Off-axis Structure Research Articles

Basalts from MAR at 13°15′–13°40′N: What mixed?

We present new data on chemical composition of basalt glasses collected within the geochemical anomaly of the Mid-Atlantic ridge at 13°25′–13°40′N, where fresh quenched lavas occur dominantly in asymmetric off-axial structures. The collected samples indicate wide compositional ranges from strongly depleted D-MORB with 0.04 wt% K2O, K2O/TiO2 = 0.08 and (La/Sm)N = 0.69 to the most enriched E-MORB with 0.92 wt% K2O, K2O/TiO2 = 0.42 and (La/Sm)N = 2.45. Clear correlations are traced between incompatible element ratios (K2O/TiO2, La/Sm, Nb/Zr), concentrations of MgO, K2O, H2O, and 87Sr/86Sr ratio, suggesting variable contribution to the compositional diversity of the glasses from two distinct source materials, one of which is depleted mantle. Testing the hypothesis of pyroxenite-derived melts as an enriched end-member failed to reproduce the observed REE patterns, (Sr/Zr)N, and (Ba/Nb)N ratios, and the K2O–K2O/TiO2 relations. Two alternative hypotheses – melts derived from melting remnants of continental crust (1) or oceanic core complex (OCC) gabbro (2) – are suggested based on the complementary character of the REE patterns of the basalt glasses and partial melts compositions calculated at 1000 °C/50 MPa from either bulk continental crust as estimated by Taylor and McLennan (1995) (1) or OCC gabbro sampled in the study area (2). Complementarity of the two sources with the D-MORB holds also for the other geochemical parameters: (Sr/Zr)N vs (Ba/Nb)N, (La/Sm)N vs (Rb/Nb)N, and for the K2O–K2O/TiO2 relations. The first hypothesis calls upon partial melting of continental crustal material preserved in the vicinity of ridge-transform fault system, while the second suggests melt-rock interaction within the off-axial structures of the pre-existed gabbro assemblages, with concurrent melting of the wall-rock material and dissolution of the resulting melt in the intruded magma. Both scenarios, operating either separately or jointly, might contribute to the MORB geochemical variability documented in the present study.

Femtosecond laser-inscribed off-axis high-order mode long-period grating for independent sensing of curvature and temperature.

We propose and demonstrate a novel curvature and temperature sensor based on an off-axis small-period long-period fiber grating (SP-LPG) which is inscribed in a single mode fiber by a femtosecond laser in one step. The total length of the SP-LPG is only 2.1 mm. The period of the SP-LPG is 30 µm, which is smaller than that of conventional long period fiber gratings. Essentially, the SP-LPG is a high-order mode long period fiber grating. Due to the off-axis structure, the SP-LPG can be used for two-dimensional vector bending sensing. The curvature can be demodulated by the intensity variation of the dips in the transmission spectrum. When the incident light is polarized, the instantaneous curvature sensitivity of the SP-LPG can exceed 20 dB/m-1. Meanwhile, a series of Bragg resonant peaks can be observed in the reflection spectrum, which can be used to monitor the fluctuation of temperature. The transmission dip is insensitive to temperature and the reflection peak is insensitive to curvature, which allows the SP-LPG to measure curvature and temperature independently. The characteristics of high curvature sensitivity, two-dimensional bending direction identification, real-time temperature measurement, and compact structure make the device expected to be applied in the field of structural health monitoring and intelligent robotics.

A Compact MEMS-Based Optical Scanning System with Large Field of View for Lidars

In this work, a design of a compact optical MEMS-based lidar scanning system with a large field of view (FOV) and small distortion is presented. The scanning system applies an off-axis structure and the length of the system can be reduced to about 10 cm in an optimized way. Simulation results show that a large FOV is achieved under a uniform scanning scheme. In addition, the spot size less than 20 cm at distance of 100 m is also realized. The optical scanning system can be used for the vehicle-mounted Lidar.

Off-Axis Diffractive Optics for Compact Terahertz Detection Setup

Medical and many other applications require small-volume setups enabling terahertz imaging. Therefore, we aim to develop a device for the in-reflection examination of the samples. Thus, in this article, we focus on the diffractive elements for efficient redirection and focusing of the THz radiation. A terahertz diffractive optical structure has been designed, optimized, manufactured (using extrusion-based 3D printing) and tested. Two manufacturing methods have been used—direct printing of the structures from PA12, and casting of the paraffin structures out of 3D-printed molds. Also, the limitations of the off-axis focusing have been discussed. To increase the efficiency, an iterative algorithm has been proposed that optimizes off-axis structures to focus the radiation into small focal spots located far from the optical axis, at an angle of more than 30 degrees. Moreover, the application of higher-order kinoform structure design allowed the maintaining of the smallest details of the manufactured optical element, using 3D printing techniques.

Robust whispering gallery mode resonator for humidity measurement

Abstract A fiber-optic humidity sensor based on microsphere resonators with graphene oxide (GO) coated is proposed. A variable pitch off-axis spiral structure (VPOASS) excites multiple higher-order cladding modes in single-mode fiber (SMF) and introduces a strong evanescent field. Hollow glass microspheres are deposited on the surface of the VPOASS, and the GO film coated on the surface of the microspheres and the VPOASS. We used the VPOASS with ~ 125 μm diameter to excite the whispering gallery modes (WGMs) by evanescent coupling. When water molecules enter the GO film, the refractive index (RI) and the size of the GO film will be changed, and then the size and effective RI of the microspheres, as well as the effective RI of the cladding modes propagating in SMF will be changed, resulting in the shift of transmission spectrum. The humidity sensitivity of the proposed sensor prototype is −37.3 pm/% RH over the range of 10% RH to 60% RH. The proposed sensing structure has potential application prospects in the field of humidity or volatile organic compounds sensing.

Design and analysis of polarization imaging lidar and short wave infrared composite optical receiving system

<sec> The basic principle of three-dimensional (3D) imaging lidar-an active imaging technology, is parallel laser ranging. Compared with traditional passive sensor imaging and microwave radar, the 3D imaging lidar has obvious advantages, so it promises to possess a wide application prospect. Non-scanning 3D imaging lidar has seven modulation modes. Among them, the 3D imaging lidar based on polarization modulation has the advantages of large measurement range, high measurement accuracy, fast imaging speed, and no motion artifacts. At the same time, it is not limited by other modulation methods, such as intensified charge coupled device and avalanche photodiode array detectors, and its process is complex but easy to saturate and damage. However, its disadvantage is that it requires two cameras, electro-optic crystal limits the imaging field of view, and is easily affected by atmospheric conditions such as incident angle and cloud and mist. </sec><sec> In order to overcome the above shortcomings, in this paper we propose to use polarization imaging lidar and short-wave infrared zoom optical system to construct a dual-mode target detection imaging system by means of common aperture, which can not only reduce the volume of the two systems and solve the coaxial problem of the two systems, but also solve the problems such as the influence of atmospheric conditions (small viewing angle, incident angle and cloud and mist) on imaging quality of polarization modulation imaging lidar and the limitation of low energy of short-wave infrared imaging targets. According to the above ideas, the design and research of polarization imaging lidar and shortwave infrared composite optical system are carried out. The optical design software is used to complete the optical design of the telescope group, shortwave infrared imaging lens group, polarization modulation lens group and the system as a whole. In the telescope group the off-axis three-mirror structure is used to solve the blocking problem of the center of the field of view, and in the shortwave infrared lens group the type of mobile zoom compensation group is used to realize zooming. Analysis of the image quality of the optical system shows that the designed optical system has high imaging quality and its optical design meets the requirements for system design. The optical simulation software is used to simulate the imaging process of the optical system. The results show below. The polarization imaging lidar and shortwave infrared imaging have high quality, the stray light has little influence on the imaging of the system, the target edge imaging is clear, and the independent square targets with a 1-m in diameter can be distinguished. The field of view of the short-wave infrared short-focus mode is 9 times that of the long-focus mode. The shortwave infrared telescopic mode is basically consistent with the field of view of polarization imaging lidar. The received illuminance value of polarization imaging lidar is about 2.4 times that of short-wave infrared long focal length mode. The overall energy distribution of polarization imaging lidar is more balanced, and the imaging effect is better. The method adopted in this paper provides a new idea for studying the polarization modulated imaging lidar. The next step in experimental research is to complete the physical processing, assembly and adjustment, and selection of suitable targets. </sec>

Asymmetric crustal structure of the ultraslow-spreading Mohns Ridge

ABSTRACTNew analysis of the geophysical data of the ultraslow-spreading Mohns Ridge and its off-axis structure reveals a distinctive asymmetric structure. We calculate residual bathymetry (RB) and residual mantle Bouguer gravity anomaly (RMBA) and decompose the anomalies into symmetric and asymmetric components between the ridge conjugates. The western flank of the Mohns Ridge at crustal age of ~50–15 Ma is characterized by a broad zone of elevated RB and more negative RMBA, which we term the Vesteris Plateau (VP). The VP anomaly has a surface area of ~1.12 × 105 km2 and an excess crust volume of ~2.33 × 105 km3, making it a significant anomaly comparable to other anomalies such as the Bermuda Rise. Extending north of the Kolbeinsey Ridge for more than 500 km, the VP lies above an anomalous upper mantle region of low shear-wave seismic velocity, indicating that the VP might represent the northernmost reach of the Iceland-Jan Mayen mantle anomaly. In addition, the western ridge flank of the Mohns Ridge at crustal age of 6–0 Ma is associated with higher RB and more positive RMBA relative to the eastern conjugate, indicating tectonic uplift and associated exposure of lower crust and upper mantle near the ridge axis.

Automatic obscuration elimination for off-axis mirror systems

The degree of automation in optical design has always been improving, and several human-competitive automatic lens design programs have been developed. However, to the best of our knowledge, no such work on off-axis systems has been reported, which we think is largely due to the complicated unfeasible conditions caused by obscuration. Here, we propose a model to detect and evaluate the degree of obscuration for off-axis mirror systems and also a method to automatically eliminate the obscuration by structural optimization. This effect of obscuration elimination is demonstrated by several examples. It can greatly facilitate the design of off-axis mirror systems. Particularly, the method can be applied in the search for feasible off-axis structures from on-axis ones. This work may provide insight for further study of human-competitive automatic design of off-axis systems.

Off-axis photonic bands of hexagonal plasma photonic crystal fiber containing elliptical holes with defect of high index material for nonlinear waves by PWE method

A novel model of hexagonal photonic crystal fiber (PCF) composed of fluoride-doped silicate and plasma materials for estimating the off-axis band structure has been presented. The well-known plane wave expansion (PWE) method has been adopted for the analysis of band structure. We have observed the influence of intensity of field on photonic band gap (PBG) by creating different types of defect in the holes of the PCF structure for the design of waveguide and narrow-band filter. A dynamic shift in bands and photonic band gaps (PBGs) has been reported and compared with other designs. The PCF containing the defect of high index material in the presence of plasma has been found to be more suitable to control the propagation of photon for nonlinear waves. The PWE calculations have shown that the four off-axis PBGs for the different contribution of plasma holes could exceed by 1.0 normalized frequency or they could compensate within 0.24 normalized frequencies on introducing alternate distribution of high index material like SF57 in the cladding.

Design and Research of Off-Axis Three-Mirror Space Remote Sensor Structure

On the basis of characteristics of optical system of three-mirror off-axis, with the method of topology optimization, the mirrors’ support structure and the frame structure which is a truss structure of the optical system were designed and investigated, the lightweight of the support structure and the truss structure are important, the structure optimization design of the system was completed, which quality is very light, by means of the finite element analysis techniques, we know that the shape error variation RMS and PV of optical mirror which are important indexes of image quality. The modal analysis and dynamic simulation calculation were carried out and the response character of the structure under dynamic environment was solved. Finally, the correctness of the finite element analysis results and the rationality of the design are validated by environmental testing. the analysis and test results indicate that the PV and RMS meet the design indexunder the comprehensive influence of gravity and thermal load which is in the control range, the overall structure have a high enough dynamic stiffness and reasonable distribution of modal, and the dynamic response of Space Remote Sensor was within the allowable range, which meet the use requirement.

Compensation of elemental image using multiple view vectors for off-axis integral floating system.

A novel method is proposed to compensate the distortion caused by the off-axis structure in integral floating with a concave mirror. The proposed method of this paper can generate the elemental image that is integrated into the multiple predistortion images for the corresponding multiview directions, which cannot be performed by the predistortion method using a single-view vector. The fundamental concept of the proposed method is that the predistortion images can be generated for more than two view vectors, which are defined by each set of corresponding elemental lens and subimage, and captured onto the subimage. In addition, the subimage can be divided into the several segments to increase the number of view vectors, so that the predistortion images generated by more view vectors can enhance the degree of compensation. The proper number of the view vectors per subimage is discussed and analyzed based on the small-angle approximation. Experiments to verify the feasibility of the proposed method are performed.

Off-axis structures of spreading zones according to results of experimental modeling

The off-axis topography of spreading ridges is a result of tectonic and magmatic processes occurring in the axial zone and operating off the ridge axis during further evolution of the crust. The results of physical and numerical simulations have shown that differences in topography roughness, rift valley depth, frequency and amplitude of normal faults, and geometric stability of the rift axis are determined by (a) the rate of extension and accretion of the new crust, (b) the thickness of the brittle lithospheric layer, and (c) the temperature of the underlying asthenosphere. Under conditions of the fast spreading, the stationary axial magma chamber in the crust predetermines the existence of the thinner and weakened lithosphere. As a result, the axis jumps for a short distance and the axis geometry remains almost rectilinear. The destruction of the thin axial lithosphere with a low mechanical strength results in formation of frequent and low-amplitude normal faultings. All these factors lead to the formation of the characteristic poorly dissected topography of fast-spreading ridges. Without a stationary axial magmatic chamber in the crust of slow-spreading ridges and with a thick and strong lithosphere, a deeply dissected axial and off-axis topography arises. The axis jumps for a significant distance within the rift valley, giving rise to geometric instability of the axis and development of transform and nontransform offsets.

Analysis of Off-axis Integral Floating System Using Concave Mirror

An off-axis integral floating system using a concave mirror is analyzed to resolve the image distortion incurred by the off-axis optical arrangement. The concave mirror can be adopted as the floating device to improve the optical efficiency. The image distortion due to the tilting axis of the concave mirror needs to be analyzed precisely to generate the pre-distortion image. In this paper, we calculate the image deformation in the off-axis structure of the concave mirror using the geometrical optics. Using the calculation results, the compensated elemental image can be generated for the pre-distortion integrated image, which can be projected to the floating 3D image without image distortion. The basic experiments of the off-axis integral floating are presented to prove and verify the proposal.

A computational study of hydrogen bonding complexes between 1,2,3-triazine and water

The hydrogen-bonded complexes between 1,2,3-triazine and water have been studied using density functional theory, second-order Moller-Plesset perturbation theory and complete-active-space self-consistent-field methods. For the 1,2,3-triazine–H 2O complex, our calculations predicted two comparably stable hydrogen bonding formations with the water molecule interacting to the axis nitrogen and to the off-axis nitrogen of 1,2,3-triazine, respectively. In the lowest 1( n, π*) excited state, only the off-axis structure is found. This prediction of a ground-state like excited-state structure arises due to localization of the excitation on the central nitrogen; it presents a distinctly different paradigm for excited state hydrogen bonding than has been previously identified.

Betatron harmonic radiation from harmonic undulators

In this paper we discuss the spectral properties of undulator radiation with a harmonic undulator field to include the off-axis field structure in the analysis. The analysis is aimed to clarify the role of betatron oscillation in a harmonic undulator which arise when the electrons are emitted off the undulator axis.

Electrical resistivity structure of the Valu Fa Ridge, Lau Basin, from marine controlled-source electromagnetic sounding

SUMMARY In December 1995 we carried out a comprehensive controlled-source electromagnetic survey of the Valu Fa Ridge at 22u25k Si n the Lau Basin. The Valu Fa Ridge is ab ack-arc spreading centre of intermediate spreading rate and is a site of extensive hydrothermal activity. Seismic studies have imaged a melt lens at an average depth of 3.2 km below the seafloor, surrounded by a zone of lowered seismic velocity, interpreted as a region of partial melt in the crust. The electromagnetic experiment was part of a multidisciplinary study which included wide-angle and reflection seismics, bathymetry and potential field measurements. Electromagnetic signals at frequencies between 0.25 and 40 Hz were transmitted from a horizontal electric dipole towed close to the seafloor and were recorded by an array of 11 sea-bottom receivers at ranges of up to 20 km from the source. Over 80 hr of data, consisting of the magnitude of the horizontal electric field at the seafloor, were collected. These data have extremely low scatter compared to similar data from previous surveys. The data were interpreted using a combination of 1- and 2-D forward modelling and inversion. The vertical resistivity gradient in the upper crust at the Valu Fa Ridge is abnormally low, with resistivities of less than 10 V m observed throughout layer 2 of the crust to a depth of 3 km. This is significantly more conductive at depth than the axis of the slow-spreading Reykjanes Ridge at 57u45kN, and the fastspreading East Pacific Rise at 13uN, where similar data sets have been collected in the past. Although the structure of layer 2 is well constrained by the electromagnetic data, its extremely low resistivity causes rapid attenuation of electromagnetic signals diffusing through it, and hence the data are not sensitive to the structure in layer 3, in particular the structure of the melt lens or surrounding low-velocity zone. The seismic velocity structure of the Valu Fa Ridge, determined from the coincident wide-angle seismic study, is similar to that observed at other mid-ocean ridges, with a steep seismic velocity gradient through layer 2 (although overall velocities are slightly lower). The seismic velocity anomaly calculated relative to an average off-axis structure is also small. This suggests that the very low resistivities observed at the axis are not caused by an upper crust of abnormally high porosity. However, hot and/or saline fluids permeating the crust can explain the low resistivities without affecting the seismic velocity. Since the conductive region extends unbroken from 3 km depth to the seafloor, it is probable that these fluids circulate to (or close to) the magma chamber itself.

Oceanic ridge off-axis deep structure in the Mansah region (Sumail massif, Oman ophiolite)

Large scale structural mapping of the Oman ophiolite indicates that the Mansah area (Sumail massif) was a ridge off-axis region at the time the ophiolite was detached. This paper presents a detailed structural mapping of the region. We show that, as opposed to other off-axis areas, it contains plunging lineations, correlated with a thick Moho transition zone and chromite pods, indicative of a mantle diapir. However this diapir has a discontinuous structure, it is bounded by shear zones and types of diabases that are not found elsewhere in Oman; it also has a broken crust, strongly affected by hydrothermal alteration. This suggests that Mansah fossilized an off-axis diapir intruding a cooling lithosphere. It may be a good candidate to be the root of an off-axis seamount such as those found in the East Pacific, and may bring new insights into this particular volcanism which we are only beginning to explore.

Horst and graben structures on the flanks of the Mid-Atlantic ridge in the MARK area (23°22′N): Submersible observations

South of the Kane fracture zone (23°40′N), the Mid-Atlantic ridge is segmented into 20–100-km-long spreading cells in which morphology, seismic and gravity signatures change along and across the ridge-axis. The rift valley, considered as a typical structure along slow-spreading ridges, can be symmetric or asymmetric, and segment centers experience strong magmatic activity whereas low magma supply results in thinning of the crust at segment tips. Along the segment centered on the Snake Pit neovolcanic ridge (23°22′N), the rift valley is clearly asymmetric, and mantle and lower crustal rocks are commonly exposed on the steepest and highest ridge flanking wall. In this area, we analyzed submersible observations ( Gravinaute cruise) collected up to 50 km on both sides of the axis to discuss the proceses responsible for the axial valley shape, its possible relationship with “deep” rock exposures, and to determine the origin of off-axis structures. Our data reveal that the structure and the geology vary on both walls of the axial valley and is different from the volcanic and tectonic organization observed on the neovolcanic ridge itself. Furthermore, the structure of the off-axis domain in different from the axial valley and rift mountains are organized in a set of regularly spaced relief (about 10 km) on both flanks of the ridge. Scarps which built these topographic highs face either toward the axis or away. Thus, the off-axis morphology appears as a set of horsts and grabens which could partly result from off-axis tectonic processes and/or from a shifting of the volcano-tectonic activity out of the axial valley during the last 3 Ma. Off-axis data show that serpentinized peridotites, more commonly observed on the western rift valley wall, crop out on the western flank up to 30 away from the axis. Models proposed to account for such rock exposure are usually related to the formation of the deep axial valley along slow-spreading ridges. Here, we propose that mantle rocks are exposed only in a very particular structural context which is directly controled by the ridge segmentation and is independent of the shape of the axial valley (symmetric or not). Serpentinites crop out within a V-shaped structure corresponding with the boundary between two adjacent segments, where seismic and gravity data reveal that the crust is thin and the lithosphere is thick. Here, the crust is fed by a lower magma supply than at the segment center (Snake Pit area). Thus, we interpret this segment end to be a region of extremely thin crust, where modest normal fault can bring mantle rocks to the surface.

Mode structure of a resonator with non-Gaussian components. I. Axial mode structures

A study is made of the mode structure of a resonator containing a component with non-Gaussian optical inhomogeneities. Use is made of geometric optics to show that, in addition to the traditional axial structure, fundamentally new non-Gaussian mode systems can appear in a non-Gaussian resonator. In particular, new systems include multipass off-axial structures, regions with stochastic behaviour of rays, and ray fluxes with a complex structure. An analytic investigation is reported of the structure of the axial region. It is shown that for certain resonator parameters a radical modification of the axial mode structure may be induced by even small aberrations. Complex ray fluxes and paraxial multipass systems are formed. The analytic results are illustrated by a large number of examples of numerical modelling of the behaviour of rays in a non-Gaussian resonator.

Mode structure of a resonator with non-Gaussian components. II. Multipass off-axial structures

A study is made of the mode structure of a resonator containing a component with non-Gaussian optical inhomogeneities. Use is made of geometric optics to show that, in addition to the traditional axial structure, fundamentally new non-Gaussian mode systems can appear in a non-Gaussian resonator. The new systems include multipass off-axial structures. It is shown that the behaviour of multipass modes is governed not only by the nature of aberrations, but also by the configuration of the resonator system. An analytic method for calculations relating to multipass modes is described. The results of the investigation are illustrated by a large number of numerical modelling examples.