Scanning holographic microscopy with transverse resolution exceeding the Rayleigh limit and extended depth of focus

We demonstrate experimentally that the method of scanning holographic microscopy is capable of producing images reconstructed numerically from holograms recorded digitally in the time domain by scanning, with transverse and axial resolutions comparable to those of wide-field or scanning microscopy with the same objective. Furthermore, we show that it is possible to synthesize the point-spread function of scanning holographic microscopy to obtain, with the same objective, holographic reconstructions with a transverse resolution exceeding the Rayleigh limit of the objective up to a factor of 2 in the limit of low numerical aperture. These holographic reconstructions also exhibit an extended depth of focus, the extent of which is adjustable without compromising the transverse resolution.     

Reconstruction of spatial, phase, and coherence properties of light

Image reconstruction of partially coherent light is interpreted as quantum-state reconstruction. An efficient method based on the maximum-likelihood estimation is proposed for acquiring information from blurred intensity measurements affected by noise. Connections with incoherent-image restoration are pointed out. The feasibility of the method is demonstrated numerically. Spatial and correlation details significantly below the diffraction limit are revealed in the reconstructed pattern.     

网络修饰体对铕-镝共掺铝硼硅酸盐玻璃白光发光影响

采用高温熔融的方法,在空气中制备了一系列添加不同网络修饰体氧化物的Eu2 O3和Dy2 O3共掺杂铝硼硅酸盐玻璃,并测试了其在紫外光激发下的发光性能.从发射谱中可以看到归属于Eu2+、Eu3+和Dy3+离子能级跃迁的蓝、绿、黄、红等多色发射带共存.这些发射带之间的相对强度会随着网络修饰体氧化物的改变而变化,从而导致发光色度的变化.加入适当的网络修饰体氧化物可得到合适的白光发射.此外,在空气中制备过程中发生了Eu3+→Eu3+的还原反应.用Li2O取代ZnO时,该还原反应程度降低,而用CaO取代BaO时该还原反应程度增强,其机制与玻璃组分的光碱度有关.     

Effects of source coherence and aperture array geometry on optical sectioning strength in direct-view microscopy

Laser sources offer a possible solution to the problem of low light throughput in direct-view microscopes (DVMs). However, coherent source DVMs have been shown to suffer from problems such as increased sidelobes in the depth response because of coherent cross talk between neighboring apertures. We explore theoretically how source coherence affects the depth responses of DVMs by employing various aperture spacings and number of apertures. We show that, contrary to expectation, closely spaced apertures can result in decreased full width at half-maximum of the depth response curve. We explain this as an effect of destructive interference when cross talk between neighboring apertures occurs. Using apertures arranged in a square grid as an example, we move on to show that the use of aperture arrays that consist of regularly arranged apertures can accentuate the problematic sidelobes of the depth response. We show that arranging pinholes in a rectangular grid rather than a square grid can improve the optical sectioning strength significantly. Finally, by examination of the depth responses corresponding to the infinite-pinhole-array limit, we make some general statements about source coherence and the characteristics of arrays that are likely to perform well.     

Electrochemical monitoring of the fluorescence emission of tetrazine and bodipy dyes using total internal reflection fluorescence microscopy coupled to electrochemistry

A very sensitive technique where an electrochemical cell is coupled to a total internal reflection fluorescence microscopy setup is described and applied for the first time to the electrochemical monitoring of the fluorescence of organic dyes in solution. It is shown that this setup basically allows both spatial and time resolution for the recorded fluorescence signal as a function of the electrode potential: indeed the variations of the emission intensity are recorded within the diffusion layer for a classical cyclic voltammetry or chronoamperometry experiment inducing the redox conversion of an emissive form into a non emissive one (and conversely). Simultaneously, the variations of the emissive state lifetime are measured to discriminate between a mechanism involving only the conversion into a non emissive form from one involving a quenching between the emitter and the electrogenerated species. The results concerning the investigation of the electrochemical monitoring of the fluorescence properties for two types of original dyes are presented, demonstrating the possibility to switch on and off the emission in a fully reversible way and to investigate in depth the mechanisms associated to this switch.     

Scanning holographic microscopy with resolution exceeding the Rayleigh limit of the objective by superposition of off-axis holograms

We present what we believe to be a new application of scanning holographic microscopy to superresolution. Spatial resolution exceeding the Rayleigh limit of the objective is obtained by digital coherent addition of the reconstructions of several off-axis Fresnel holograms. Superresolution by holographic superposition and synthetic aperture has a long history, which is briefly reviewed. The method is demonstrated experimentally by combining three off-axis holograms of fluorescent beads showing a transverse resolution gain of nearly a factor of 2.     

Field emission properties of one-dimensional single CuO nanoneedle by in situ microscopy

In this article, the field-emission property of individual CuO nanoneedle was investigated to explore its tip image and real work function using in situ transmission electron microscopy. The maximum emission current of nanoneedle used in this study was 1.08 μA, and two different slopes in the corresponding F–N graph existed with work functions of the CuO nanoneedle being 1.12 and 0.58 eV. In comparison with the single CuO nanoneedle, the field enhancement β and parameter s of the CuO nanoneedle’s film arrays were also studied, which showed that the screening effect played a key role in the field-emission process.     

White light emission and electrical properties of silicon oxycarbide-based metal-oxide-semiconductor diode

White light emission from silicon oxycarbide-based metal-oxide-semiconductor diode has been realized in this work. Emitted light is visible to the naked eyes as the bias voltage is increased higher than 15 V. Electroluminescence intensity increases linearly with current density. According to the analysis of conduction mechanisms in device, electron-hole radiative recombination at twofold coordinated silicon lone-pair centers, neutral oxygen vacancies, and E_δ′ defect centers in film is responsible for the light emission.     

Optical resolution and the duality of light

For 15 years, lensless microscopes have been constructed based on the use of holography, a digital CCD detector, and a computer for image reconstruction by use of, e.g., Fourier transformation. Thus, no lens is involved and therefore the conventional resolution limit of half the wavelength no longer applies. Instead of being limited by the wavelength, the resolution is in this case limited by how exact one can measure the phases of the light. It is remarkable that the interference-limited resolution is approximately 0.01 lambda, whereas the diffraction-limited resolution is only of the order of 0.5 lambda. It is my hope that by combining these two techniques it will be possible to increase the magnification in optical systems by at least an order of magnitude. The calculations also indicate that information does not necessarily decrease with distance.     

Polymer light emission: control of properties through chemical structure and morphology

We report on recent work concerning polymers for improved electron injection and transport, for enhanced photoluminescence quantum efficiency and for polarised emission. A new blue-emitting triazole containing co-polymer with high photoluminescence efficiency is described. This polymer acts to enhance the electroluminescence efficiency when used in two layer devices with poly(p-phenylene-vinylene) [PPV] as a hole transporting emitter. The two layer device has an external quantum efficiency of ≈ 0.08% at a luminance of 250 cd/m² for a current density of 100 ma/cm². Use of a meta-phenylene-vinylene conjugation interrupting unit as a means of enhancing photoluminescence quantum efficiency is also described. The resulting co-polymer allows fabrication of three layer devices that have an external efficiency of ≈ 1% at a luminance of 96 cd/m² for a current density of 3.7 mA/cm². Finally, we report on the orientation of a polyfluorene conjugated polymer via alignment of its liquid crystal phase on rubbed substrates. Thermotropic liquid crystal phases offer an approach to polarised electroluminescence emission and we discuss the merits of this and various other approaches.     

测试环境对碳纳米管场发射性能的影响

采用CVD法在Ni丝上直接沉积碳纳米管,并应用二极管结构对其场发射性能进行测试,测试结果表明:(1)碳管表面态对其场发射稳定性影响明显,运用密度泛函平面波赝势方法(PWP)和广义梯度近似(GGA)对碳管表面吸附水分子前后电子能带结构和态密度作比较,发现吸附水分子后碳管功函数降低,费米能级处电子态密度增大,有利于增大碳管场发射电流;(2)高真空是获得碳管场发射稳定性一个必要条件;(3)荧光粉对碳管场发射电流也有一定贡献,但大的场发射电流情形下可忽略其影响。     

Effects of residual gas exposure on the field emission properties of ZnO nanorods

We compare the effects of O2, CO2, N2, H2, and Ar residual gas exposure on the field emission (FE) properties of ZnO nanorods. In contrast to carbon nanotubes and Mo metal microtips, we find that O2 and CO2 exposures do not significantly degrade the FE properties of ZnO nanorods. However, N2 exposure significantly degrades the FE properties. We propose that this could be due to the dissociation of N2 into atomic nitrogen species and the reaction of such species with ZnO. H2 and Ar exposures are not observed to significantly degrade the FE properties.     

Coherent use of opposing lenses for axial resolution increase in fluorescence microscopy. I. Comparative study of concepts

We study the use of coherent counterpropagating interfering waves to increase threefold to sevenfold the optical bandwidth and the resolution of fluorescence microscopy along the optic axis. Systematic comparison of the point-spread function and the optical transfer function (OTF) for the standing-wave microscope (SWM), the incoherent illumination interference image interference microscope (I5M), and the 4Pi confocal microscope reveals essential differences among their resolution capabilities. It is shown that the OTF's of these microscopes differ strongly in contiguity and amplitude within the enlarged range of transferred frequencies, and therefore they also differ in their ability to provide data from which interference artifacts can be removed. We demonstrate that for practical aperture angles the production of an interference pattern is insufficient for improving the axial resolution by the expected factor of 3-7. Conditions of the OTF for unambiguous improvement of axial resolution of arbitrary objects are fulfilled not at all in the SWM, partially in the I5M, and fully in the two-photon 4Pi confocal microscope.     

Effects of soluble surfactants on the Langmuir monolayers compressibility: A comparative study using interfacial isotherms and fluorescence microscopy

Langmuir monolayer isotherms and fluorescence microscopy (FM) techniques have been used to study the effect of two soluble surfactants on the methyl octadecanoate monolayer's compressibility at the air/water interface. The combination of these two techniques allows one to bridge the mechanical and morphological properties of the monolayer at different surfactant subphase concentrations. Our results show that the presence of sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium bromide (DTAB) affects the monolayer elasticity differently. In addition, the outcome of this study emphasizes the role of the cationic and anionic surfactants on the monolayer compressibility. In fact, their effect was found to be primly depending on the monolayer thermodynamic situation. The isotherms of the monolayers at different surfactant concentrations underneath the monolayer preserve the characteristics behavior of the monolayer as imaged by FM. The calculated monolayer compressibility shows two different trends depending on the monolayer pressure and the surfactant type. A decreasing compressibility as a function of SDS concentration was found at pressure π = 5 mN/m, while no noticeable effect was found due to DTAB. At π = 10 mN/m both surfactants convert the monolayer from rigid to soft monolayer. Such characteristic behavior of the monolayer has been confirmed by FM.     

Effects of surface modification on the fluorescence properties of conjugated polymer/ZnO nanocomposites

We report the effects of surface modification on the fluorescence properties of conjugated polymer/zinc oxide nanocomposites. Zinc oxide nanoparticle surface was partially capped by poly(vinylpyrolidone) (PVP) during hydrolysis of zinc acetate dihydrate in methanol in ambient condition. The ZnO-capped nanoparticles were characterized by XRD and TEM. The fluorescence properties of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV)/ZnO nanocomposites with different mass ratios were studied by steady-state and time-resolved spectroscopy. The results indicate that the surface-modified ZnO nanoparticles are more effective to quench the emission of MEH-PPV by charge transfer process than the non-capped ZnO. The more effective charge transfer in MEH-PPV/ZnO-capped is attributed to the better dispersion of the nanoparticles in MEH-PPV matrix and THF solvent.     

Influence of saline media on the fluorescence emission of Bacillus spores

Single-particle levitation in conjunction with 264.3-nm laser excitation is used to measure the fluorescence emission of individual particles of Bacillus globigii spores. With precise humidity control, the fluorescence emission of wetted and desiccated Bacillus spore particles is measured from 300 to 450 nm. Comparison of spectra for Bacillus spores suspended in a standard buffer aqueous solution and for a desiccated 10-mum-diameter aggregate Bacillus spore particle shows that the spectra is virtually indistinguishable. However, at 85% relative humidity, corresponding to a 4.5M sodium chloride solution, the spore spectra redshifts by approximately 25 nm. It is postulated that the spectra redshifting is a result of specific interactions between the tyrosine fluorophore of the Bacillus spore and the phosphate moieties in the buffer solution.     

Electrochemical surface plasmon excitation and emission light properties in poly(3-hexylthiophene) thin films

The attenuated total reflection (ATR) and emission light properties utilizing surface plasmon (SP) excitations were measured for the electrochemical change of poly(3-hexylthiophene-2,5diyl) (P3HT) thin films in-situ. The SP emission light could detect the SP excited by molecular luminescence of P3HT. The ATR and SP emission light properties were observed for the doped–dedoped states of P3HT thin film. The ATR and SP emission light properties were remarkably changed with the electrochemical doping and dedoping. The SP emission light also decreased by decrease of the molecular luminescence of P3HT by doping. For the dedoped-state P3HT thin film, SP emission light also increased by increase of the molecular luminescence. The SP emission light excited by molecular luminescence can be controlled by the control of doping–dedoping state.