Designing superresolution optical pupil filter with constrained global optimization algorithm

In this paper, a new method for designing three-zone optical pupil filter is presented. The phase-only optical pupil filter and the amplitude-only optical pupil filters were designed. The first kind of pupil for optical data storage can increase the transverse resolution. The second kind of pupil filter can increase the axial and transverse resolution at the same time, which is applicable in three-dimension imaging in confocal microscopy.     

改善共焦系统轴向分辨率的位相型光瞳滤波器

利用约束全局优化算法———CGO算法,设计了两种用于共焦系统的三区位相型光瞳滤波器.第一种滤波器在不改变系统的横向分辨率的同时,可以大幅度地提高轴向分辨率,提高了系统的层析能力.第二种滤波器在提高系统轴向分辨率的同时,又能提高其横向分辨率,适用于系统的三维成像. 关键词： CGO算法 光瞳滤波器 超分辨     

位相型光瞳滤波器对共焦系统离焦工作状态横向分辨特性的影响

分析了共焦显微系统(CMS)离焦状态工作时分辨特性的变化,指出了离焦状态是导致CMS横向分辨特性变差的主要影响因素之一。提出并采用了位相型超分辨光瞳滤波技术来改善CMS工作在离焦状态下的横向分辨特性,分析了超分辨光瞳滤波器位置变化对CMS横向分辨特性的影响。理论分析和实验验证表明,位相型超分辨光瞳滤波技术的引入,显著抑制了CMS工作在离焦状态时艾里斑旁瓣的增长,克服了CMS因工作在离焦状态而引起的横向分辨特性下降的缺点。     

Differential confocal technology based on radial birefringent pupil filtering principle

In order to improve the spatial resolution of a confocal system, a radial birefringent pupil filter (RBPF) is introduced into a differential confocal system. RBPF consists of two polarizers with a birefringent element between them, and its pupil function is deduced from Jones matrix. The thickness and curvature radius of RBPF are optimized independently, using the first zero coordinate ratio. The pupil function is modulated by RBPF to enhance the half-width of the response function, and lateral resolution is improved when response curve is changed with the position of RBPF as well as the polarization; then axial super-resolution of the system can be guaranteed using differential confocal detection mechanism. In comparison with conventional pupil filtering technology, RBPF features high lateral resolution and can be easily produced; moreover, it also has a simple structure. Together with its low cost, RBPF provides a new way for the improvement of super-resolution of confocal system. It is indicated from theoretical analysis and preliminary experiments that the lateral resolution can be significantly improved and the measurement error is reduced by 76 nm when measuring a standard grating of period 3 μm; the axial resolution up to 3 nm has been achieved using the optimized pupil filter. In addition to its application for measurement of a small irregular surface in a limited space, the whole differential confocal system proposed can be fitted onto a coordinate measuring machine for non-contact measurement of dimensions and surface roughness.     

Improvement of confocal microscope performance by shaped annular beam and heterodyne confocal techniques

In order to further improve the performance of a confocal microscope (CM) used for measurement of surface profiles and 3D microstructures, a shaped annular beam heterodyne confocal measurement method based on annular pupil filter technique and reflection confocal microscopy, is proposed to expand the measurement range and to improve the defocused property of CM. The approach proposed uses a confocal dual-receiving light path arrangement and a heterodyne subtraction of two signals received from detectors with axial offset to enable CM to be used for bipolar absolute measurement and to improve the defocused property of CM, and it uses the annular pupil filter technique to produce a binary optical shaped annular beam, which expands the measurement range by expanding the full-width at half-maximum of intensity curve received from two detectors in a heterodyne confocal microscopy system. Theoretical analyses and experimental results indicate that a shaped annular beam heterodyne microscope has a measurement range expanded from 4 to 14 μm, achieved an axial resolution of 2 nm and improved the defocused property, when ε=0.5 and NA=0.65. It can be therefore concluded that the shaped annular beam heterodyne confocal measuring method proposed is a new approach to ultraprecision measurement of surface profiles and 3D microstructures.     

The aberration and the modulation transfer function in LASEK and LASIK: Pupil size dependence

The wave-front aberrations on the postoperative eyes with two different type of excimer laser surgery have been measured by a Hartmann-Shack wave-front sensor. We have calculated the aberrations for both 3 and 6 mm pupils, and with which to acquire the MTF of the eye. There are no significant differences in wave-front aberrations postoperatively (P>0.05) for 3 mm pupil size, but with 6 mm pupil, LASIK-treated eyes exhibit significant higher aberrations than LASEK-treated eyes for 4th and 5th-order aberrations. For individual Zernike terms, there are significant difference in , and . The MTF for 6 mm pupil is much lower than those for 3 mm pupil across all spatial frequencies. The LASEK curve shows higher than that with LASIK at spatial frequencies less than 60 c/d, which means that the optical quality in LASEK-treated eyes showed better than in LASIK-treated eyes.     

Effect of fabrication errors on axial super-resolution property of a three-zone pupil filter

Two models have been established using the basic definitions of super-resolution characteristic parameters for normalized spot size G_A and Strehl ratio S_A, of a three-zone axial super-resolution pupil filter with fabrication errors, to quantitatively analyze the effect of these fabrication errors on the axial super-resolution property. These new models established to describe the analytic relationship of G_Ae and S_Ae of a pupil filter with its fabrication errors and its transmission function A(ρ), phase function φ(ρ) and structural parameters, directly relate the super-resolution parameters of a three-zone axial super-resolution pupil filter to its fabrication errors to make the quantitative analyses of the effect of fabrication errors easier, thereby providing a theoretical basis for the analysis, design and fabrication of a three-zone axial super-resolution pupil filter. The models established for G_Ae and S_Ae have been used to analyze the effect of the fabrication errors of a pupil filter on its super-resolution property, with a three-zone phase-only pupil filters as example.     

Effect of fabrication errors on lateral super-resolution property of a three-zone pupil filter

Two models have been established using the basic definitions of super-resolution characteristic parameters for normalized spot size G_T and Strehl ratio S_T of a three-zone lateral super-resolution pupil filter with fabrication errors to quantitatively analyze the effect of these fabrication errors on the lateral super-resolution property. These new models established to describe the analytic relationship of G_Te and S_Te of a pupil filter with its fabrication errors and its transmission function A(ρ), phase function φ(ρ) and structural parameters directly relate the super-resolution parameters of a three-zone lateral super-resolution pupil filter to its fabrication errors to make the quantitative analyses of the effect of fabrication errors easier, thereby providing a theoretical basis for the analysis, design and fabrication of a three-zone lateral super-resolution pupil filter. The models established for G_Te and S_Te have been used to analyze the effect of the fabrication errors of a pupil filter on its super-resolution property with a three-zone phase-only pupil filter as an example.     

FTIR and diode laser spectroscopy of isobutylene: Analysis of the rotational structure in the v28 fundamental band

Rotational structure in the fundamental band of isobutylene has been examined at room temperature using a combination of FTIR and Pb-salt diode laser instruments. The highest spectral resolution for the FTIR measurements was 0.125 cm⁻¹. Even at this resolution however, rotational structure for the band could be observed and appeared to possess a very regular pattern. A preliminary spectral assignment was obtained using the Watson/Gora asymptotic approximation for a rigid oblate asymmetric rotor. Within this approximation, the band origin was determined to be 890.937 (4) cm⁻¹. Excited state rotational constants, without the inclusion of centrifugal distortions terms, are A = 0.3033(16), B = 0.2801(12) and C = 0.15362 (8) cm⁻¹ respectively. Finally, a full set of spectroscopic constants, including quartic centrifugal distortion constants, were obtained for the band by including the high resolution Pb-salt spectra.     

三环位相型光瞳滤波器的横向超分辨与轴向焦深扩展

用矢量衍射方法分析了线偏振光入射到带有三环位相型光瞳滤波器的高数值孔径物镜时,焦点的轴向和横向光强分布.数值模拟结果表明,高数值孔径物镜聚焦时需同时考虑光强的轴向和横向分布.通过加入三环位相光瞳滤波器,在实现横向超分辨的同时实现了光学系统轴向焦深扩展和轴向光强分布平坦化,并且位相调制深度变化时,会出现轴向焦移现象.对三环位相光瞳滤波器结构进行了优化,得出了优化结果. 关键词： 光学超分辨 扩展焦深 位相型光瞳滤波器 矢量衍射方法     

Growth of well-aligned Bi nanowire on Ag(1 1 1)

We report the fabrication of one-dimensional (1D) Bi nanowires grown on Ag(1 1 1) with average lateral width from 9 to 20 nm by physical vapor deposition in ultra high vacuum conditions. In situ low-temperature scanning tunneling microscopy analyses reveal that the preferred growth of 1D Bi nanostructures is driven by the highly anisotropic bonding in the crystallographic structure of the Bi(1 1 0) plane. The Bi nanowires grow along direction and align with the directions on Ag(1 1 1). The growth of the Bi nanowires proceeds in a bilayer growth mode resulting from the layer pairing in Bi(1 1 0) which saturates the dangling bonds and lowers the total energy.     

Effect of an annular pupil filter on differential confocal microscopy

Combining differential confocal microscopy and an annular pupil filter, we obtained the normalized axial intensity distribution curve of an optical system. We used the sharp slopes of the axial response curve of the optical system to measure the surface profile of a reflection grating. Experimental results prove that this method can extend the axial dynamic range and improve the transverse resolution of three-dimensional profilometry by sacrificing axial resolution.     

Crystallisation progress in Si-rich ultra-soft nanocomposite alloy fabricated by melt spinning

The crystallisation process and the ultras-soft magnetic properties of amorphous/nanocomposite alloy Fe_73.5Si_17.5B₅Nb₃Cu₁ fabricated by conventional melt-spinning technique are systematically investigated in terms of thermal analysis and in-situ measurement of magnetisation dynamics. The thermal analysis using differential scanning calorimetry showed that crystallisation from Fe-based amorphous state to α-Fe(Si) started at . Further heating the sample leads to a transformation from the α-Fe(Si) to Fe-B phases at . Crystallisation activation energies were determined using two models: Kissinger and John-Mehl-Avrami (JMA), which were consistent to each other with a value of . High resolution transmission electron microscopy investigation revealed an ultrafine structure of α-Fe(Si) nanocrystallite with mean size of 12.5 nm embedded in an amorphous matrix. At a volume fraction of 86% of α-Fe(Si) phase, optimum soft magnetic properties were obtained with very high permeability of 110,000 and a very low coercivity of 0.015 Oe by annealing the amorphous alloy at in 40 min.     

Sapphire (0 0 0 1) surface modifications induced by long-pulse 1054 nm laser irradiation

We have investigated modifications of sapphire (0 0 0 1) surface with and without coating, induced by a single laser pulse with a 1054 nm wavelength, 2.2 s duration, 7.75 mm spot and energy of 20-110 J. A holographic optical element was used for smoothing the drive beam spatially, but it induced small hotspots which initiated damage on the uncoated and coated surfaces. The individual damage effects of hotspots became less pronounced at high fluences. Due to high temperature and elevated non-hydrostatic stresses upon laser irradiation, damage occurred as fracture, spallation, basal and rhombohedral twinning, melting, vitrification, the formation of nanocrystalline phases, and solid-solid phase transition. The extent of damage increased with laser fluences. The formation of regular linear patterns with three-fold symmetry ( directions) upon fracture was due to rhombohedral twinning. Nanocrystalline -Al₂O₃ formed possibly from vapor deposition on the coated surface and manifested linear, triangular and spiral growth patterns. Glass and minor amounts of -Al₂O₃ also formed from rapid quenching of the melt on this side. The - to -Al₂O₃ transition was observed on the uncoated surface in some partially spalled alumina, presumably caused by shearing. The nominal threshold for laser-induced damage is about 47 J cm⁻² for these laser pulses, and it is about 94 J cm⁻² at the hotspots.     

Laser diode beam shaping with GRIN lenses using the twisted beam approach and its application in pumping of a solid-state laser

We report a novel beam shaping method for laser diodes based on the concept of twisted Gaussian Schell-model beams using GRIN lenses. This method enables a more symmetric pump as well as a compact setup for pumping of solid-state lasers. In the experiment with a standard 2 W diode, the beam quality factors in the two orthogonal directions were equalized to and , respectively, which pumped an intra-cavity frequency-doubled Nd:YAG laser at 946 nm with an output of 28 mW at 473 nm.     

Anisotropic defect reduction in non-polar a-plane GaN grown by hydride vapor phase epitaxy on maskless patterned templates

Several non-polar a-plane GaN films had been grown by hydride vapor phase epitaxy (HVPE) on different designed metal organic chemical deposition (MOCVD) GaN templates, which exhibited various ridge-like sidewall facets surface morphologies. The templates induced a lateral growth at the early stage of the HVPE growth, and resulted in a kind of maskless epitaxy lateral overgrown (ELO) process. It is found that the dislocation reduced differently along [1 0 0 0] and [] directions in these HVPE a-plane GaN layers. In [0 0 0 1] direction, the dislocation reduction resulted from the optimal surface roughness value of the template. In [] direction, the inclined facet might be a main factor for the dislocation reduction in HVPE-GaN films. The maskless ELO process had a significant influence on decreasing the dislocation density.     

Signal processing efficiency of Doppler global velocimetry with laser frequency modulation

Novel Doppler global velocimeters using laser frequency modulation can optically measure flow velocity fields and offer promising perspectives, but so far unknown limits, for achieving low measurement uncertainties. One approach, e.g. is based on sinusoidal frequency modulation and a harmonic signal analysis. In order to determine the minimum achievable measurement uncertainty, the known theorem of Cramér and Rao is applied to a derived signal model, initially excluding the harmonic signal analysis. For a typical scattered light power of 1 nW and a desired temporal resolution of 16 ms, the calculated minimum velocity standard deviation amounts to 0.02 and 0.06 m/s for signal dependent (quantum shot) noise and signal independent (thermal and dark current) noise, respectively. It is subsequently investigated, how efficient the harmonic signal analysis extracts the Fisher information content. The ratio of the Cramér-Rao lower bound and the estimated measurement uncertainty, where the signal processing is taken into account, was found to be >75% in terms of standard deviations in the entire measurement range of about . For the challenge of measuring velocity fields in turbomachine flows (requirements: 5 kHz measurement rate, ≤1% statistical error, velocities (50-240) m/s), the presented results indicate a necessary minimum scattered light power of 1.5 nW, which seems feasible.     

Nanoscopic nickel aluminate spinel (NiAl2O4) formation during NiAl(1 1 1) oxidation

Oxidation of a NiAl(1 1 1) single crystal surface was investigated using high resolution soft X-ray photoelectron spectroscopy (HRSXPS), high resolution scanning electron microscopy (HRSEM), energy dispersive X-ray spectroscopy (EDS), X-ray mapping, and atomic force microscopy (AFM). After repeated oxygen exposure, annealing, and cleaning cycles under ultrahigh vacuum conditions, a new oxide phase in the form of tiny 3-dimensional surface structures was detected. These features are several micrometers long and ∼300 nm high and oriented along low index directions in the plane of the substrate; they have nickel aluminate spinel (NiAl₂O₄) stoichiometry. We propose that repeated cycles of oxygen dosing and annealing of the NiAl(1 1 1) surface leads to oxygen diffusion into the bulk and nucleation of spinel below the surface.     

Blue and infrared cathodoluminescence induced by carbon-irradiation in SrTiO3 single crystal

We show that blue-CL can be induced in SrTiO₃ single crystal at room temperature by irradiating it with 60 KeV carbon ion (C⁻) beam. An infrared CL-emission is induced simultaneously. Transmission electron microscopy (TEM) measurement exhibits an 200 nm thick surface layer formed by the C⁻ irradiation. We show that the emitting region can be patterned into any desired shape by fabricating the STO surface using Pt-based micro-lithography technique.     

Investigation of the impulse response of an image inversion interferometer

Based on the proposal of Wicker and Heintzmann “Interferometric resolution improvement for confocal microscopes” [1] we demonstrate in principle the functionality of an image inversion interferometer (III) experimentally, which can be described by an appropriate frequency transfer function. Thereby, the FWHM of the impulse response narrows around 30% compared to the PSF of a classical system. The experimental data yield a FWHM of the impulse response of 0.83 μm as compared to the theoretical value of 1.21 μm at by a wide field detection (NA=0.25) without an interferometer.