A spherical-wave source based on a probe for a near-field microscope

A new type of a spherical-wave source for precise interferometry based on a fiber probe for a nearfield microscope is proposed. Data on distortions of generated wavefronts are reported. For the optical numerical aperture NA = 0.24, the root-mean-square distortions do not exceed λ/2000.     

Fiber-optic evanescent field absorption sensor: A theoretical evaluation

Abstract

A comparative study of the fiber-optic evanescent field absorption sensors based on parabolic, linear, and exponential-linear taper profiles has been carried out. The expressions for the effective evanescent absorption coefficient of the fluid have been derived for a diffuse source as well as a collimated source–microscope objective combination. It has been shown that the sensitivity of the sensor depends on the taper profile and the type of the source used in addition to the numerical aperture of the fiber and the refractive index of the fluid. For a given taper profile, the sensitivity is more in the case of the collimated source–microscope objective combination as compared to the diffuse source illumination. Further, the sensor with the exponential-linear taper profile is more sensitive than those having parabolic and linear profiles in the case of both sources.     

Electron microscopes using field emission source

The high brightness and small physical dimensions of a field emission source make it extremely attractive as the source of electrons in scanning electron microscopes. Using this kind of source considerable improvements have been made in this type of instrument so that at the present time the surfaces of solid objects can be viewed at a resolution of 30 Å and thin specimens can be viewed with a resolution of 2.5 Å. The particular nature of the scanning electron microscope allows some unique forms of contrast to be obtained so that the micrographs which can be taken with these microscopes are different in content and quality than those taken on conventional microscopes. As one example, we have been able to study the motion of single heavy atoms on thin carbon films. The resolution is, of course, not as high as that which can be obtained with a field ion microscope but the kind of specimen which can be viewed is different so that the two instruments are complementary in nature.     

Design of a mirror aberration corrector and a beam separator for LEEM

A SPLEEM (spin polarized low energy electron microscope) has been designed with a numerical simulation of electrostatic and magnetic field distributions and electron ray trajectories. Highly (more than 90%) spin polarized electron source has been used. A Wien type spin manipulator and a magnetic lens type spin rotator are used to align spin direction. A magnetic field free objective lens is designed to observe magnetic domain structure of magnetic materials. High or low magnification mode can be selected by using a combined electrostatic and magnetic objective lens for a high spatial resolution and a wide imaging area observation. An electrostatic mirror aberration corrector is installed after the image forming objective lens. A double deflection 45° beam separator is used to bend the direction of electrons from the source to the objective lens and from the objective lens to the mirror aberration corrector.     

Fluorescence lifetime imaging with a low-repetition-rate passively mode-locked diode-pumped Nd:YVO4 oscillator

We report a wide-field fluorescence lifetime imaging microscope based on a low-repetition-rate (3.7-MHz) passively mode-locked diode-pumped laser source. This inexpensive and compact laser source operating in the visible and UV range can excite a wide range of fluorophores of biological interest. We demonstrate that the power of this laser source is highly sufficient for studying biological systems with low quantum yields (autofluorescence of tissues and stained living cells). The maximum measurable lifetime is also strongly increased with this laser source, as fluorescence intensity measurement can occur 250 ns after the excitation pulse.     

Fresnel diffraction model for the point spread of a laser light profile microscope (LPM)

Light profile microscopy is a new method of thin film imaging in which a microscope forms an image of a laser beam intersecting a thin layer along its depth axis. Emission (luminescence or scatter) from the beam volume is transmitted through a cross sectional view surface and used by a microscope to form an image of the beam propagating through the sample. Fresnel diffraction theory is used in this work to derive a point spread model for a microscope operating in this configuration, assuming that the emission from the source beam is completely incoherent. This theory illustrates the dependence of the image resolution on the laser beam radius, which determines the effective thickness of the system object seen by the microscope. The effect of relative displacement of the source beam center from the object plane of the microscope is evaluated. The present theory shows that radial resolution may be evaluated by means of an object focus envelope and a focal energy distribution computed for the objective lens. PACS 42.25Fx; 07.60Pb     

KBA显微镜成像系统的成像模拟及X光成像实验的研究

KBA显微镜是一种非轴对称、非共轴的掠入射成像系统。其结构复杂,调节精度要求很高,在实际成像实验操作中难以掌握其成像特性。利用光学设计软件模拟其成像,对系统的调节和成像分析提供有益的参考。利用光学设计软件ZEMAX模拟了KBA显微镜对点源的成像过程,给出了KBA显微镜成像系统的焦深约为1 mm,景深为50 mm左右。并且由模拟可知,掠入射角对成像的影响很大。对像素尺寸约10μm的探测设备,模拟得出KBA成像系统的空间分辨力上限为3μm左右。基于星光Ⅱ装置对周期为20μm的网格靶成像,获得了KBA显微镜较为清晰的X光图像。该项工作为进一步开展掠入射成像系统的研究奠定了基础。     

Thin-film deposition by combining plasma jet with spark discharge source at atmospheric pressure

This study demonstrates a method for the deposition of CuO_x thin films by combining atmospheric pressure plasma jet with spark discharge. In this type of discharge source, the bulk copper material of spark discharge electrodes plays the role of a precursor. Copper atoms and particles go through the physical processes of sputtering, evaporation, and further agglomeration and condensation in the plasma jet and on the substrate. The experiments were carried out with and without a combination of discharges. The material coated on the substrate was studied using a scanning electron microscope, Raman spectroscopy, and energy-dispersive X-ray spectroscopy. The characteristics of the set-up and plasma, such as I-V curves, optical emission spectra, and substrate temperature, were also measured. Copper electrodes were examined for erosion by a scanning electron microscope. The results demonstrate that deposits coated by combined discharge show denser and thicker films.     

Compact soft x-ray microscope using a gas-discharge light source

We report on a soft x-ray microscope using a gas-discharge plasma with pseudo spark-like electrode geometry as a light source. The source produces a radiant intensity of 4 x 10(13) photons/(sr pulse) for the 2.88 nm emission line of helium-like nitrogen. At a demonstrated 1 kHz repetition rate a brilliance of 4.3 x 10(9) photons/(microm2 sr s) is obtained for the 2.88 nm line. Ray-tracing simulations show that, employing an adequate grazing incidence collector, a photon flux of 1 x 10(7) photons/(microm2 s) can be achieved with the current source. The applicability of the presented pinch plasma concept to soft x-ray microscopy is demonstrated in a proof-of-principle experiment.     

适用于表面分析的小型低能电子显微镜

介绍并表征了一套单法兰集成的低能电子显微镜. 这套显微镜中采用了10o偏转角的磁分束器,从而有利于将其集成到一个10 in的法兰上. 电子光学系统中的一些修正单元被简化,以使其结构简单,容易操作. 样品被置于地电位,方便各静电透镜浮在高电压上. 通过几个实验展示了这台显微镜在典型的低能电子成像、低能电子衍射和光电子成像模式下的性能. 低能电子成像的空间分辨率为51 nm. 利用飞秒激光做光源,相应的非线性光电子发射过程使得这台设备非常适合进行光学近场现象的观察,并获得110 nm的光电子成像空间分辨率.     

Extension of a DNA molecule by local heating with a laser

Thermal convection and thermophoresis induced by mum-scale local heating are shown to elongate a single DNA molecule. An infrared laser used as a point heat source is converged into a dispersion solution of DNA molecules, which is observed under a fluorescent microscope. The thermal convection around the laser focus manifests as extensional flow for the long DNA chain. A simulation of thermal convection that reproduces the experimental condition provides numerical support for the stretching caused by thermal convection. This DNA elongation technique is a novel method for manipulating the intact single DNA molecules, and it can be applied to a "lab on a chip".     

Stimulated-emission-depletion microscopy with a multicolor stimulated-Raman-scattering light source

We describe a subdiffraction-resolution far-field fluorescence microscope employing stimulated emission depletion (STED) with a light source consisting of a microchip laser coupled into a standard single-mode fiber, which, via stimulated Raman scattering (SRS), yields a comb-like spectrum of seven discrete peaks extending from the fundamental wavelength at 532 nm to 620 nm. Each of the spectral peaks can be used as STED light for overcoming the diffraction barrier. This SRS light source enables the simple implementation of multicolor STED and provides a spectral output with multiple available wavelengths from green to red with potential for further expansion.     

Low energy electron point source microscopy

The setup of the LEEPS (low energy electron point source) microscope is described and images of carbon fibres and nanotubes are shown and compared to simulated images. We used a Kirchhoff-Helmholtz type transform to reconstruct the (wave front at the) object. We also showed that this transform can be used to reconstruct optical in-line holograms.     

Wolter显微镜成像系统的光线追踪模拟研究

利用光学设计软件ZEMAX模拟Wolter显微镜对点光源成像。在只考虑几何光学成像的条件下,分三种情况讨论:两曲面同轴共焦点,两曲面不同轴,两曲面同轴不共焦点,对点源通过Wolter系统成像分别进行了光线追踪模拟。通过模拟,定量给出了Wolter显微镜的焦深和景深,分析了处于不同视场点源所成的像,以及两个曲面不同轴时和不共焦点的情况下点源所成的像, 得知Wolter显微镜对物像距的要求很严格,两曲面的不同轴度和两曲面的不共焦点对成像影响非常大,这些模拟结果为Wolter显微镜的成像分析提供了依据。     

Autoconfocal microscopy with a cw laser and thermionic detection

We introduce an application of thermionic emission in a PMT photocathode. Because of the nonlinear dependence of thermionic emission on absorbed laser power, a conventional PMT is found to produce a virtual pinhole effect that rejects unfocused light at least as strongly as a physical pinhole. This virtual pinhole effect is exploited in a scanning transmission confocal microscope equipped with a cw laser source. Because the area of the PMT photocathode is large, signal descanning is not required and thermionic detection acts as a self-aligned pinhole. Our technique of thermionic-detection autoconfocal microscopy is further implemented with graded-field contrast to obtain enhanced phase-gradient sensitivity in unlabeled samples, such as rat hippocampal brain slices.     

Optically sectioned fluorescence lifetime imaging using a Nipkow disk microscope and a tunable ultrafast continuum excitation source

We demonstrate an optically sectioned fluorescence lifetime imaging microscope with a wide-field detector, using a convenient, continuously tunable (435-1150 nm) ultrafast source for fluorescence imaging applications that is derived from a visible supercontinuum generated in a microstructured fiber.     

A new idea for high brightness pulsed electron microscope

We proposed to equip an electron microscope with laser-driven photocathode and make it operate in a CW state or ps pulse state with high brightness as an ideal electron beam source for pulsed electron microscope.     

Field-induced transfer of lithium in a scanning tunneling microscope

Field-induced transfer of Li atoms from a [110]-oriented W tip to a Pt sample is realized in the scanning tunneling microscope (STM) under UHV conditions, using a working principle of the new solid state Li surface diffusion metal ion source (Li-SDMIS), in which the supply of Li to the apex of the tip occurs via surface diffusion. By applying 5–10 μs voltage pulses to the Li-covered W tip placed within tunneling range, single Li hillocks (400 × 400 Ų) were formed on the chosen area of the Pt(110) sample in a well-rep way. The pulse magnitude necessary for Li emission displays a distinct threshold character. A comparative analysis of the energetics of Li field desorption in the STM and Li-FDM (lithium field desorption microscope) modes indicates chemically-assisted field desorption of Li as the field-induced transfer mechanism.     

Transmission positron microscopes

Immediate and near-future plans for transmission positron microscopes being built at KEK, Tsukuba, Japan, are described. The characteristic feature of this project is remolding a commercial electron microscope to a positron microscope. A point source of electrons kept at a negative high voltage is changed to a point source of positrons kept at a high positive voltage. Positional resolution of transmission microscopes should be theoretically the same as electron microscopes. Positron microscopes utilizing trapping of positrons have always positional ambiguity due to the diffusion of positrons.