Trapping single molecules by dielectrophoresis

We have trapped single protein molecules of R-phycoerythrin in an aqueous solution by an alternating electric field. A radio frequency voltage is applied to sharp nanoelectrodes and hence produces a strong electric field gradient. The resulting dielectrophoretic forces attract freely diffusing protein molecules. Trapping takes place at the electrode tips. Switching off the field immediately releases the molecules. The electric field distribution is computed, and from this the dielectrophoretic response of the molecules is calculated using a standard polarization model. The resulting forces are compared to the impact of Brownian motion. Finally, we discuss the experimental observations on the basis of the model calculations.     

Phase imaging with rotating illumination

A modified extended-ptychographical-iterative-engine （ePIE） algorithm is proposed to overcome the dis- advantages of ePIE technique and reduce the influence of stage hysteresis or backlash error. The exit wave of a rotatable ＂screen＂ illuminated by plane wave is used as the illumination on the specimen, and the complex transmission functions of the rotatable object and specimen can be simultaneously reconstructed. Compared with the standard x - y scanning PIE algorithm, the proposed algorithm can completely avoid the influence of stage hysteresis （or backlash error）. The proposed algorithm also has higher convergence s!oeed and better accuracy than the standard PIE algorithm.     

Orientational selection of molecules in combined laser and electrostatic fields

It is shown that the combined effects of electrostatic and resonant laser fields on a molecular ensemble can be used to control the orientation of molecules by changing their internal state. In contrast to most other schemes for controlling molecular orientation, the proposed method does not require rotational cooling and can be highly efficient at room temperature.     

Orientational order in liquid crystals exhibited by some binary mixtures of rod-like and bent-core molecules

We report measurements of the temperature variations of the optical birefringence in the nematic (N) and partial bilayer SmA (SmA_d) phases in 4-n-octyloxy 4^′ -cyanobiphenyl made of rod-like (R) molecules and five mixtures of this compound with 1,3-phenylene bis[4-(3-methylbenzoyloxy)] 4^′ -n- dodecylbiphenyl 4^′ -carboxylate, made of bent-core (BC) molecules. The birefringence decreases with the concentration x of the BC molecules but the macroscopic order parameter initially decreases upto 11mol% of BC molecules and subsequently increases with x . This is attributed to the possible formation of polar clusters of BC molecules. Orientation of BC molecules changes between the N and SmA_d phases and the birefringence data in the two phases imply that the kink angle of the BC molecules is ∼ 90^° rather than ∼ 110^° as obtained from calculations which minimize the energy of the molecule. IR spectroscopic measurements on the mixture with 11mol% of BC molecules have been used to estimate the molecular order parameter S of the R molecules, and to provide additional support for a relatively small kink angle of BC molecules.     

Orientational order and polarizability of molecules in a nematic liquid crystal

The influence of the orientational order of molecules in a nematic liquid crystal on the mean value $\bar \gamma$ and anisotropy Δγ of the molecular polarizability has been studied in the framework of the molecular statistical approach with allowance for the perturbation of the electronic structure of molecules due to the change in the conformation of their aromatic core and intermolecular interactions. Experimental dependences of $\bar \gamma$ and Δγ on the molecular orientational order parameter S have been derived, and their specific features for the known objects have been explained. The possibility of separating the contributions of opposite signs to the dependence Δγ(S) due to the change in the conformation of molecules and intermolecular interactions has been shown using nematic MBBA as an example.     

Longitudinal field modes probed by single molecules

We demonstrate that a strong longitudinal, nonpropagating field is generated at the focus of a radially polarized beam mode. This field is localized in space and its energy density exceeds the energy density of the transverse field by more than a factor of 2. Single molecules with fixed absorption dipole moments are used to probe the longitudinal field. Vice versa, it is demonstrated that orientations of single molecules are efficiently mapped out in three dimensions by using a radially polarized beam as the excitation source. We also show that there is no momentum or energy transport associated with the longitudinal field.     

Three-dimensional particle imaging by defocusing method with an annular aperture

We propose an annular-aperture-based defocusing technique for three-dimensional (3D) particle metrology from a single camera view. This simple configuration has high optical efficiency and the ability to deal with overlapped defocused images. Initial results show that an uncertainty in depth of 23 microm can be achieved over a range of 10 mm for macroscopic systems. This method can also be applied in microscopy for the measurement of fluorescently doped microparticles, thus providing a promising solution for 3D flow metrology at both macroscales and microscales.     

Sensing single electrons with single molecules

We propose a new methodology for probing transport of just one electron, a process of great importance both in nature and in artificial devices. Our idea for locating a single electron is analogues to the conventional GPS where signals from several satellites are used to locate a macro object. Using fluorescent molecules as tiny sensors, it is possible to determine 3D displacement vector of an electron.     

Real time measurements of rough object vibration by imaging of Gaussian illumination

A real time method for measuring the vibration of rough surface using image of gaussian illumination is suggested. Theoretical prediction is done by assumption of gaussian distribution of image intensity. Experiments confirming the usefulness of the method have been performed.     

High-resolution imaging of single fluorescent molecules with the optical near-field of a metal tip

We show that a concentration of light at a metal tip allows near-field optical imaging of single fluorescent dye molecules at very high resolution, despite strong quenching effects. Details as small as 10 nm were observed in the fluorescence patterns of single Cy-3 dyes bound to the termini of DNA. Data evaluation by model fitting determines the positions of the dyes to an accuracy even better than 1 nm and also yields their 3D orientation. The metal tip simultaneously provides high-resolution topographic imaging complementing the optical signal for a detailed surface examination.     

Lens-free coherent modulation imaging with collimated illumination

We propose a lens-free coherent modulation imaging(CMI) method for reconstructing a general complex-valued wave field from a single frame of a diffraction pattern. A numerical Fourier transform is introduced in the iterative reconstruction process to replace the lens or zone plate used in the current CMI technique to adopt the constraint on the Fourier components of the exit wave field of the sample. While the complexity of the experimental setup is remarkably reduced by replacing the zone plate and additional accessories with the numerical processing, the energy fluence loss induced by the undesired diffraction orders of the zone plate can be also avoided. The feasibility of the proposed technique is verified experimentally with visible light.     

Coherent x-ray diffraction imaging with nanofocused illumination

Coherent x-ray diffraction imaging is an x-ray microscopy technique with the potential of reaching spatial resolutions well beyond the diffraction limits of x-ray microscopes based on optics. However, the available coherent dose at modern x-ray sources is limited, setting practical bounds on the spatial resolution of the technique. By focusing the available coherent flux onto the sample, the spatial resolution can be improved for radiation-hard specimens. A small gold particle (size <100 nm) was illuminated with a hard x-ray nanobeam (E=15.25 keV, beam dimensions approximately 100 x 100 nm2) and is reconstructed from its coherent diffraction pattern. A resolution of about 5 nm is achieved in 600 s exposure time.     

Orientational resolvation of S1-excited 4,4'-dinitrophenyl-1,3,5-hexatriene molecules in alcohols

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 53, No. 6, pp. 961–967, December, 1990.     

单分子的光学探测

介绍了三能级结构单分子光子源的工作原理,研究了利用Hanbury-Brown-Twiss探测方法,记录两个单光子计数器响应的单分子光子源输出的每一个事件,分析单事件的光子统计概率P(n, n=0,1,2)与Mandel参数.     

单分子的光学探测

介绍了三能级结构单分子光子源的工作原理,研究了利用Hanbury-Brown-Twiss探测方法,记录两个单光子计数器响应的单分子光子源输出的每一个事件,分析单事件的光子统计概率P（n,n=0,1,2）与Mandel参数.研究结果表明,当信号背景比SBR＞2.41时,P（2）＜（2-√4-2n^-）^2 /2是判别单分子的充分条件,n^-为每个激发周期内探测到的平均光子数。     

Orientational order of uniaxial nematic liquid crystals using electron spin resonance of solute molecules

Summary We present here measurements of hyperfine splittings andg factors of two nitroxide spin probes dissolved inp-azoxyanisole, a wellknown uniaxial nematic liquid crystal, about one part to a million in their molecular ratio. The spin probe molecules used are 1) 17β-hydroxy-4′, 4′-dimethylspiro-/5α-androstane-3, 2′-oxazolidin/-3′-yloxyl, and 2) 2-(3-Carboxypropyl)-4, 4-dimethyl-2-tridecyl-3-oxazolidinyloxyl methyl ester; the former is known to have rigid and the latter flexible structures. These results are used to demonstrate the validity of our model that relates the orientational-order tensor of liquid crystals to the above quantities obtained by the electron spin resonance technique. The model is free of restrictions on the nature of the solute molecules, rigid or flexible. The relation between these directly measured quantities and the components of is established in two steps: first by relating them to , an order parameter tensor defined by a unit vector along the so-called long axis of solute molecules, and then by the use of , wherek is a scalar constant. This latter relation is obtained on the plausible arguments of solute-solvent and solvent-solvent interactions giving rise to and , respectively, andk representing their relative strengths. In spite of appreciable structural differences existing between these two solute molecules, very satisfactory agreements between the theory and experiment are observed for both. Such agreements are essentially independent of uncertainties in our knowledge of the parameters involved. Furthermore, we show that important molecular parameters can also be obtained from such measurements. Deceased.     

Extinction coefficient imaging of turbid media using dual structured laser illumination planar imaging

We demonstrate a technique, named dual structured laser illumination planar imaging (SLIPI), capable of acquiring depth-resolved images of the extinction coefficient. This is achieved by first suppressing the multiply scattered light intensity and then measuring the intensity reduction caused by signal attenuation between two laser sheets separated by Δz mm. Unlike other methods also able to measure this quantity, the presented approach is based solely on side-scattering detection. The main advantages of dual SLIPI is that it accounts for multiple scattering, provides two-dimensional information, and can be applied on inhomogeneous media.