Saturated Förster resonance energy transfer microscopy with a stimulated emission depletion beam: a pathway toward single-molecule resolution in far-field bioimaging

We theoretically demonstrate that the spatial resolution of stimulated emission depletion (STED) microscopy can be substantially enhanced without increasing the intensity of the STED beam. In our scheme, tiny nanobeads codoped with donor and acceptor molecules are used as fluorescent probes, in which F?rster resonance energy transfer (FRET) can occur with an ~100% efficiency between the donors and acceptors. Enhancement of the depletion of acceptors in the nanobeads with the doughnut-shaped depletion beam can lead to an increase of FRET efficiency in the outer area of the excitation spot, which itself is used for deexciting donor molecules and, consequently, enhancing the optical resolution.     

Stimulated emission depletion microscopy with a supercontinuum source and fluorescence lifetime imaging

We demonstrate stimulated emission depletion (STED) microscopy implemented in a laser scanning confocal microscope using excitation light derived from supercontinuum generation in a microstructured optical fiber. Images with resolution improvement beyond the far-field diffraction limit in both the lateral and axial directions were acquired by scanning overlapped excitation and depletion beams in two dimensions using the flying spot scanner of a commercially available laser scanning confocal microscope. The spatial properties of the depletion beam were controlled holographically using a programmable spatial light modulator, which can rapidly change between different STED imaging modes and also compensate for aberrations in the optical path. STED fluorescence lifetime imaging microscopy is demonstrated through the use of time-correlated single photon counting.     

Super‐resolution deep imaging with hollow Bessel beam STED microscopy

Stimulated emission depletion (STED) microscopy has become a powerful imaging and localized excitation method, breaking the diffraction barrier for improved spatial resolution in cellular imaging, lithography, etc. Because of specimen‐induced aberrations and scattering distortion, it is a great challenge for STED to maintain consistent lateral resolution deep inside specimens. Here we report on deep imaging STED microscopy using a Gaussian beam for excitation and a hollow Bessel beam for depletion (GB‐STED). The proposed scheme shows an improved imaging depth of up to about 155 μm in a solid agarose sample, 115 μm in polydimethylsiloxane, and 100 μm in a phantom of gray matter in brain tissue with consistent super resolution, while standard STED microscopy shows a significantly reduced lateral resolution at the same imaging depth. The results indicate the excellent imaging penetration capability of GB‐STED, paving the way for deep tissue super‐resolution imaging and three‐dimensional precise laser fabrication.

     

Self-aligned fiber-based dual-beam source for STED nanolithography

A fiber-based source that can be exploited in a stimulated emission depletion(STED) inspired nanolithography setup is presented. Such a source maintains the excitation beam pulse, generates a ring-shaped depletion beam, and automatically realizes dual-beam coaxial alignment that is critical for two beam nanolithography. The mode conversion of the depletion beam is realized by using a customized vortex fiber, which converts the Gaussian beam into a donut-shaped azimuthally polarized beam. The pulse width and repetition frequency of the excitation beam remain unchanged, and its polarization states can be controlled. According to the simulated point spread function of each beam in the focal region, the full width at half-maximum of the effective spot size in STED nanofabrication could decrease to less than 28.6 nm.     

微束X射线荧光分析

用能量色散微束X射线荧光分析仪实际测量了微束准直器孔径和X射线强度对微束空间分辨率的影响,在准直器孔径为0.1mm条件下,获得以FWHM定义的空间分辨率最好为0.073mm。通过微束扫描测量出某硫化锰矿微区内的Mn、Fe、Zn、Pb的三维等高线荧光强度分布图和不同小区域内的能谱。     

利用后向散射光空间谱强度分布探测尾流气泡的实验研究

利用自行设计制作的尾流模拟系统产生气泡，应用散射光空间频谱测量分析系统，对水中气泡群的后向散射光空间谱强度分布进行测量和分析，研究了不同探测距离的散射光衰减对其强度分布的影响.结果表明，在气泡密度、大小分布不变的情况下，扩束光照明时，由于参与光散射的气泡数目增加对散射光在水中传播衰减的补偿，散射空间谱强度分布的峰值和半宽值均不随探测距离变化；而细光束照明时，散射谱强度分布峰值随探测距离的增加而减小，半宽值则逐渐增大.所以在远距离探测时，细光束的探测效果好.     

Cathodoluminescence of radiative centers in wide-bandgap materials

Features of the local cathodoluminescence method during the investigation of wide-bandgap materials doped by rare earth ions are considered. The high energy of the primary electron beam, the possibility of variation of the specific excitation power by orders of magnitude, and the locality of the method allow one to study transitions, which require radiation with an energy of more than 5 eV to be excited, to study homogeneity of the dopant distribution with a spatial resolution better than 1 μm, and to investigate spectra of radiation emitted from various depths by a nondestructive technique. A model is proposed that allows one to evaluate the efficiency of radiative level excitation and the content of luminescent centers. We suggest a new approach to the investigation of electronic traps in wide-bandgap samples using variation of radiation intensity under stationary exposure.     

轴对称-折叠组合腔CO_2激光器原理性实验研究(英文)

报道了轴对称-折叠组合腔CO2激光器原理性实验研究,激光器能在CW模式下成功运行。研究得到了激光器最佳的气体比率和气体压强。通过研究CO2激光器的不同方面,如激励门电压和输出功率等,发现它们随着放电电流的变化而变化。通过实验得到了激光光束的光斑和聚焦的实验光斑,并模拟了光强分布。激光器已经成功的组建、运行和调试,获得的最大输出功率为58 W。     

Visible-super-resolution infrared microscopy using saturated transient fluorescence detected infrared spectroscopy

A scanning visible-super-resolution microscope based on the saturation behaviour of transient fluorescence detected infrared (TFD-IR) spectroscopy is proposed. A Gaussian IR beam, a Gaussian visible beam and a Laguerre-Gaussian (LG) visible beam are used to obtain two separate two-color excitation fluorescence (2CF) images of the sample. The final image is obtained as the difference between the two recorded images. If the peak intensity of the LG beam is high enough to induce saturation in the fluorescence signal, the image can, in principle, have unlimited spatial resolution. A ∼3-fold improvement in transverse resolution over the visible diffraction limit (and far exceeding the IR diffraction limit) is easily achievable in present experimental setups.     

饱和激发情况下的荧光关联谱测量

研究了激发光增强时其对荧光关联谱(FCS)测量的影响. 强激发光产生的饱和激发会改 变激光诱导荧光的空间分布函数,从而影响FCS的测量结果. 首先根据饱和吸收的物理模型,推导出强激发光情况下有效探测区域变化的定量公式,获得了FCS测量所得到的粒子数和扩散时间与饱和激发光强和激光光强的函数关系,并用于消除饱和吸收造成的系统误差.采用Monte-Carlo模拟方法和实验,对理论分析结果进行了验证. 这将有助于完善FCS分析方法的理论模型,为高激发光强度下的FCS探测提供依据. 关键词： 荧光关联谱 饱和激发 Monte-Carlo模拟     

Rate of generation of nonequilibrium charge carriers by a focused X-ray beam

A model of the interaction between an X-ray beam and a semiconductor sample is proposed for the X-ray-beam induced current method. The spatial distribution of the generation rate of nonequilibrium charge carriers (also called the generation function) is obtained using this model. It is shown that the generation function is proportional to the X-ray probe intensity for a rather broad X-ray beam. The results of calculating contrast profiles of the induced current for the described generation function are compared with those for the generation function proportional to the X-ray probe intensity and also with experimental profiles.     

隐失驻波全内反射荧光显微术的数值计算

从理论上详细计算了在全内反射的条件下，两束入射光产生的隐失干涉场(即隐失驻波)的强度分布，并分析了其不同于传统传播波干涉场的特点。同时使用数值模拟证明了利用隐失干涉场，即隐失驻波的激发方式，可以提高系统的分辨力，在横向实现超经典分辨的荧光成像。具体的分析表明，两束光以相等的角度入射，同时振幅相等，偏振态相同，所形成干涉条纹的反衬度最高，此时成像系统的有效点扩展函数最优化；入射介质1的折射率越大，隐失干涉场的空间周期越短(空间频率越高)，其对应的调制点扩展函数中心瓣的半峰全宽越小，可能分辨更小的物体，但同时旁瓣的强度也增强，最终成像的分辨力受两者的共同制约。     

940 nm low beam divergence tapered window laser arrays

The structures of 940 nm low vertical beam divergence semiconductor lasers grown by molecular beam epitaxy are presented. The high power laser consists of an array of closely spaced tapered waveguides giving lower parallel beam divergence and window structure. The emission wavelength is 939 nm. The FWHM of the far field pattern is 8×30°. The maximum continuous wave (CW) output power of 30 W has been achieved. In the aging tests, the laser arrays have been operating for over 3000 h under the CW condition of 25 W.     

The application of high-speed TV-holography to time-resolved vibration measurements

We describe an electronic speckle pattern interferometer (ESPI) system that has enabled non-harmonic vibrations to be measured with μs temporal resolution. The short exposure period and high framing rate of a high-speed camera at up to 40,500 frames per second allow low-power CW laser illumination and fibre-optic beam delivery to be used, rather than the high peak power pulsed lasers normally used in ESPI for transient measurement. The technique has been demonstrated in the laboratory and tested in preliminary industrial trials. The ability to measure vibration with high spatial and temporal resolution, which is not provided by techniques such as scanning laser vibrometry, has many applications in manufacturing design, and in an illustrative application described here revealed previously unmeasured “rocking” vibrations of a car door. It has been possible to make the measurement on the door as part of a complete vehicle standing on its own tyres, wheels and suspension, and where the excitation was generated by the running of the vehicle's own engine.     

可调空间分辨USEDCARS技术研究

相干反斯托克斯拉曼散射（CARS）技术是一种非常重要的燃烧诊断技术,该技术具有非常强的抗干扰能力和非常高的测量精度。但空间分辨力不足会使CARS技术产生很强的空间平均效应,引起成CARS光谱畸变,进而造成CARS光谱分析困难,无法通过CARS光谱反演燃烧场参数。针对非稳腔空间增强探测CARS（USEDCARS）技术存在的空间分辨不足以及空间分辨力不易改变的特点,分析了影响USEDCARS技术测量空间分辨力的各种因素,采用一组轴棱锥对USEDCARS系统中的泵浦激光进行环状光束整形,并通过调节轴棱锥之间的距离获得了不同直径的环状光束,在此基础上,建立了空间分辨可调USEDCARS诊断系统。开展了空间分辨力分析实验,获得了CARS信号强度随空间位置的分布数据,以CARS信号总强度95%包含的空间区域代表CARS的纵向空间分辨力,以此计算得到了CARS系统空间分辨力为1.7～6.5 mm连续可调。其中,高分辨力情况,达到了现有BOXCARS技术的空间分辨力。利用所建立的空间分辨可调USEDCARS诊断系统测量了酒精/空气预混火焰温度参数,获得了不同空间分辨条件下的CARS光谱。空间分辨力为1.7 mm时,获得了高质量CARS光谱,通过光谱拟合给出了所测火焰的温度信息。分辨力分别为4.9和6.5 mm时获得了较强的CARS信号,但存在光谱畸变。结果显示,空间分辨力对CARS信号的强度和空间平均效应有很大地影响,提高测量的空间分辨力可以有效消除空间平均效应,获得准确的CARS光谱,增强光谱拟合精度,同时空间分辨可调的特性使该系统能够更好地适应不同实验条件下的诊断工作。     

Excitation of electronic states of Ar, H(2), and N(2) by positron impact

We have measured the first state-resolved, absolute cross sections for positron excitation of electronic states of an atom or molecule using a high resolution (Delta E approximately 25 meV FWHM) beam of positrons from a Penning-Malmberg trap. We present cross sections for the excitation of the low-lying levels of Ar, H(2), and N(2) for incident positron energies between threshold and 30 eV. For Ar and H2, comparison can be made with theoretical calculations, and, in the case of H(2), the results resolve a significant discrepancy between the only two available calculations.     

Optical spatial solitons supported by photoisomerization nonlinearity in a polymer

We present a theory for a new type of optical spatial soliton that is based on the angle hole burning mechanism of photoisomerization in some polymers. We predict that the photoisomerization nonlinearity can support steady-state dark and bright spatial solitons in the polymer. We also discuss the dependence of the FWHM of the spatial soliton on wavelengths of the background beams and on the ratio of the intensity of the background beam to that of the signal beam.     

Theoretical investigation of optical patterning of monolayers with subwavelength resolution

We formulate a model of monolayer patterning via optically-controlled chemical reactions, with the goal of beating the diffraction limit in photolithography. We consider the use of the proven technique of STimulated Emission Depletion (STED) to selectively place a handful of molecules in a reactive excited state. We show that repeated optical excitation has a greater effect on pattern formation than increasing the reaction rate, auguring well for experimental work. We also consider optically-controlled deposition of a soluble species via STED, and show that even for very large concentrations and excited state lifetimes the full width at half maximum of the features formed is robust against the effects of diffusion and saturation.     

Rapid in situ X‐ray position stabilization via extremum seeking feedback

X‐ray beam stability is crucial for acquiring high‐quality data at synchrotron beamline facilities. When the X‐ray beam and defining apertures are of similar dimensions, small misalignments driven by position instabilities give rise to large intensity fluctuations. This problem is solved using extremum seeking feedback control (ESFC) for in situ vertical beam position stabilization. In this setup, the intensity spatial gradient required for ESFC is determined by phase comparison of intensity oscillations downstream from the sample with pre‐existing vertical beam oscillations. This approach compensates for vertical position drift from all sources with position recovery times <6 s and intensity stability through a 5 µm aperture measured at 1.5% FWHM over a period of 8 hours.     

Kinoform单透镜的硬X射线聚焦性能

Kinoform单透镜可以高效聚焦硬X射线至纳米量级, 在X射线纳米显微学和纳米光谱学领域有着重要的应用前景. 基于衍射光学和傅里叶光学理论, 给出了X射线经由Kinoform单透镜聚焦的物理模型, 基于数值模拟, 研究了不同材料、光子能量、台阶数量和顶点曲率半径对Kinoform单透镜聚焦性能的影响. 结果表明, 孔径为1 mm的Kinoform单透镜对30 keV的X射线聚焦, 可以得到14 nm焦斑、62 μm焦深, 且可实现4个量级的光强增益和大于30%的光强透过率.