Fugui Yang

Laser Induced Blue Luminescence Phenomenon

Laser induced strange blue luminescence in several Raman crystals has been investigated. The blue luminescence at about 473 nm has the characteristic of no orientation and only produced in the crystal where the fundament laser oscillated. The experimental results show that the blue luminescence must result from the fundamental laser around 1.0 µm rather than Stokes-shifting. The spectrum detected is similar for different crystals. This blue luminescence is obviously strange and inconsistent with traditional luminescence theories, which maybe a brand-new luminescence theory.

Numerical studies on the Chin–Shifrin inversion method for particle sizing

The Chin–Shifrin (C-S) inversion method based on Fraunhofer diffraction is an inversion method for recovering size distribution from an optical pattern. The truncation error of the diffraction approximation limits the application of the C-S inversion method. In order to give a quantitative description of the truncation error, a new approximation error, ε, is defined by considering the characteristic of the integrand ECShCS . The inversions show that the true peak does not shift along with the variation of upper limit of integral angle when the corresponding ε is small. As the larger upper limit of integral angle can recover a more accurate size distribution, estimation of maximum approximation angle, θ max, for different sets of ε and refractive index, m, is made. The direct results for θ max are the minimum size parameter and new criterion for maximum angular resolution with which the C-S integral inversion can work. They are investigated using sampling theory.

Laser-heating-based active optics for synchrotron radiation applications

Active optics has attracted considerable interest from researchers in synchrotron radiation facilities because of its capacity for x-ray wavefront correction. Here, we report a novel and efficient technique for correcting or modulating a mirror surface profile based on laser-heating-induced thermal expansion. An experimental study of the characteristics of the surface thermal deformation response indicates that the power of a milliwatt laser yields a bump height as low as the subnanometer scale and that the variation of the spot size modulates the response function width effectively. In addition, the capacity of the laser-heating technique for free-form surface modulation is demonstrated via a one-dimensional surface correction experiment. The developed method is a promising new approach toward effective x-ray active optics coupled with at-wavelength metrology techniques.

Determination of particle-size distributions from light-scattering measurement using Lucy-Richardson algorithm

Abstract. A classical iterative Lucy-Richardson (LR) inversion algorithm used for recovering particle-size distributions (PSD) from light-scattering data is proposed. The convergence of iteration is validated in the numerical simulation for three different distributions: the gamma, the log-normal, and the Rosin-Rammler. The accuracy of the inversion is checked graphically against the exact distribution with good results, even for the synthesized intensity data of a signal-noise-ratio smaller than 20 dB. Finally, an experiment with linear charge coupled device as the detector is carried out, and the PSD is recovered successfully by the LR inversion method.

A novel optical approach based on subjective speckle for tracking on smooth glass

This paper presents an improvement approach to realize tracking on smooth glass surface based on subjective speckle. The scattering mechanism on glass surface is analyzed and the affection on tracking precise and range for tracking with subjective speckle is researched. The speckle captured by CCD just from the upper surface of the glass is achieved by grazing incidence of the laser beam and the noise mixed with the signal is eliminated by a barrier above the surface. Based on the apparatus of subjective speckle tracking, the speckle contrast is improved from 0.25 to 1.25 by non-Gauss effect and the range of the tracking has been increased from 200 μm to 400 μm compared with the objective speckle method on the same condition.

Speckle analysis in laser scanning display system

The theory of speckle formation in laser scanning display system is established based on the averaging effect of eye response as laser beam scanning through an eye resolution spot. It is analyzed that speckle reduction can be obtained by averaging states of speckle during scanning. The theoretical results show that a smaller correlation length of screen surface and the narrowing of laser beam in scanning direction can reduce speckle contrast for this system.

Study on far-field image using microlens array integrated with LCD

We firstly propose the technique to realize far-filed image by integrating the microlenses array with LCD. This technique is expected to resolve eye-gazing problem in common teleconferencing system without affecting the display performance of LCD. The characteristics of far-field diffraction image and geometric image formed by single microlens are simulated and analyzed. The simulation shows that the quality of image is seriously reduced by geometric aberration and diffraction of the small aperture diameter for aspherical and spherical surface profile refractive microlens. The main problem of image acquisition with high resolution is that the signal obtained by cell detector is contributed not only by the sampling point in the axis of the corresponding cell microlens but also sampling points nearby. In simulation, Microlenses of 300μm diameter same with pixel size of LCD were used in orthogonal array at 1mm pitch, which is also the sampling interval in object space. These microlenses array with unit number 213x246 are placed up to 600mm away from object surface. Monte Carlo optimization algorithm is adopted to give accurate inversion results. The typical results are presented with our main conclusions.

Two dimensional surface slope metrology with enhanced spatial resolution based on wavefront coding method

The quality of X-ray optics on beamline is a key factor that limits the performance of the beam line to play. For X-ray mirror surface characterization with high accuracy, long trace profiler and NOM for flat or slight curved mirror have been developed. However, these two kind of instruments cannot measure the highly curved mirror since requirement of high precision and that of large range contradict each other. In this paper, we proposed a novel wavefront-coding-based surface slope metrology technique. Four-dimension information of the optics under test, including x-y position and sagittal/tangential angle, is provided. Due to the focused beam used and the high speed DMD (Digital Mirror Device), high spatial resolution of the measurement is obtained. In experiment, we demonstrated this technique by measuring bend-based high energy monochromator developed in BSRF.

Design consideration for nano-accuracy long trace profiler at BSRF

The third generation synchrotron radiation source like High Energy Photon Source (HEPS, Beijing) requires X-ray optics surface with high accuracy. It is crucial to develop advanced optics surface metrology instrument. The Long Trace Profiler (LTP) is an instrument which measures slope in the long dimension of an optical surface. In order to meet the accuracy requirements for synchrotron optics, a number of researches have been carried out to improve the LTP during the last decades. Many variations have been installed worldwide. As a part of the advanced research of HEPS, the metrology laboratory at Beijing Synchrotron Radiation Facility (BSRF, Beijing) has been conducting work of building a new LTP since 2012. The accuracy of the instrument is expected to be <0.1μrad rms for component up to 1m in length. In this paper, we present some design consideration for nano-accuracy LTP. Two error sources, including the deformation of the granite structure and imperfect optical surface, are studied. We report our optimized configuration of the granite structure and the dependences of the measurement error on the surface error. The results are considered as an important instruction for the proper choice of each component in the profiler. We expect to bring the profiler into operation in 2015.

Image Restoration for Indirectly Far-field Image using Microlenses Array Integrated with LCD

Image restoration for constructing high-spatial-resolution images in an imaging system which realizes indirectly far-filed imaging by integrating the microlenses array with LCD is reported. We have investigated the indirectly far-field imaging condition where adjacent sampling points contribute the detected signal. Experimental setup with microlens of 500 μm diameter and 8 mm focal length is built to prove this condition by studying performance of image restoration using modified point spread function (PSF). Since any one iterative method is not optimal for all image deblurring problems, some deblurring algorithms including direct deconvolution and iterative deconvolution are applied to our imaging system and we compared the effectiveness of these iterative procedures to choose right one for our use.