes stimulated Raman scattering lines of liquid benzene. To explain this new effect, a photon‐scattering model of Raman‐induced optical Kerr effect, named as Raman–Kerr scattering, is proposed.

Surface magneto‐optical Kerr effect for ultrathin Ni‐Fe bilayers

Abstract: Surface magneto‐optical Kerr effect is used to measure magnetic hysteresis loops for Ni‐Fe bilayers previously studied by ferromagnetic resonance [Phys. Rev. 38, 12879 (1988)]. The approach to saturation in the [11] direction confirms the existence of enhanced fourfold in‐plane magnetic anisotropy, attributed to the effect of arrays of misfit dislocations arising during the epitaxial growth of bcc Ni overlayers on ultrathin layers of bcc (001)Fe. The [11] magnetization curves for 10 monolayers (ML) of Ni on 7 ML of Fe shows a breaking of symmetry between positive and negative fields. This is ascribed to spin configurations frozen during growth.

Magneto‐optical properties of Co/Pd superlattice thin films

Abstract: We present the remnant polar Kerr rotation and ellipticity for a Co/Pd superlattice. The magneto‐optical properties of Co/Pd superlattice thin films have been investigated by measuring both the polar Kerr and ellipticity hysteresis loops at a wavelength of 780 nm. It was found that the remnant Kerr rotation was strongly dependent on the thickness of Co and Pd sublayers as well as the total film thickness. In this system, the maximum polar Kerr rotation of 0.43° was observed at the film thickness of 110 A, where each bilayer was composed of 2‐A‐thick Co and 9‐A‐thick Pd sublayers.

Kerr effect imaging of dynamic processes in magnetic recording heads

Abstract: Techniques for imaging microscopic dynamic magnetic phenomena in magnetic recording heads are reviewed. Two experimental apparatus which utilize the Kerr magnetooptic effect are described. A scanning magnetooptic photometer uses the principles of confocal optical microscopy in which a focused laser spot serves as a high-resolution ( approximately 0.3 mu m) probe of magnetic activity to very high frequencies (250 MHz). Magnetooptic flash photography uses the technique of stroboscopic imaging with digital image processing to provide instantaneous (10 ns exposure time) images of magnetic phenomena on a microscopic scale by utilizing a pulse laser for illumination. Results from various studies of ferrite, metal-in-gap, and thin-film magnetic recording heads using these apparatus are reviewed along with their methods. >

Observation of polarization instabilities and modulational gain in a low-birefringence optical fiber.

Abstract: Intense linearly polarized light has been used to observe polarization instabilities due to the optical Kerr effect in a low-birefringence optical fiber. Near the onset of instability small intensity modulations are amplified and a sixfold increase in modulation depth is observed. The transmission through a crossed polarizer is markedly different for intense beams aligned near the fast and slow axes. The critical power of 250 W is in agreement with theoretical predictions.

Large room‐temperature magneto‐optical Kerr effect in CuCr2Se4

Abstract: The magneto‐optical polar Kerr effect has been measured on CuCr2Se4 single crystals between 0.55 and 5.0 eV. The single Kerr ellipticity eK reaches −1.19° at 0.96 eV which is (besides PtMnSb with θK=−1.27° at 1.72 eV) the highest value ever observed at room temperature. The figure of merit R1/2(θ2K + e2K)1/2 has a maximum value of 0.84° at 0.88 eV which is as high as in PtMnSb (0.83° at 1.57 eV). This large magneto‐optical Kerr effect is due to the steep plasma edge observed in the reflectivity R. First experiments show that the photon energy at which the plasma edge occurs can be shifted by suitable substitutions in CuCr2Se4.

Nonlinear optical properties of H2 and D2

Abstract: Accurate wave functions of the James–Coolidge type, which account for electron correlation, are used to calculate for H2 and D2 the dynamic second hyperpolarizabilities (γ) which mediate the nonlinear optical processes: dc Kerr, dc electric‐field‐induced second‐harmonic generation and third‐harmonic generation. Values are given for a range of frequencies (ω=0 to ω=0.05 a.u.) as well as for some common laser frequencies. The effects of vibration are explicitly considered. As well, values of the dynamic field‐gradient polarizabilities B and C are found. The results are more accurate than those previously published.

Frequency‐domain observation of the ultrafast inertial response of the optical Kerr effect in CS2

Abstract: Time‐domain experiments using femtosecond pulses have recently revealed the inertial aspect of the nuclear‐orientation component of the optical Kerr effect in carbon disulfide. We present frequency‐domain measurements, performed with the tunable‐laser‐induced grating technique, which also demonstrate the need to incorporate inertial behavior in models of the nuclear‐orientation contribution to this ultrafast response. No previously suggested model, however, yields a fit to our data that passes standard goodness‐of‐fit tests at an acceptable level.

High Contrast Polarizers For The Near Infrared.

Abstract: Corning has extended the performance of its PolarcorTm near infrared glass polarizers to contrast ratios k1 /k2 of over 10,000. These polarizers offer broader bandwidth, higher transmittance, higher temperature resistance, better durability, and improved contrast (extinction) when compared to plastic and wire grid polarizers. Acceptance angle, cost, and compactness are significantly better than crystal polarizers. Applications include optical isolators, Faraday rotators, magneto-optic devices, fiber optic sensors, Kerr effect devices and optical data storage devices. Polarcor contains elongated, submicron silver metal particles aligned along a common axis. These particles preferentially absorb the polarization component of light which is aligned with the elongation axis of the particles. The mechanism is believed to be resonant absorption by the silver conduction electrons. Careful process control allows the polarizer performance to be optimized at various laser lines, although a wide bandwidth provides polarization over a range of wavelengths. The polarization results from a very thin layer on the surface of the polarizer, thus allowing high contrast from a very thin package. Recent advances in processing have resulted in increases in the contrast ratio from 500 to over 10,000 while maintaining k1 values of 87-91%, depending on wavelength. The corresponding values of Ho and Hgo are 38-41% and 7.6-8.5x10 -5 , respectively. Performance may be improved by application of high efficiency anti-reflective coatings. This paper reports on a characterization study of the performance of newly developed Polarcor high contrast polarizers optimized for applications from 725-1550 nm.

Magneto‐optical measurement of anisotropy energy constants on amorphous rare‐earth transition‐metal alloys

Abstract: Measurements of the magneto‐optic polar Kerr effect are performed on samples with perpendicular magnetization using in‐plane magnetic fields. The magnetic anistropy constants are then determined from these measurements. The applied in‐plane magnetic field varies from −20 to 20 kOe. Samples are mounted in a temperature‐controlled chamber whose temperature is varied in the range of 80–475 K. In the theoretical model the anisotropy energy is expressed as the sum of terms containing sin2 φ and sin4 φ with two anisotropy constants, K1 and K2, to be determined. By matching the theoretical curves with the experimental data, we obtain two functions α(T) and β(T), which are the normalized values of K1(T) and K2(T) with respect to the saturation magnetization Ms(T).

Theory of nonlinear surface magneto-optics for ferromagnetic nickel: Effects of band structure and matrix elements

Abstract: The nonlinear magneto-optical Kerr effect has been proposed as an ultrafast spectroscopic probe for the magnetic and electronic properties of ferromagnetic surfaces. We extend our previous calculation of the linear (first-order) and nonlinear (second-order) magneto-optical susceptibilities by the inclusion of the complete nickel band structure and the dipole transition matrix elements within the combined interpolation scheme. As ab initio band-structure calculations usually cannot describe optical and magneto-optical absorption (especially in nickel), the band-structure parameters are taken from a fit to spin-polarized photoemission data and de Haas\char21{}van Alphen measurements of the Fermi surface. The detailed shape of the Brillouin zone is included. Comparison to linear magneto-optical Kerr-effect measurements shows that the inclusion of the full anisotropic band structure and of the dipole matrix elements is necessary to remove parameter ambiguities and leads to strongly improved agreement between theory and experiment. This electronic theory confirms the previous assertion that the nonlinear magneto-optical Kerr effect should be observable and clearly shows that this effect contains detailed information about the electronic and magnetic surface properties (band structure, exchange interaction, spin-orbit coupling). Thus, the theory can help to interpret forthcoming nonlinear magneto-optical measurements. We discuss possible geometries for experimental and technological applications.

All-optical ultrafast nonlinear switching utilizing the optical Kerr effect in optical fibers

Abstract: An ultrafast switching technique utilizing the optical Kerr effect in optical fibers is described and its switching characteristics are considered, taking into account chromatic and polarization dispersion. Experimental results on picosecond optical Kerr modulation and 2 Gb/s all-optical complete demultiplexing of a 30 ps probe pulse train, as well as all-optical chirping manipulation of ultrashort optical pulses, are presented. Applications of the optical Kerr switching technique to the determination of the nondiagonal component n281 ofthe nonlinear refractive index in nonlinear optical media and to the generation of ultrafast pulse trains are also discussed.