Hongyi Gao

Design of adjustable superresolving filters based on birefringent crystals

A two-mode adjustable superresolving filter based on a birefringent filter is proposed. This kind of filter has superresolution in two modes of adjustment. One is rotation of the binary pupil filter on the optical axis of the system and the other is the tilt of the filter away from the pupil plane on axis parallel or perpendicular to the optical axis of the crystal. The filters act as complex amplitude filters in the former mode, and as pure phase filters in the latter. By analyzing two superresolving parameters, we obtain the optimal design parameters that ensure a large field of view, a large superresolving range, and a high setting accuracy. This kind of filter can provide more flexibility in practical applications.

Near-field x-ray phase contrast imaging and phase retrieval algorithm

Theoretical analyses of x-ray diffraction phase contrast imaging and near field phase retrieval method are presented. A new variant of the near field intensity distribution is derived with the optimal phase imaging distance and spatial frequency of object taken into account. Numerical examples of phase retrieval using simulated data are also given. On the above basis, the influence of detecting distance and polychroism of radiation on the phase contrast image and the retrieved phase distribution are discussed. The present results should be useful in the practical application of in-line phase contrast imaging.

A method of improving spatial resolution in X-ray fluorescence holography

Summary X-ray fluorescence holography (XFH) is a promising method for determination three-dimensional (3D) structure of local atoms. In this paper, we propose a method to improve the resolution of reconstructed atomic images in x-ray fluorescence holography. A Fe single crystal of body-centred lattice was used as a model for calculation of a hologram. Angular range dependence on spatial resolution of atomic images is discussed. The spatial resolution of the reconstructed image is proportional to the size of the hologram. A hologram recorded in the full 4π sphere can provide complete holographic information. On the other hand, an atomic image obtained from a single energy XFH appears many aberrations and artifacts. By summing images reconstructed from the holograms recorded at several different energies, the atomic image became clearer. Furthermore, the spatial resolution of the atomic image increases with increase in the incident energy. And, the wider the range of incident energy is, the fewer aberrations and artifacts are. So, if an X-ray fluorescence hologram are recorded with the high incident energy and wide multiple-energy range in a 4π solid angle, the atomic images can be reconstructed from the hologram with a high spatial resolution.

X‐ray Double‐Exposure Holography

Double‐exposure holography for measuring phase information in X‐ray fields is suggested in this paper. The double‐exposure method cannot only obtain directly the phase information, but also gives qualitative and quantitative results. This means also that one can obtain simultaneous information about both the amplitude and phase in an experiment.

Analysis of bottleneck factors affecting precision manufacturing and possible solutions

At present, the Nano Scale Precision (NSP) has not been achieved at an enough satisfactory level yet which is required highly on measuring, processing and fabrication arts of semiconductor and integrated circuit chips. The applications are also found in such as the lithography machines of high resolution, fine optical film, lens processing and so on. The main negative factors that effect the NSP improvement can be summarized as follows: the perturbance from the surrounding atmosphere, the random vibration from the supporting structure, the temperature drift, the dust particles, the humidity and the error transfer within the system. In this paper, the factors that blocking the improvement of high-precision manufacturing industries are analyzed. Specially, a method used in setting up a higher stability vibration-resistant platform without air cushion and mechanical pump power source is proposed. The basic solution of digital process used for measuring the disturbance surrounded the system is introduced.

Continuous radial superresolution filters with large focal depth

A new set of continuous superresolution filters is proposed which exhibits a radial superresolution performance with an extended depth of focus in an optical system by properly choosing the design parameters. Numerical simulation results of the performance parameters of the superresolution gain, the radial central core size, the Strehl ratio, the side-lobe factor and the depth of focus with different design parameters for the optimized patterns are displayed. We also give a design example for this kind of filter characterized by a birefringent element inserted between two parallel polarizers. This kind of filter would be useful in fields such as optical data storage systems.

Hard X-ray holography and numerical simulation

Two kinds of hard X-ray holography with atomic resolution including inside source holography and inside detector holography are presented, and the numerical simulation of X-ray fluorescence hologram and the reconstructed real space images are given.

Recent research on X-ray imaging techniques in China

Recent research on X-ray imaging techniques including X-ray contact microscopy, X-ray holography, holographic tomography and phase contrast imaging in China is presented.

Soft X -ray Holography and Microscopy of Biological cells

Some experimental results on soft X-ray microscopy and holography imaging of biological specimens are presented in the paper. As we know, due to diffraction effects, there exists a resolution limit determined by wavelength λ and numerical aperture NA in conventional optical microscopy. In order to improve resolution, the num erical aperture should be made as large as possible and the wavelength as short as possible. Owing to the shorter wavelength, X-rays provide the potential of higher resolution in X-ray microscopy, holography image and allow for exam ination the interior structures of thicker specimens. In the experiments, we used synchrotron radiation source in Hefei as light source. Soft X-rays come from a bending magnet in 800 M eV electron storage ring with characteristic wavelength of 2.4 nm. The continuous X-ray spectrums are monochromatized by a zone-plate and a pinhole with 300 m diameter. The experimental set-up is typical contact microscopic system, its main advantage is simplicity and no special optical element is needed. The specimens used in the experiments of microscopic imaging are the colibacillus, the gingko vascular hundle and the fritillaries ovary karyon. The specimen for holographic imaging is the spider filam ents. The basic structures of plant cells such as the cell walls, the cytoplasm and the karyon especially the joint structures between the cells are observed clearly. An experimental study on a thick biological specimen that is a whole sporule w ith the thickness of about 30 μm is performed. In the holographic experiments, the experimental setup is typical Gabor in-line holography. The specimen is placed in line with X-ray source, which provides both the reference w aves and specimen illum ination. The specimen is some spider filament, which adhere to a Si3N4 film. The recording medium is PM M A, which is placed at recording distance of about 400 μm from the specimen. The hologram s were reconstructed by digital method with 300 nm resolutions. A novel method for recording in-line hologram is proposed which is called X-ray in-line holography with zone-plate magnification in this paper. The magnification factor of the micro zone plate imaging is about 103. The transverse resolution can be 48 nm in this method.

A New Method for X‐ray Spatial Coherence Measure

In this paper, a new method for X‐ray spatial coherence measure is suggested by means of a quasi‐equal optical path interference device with a Fresnel zone plate. It is also feasible to take Gabor in‐line holograms of higher resolution using a lower resolution recording medium on this device.