Study of strip-shaped chromatic aberration defects on the surface of an electro-galvanized fingerprint-resistant sheet

Strip-shaped chromatic aberration defects on the surface of an electro-galvanized fingerprint-resistant sheet were systematically studied using Thermo-Calc thermodynamic calculations,scanning electron microscope and X-ray diffractometer analyses,and rapid heat treatment simulation technology.The formation mechanism of these defects was also analyzed.The results show a strong correlation between the defects and the uneven distribution of the Fe(001)component on the surface of the steel substrate.The relatively high proportion of Fe(001)components on the surface of the steel substrate affects the distribution density of the Zn crystal cells in different orientations during the electrodeposition process,which causes the reflection intensity of the light of the galvanized layer to differ from various visual perspectives,and macroscopic strip-shaped chromatic aberration defects are finally formed.The high proportion of the Fe(001)component on the surface of the steel substrate is mainly related to the following two factors.First,when the strip steel is hot-rolled,the finishing hot-rolling temperature is close to theγ→αphase transition temperature.When the local temperature on the upper surface of the strip steel is low,γ+αtwo-phase rolling easily occurs,and this results in an uneven stress distribution between theγandαphases after the hot-rolling process.This uneven distribution of hot-rolling stress results in the formation of a coarse grain structure in the local area on the surface of the hot-rolled sheet,which strongly affects the subsequent cold rolling and annealing process,and the annealed steel sheet substrate ultimately contains a greater proportion of the Fe(001)component.And second,a fast cooling rate(>10 K/s)during the slow cooling stage in the continuous annealing process inhibits the transformation of the Fe(001)to the Fe(111)component on the surface of the cold-rolled steel sheet,and it is then not possible to effectively eliminate the influence of the unevenly distributed Fe(001)component on the surface of the annealed steel sheet(originating from the uneven hot-rolled microstructure).This uneven distribution of the Fe(001)component on the surface of the annealed steel sheet following the continuous annealing heat treatment has a strong effect on the electrodeposition behavior of the Zn crystal cell in the subsequent electroplating process and the formation of macroscopic strip-shaped chromatic aberration defects on the surface of electro-galvanized fingerprint-resistant sheet.

Simultaneous quantification of longitudinal and transverse ocular chromatic aberrations with Hartmann-Shack wavefront sensor

A simple method to objectively and simultaneously measure eye's longitudinal and transverse chromatic aberrations was proposed.A dual-wavelength wavefront measurement system using two Hartmann-Shack wavefront sensors was developed.The wavefronts of the red(639.1 nm)and near-infrared(786.0 nm)lights were measured simultaneously for different positions in the model eye.The chromatic wavefronts were converted into Zernike polynomials.The Zernike tilt cofficient(irst term)was used to calculate the transverse chromatic aberration along the ax-direction,while the Zernike defocus coefficient(fourth term)was used to calculate the longi-tudinal chromatic aberration.The measurement and simulation data were consistent.

Liquid crystal integrated metalens with tunable chromatic aberration

Overcoming chromatic aberrations is a vital concern in imaging systems in order to facilitate fullcolor and hyperspectral imaging.By contrast,large dispersion holds opportunities for spectroscopy and tomography.Combining both functions into a single component will significantly enhance its versatility.A strategy is proposed to delicately integrate two lenses with a static resonant phase and a switchable geometric phase separately.The former is a metasurface lens with a linear phase dispersion.The latter is composed of liquid crystals(LCs)with space-variant orientations with a phase profile that is frequency independent.By this means,a broadband achromatic focusing from 0.9 to 1.4 THz is revealed.When a saturated bias is applied on LCs,the geometric phase modulation vanishes,leaving only the resonant phase of the metalens.Correspondingly,the device changes from achromatic to dispersive.Furthermore,a metadeflector with tunable dispersion is demonstrated to verify the universality of the proposed method.Our work may pave a way toward active metaoptics,promoting various imaging applications.

Three-dimensional hexapole focusing of pulsed molecular beam for state selection

We theoretically investigate three-dimensional （3D） focusing of pulsed molecular beam using a series of hexapoles with different orientations. Transversely oriented hexapoles provide both the transverse and longitudinal focusing force and a longitudinally oriented one provides only the transverse force. The hexapole focusing position are designed to realize the simultaneous focusing in three directions. The additional longitudinal focusing compared with the conventional hexapole can suppress the effect of chromatic aberration induced by the molecular longitudinal velocity spread, thus improving the state-selection purity as well as the beam density. Performance comparison of state selection between this 3D focusing hexapole and a conventional one is made using numerical trajectory simulations, choosing CHF3 molecules as a tester. It is confirmed that our proposal can improve the state-selection purity from 68.2% to 96.1% and the beam density by a factor of 2.3.

Mechanism underlying the formation of cloud-shaped defects in 304 stainless steel after hot-rolled annealing and pickling

It is highly imperative to understand the mechanism underlying the formation of cloud-shaped defects in stainless steel to reduce the defect incidences. This study investigated the defect microstructure by SEM, simulated pickling in the laboratory, and performed structure analysis of oxide scales after hot rolling. Results show that the cloud-shaped defects in 304 No. 1 surface （after hot-rolled annealing and pickling） cause the pickling chromatic aberration between the honeycomb-shaped grains of the Cr-depleted layer and the smooth grains of the stainless steel matrix, which is formed in the case of insufficient pickling. The chromatic aberration is related to the uneven oxide scales formed before pickling. With the improvement of pickling capacity, it is possible to completely pickle the Cr-depleted layer and eliminate the cloud-shaped defects.

Image blur in high energy proton radiography

Proton radiography has provided a potential development direction for advanced hydrotesting, and its image blur is a crucial point that needs to be deeply studied. In this article, numerical simulation by using the Monte Carlo code Geant4 has been implemented to investigate the entire physics mechanism of high energy proton beam travelling through the object and beamline and arriving at the image plane. This article will mainly discuss the various factors which cause the image blur, including the chromatic aberration of the imaging beamline, the insumcient modulation of an incident particle＇s transverse displacement and angle deviation, the longitudinal length of an object, the influence of containment vessel and otherwise.

Systematic study of spatiotemporal influences on temporal contrast in the focal region in large-aperture broadband ultrashort petawatt lasers

Temporal contrast is one of the crucial physical determinants which guarantee the successful performance of laser–matter interaction experiments. We generally reviewed the influences on the temporal contrast in three categories of noises based on the requirement by the physical mechanisms. The spatiotemporal influences on temporal contrast at the focal region of the chromatic aberration and propagation time difference introduced by large-aperture broadband spatial filters, which were spatiotemporally coupled with compression and focusing, were calculated and discussed with a practical case in SG-Ⅱ5 PW ultrashort petawatt laser. The system-wide spatiotemporal coupling existing in large-aperture broadband ultrashort petawatt lasers was proved to be one of the possible causes of temporal contrast degradation in the focal region.

Multi-layer magnetic recording driven by a tunable laser

All-optical magnetization switching with features of low-power consumption and high writing speed is a promising road map to satisfy the demand for volume data storage. To promote denser and faster magnetic recording technologies, herein, all-optical helicity-dependent switching(AO-HDS) in multi-layer magnetic recording is proposed based on the chromatic aberration of an optical lens(Thorlabs’ s N-BK7 plano-convex uncoated lens).The power of the incident beams and the thickness of the multi-layer magnetic recording film are designed carefully. Besides, the uniformity of this multi-layer magnetic recording is optimized. At last, a prototype system of information multiplexing based on this multi-layer magnetic recording technology is constructed as well. Flexible and controllable magnetization reversals in different layers are also demonstrated by tuning the wavelength and helicity of working beams. We believe that such a prototype system can pave the way for increasing the storage density in an effective and low-cost mode.

Optical metalenses:fundamentals,dispersion manipulation,and applications

Metasurfaces,also known as 2D artificial metamaterials,are attracting great attention due to their unprecedented performances and functionalities that are hard to achieve by conventional diffractive or refractive elements.With their sub-wavelength optical scatterers,metasurfaces have been utilized to freely modify different characteristics of incident light such as amplitude,polarization,phase,and frequency.Compared to traditional bulky lenses,metasurface lenses possess the advantages of flatness,light weight,and compatibility with semiconductor manufacture technology.They have been widely applied to a range of scenarios including imaging,solar energy harvesting,optoelectronic detection,etc.In this review,we will first introduce the fundamental design principles for metalens,and then report recent theoretical and experimental progress with emphasis on methods to correct chromatic and monochromatic aberrations.Finally,typical applications of metalenses and corresponding design rules will be presented,followed by a brief outlook on the prospects and challenges of this field.