2014 Vol. 7, No. 1
This paper provides the state-of-art review to the research works in diffraction-limit breaking focusing and imaging. Firstly, the research background and significance of the research in this field are given, and the well-developed super-resolution methods and the definition of scattering media towards diffraction-limit breaking imaging are also introduced. Secondly, the time reversal technique utilizing the scattering property in acoustics and electromagnetics for signal compressing and focusing are specified. The realization method of time reversal in domain of optics is presented. As a foundation for better understanding, the advantages brought about by inserting a plate of scattering media into certain optical imaging system are further elaborated. Thirdly, this review analyzes the serial feedback controlling method, optical phase conjugation and the transmission measurement based on phase conjugation for finest focusing. The groundbreaking transmission matrix measurement in both spatial and spatial frequent domain is introduced, which is followed by the preparation of scattering media aiming at the far-field and wide-field diffraction-limit breaking imaging using transmission matrix method. Finally, the advances and prospect on techniques of breaking diffraction limication using scattering medium are preposed.
In this paper, several aspheric testing methods for different fabrication steps and their new research progresses are introduced. Especially, we emphasis on the testing methods for precision polishing step, in which subaperture stitching interferometric testing and non-null partial compensating testing method are described in detail. Moreover, several combined interferometric testing methods which perform well in measuring large and steep aspherics are introduced. In addition, we provide a general description of free-form surface testing. The further development of aspheric surface testing methods is also prospected.
In this paper, the research achievements on dye-sensitized solar cells using graphene-based electrodes ae tracked in recent year. The reason for the change of Power Conversion Efficiency(PCE) is analyzed when various modified graphene-based electrodes are used in dye-sensitized solar cell. The physical mechanism is studied deeply to improve the reducing electric catalytic reacivity of graphene on electrolyte. Finally, suggestions are given for the future research work in this area to clarify the thoughts for solving the problems of the dye sensitized solar cell.
This review focuses on the nanofilm-modified Long Period Fiber Grating(LPFG) and makes a brief presentation for progress of its applications in refractive index biosensor. The influence of nanomembranes on refractive index sensing performance of LPFG is elaborated. Furthermore, applications of nanofilm-modified LPFG in the field of biological and chemical analysis are discussed in detail. At last, the further development and application of nanofilm-modified LPFG refractive index sensor are prospected.
Blind image restoration is an approach to estimate both the original image and the point spread function from degraded images, when there is no or little knowledge of the point spread function of the degraded process. In this paper, the main algorithms of blind image restoration are reviewed and classified into four types, according to their theory origins and relationships, and analysis is made for all the types of blind image restoration algorithms and relevant improved algorithms. This will be helpful to better understand the theory of blind image restoration and to restore degraded images.
This paper reviews the in situ surface analysis and monitoring techniques for contamination induced in Extreme Ultraviolet Lithography(EUVL). It introduces the EUV lithography, reflective multilayer mirror and the mechanism of carbon contamination induced by EUV. It points out the requirement of the in situ surface analysis techniques in EUV lithography. The mainly surface analysis techniques are discussed. Analyzed results show the applied potentiality of each measurement used in the EUV optical system. Finally, it points out that the Fiber-based ellipsometry has further application prospect in in situ surface contamination monitoring of EUV lithography.
After summarizing the fundamentals of optical chaos generation and synchronization with coupled semiconductor lasers, we consider their application in optical cryptography, and present basic and more advanced schemes of data coding on chaotic carriers, as proposed in the literature, including Chaos masking(CM) and Chaos Shift Keying(CSK). Finally, we outline some recent developments of the chaos secure transmission technique, such as Phase Modulation(PM), Free-Space Optical Link(FSOL), multi-laser and multi-user schemes.
In order to realize high resolution retinal imaging, the technique of Liquid Crystal Adaptive Optics(LC-AO) and its utilize in retinal imaging is under investigation. Problems are settled in the research such as energy loss by polarization, limitation on field of view(FOV) and universality of LC-AO system in retinal imaging. Open-loop adaptive optics system is introduced to avoid the energy loss by polarization in closed-loop system. View field of imaging system is expanded by adhibition of an alterable diaphragm. Exposure ratio is reduced by a pulsed light source. Illumination is polarized to increase energy efficiency. Trial lens and dynamic, advanced target at infinite are used to increase the stability of pupil and reduce the impact of individual differences on human-eyes. Definition and contrast of images after correction are remarkably increased. FOV is enhanced from 200 m to 500 m. Exposure ratio is reduced to 1/2~1/3. High definition images are taken from samples with low resolution before. Most problems of LC-AO system for high resolution retinal imaging are settled.
In synchrotron radiation beamlines, the increasing light flux will lead to more thermal load on optical elements. The thermal load on the Plane Mirror(PM) of variable included angle plane-grating monochromator will decrease the resolution. This paper proposes a method to recover the resolution by optimizing the value of focusing constant(Cff). Firstly, the absorption spectra of thermal power with different values of Cff are obtained by calculation. Then thermo-mechanical analysis of PM is conducted to get variable deformations on PM with different thermal power. Secondly, the resolution is calculated by combining the function of ideal resolution and the software of ray tracing. Finally, the resolution is compensated by optimizing Cff. The result indicates that taking the soft X-ray spectroscopy micro beam line station of SSRF for example, the resolution can be improved by changing the value of Cff from 1.8 to 1.84 when the photon energy is 1 000 eV. So optimizing the value of Cff is an effective way to recover the decreased resolution induced by thermal power on PM.
To develop and refine the laser guided and stabilized(LGS) welding process, the conductivity of the electric arc must be maximized using laser radiation. The optogalvanic effect(OGE) is the leading factor in controlling it, and if optimized it will lead to the stabilization of the electric arc. The OGE raises the probability of ionization of the particles in the plasma, and thus, the conductivity of the electric arc. The interaction between the photons of the laser and the Argon atoms through electron-atom collisions create charged particles. The higher the rate of ionization is, the higher the conductivity of the electric arc. Many tests were conducted to discover how to make best use of this effect. The position of the focus of the beam in relation to the work piece, the shape of the beam, and the laser wavelength used were all taken into account.
Surface enhanced Raman spectroscopy(SERS) is an ultrasensitive vibrational spectroscopic technique to detect molecules. At present, adding salts is a main way to induce nanoparticles aggregation to get giant enhancement. However, this method needs more procedures and salts may etch nanoparticles. Here an effective and simple method is reported to enhance SERS effect by the aggregation of silver nanoprisms(AgNPRs) induced by 785 nm laser. Silver nanoprisms were prepared by ligand-assisted chemical reductions method. AgNO3 were reduced by NaBH4 in the presence of trisodium citrate, poly(vinylpyrrolidone) and H2O2.The edge of silver nanoprisms is about 80 nm. Surface plasmon band of silver nanoprisms is around 774 nm which could effectively absorb 785 nm laser. When laser irradiating silver nanoprisms during the detection of Raman spectra, these nanoprisms gradually aggregated and SERS spectra of analytes(4-mercaptobenzoic acid, 4-MBA) were gradually enhanced. And enhancement factor of Raman spectra ~109 is obtained by this method. Due to the huge magnitude of SERS in the near infrared region(excitation wavelength 785 nm), this technique has the potential in the field of biochemical tests.
The flower-like Cd-doped ZnO nanostructures were synthesized by hydrothermal method using zinc chloride(ZnCl2), cadmium chloride(CdCl2), sodium hydroxide(NaOH) as reactants. Then, the photocatalytic activities of as-grown samples were investigated by photo-degradation of rhodamine B(RhB). The samples were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), energy-dispersive X-ray analysis(EDS), photoluminescence(PL) spectroscopy, UV-visible spectroscopy. Experimental results show that with the Cd doping, the morphologies of ZnO changed greatly, and the size of ZnO became smaller. In addition, compared with the undoped ZnO, the absorption edge and the UV emission peak of the Cd-doped ZnO nanoflowers made a red shift clearly. The band gap decreased from 3.24 eV to 3.16 eV. Finally, in the photocatalytic experiment, the photocatalytic activity of Cd-doped ZnO was enhanced, and the degradation of rhodamine B(RhB) was up to 98% after the irradiation for 3 h. So the photocatalytic activities of Cd-doped ZnO nanoflowers were higher than that of the undoped ZnO.
In order to fabricate metallic meshes based on ZnS which can shield electromagnetic wave, a new type of photolithography copy technology process is adopted, in which photoresist is coated firstly and then plated in vacuum machine. But the color of polycrystalline ZnS resembles that of photo-resist, it is hard to estimate the developing degree of meshes during the process of making metallic meshes, which affects the preparation of metallic meshes film in the process of vacuum plating. A new method by plating a transition film is proposed, in which the processes including vacuum coating, spin-coating, developing, etching, vacuum coating, removing, etching are adopted combining the fabrication technology of metallic meshes. The testing results indicate that the metallic meshes with the line width of 8 m and the line period of 400 m are fabricated successfully. With this technology, the yield of metallic meshes is improved up to 90%.
Conventional testing methods for the curvature radius of spherical mirror with large aperture are introduced briefly, and a novel method using combined rods and laser interferometer is proposed. Firstly, the surface figure of spherical mirror is tested with laser interferometer. The position of interferometer and tested mirror is adjusted to make the focus of the exit wave front and the center of curvature of tested mirror to be confocal. Then the suitable combined rods are setup, and the position of probe spheric head which is close to interferometer is adjusted to make the focus of the exit wave front and the center of the probe spheric head con-focal. Next, another probe spheric head is adjusted to contact the surface of the tested mirror. The curvature radius of the spheric mirror can be calculated by the data. The basic principle of the testing method is analyzed. A telescope spheric primary mirror with a aperture of 600 mm is tested many times with this method. The average radius of curvature is calculated to be 2 836.774 mm,and the root mean square is 0.071 mm. Finally, the measurement uncertainty of this method is analyzed, and the main factors affecting the measurement accuracy are found out, and the composed standard uncertainty is 0.061 mm.
To acquire the spatial frequency response of the interferometer, the testing method on instrument transfer function(ITF) of interferometer was researched. First, the theoretical calculation model of instrument transfer function of imaging system was established, and the testing model of Fizeau interferometer was simulated via lens design program. Then the theoretical value was calculated and anaysed. Comparing ITF based on the method of sine phase plate with the theoretical ITF, the error is less than 0.6%, and this method is proved to be feasible via the simulation of the optical design program.
As for the nonlinear effects of infrared focal plane arrays intensity response, a nonlinear calibration method is proposed based on single wavelength laser. Experimental equipment is designed for measuring, and the nonlinear calibration curve of the focal plane array is obtained through the measuring equiprment. Experimental results show that this method aviods the influence of infrared focal plane arrays spectral response nonuniformity, and meets the requirement of generality and practicability of the device in the engineering technology, which ensures the high accuracy of measurement as well as simpleness.
In order to keep high accuracy of temperature measurement of the cooled medium-wave infrared thermal imager after nonuniformity correction under different ambient temperatures, the calibration model of the medium-wave infrared thermal imager is analyzed with the consideration of the effect of the nonuniformity correction temperature. The nonuniformity of thermal imager is corrected using surface blackbody under different temperatures. The relationship between the gray and blackbody radiance is obtained by thermometry experiment of blackbody target. The mathematical calculation model of target temperature is established and the error of thermometry result is analyzed. The results show that the drift of gray of thermal image as nonuniformity correction radiance under different correction temperatures can be treated linearly, and is independent on the target temperature. When the nonuniformity is low, the temperature measurement error of the thermal imager is less than 0.22 ℃, which greatly reduces the temperature measurement error of the cooled medium-wave infrared thermal imager after nonuniformity correction under different correction temperatures.
Firstly, Power Spectral Density(PSD) is proposed for mirror surface figure evaluation in the large aperture telescope system as for some difficulties for Root Mean Square(RMS) in the evaluation of large scale variety and disadvantage of robust for rigid body displacement. Then, the decomposition arithmetic of PSD is analyzed with Zernike polynomial, and Zernike polynomial spectrum energy distribution is analyzed in some order. The algorithm has been used in the surface figure evaluation of a 500 mm mirror, and energy distribution in the frequency domain of the actual mirror surface has been obtained. The experimental results indicate that the evaluation of PSD is more practical when used in large aperture mirror for their manufacture and testing and for the error budget allocation in telescope system. Finally, a kind of noncorrelative sub-aperture stitching method for evaluation of reflective mirror shape based on PSD is proposed which can be used in the large aperture telescope.
The main technical parameters and the zoom method for the camera with small size and large zoom ratio are introduced. Each structural part of the camera is described in detail. The zoom and compensating lens group slide in the main body through the slide frame, whose movements are assured by the movement of the guide pin in the cam curve groove. The measures to ensure the quality and the precision taken in the process and assembling of the camera are expatiated. The clearance between cam curve groove and roller is controlled about 6~9 m, and the stiffness and column of the main body are insured. The return errors are less than 2 when the zoom and compensation slide frame slide in the main body. The ratio between diameter and length of the slide frame should be no less than 1. The results show that optical transfer function of the camera is more than 0.2 in the space frequency of 50 lp/mm after high-and-low temperature vibration tests, and the location images of camera are clear.