Modified holographic recording setup for photopolymerizable/flexible recording materials

An improvement in the conventional holographic recording setup has been done for liquid (photopolymerizable) or flexible recording materials. The new vertical recording setup that comprises a horizontal substrate holder permits holographic recording on such materials without positioning them between two substrates, as has been done until now. This setup can be conveniently used for the fabrication of transmission, reflection, Fourier transform, and computer-generated holograms with few simple modifications as indicated.     

Direct Solution of Medium Field and Cross-Track Characteristics of Read Sensors

This paper describes a direct calculation method for medium fields in perpendicular recording systems. The method accounts for the effect of the zig-zag transition in the written medium pattern which can be obtained using micromagnetic simulations. The described method is useful for studying the cross-track characteristics of read sensors. The method is able to deal with a recording medium layer with nonunity relative permeability. The computed medium field in the gap region under the read head is compared with that obtained using the finite-element method. The purpose of this study is to develop a fast and effective tool for producing read-back signals based on computer modeling and simulation.     

Transverse recording using thin film recording heads

This paper presents the results of an investigation of a high density magnetic recording technique utilizing a thin film recording head and a transverse mode of recording on thin media. The significant results of this investigation are as follows. 1) Densities as high as 18 500 transitions per inch were experimentally written in a 300-Å thick FeCr medium having an Hcof 70 oersteds. 2) These densities were written with a thin film, vapor-deposited, recording head having a MATED-FILM® structure with a 0.4-mil etched gap. 3) Track widths of 1-mil on 2-mil centers were experimentally achieved. 4) Optical readout of a 0.2-mil wide transition (width of beam) region corresponding to 5000 transitions per inch was achieved using a laser beam and a linear motion transport system under ideal experimental conditions. 5) The magnetic field from the Néel wall separating recording domains was detected using a MATED-FILM Etched Gap head making this a possible readout method. Maximum achieved linear bit densities as a function of recording media coercivities are given.     

Transversal recording on radially anisotropic disc

Transversal recording has been described in the sixties, as a promising mode to achieve high density magnetic recording [1]. Because of the improvements in longitudinal and vertical recording introduced by thin film technologies for heads and media, research labs took no further interest in this transversal mode, partly due also to the fact that media and heads were not available at that time. However technological advances of recent years such as the attainment of high B(H) loop squareness for amorphous or crystallized magnetic alloys such as CoxSm1-x[2] and the capability of conventional ferrite heads to record vertical bits on a strongly anisotropic medium [3] allow us to assert that transversal magnetic recording (TMR) can be developed today. This paper describes recent studies for a radially anisotropic disc on a new TMR system. Experimental results on Co-Sm are presented, and the complementary features between the transversal mode and both vertical and longitudinal magnetic recording are discussed.     

Perpendicular stand-still recording in Co-Cr films

Some features of perpendicular recording were investigated by means of stand-still recording experiments. For this purpose several radio frequency (RF)-sputtered Co-Cr layers of two different compositions were used as media while a Permalloy single pole (SP) head was used as a write transducer. A magnetoresistive transducer (MRT) was utilized to read the recorded pattern. Further, an analytical model was developed enabling the magnetization induced by the head field in the recording medium to be calculated. Both calculations and experimental results show a sharpening of the transition, due to the demagnetizing field. For a good approximation it is sufficient to consider only the vertical head field component and vertical magnetization in the recording medium. This is a consequence of the well-developed perpendicular anisotropy and negligible in-plane remanence of the Co-Cr layers. In addition the read-out signal is completely determined by the magnetic surface charges. The remanent magnetization in the recording medium and therefore the read-out amplitude is limited by demagnetization and consequently determined by the coercivity of the Co-Cr layer. The medium noise of a dc-erased medium indicates magnetic structures of much larger dimensions than the size of the individual crystallites. This noise appears to be dependent on the saturation magnetization of the Co-Cr medium. Activation of the single pole head by a homogeneous field results in a nonlinear behavior, caused by head saturation effects. This is supported by simple one-dimensional calculations of the head field.     

Large-viewable-angle rainbow holography

A new, to our knowledge, method for recording rainbow holograms of three-dimensional diffused objects in one step without the use of slits is proposed. No lens is needed for recording in this kind of holography; instead, multiple synthetic slits are created by displacement and multiple exposure of an object to expand the horizontal and the vertical viewing angles of the hologram.     

Influence of background vertical motions on free convection over a thermally inhomogeneous horizontal surface

In a linear approximation the problem of the influence of background vertical motions on free convection over a thermally inhomogeneous horizontal surface has been solved analytically. The dimensionless number that determines this influence and that represents the ratio of the product of the characteristic velocity of background vertical motions and of the horizontal scale of thermal inhomogeneities to the coefficient of thermal diffusivity of the medium has been found. Descending motions may effectively suppress convection (not only decrease the height of penetration of convective motions into the medium but also to decrease their amplitude substantially). Ascending motions increase the height of penetration of convective motions into the medium and, to a lesser extent, the vertical component of convective velocity. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 1, pp. 97–101, January–February, 2008.     

5.25 inch floppy disk drive using perpendicular magnetic recording

5.25 inch high density perpendicular magnetic recording floppy disk drive has beer developed by employing new types of high saturation magnetization ring head, Co-Cr single layer medium with Ge underlayer, head slider with ellipsoidal surface configuration to assure intimate head to medium contact, and signal equalization. By these combination, recording density D50 of 145 kFCI, peakshift of 28 % at 100 kFCI, signal to noise ratio of 40.4 dB for cut-off frequency 4.25 MHz, overwrite signal to noise ratio of 27 dB, measured by writing signals at 48 kFCI over previously written 100 kFCI signals were obtained as typical recording characteristics. These results would indicate that floppy disk drive with 100 kFCI recording density has enough system margin by above-mentioned combination. In this paper, design and performance of newly developed floppy disk drive are described.     

Fundamental properties of perpendicular magnetic recording

A two dimensional computer simulation model of the magnetic recording process has been, developed to assess the fundamental properties of perpendicular magnetic recording. It was found that vertical anisotropy media are well suited to abrupt and closely spaced magnetic transitions. The demagnetizing fields support short transitions in the perpendicular mode as opposed to degrading transitions in the longitudinal mode. However, gapped heads may have difficulty in delivering high intensity vertical fields to saturate the medium. Novel write head designs might be required.     

Methylene blue sensitized poly(methyl methacrylate) matrix: a novel holographic material

Methylene blue sensitized poly(methyl methacrylate) is shown to be an efficient medium for recording three-dimensional holographic gratings. Phase and/or amplitude holograms can be written in the methylene blue sensitized films of poly(methyl methacrylate) with a conventional source of light, a He-Ne laser operating at 632.8 nm. Diffraction efficiencies of 60% were found for thick holograms. Multiple holograms were recorded in the described system, and an optical erasing of holograms was achieved. Hologram recording speed was found to increase with temperature.     

Comparison of Micromagnetic and Point Probe Model in Magnetic Force Microscope Simulation

We developed a micromagnetic model of magnetic force microscopy (MFM) tip to compare it with the simple point probe model. We simulated the MFM signal to provide an understanding of the measurement of the field generated by the write head in perpendicular recording hard disk drives. When the magnetic pole density at the air-bearing surface of the head's main pole is increased from 0.2 T to 1 T, the MFM tip with vertical anisotropy shows a flower-state magnetization, while the tip with horizontal anisotropy has more complicated switching modes. It is found that the signal ratio of the two MFM tips with vertical/horizontal anisotropy does have a one-to-one correspondence to the average magnetic field in the tip; however, the signal ratio may change sign because of the magnetic moments' switching in the tip with vertical anisotropy. The result of micromagnetic simulation is quite similar to that of the point probe model, and has good agreement with experiments.     

Hydrodynamics in Falling Liquid Films on Surfaces with Complex Geometry

The paper present the results of experimental studies on dynamics of the film flow of cryogenic liquid over the complex surfaces: vertical plane and ribbed aluminum plates with horizontal wave microtexture. Experimental results were obtained at the flow of liquid nitrogen. According to high-speed video recording, in case of horizontal microstructure the wave dynamics influences considerably liquid redistribution in transverse direction. This is caused by the fact that liquid flows intensively at propagation of secondary waves along the channels of horizontal microstructure. According to results of experiments on the ribbed structured perforated aluminum surfaces with the horizontal microstructure with the use of highly wetting low-viscous liquids, the film flow character depends significantly on the irrigation rate. The direction and parameters of microstructure, position and diameter of holes effect significantly the zones of liquid spreading and its distribution over the surface of the ribbed structured plates, especially, within the range of low liquid flow rates.     

Pulse-laser electroholography by use of interference fringe patterns captured by a CCD

Digital holography is combined with a pulse-laser electroholographic system for a real-time three-dimensional display. Owing to the one-dimensional characteristics of the Bragg-regime acousto-optic spatial-light modulator, vertical parallax cannot be generated from the acoustic signal propagating along the fan-shaped beam direction of the incident laser. To obtain a proper interference pattern, we attach a horizontal slit to the confocal lens system for recording the fringe data, significantly reducing the bandwidth of the vertical fringe data. When the bandwidth-reduced fringe data are displayed by use of a pulse-laser electroholographic system, the clarity and the quality of the image are found to be appreciably improved.     

Magnetic field of a ring head on a double layer medium

A simple theoretical model is developed for a Karlquist-type recording head interacting with a two layer recording medium in which the sublayer has a high but finite permeability. During readback the vertical H fields far from the gap are shown to decay exponentially with a characteristic length r given byr = t ast h ast uwhere t is the sublayer thickness, h is the spacing between the head and the sublayer, and u is the relative permeability of the sublayer. The long tails of this field account for observed readback wave forms. The model also predicts that the spatial extent of sublayer saturation during the write process will be twenty to one hundred gap lengths, justifying the assumption that during write one may ignore the sublayer. The write prediction was tested experimentally by making a standstill recording with a Winchester-type head on a double layer medium and measuring the fringing field above the medium with a high-resolution Hall probe. The data were compared to the predictions of an iterative simulation in which the sublayer was either present or absent during write. A significantly better fit was found when the simulated medium contained no sublayer during the write process.     

Toward the theory of convection in a rotating stratified medium over a thermally inhomogeneous horizontal surface

Stationary convection in a rotating medium uniformly heated from above and nonuniformly cooled from below has been studied analytically in the linear approximation. As distinct from a number of previous works, the case of the presence of both a stable background stratification and of intense rotation around a vertical axis has been analyzed. One of the interesting properties of the solution found is that despite the stable stratification the perturbations of temperature, pressure, and of the vertical velocity over the thermal inhomogeneities of the horizontal surface, in the case of strong rotation, penetrate deep into the medium (up to heights of the order of the horizontal scales of the inhomogeneities mentioned.) The ascending motions over the "warm spot" transfer relatively cold volumes of the medium upwards, so that beginning from a certain level a vast "cold" region can be formed and the related positive deviation of pressure (of the weight of the medium column). This leads to the formation of the anticyclonic vortex perturbation.     

Three-dimensional force calibration of optical tweezers

Abstract

We demonstrate a method for 3-dimensional force calibration of optical tweezers by recording the trapping dynamics of polystyrene beads. This is realized by time-resolved detection of the horizontal and vertical position of a bead which is drawn to the focus of a laser beam. The method provides real time characterization of the force profile of an optical trap in all directions.     

长柱药包爆破振动位移特性研究

通过研究长柱药包爆破振动波在围岩介质中的传播规律,得到了长柱药包爆破产生的围岩介质位移数值解。对爆破质点位移的分析表明,质点水平和竖向位移在距离爆源一定水平距离时达到最大,该距离与药包的长度和埋深有关。而沿着竖向的质点位移分布规律表明,长柱爆破振动效应在柱体中心两侧并不是对称的。这些规律对进一步研究长柱爆破振动效应有一定的指导意义。     

Interpretation of spectral response in perpendicular recording

A previously published voltage spectrum in perpendicular recording is analyzed here utilizing the exact fields of a probe head and keepered medium. It is concluded that sharp transitions have been written at a negligible spacing. Previous analysis which utilized a duality between a ring head and a probe-keeper head yielded a non-zero spacing or recorded transition length. Measurements of D50for varying record geometries are analyzed in terms of scaling laws.     

Fabrication and MFM study of 60 nm track-pitch discrete track media

Discrete track magnetic recording media with a 60 nm track pitch and prewritten servo patterns were fabricated and tested for read/write performance, and a feasibility analysis of the embedded servo was performed. The fabrication process consisted of ultraviolet nanoimprint lithography (UV-NIL) and sequential ion beam etching on a conventional perpendicular magnetic recording medium. Magnetic patterns were written to the fabricated tracks at 700 kilo flux changes per inch (kFCI) using a spin stand and were read using magnetic force microscopy (MFM), with a resulting signal-to-noise ratio (SNR) of 12.15 dB. The servo pattern was also visualized with MFM. These results demonstrated the feasibility of writing to a 30 nm wide discrete data track and the workability of the embedded servo pattern.     

Geometric effects in the magnetic recording process

A simplified view of magnetic recording is presented in which the effect of head-medium geometry is clearly exhibited. The model is applied to contact recording with a ring head on thick particulate media. Demagnetization fields are neglected and identical particles with angularly invariant switching fields are considered with various orientation distributions in the recording plane. For all orientation distributions symmetric about the longitudinal direction the longitudinal magnetization component vanishes at the head surface and increases with depth into the medium. Conversely, the vertical component is maximum at the head surface and decreases with depth. The resulting recording spectra therefore have greater magnitudes for vertically well-oriented particles and isotropic distributions of particles with biaxial symmetry. At short wavelengths these distributions give approximately 5 dB more output than longitudinally well-oriented media. The depth variation of longitudinal magnetization also provides one explanation for the peak in the short wavelength input-output curve measured on longitudinal media. These conclusions are expected to be dependent on the assumed angular variation of the particle nucleation field.