Implementation of phase-shift patterns using a holographic projection system with phase-only diffractive optical elements

We proposed a method to implement spatial phase-shift patterns with subdiffraction limited features through a holographic projection system. The input device of the system displayed phase-only diffractive optical elements that were calculated using the iterative Fourier-transform algorithm with the dummy-area method. By carefully designing the target patterns to the algorithm, the diffractive optical elements generated the Fourier-transformed images containing the phase-shift patterns in which the widths of dark lines were smaller than the diffraction limit. With these demonstrations, we have successfully shown that the near-field phase-shift lithographic technique can be realized through an inexpensive maskless lithographic system and can still achieve subdiffraction limited images.     

Simultaneous,hybrid single-molecule method by optical tweezers and fluorescence

As studies on life sciences progress toward the single-molecule level, new experiments have put forward more requirements for simultaneously displaying the mechanical properties and conformational changes of biomolecules. Optical tweezers and fluorescence microscopy have been combined to solve this problem. The combination of instruments forms a new generation of hybrid single-molecule technology that breaks through the limitations of traditional biochemical analysis. Powerful manipulation and fluorescence visualization have been widely used,and these techniques provide new possibilities for studying complex biochemical reactions at the singlemolecule level. This paper explains the features of this combined technique, including the application characteristics of single-trap and dual-traps, the anti-bleaching method, and optical tweezers combined with epifluorescence, confocal fluorescence, total internal reflection fluorescence, and other fluorescence methods.Using typical experiments, we analyze technical solutions and explain the factors and principles that instrument designers should consider. This review aims to give an introduction to this novel fusion technology process and describe important biological results.     

Manipulation of live mouse embryonic stem cells using holographic optical tweezers

We report the ability to move and arrange patterns of live embryonic stem cells using holographic optical tweezers. Single cell suspensions of mouse embryonic stem cells were manipulated with holographic optical tweezers into a variety of patterns including lines, curves and circles. Individual cells were also lifted out of the sample plane highlighting the potential for 3D positional control. Trypan blue dye exclusion and Live/Dead? staining (CMFDA^?1, EthHD^?1) showed that the cells were still viable after manipulation with the optical tweezers. The ability to move individual stem cells into specific, pre-defined patterns provides a method to study how arrangement and associated small-scale interactions occur between neighbouring cells.     

Permanent 3D microstructures in a polymeric host created using holographic optical tweezers

Abstract

Permanent 3D microstructures are created within a gel using holographic optical tweezers. The micron-sized particles are arranged in a precise geometry within an appropriate liquid, and become fixed in position upon polymerisation of the surrounding media. The flexibility of the holographic approach enables any structural arrangement to be produced, dependent upon application. We demonstrate the technique by creating structures within a biocompatible host, enabling future applications in biotechnology.     

折/衍混合透视型头盔显示器光学系统设计

为满足头盔显示器(HMD)对大视场、高像质和彩色显示的要求,提出了改进型 HMD 光学系统。该系统以彩色 LCD 为图像源实现彩色显示;以折/衍混合单透镜代替双胶合,利用其负色散和波面任意整形特性消除系统色差及改善波前像差。图像源发出的光束在分束器附近成中间像,可增大系统视场;出瞳在中继光学组元中间成像,可减小系统口径,增大出瞳直径;球面耦合器将分束器反射过来的光束准直后投射到人眼,能消除人眼反复观察不同焦距的视频图像和外界图像所造成的疲劳。该系统垂轴色差小于 42μm,视场扩大为 40°(水平)×30°(垂直),分辨力接近人眼的最小分辨能力;口径小于 46mm,重量比现有 HMD 光学系统下降 47%。     

Sorting of micron-sized particles using holographic optical Raman tweezers in aqueous medium

We have constructed a holographic optical tweezers system combined with Raman spectroscopy to sort trapped particles. Our software automatically moves the trapped objects to the measurement positions to obtain individual Raman signals from multiple trapped particles. We performed the sorting by comparing their spectra with the previously measured training dataset using the correlation coefficients. We used yeast cells and polystyrene beads as test particles. This study aims to show that biological particles can be separated using single cell analysis with combined holographic optical tweezers and Raman spectroscopy system.     

Spectral multi-demultiplexer based on a three-dimensional holographic wedge-shaped optical element

An analysis is made of the possibility of developing a new holographic multi-demultiplexer using the principle of a series device constructed as a single three-dimensional optical wedge-shaped element. Pis’ma Zh. Tekh. Fiz. 24, 79–86 (September 26, 1998)     

Iterative optimization of phase-only diffractive optical elements based on a lenslet array

We describe the design of Fourier-type phase-only array generators. The numerical optimization employs the Fienup algorithm, where the parageometric design of the phase retardation profile, with the form of a lenslet array, is used as the initial guess of the optimization process. This approach provides designs with high performance that can be obtained with comparatively low computing effort. This is particularly true for elements generating large spot arrays. For symmetric reconstruction fields, the optimized phase profile typically has the same symmetry as that for the reconstruction field and can be easily unwrapped.     

Controlling the transverse momentum distribution of a light field via azimuth division of a hologram in holographic optical tweezers

This study proposes a method for creating a light field with controlled distribution of transverse momentum (TM) by displaying a hologram only in an azimuth region that centers at θ(0) and has a range of Δθ of a spatial light modulator in holographic optical tweezers. This study utilized ray optics to analyze the TM of the resultant field, revealing that the direction of the TM is determined by the center angle of the azimuth region and that the magnitude of the TM is proportional to sin(Δθ/2), without regarding the intensity. The relationship was verified experimentally. In addition, this study demonstrated moving particles along a designed path and depleting particles by the fields.     

Takens-Bogdanov bifurcation in a two-component nonlinear optical system with diffractive feedback

Abstract

We analyse the conditions for stationary and oscillatory instabilities in a system consisting of two nonlinear Kerr-type elements. For the nonlinearities of the opposite sign, there is a degenerate point in the parameter space where both instabilities have equal thresholds and the same spatial frequency. In a vicinity of this point the dynamics are extremely sensitive to variation in control parameters, demonstrating a complex superposition of steady and time-periodic solutions. We relate this behaviour to the theory of the Taken-Bogdanov bifurcation.     

Axial optical trapping forces on two particles trapped simultaneously by optical tweezers

Optical tweezers, which utilize radiation pressure to control and manipulate microscopic particles, are used for a large number of applications in biology and colloid science. In most applications a single optical tweezers is used to control one single particle. However, two or more particles can be trapped simultaneously. Although this characteristic has been used in applications, no theoretical analysis of the trapping force or the status of the trapped particles is available to our knowledge. We present our calculation, using a ray optics model, of the axial trapping forces on two rigid particles trapped in optical tweezers. The spherical aberration that results from a mismatch of the refractive indices of oil and water is also considered. The results show that the forces exerted by the optical tweezers on the two particles will cause the two particles to touch each other, and the two particles can be stably trapped at a joint equilibrium point. We also discuss the stability of axial trapping. The calculation will be useful in applications of optical tweezers to trap multiple particles.     

Compensation of beam ellipticity and astigmatism based on holographic diffractive elements recorded onto spherical substrates

Abstract

Edge emitting diode lasers with their divergent, highly elliptical and astigmatic beams in the visible spectrum are widely used in all branches of photonics. Usually the beams must be transformed into circular anastigmatic beams for the majority of applications. Holographic diffractive elements on spherical substrates are devised for transformation of beams to circular collimated beams. An off-axis holographic set-up is used to record diffractive elements into a thin photoresist layer as shallow surface-relief gratings working in reflection mode with curved and chirped grooves. The elements are destined for the diode lasers emitting at a suitable wavelength and with appropriate ellipticity and astigmatism. The performance of the elements is tested on the basis of intensity patterns and the elements produced at a focal plane on their illumination with a collimated expanded beam of a HeNe laser.     

Speckle suppression in holographic projection displays using temporal integration of speckle images from diffractive optical elements

Speckles on images in holographic projection displays (HPDs) were efficiently suppressed by the temporal sum of two diffractive images generated from diffractive optical elements (DOEs). Using a modified iterative Fourier transform algorithm, we obtained pairs of phase-only DOEs that generated the diffractive images with high negative correlation coefficients of -0.827 and -0.490 in the one-dimensional and the two-dimensional simulations, respectively. The suppression ratios of the speckles in the two simulations were 0.301 and 0.457, which were 61% and 35% lower, respectively, than the sum of the two uncorrelated images. We have successfully demonstrated that the sum of two negatively correlated images from DOEs can effectively reduce the image speckles and improve the image quality in HPD systems.     

Effects of fabrication errors in the diffractive optical element on the modulation transfer function of a hybrid lens

Diffractive optical elements (DOEs) are often used to improve the performance of optical systems. However, when a blazed DOE is machined, shape errors can be generated in the discontinuity region of the DOE due to the finite radius of the processing tool. We simulated the effects of this shape error on the optical path and modulation transfer function (MTF) in a hybrid lens for a compact camera module. The decrease rate of the MTF was larger in the low-spatial-frequency domain and when the light entered at a low incident angle.     

Algorithm based on rigorous coupled-wave analysis for diffractive optical element design

Diffractive optical element design is an important problem for many applications and is usually achieved by the Gerchberg-Saxton or the Yang-Gu algorithm. These algorithms are formulated on the basis of monochromatic wave propagation and the far-field assumption, because the Fourier transform is used to model the wave propagation. We propose an iterative algorithm (based on rigorous coupled-wave analysis) for the design of a diffractive optical element. Since rigorous coupled-wave analysis (instead of Fourier transformation) is used to calculate the light-field distribution behind the optical element, the diffractive optical element can thus be better designed. Simulation results are provided to verify the proposed algorithm for designing a converging lens. Compared with the well-known Gerchberg-Saxton and Yang-Gu algorithms, our method provides 7.8% and 10.8%, respectively, improvement in converging the light amplitude when a microlens is desired. In addition, the proposed algorithm provides a solution that is very close to the solution obtained by the simulated annealing method (within 1.89% error).     

Plasmon-exciton interactions on single thermoresponsive platforms demonstrated by optical tweezers

Optical and hydrodynamic-size studies on single bare thermo-responsive microspheres, and microspheres covered either with Au nanoparticles, CdSe/CdS quantum dots, or a combination of both have been performed by optical tweezers. The photothermal heating of water in the focal region boosts the shrinkage of the microspheres, an effect that is intensified in the presence of Au nanoparticles. In contrast, bigger microspheres are measured when they are covered with quantum dots. Plasmon-exciton interactions are observable in the trap in the combined Au and quantum dots hybrid systems.     

Efficient optimization of diffractive optical elements based on rigorous diffraction models.

An efficient optimization strategy for the design of diffractive optical elements that is based on rigorous diffraction theory is described. The optimization algorithm combines diffraction models of different degrees of accuracy and computational complexity. A fast design algorithm for diffractive optical elements is used to yield estimates of the optimum surface profile based on paraxial diffraction theory. These estimates are subsequently evaluated with a rigorous diffraction model. This scheme allows one to minimize the need to compute diffraction effects rigorously, while providing accurate design. We discuss potential applications of this scheme as well as details of an implementation based on a modified Gerchberg-Saxton algorithm and the finite-difference time-domain method. Illustrative examples are provided in which we use the algorithm to design Fourier array illuminators.     

On-line surveillance of a dynamic process by a moving system based on pulsed digital holographic interferometry

A method based on pulsed digital holographic interferometry for the measurement of dynamic deformations of a surface by using a moving system is presented. The measuring system may move with a speed of several meters per minute and can measure deformation of the surface with an accuracy of better than 50 nm. The deformation is obtained by comparison of the wavefronts recorded at different times with different laser pulses produced by a Nd:YAG laser. The effect due to the movement of the measuring system is compensated for by digital processing of the different holograms. The system is well suited for on-line surveillance of a dynamic process such as laser welding and friction stir welding. Experimental results are presented, and the advantages of the method are discussed.     

Effect of optical resonances on photochemical reactions in microdroplets

We have examined photochemical reactions in microdroplets under optical resonances for situations in which photoreactive molecules dissolve from a surrounding gas phase. The link among photochemical reaction, droplet-phase diffusion, and gas-phase mass transfer rate processes produces numerous concentration distributions of reactive molecules between two limiting distributions that are characterized by the absence of reactive molecules and by the saturation concentration level. Each distribution yields a unique intensity field. The analysis shows that the reaction rate is dependent on five dimensionless parameters and is significantly enhanced by a number of combinations of parameter values.