Parallel two-photon photopolymerization of microgear patterns

We report parallel two-photon photopolymerization of microgear patterns by exposing a photoresist to holographically generated optical vortices. The optical vortices are created by imparting a helical pitch onto the incident light using a programmable lithographic phase mask realized with a computer addressable phase-only spatial light modulator. By varying the phase levels of the spatial light modulator, the truncated helical phase of an optical vortex results in output intensity patterns that typifies that of microgears instead of perfect doughnut beams. Our experiments and simulations are in good agreement implying a more efficient and highly parallel two-photon photopolymerization scheme that can be subsequently used for non-scanning fabrication of microgears.     

Spontaneous transverse patterns in a microchip laser with a frequency-degenerate resonator

We experimentally observe the formation of high-order transverse patterns in a microchip laser with a high degree of frequency degeneracy. With a doughnut pump profile the spontaneous transverse patterns are well localized in the Lissajous trajectories. The observed transverse patterns are reconstructed with a high degree of accuracy by use of the coherent state of quantum theory. The accurate reconstruction suggests that laser resonators can be designed to obtain a more thorough understanding of the quantum-classical connection.     

复振幅光瞳滤波器的三维超分辨性能研究

超分辨技术中现有的纯振幅型或纯相位型光瞳滤波器,大部分只能实现轴向或横向超分辨而不能实现三维超分辨,三维超分辨在三维成像系统中有着重要的作用。因此为提高成像系统中的三维分辨能力,设计了一种复振幅光瞳滤波器,并对其三维超分辨性能进行了研究。详细分析了该光瞳滤波器的第一区半径和透射率对施特雷尔比、轴向和横向超分辨因子以及旁瓣能量的影响。通过一系列的模拟证明,借助于复振幅光瞳滤波器可以实现三维超分辨。该滤波器的优点是容易实现三维超分辨,且有比较高的施特雷尔比,缺点是三维超分辨的实现总是伴随着旁瓣能量的增加,但可以采用共焦扫描成像系统来加以抑制。     

Simple expressions for performance parameters of complex filters, with applications to super-Gaussian phase filters

To study the three-dimensional (3-D) behavior produced by complex filters, we have extended the expressions for the axial and the transverse gain to the case in which the best image plane is not near the paraxial focus. Super-Gaussian phase filters are proposed to control the 3-D image response of an optical system. Super-Gaussian phase filters depend on several parameters that modify the shape of the phase filter, producing tunable control of the 3-D response of the optical system. The filters are capable of producing a wide range of optical effects: transverse superresolution with high depth of focus, 3-D superresolution, and transverse apodization with different axial responses.     

Design and application of three-zone annular filters

We design three-zone annular filters to be applied to optical storage system. The designed filters extend the depth of focus and realize transverse superresolution simultaneously, which will improve the performance of optical storage system greatly. And we propose two feasible schemes to improve imaging resolution of three-dimensional imaging system. One scheme depends on a complex filter formed by cascading of a three-zone phase filter and a three-zone amplitude filter. The complex filter converge the optimized transverse superresolution and the optimized axial superresolution of two different filters onto a single filter. It can improve the three-dimensional imaging performances greatly. Another scheme depends on a single three-zone complex filter. We propose a three-zone complex filter with phase shift 0.8π, which presents bigger design margin, better imaging quality and stronger three-dimensional superresolution capability.     

Unique mode properties of optical metacavities

Unusual optical properties of a cavity that contains a layered structure with an alternating refractive index are considered. The layers with the negative refraction and the negative phase velocity provide for drastic changes to the properties of the longitudinal and transverse modes. The transverse-mode structure depends on the effective diffraction length whereas the spectrum of longitudinal modes is determined by the effective optical length of the cavity. The effective lengths can be positive, negative, or zero. In the last case, the transverse distribution of the amplitude can be arbitrary. The conditions for the stability of the metacavity are derived. It is demonstrated that an unstable empty cavity becomes stable when a metamaterial is introduced inside it.     

Near-field characteristics of highly non-paraxial subwavelength optical fields with hybrid states of polarization

The vectorial structure of an optical field with hybrid states of polarization(So P) in the near-field is studied by using the angular spectrum method of an electromagnetic beam. Physical images of the longitudinal components of evanescent waves are illustrated and compared with those of the transverse components from the vectorial structure. Our results indicate that the relative weight integrated over the transverse plane of the evanescent wave depends strongly on the number of the polarization topological charges. The shapes of the intensity profiles of the longitudinal components are different from those of the transverse components, and it can be manipulated by changing the initial So P of the field cross-section. The longitudinal component of evanescent wave dominates the near-field region. In addition, it also leads to three-dimensional shape variations of the optical field and the optical spin angular momentum flux density distributions.     

Optical doughnut for optical tweezers

We describe novel optical doughnuts for optical tweezers. With new phase functions, the proposed doughnut beams have dark cores in specified shapes. The technique can offer a simple method for creating a variety of beam shapes to match the trapped objects. One can rotate the beams directly by revolving their phase structures about their axes on the initial plane. The technique for generating the traditional Laguerre-Gaussian beam can be used to create these novel beams.     

Absorptionsbedingte Phasenselektion der Strahlung modulierter GaAs-Lumineszenzdioden vom Fabry-Perot-Typ

Incorporating the dependence on transverse position co-ordinate x of both recombination and optical absorption in a light emitting diode (LED) with laser structure, a theoretical study has been made of phase relations between a sinusoidal driving current and the light output. The theory yields a phase variation with x accordant to a carrier-diffusion controlled recombination wave, including the diode transient behavior due to charge storage. The phase selection by an appropriate absorption profile transverse to the recombination region is found to be of extraordinary importance for the bowing of the optical wave front at the radiating area.     

Coherent manipulation and guiding of Bose–Einstein condensates by optical dipole potentials

The coherent manipulation of Bose–Einstein condensates by far blue detuned optical dipole potentials is discussed in two regimes. The local manipulation of the phase of the condensate wavefunction by temporally applied dipole potentials represents a powerful tool for the design of matter waves. We use this method in particular for the creation of dark solitons in Bose–Einstein condensates and study their dynamics. Spatially inhomogeneous dipole potentials like far blue detuned doughnut laser beams can be used for the creation of Bose–Einstein condensates within a waveguide structure.     

Manipulation of doughnut focal spot by image inverting interferometry

Based on image inverting interference combined with phase modulation, we theoretically demonstrate that the doughnut focal spot can readily be manipulated, and either shrinkage or expansion of size of the central dark spot is possible in a large scale (peak-to-peak value: 0.555λ-0.830λ, or 93.3%-140.8% compared with the standard one). As the interference and phase modulation can both be achieved by a double Porro prism, it is feasible to introduce this approach into optical tweezers to improve their performance. As much as 33.9% intensity of stimulated emission depletion (STED) beam can be reduced if the further optimized configuration is utilized in STED microscopy.     

Fractional vortex lens

The properties of a fractional vortex lens are discussed and its focal plane intensity distribution is investigated. The azimuthal phase pattern of a fractional topological charge vortex and the quadratic phase variation of the lens are displayed on a spatial light modulator (SLM) that is used in the phase mode. The intensity distribution possesses a low intensity radial opening in contrast to the doughnut pattern formed by a vortex beam with integer charge. The presence of multiple singularities in the radial opening of the doughnut structure is detected interferometrically.     

Nonlinear beam shaper for femtosecond laser pulses, from Gaussian to flat-top profile

We present a straightforward method to transform a spatially Gaussian femtosecond laser beam into a flat-top shaped beam. The proposed technique takes advantage of a nonlinear phase induced in positive Kerr medium followed by a simple optical system. The variation of the refractive index with the laser intensity creates a phase plate which induces changes in the beam profile after propagation; flat-top and doughnut profiles are observed. The shaping conditions are computed numerically and confirmed experimentally. The method does not introduce energy losses. The device is very simple, self-regulated, flexible and does not need a manufactured phase plate or precise alignment. This method can be useful for light-matter interaction and laser machining.     

Quantum zigzag transition in ion chains

A string of trapped ions at zero temperature exhibits a structural phase transition to a zigzag structure, tuned by reducing the transverse trap potential or the interparticle distance. The transition is driven by transverse, short wavelength vibrational modes. We argue that this is a quantum phase transition, which can be experimentally realized and probed. Indeed, by means of a mapping to the Ising model in a transverse field, we estimate the quantum critical point in terms of the system parameters, and find a finite, measurable deviation from the critical point predicted by the classical theory. A measurement procedure is suggested which can probe the effects of quantum fluctuations at criticality. These results can be extended to describe the transverse instability of ultracold polar molecules in a one-dimensional optical lattice.     

PHASE MATCHING AND DISTRIBUTION OF OPTICAL VORTICES IN THREE COUPLING DEGENERATE GAUSS-LAGUERRE MODES

We analyze the coupling equation for three degenerate Gauss-Laguerre modes in laser. For the multimode operation, there is a phase matching relation from which the distribution of optical vortices in the transverse patterns of optical field can be determined.     

三环位相型光瞳滤波器的横向超分辨与轴向焦深扩展

用矢量衍射方法分析了线偏振光入射到带有三环位相型光瞳滤波器的高数值孔径物镜时,焦点的轴向和横向光强分布.数值模拟结果表明,高数值孔径物镜聚焦时需同时考虑光强的轴向和横向分布.通过加入三环位相光瞳滤波器,在实现横向超分辨的同时实现了光学系统轴向焦深扩展和轴向光强分布平坦化,并且位相调制深度变化时,会出现轴向焦移现象.对三环位相光瞳滤波器结构进行了优化,得出了优化结果. 关键词： 光学超分辨 扩展焦深 位相型光瞳滤波器 矢量衍射方法     

Field-induced three- and two-dimensional freezing in a quantum spin liquid

Field-induced commensurate transverse magnetic ordering is observed in the Haldane-gap compound Ni(C(5)D(14)N(2))2N(3)(PF(6)) by means of neutron diffraction. Depending on the direction of applied field, the high-field phase is shown to be either a three-dimensional ordered Néel state or a short-range ordered state with dominant two-dimensional spin correlations. The structure of the high-field phase is determined, and properties of the observed quantum phase transition are discussed.     

Structure of Energy Fluxes in Topological Three-Dimensional Dissipative Solitons

The internal structure of dissipative topological solitons has been revealed by example of three-dimensional dissipative optical solitons with one open and one closed dislocation lines of a wavefront. This structure is manifested in the existence of critical points, lines, and surfaces in the field of electromagnetic energy fluxes (Poynting vector). The conservation of the topological characteristics of such solitons, which can be formed in a homogeneous laser medium with saturated amplification and absorption or in lasers with quite large longitudinal and transverse dimensions, provides additional capabilities for information applications.     

Adaptive correction of vortex laser beam in a closed-loop system with phase only liquid crystal spatial light modulator

We propose and demonstrate the wave front correction of a vortex laser beam by using dual phase only liquid crystal spatial light modulators (LC-SLMs) and a stochastic parallel gradient descent (SPGD) algorithm. One phase only LC-SLM is used to generate vortex laser beam by loading spiral phase screen onto the wave front of input quasi-Gaussian beam. The other phase only LC-SLM under SPGD controller based on the subzone control method adaptively compensates the wave front of vortex laser beam. Numerical simulation and experimental results show that after correction, vortex doughnut like beam is focused into a beam with airy disk pattern distribution in the far field. The adaptive corrections of vortex laser beam with different optical topological charges are studied. The results show that the optical topological charge has little influence on adaptive correction. The powers in the main lobe of far field intensity distributions of vortex laser beams with different optical topological charges are all greatly improved by adaptive correction. The technique proposed in this paper can be used in optical communication, relay mirror and atmospheric turbulence correction.     

Generation and detection of optical vortices using all fiber-optic system

We demonstrate simultaneous generation, propagation and detection of optical vortices using all fiber-optic system. A fiber-optic Y-coupler was used for generating spherical and doughnut beams, simultaneously. Gaussian (TEM₀₀) beam emitted from CW red He-Ne laser is coupled into the fiber coupler and is converted into vortex beam via second arm of fiber which propagates with azimuthal phase dependence having well defined orbital angular momentum. The phase structure of vortex beam was detected by interfering both the beams using simple fiber-optic interferometer. The present all fiber-optic system might find application for detecting, sensing physical parameters and is simple and cost effective for generating and detecting optical vortices.