Optimization of computer-generated holograms for dynamic optical manipulation with uniform structured light spots

An optimized iterative technique combining the merits of conventional Gerchber-Saxton (G-S) and adaptive-additive (A-A) algorithms to design multilevel computer-generated holograms for the creation of a desirable structured intensity pattern for multiple optical manipulation is theoretically adopted. Optical trap arrays are demonstrated with the help of liquid crystal spatial light modulator and a microscopic optical tweezer system. Additionally, continuous locked-in transport and deflection of microparticles with the generated optical lattice is proven experimentally. The proposed method possesses apparent high efficiency, high uniformity, and dynamic and reconfigurable advantages.     

Improvement of reconstruction in 3D computer-generated holograms using 1D Fourier transform operations

Improvement of images reconstructed from 3D computer-generated holograms using 1D Fourier transform operations is presented. Required computing time for making 3D holograms is decreased when 1D Fourier transform method is used instead of 2D Fourier transform method, but reconstructed images from the holograms created by the 1D Fourier transform method are somewhat inferior in quality to the images by 2D Fourier transform method. In this paper, we propose a method that the disadvantageous properties of the holograms made by 1D Fourier transform are improved. We have performed two step improvements in this experiment. From the numerical experiments, the images that are reconstructed from the holograms created from 1D Fourier transform method show marked improvement.     

Optical particle trapping with computer-generated holograms written on a liquid-crystal display

Computer-generated holograms written on a liquid-crystal display can be used to generate dynamic light fields of arbitrary shape. This method was used to simultaneously trap polystyrene particles laterally and to displace them independently of one another.     

Improvement of 1D off-axis computer-generated holograms

Creation of Fresnel off-axis computer-generated holograms and improvement of images reconstructed from the holograms are described. To improve the reconstructed images, we have created the holograms with high construct diffraction patterns by using a histogram method. From reconstruction experiments of the holograms, clear images have been obtained and 3D images have been seen directly with eyes.     

Rotation of single live mammalian cells using dynamic holographic optical tweezers

We report on a method for rotating single mammalian cells about an axis perpendicular to the optical system axis through the imaging plane using dynamic holographic optical tweezers (HOTs). Two optical traps are created on the opposite edges of a mammalian cell and are continuously transitioned through the imaging plane along the circumference of the cell in opposite directions, thus providing the torque to rotate the cell in a controlled fashion. The method enables a complete 360° rotation of live single mammalian cells with spherical or near-to spherical shape in 3D space, and represents a useful tool suitable for the single cell analysis field, including tomographic imaging.     

Optical reconstruction of 3D images by use of pure-phase computer-generated holograms

A three-dimensional （3D） object reconstruction technique that uses pure-phase computer-generated holograms （CGHs） and a phase-only spatial light modulator （SLM） is proposed. The full parallax CGHs are generated by the point source method and the wave-oriented method without paraxial approximation. Different from conventional CGHs, the pure-phase information on the hologram plane is loaded on the SLM to reconstruct the 3D diffusive objects without considering the reference wave. This technique is more efficient in its utilization of the space-bandwidth product of the SLMs. Numerical simulations and experiments are performed, and the results show that our proposed method can reconstruct 3D diffusive objects successfully.     

Symmetry dependence of holograms for optical trapping

No iterative algorithm is necessary to calculate holograms for most holographic optical trapping patterns. Instead, holograms may be produced by a simple extension of the prisms-and-lenses method. This formulaic approach yields the same diffraction efficiency as iterative algorithms for any asymmetric or symmetric but nonperiodic pattern of points while requiring less calculation time. A slight spatial disordering of periodic patterns significantly reduces intensity variations between the different traps without extra calculation costs. Eliminating laborious hologram calculations should greatly facilitate interactive holographic trapping.     

Prediction of phase-mostly modulation for holographic optical tweezers

We characterize a reflective Holoeye LC-R 2500 spatial light modulator with a technique in which Jones matrices describing its polarization capabilities are obtained and then used for any arbitrary configuration. We apply this method to predict a phase-mostly modulation response with minimum amplitude contrast and a phase modulation range close to 2π rad. This allows us to generate multiple traps in a holographic optical tweezers setup with high light efficiency and hardly any unwanted energy on the zero diffraction order.     

泽尼克多项式校正全息阵列光镊像差的实验研究

像差会影响光镊对粒子的捕获效果. 全息阵列光镊中, 像差不仅来自光学元件, 由特定算法设计的光阱相位片也会在光路中引入像差. 本文通过液晶空间光调制器加载泽尼克多项式相位图, 对全息阵列光镊中由光栅透镜组型算法引起的像差进行校正. 结果显示: 利用三阶泽尼克多项式可有效消除光路中由光栅透镜组型算法引 起的慧差, 使得捕获2 μm聚苯乙烯小球的阵列光阱刚度提高了约40%; 对比不同项的像差校正结果发现, 全息阵列光镊中由算法引起的慧差 与光学元件引起的像差一样, 也会对阵列光阱的捕获效果产生较大影响; 同时根据一阶像差校正结果可得光栅透镜 组型算法对于一阶泽尼克像差具有鲁棒性. 实验结果表明, 对全息阵列光镊中由 算法引起的像差进行校正, 对于提高光阱的捕获效果和深化对算法特性的认识都具有重要意义.     

Controlled trapping and rotation of carbon nanotube bundle with optical tweezers

Controlled optical trapping and rotation of carbon nanotube bundle (CNTB) including single-walled and multi-walled carbon nanotube in aqueous solution, were performed using the optical tweezers. Vertical and horizontal trapping of CNTB was performed depending on the size of CNTB and the trapping depth. In addition, four different rotations of the trapped CNTB were described and explained by the interaction between CNTB and the laser field, and the convection of the aqueous solution induced by thermalphoresis effect. These results will pave the way to assemble some CNTs-based devices such as micro motors.     

Design and fabrication of computer-generated holograms for testing optical freeform surfaces

Freeform optical surfaces (FOSs) will be the best elements in the design of compact optical systems in the future. However, it is extremely difficult to measure freeform surface with sufficient accuracy, which impedes the development of the freeform surface. The design and fabrication of computer-generated hologram (CGH) , which has been successfully applied to the tests for aspheric surfaces, cannot be directly adopted to test FOSs due to their non-rotational asymmetry. A novel ray tracing planning method combined with successively optimizing even and odd power coefficients of phase polynomials in turn is proposed, which can successfully design a non-rotational asymmetry CGH for the tests of FOSs with an F-θ lens. A new eight-step fabrication process is also presented aiming to solve the problem that the linewidth on the same circle of the CGH for testing freeform surface is not uniform. This problem cannot be solved in the original procedure of CGH fabrication. The test results of the step profiler show that the CGH fabricated in the new procedure meets the requirements.     

Forces in optical tweezers with radially and azimuthally polarized trapping beams

It has been suggested that radially polarized beams can be used to improve the performance of optical tweezers, with reduced scattering force resulting from both the polarization and the dark center of the beam [Opt. Lett. 32, 1839 (2007)]. We calculate the forces on particles in such traps, using rigorous electromagnetic theory, comparing the results with azimuthally polarized beam, circularly polarized LG 01 beams, and Gaussian beams. Our results agree qualitatively with Opt. Lett. 32, 1839 (2007), but differ quantitatively.     

Optical levitation and manipulation of stuck particles with pulsed optical tweezers

We report on optical levitation and manipulation of microscopic particles that are stuck on a glass surface with pulsed optical tweezers. An infrared pulse laser at 1.06 microm was used to generate a large gradient force (up to 10(-9) N) within a short duration (approximately 45 micros) that overcomes the adhesive interaction between the particles and the glass surface. Then a low-power continuous-wave diode laser at 785 nm was used to capture and manipulate the levitated particle. We have demonstrated that both stuck dielectric and biological micrometer-sized particles, including polystyrene beads, yeast cells, and Bacillus cereus bacteria, can be levitated and manipulated with this technique. We measured the single-pulse levitation efficiency for 2.0 microm polystyrene beads as a function of the pulse energy and of the axial displacement from the stuck particle to the pulsed laser focus, which was as high as 88%.     

Multifunctional single-fiber optical tweezers for particle trapping and transport

We present and demonstrate a multifunctional single-fiber optical tweezer for particle trapping and transport. The fiber probe of fiber optical tweezers is constructed as a planar structure. Laser sources with wavelengths of 650 nm and 980 nm in a single-mode fiber excite the linearly polarized LP11mode and LP01mode beams, respectively. These two laser beams can achieve non-contact trapping and long-distance transport of particles after passing through a flat-facet fiber probe,respectively. This...     

Oriented imaging of 3D subcellular structures in bacterial cells using optical tweezers

Using oscillating optical tweezers, we show that controlled alignment of rod-shaped bacterial cells allows imaging fluorescently labeled three-dimensional (3D) subcellular structures from different, optimized viewpoints. To illustrate our method, we analyze the Z ring of E. coli. We obtain that the radial width of the Z ring in unconstricted cells is about 120 nm. This result suggests that the Z ring consists of an extremely sparse network of FtsZ filaments.     

Fabrication of large-area 3D photonic crystals using a holographic optical element

A holographic technique for fabricating 3D photonic crystal is presented. The key element in the fabrication system is a holographic optical element (HOE) consisting of three gratings. Used in combination with a mask, the HOE can generate four beams under single illuminating beam, and 3D lattice structures can be formed by the interference of the four beams. Holographic approach is used to make HOE, so large area lattice structures can be fabricated. Numerical simulations indicate that beam intensity ratio of central beam to outer beam is one of the factors that affects the structures fabricated in photoresist, and high diffraction efficiency of the gratings in HOE is favorable when using cw laser with relatively low power as light source. Experimental results show clear 3D lattice structures fabricated using the HOE, verifying the effectiveness of the technique.     

Near-infrared demonstration of computer-generated holograms implemented by using subwavelength gratings with space-variant orientation

We provide an experimental demonstration of novel form-birefringent computer-generated holograms at wavelengths of 1.55 and 10.6 microm. These novel devices utilize a 2-D array of cells that can be fabricated with a single lithographic step. Each cell contains a subwavelength binary grating whose orientation controls the desired continuous phase profile within the cell.     

光镊力影响因素的计算分析

运用基于T矩阵算法的开源光镊计算工具包对可能影响光镊力的微粒尺寸、相对折射率以及光束模式进行了研究,计算结果表明,这三方面因素都会对光镊力产生显著影响,微粒直径与波长相等、相对折射率尽可能大时选择恰当的光束模式能够产生最佳的光镊捕获效果.     

利用高偏振级次轴对称偏振光束实现三维光学捕获(英文)

We propose a novel single-beam multiple 3D optical trapping scheme using higher polarization order axially-symmetric polarized beams in an aplanatic focusing system. We calculate numerically the intensity distribution near the focus which presents a multi-focus-spot pattern and provides the possibility of multiple optical trapping. We also calculate the corresponding gradient force distribution near the focus. Finally we introduce a 3D optical chain by combining the single-beam system with a single diffract...     

利用高偏振级次轴对称偏振光束实现三维光学捕获

We propose a novel single-beam multiple 3D optical trapping scheme using higher polarization order axially-symmetric polarized beams in an aplanatic focusing system. We calculate numerically the intensity distribution near the focus which presents a multi-focus-spot pattern and provides the possibility of multiple optical trapping. We also calculate the corresponding gradient force distribution near the focus. Finally we introduce a 3D optical chain by combining the single-beam system with a single diffractive optical element.