Generation of bottle beam by focusing a super-Gaussian beam using a lens and an axicon

This study explores the characteristics of the bottle beams that are formed by super-Gaussian beams that impinge through an axicon and a positive lens. Analytical solutions for the on-axial intensity of Gaussian and apertured-plane beams were obtained. The barrier around the dark region has a larger variation of intensity for higher-order super-Gaussian profiles. Flattening the tops of the profiles increases the bottle lengths for a fixed second-order moment width or distance between the axicon and the lens.     

无衍射光束的产生及其应用

近年来,随着激光技术的快速发展,相继产生了多种在远距离传输后中心光斑保持不变的无衍射光束,包括贝塞尔光束、高阶贝塞尔光束、马丢光束、高阶马丢光束、余弦光束、抛物线光束以及艾里光束.无衍射光束在激光打孔、激光精密准直、光学精密控制、光学微操控、光通信、等离子体导向、光子弹产生、光通信、自聚焦光束的合成以及非线性光学等领域中有着广泛的应用.本文介绍了各类无衍射光束的数学表达式、产生方法及对应的实验结果;就无衍射光束的特性和应用进行了归纳和讨论;并对其在未来的研究与应用前景中发挥的重要作用进行了简要总结与展望.     

Tight focusing of partially coherent radially polarized beam with high NA lens axicon

Tight focusing of radially polarized partially coherent vortex beam over a high numerical aperture lens axicon system is introduced and its propagation properties are studied based on vectorial Debye theory. The effect of propagation parameters on the intensity distribution, the polarization property and the coherent property of the beam is illustrated analytically and numerically. It is shown that the correlation length and maximal NA angle has a significant influence on the intensity profile.     

Focal shift in radially polarized beam with high NA lens axicon by using radial cosine phase wavefront

Focal shift in radially polarized beam with radial cosine phase wavefront are investigated theoretically by vector diffraction theory. The wavefront phase distribution is cosine function of radial coordinate. Simulation results show that when the radially polarized beam with radial cosine wavefront phase is focused, the focal pattern differs considerably with frequency parameter in the cosine function term. On increasing C, focus can shift along optical axis and focal pattern changes remarkably. Focus may move in different direction under different condition. Focal shift distance fluctuates on increasing C, and fluctuation amplitude also increases simultaneously. In addition, focal shift direction can also be adjusted by changing frequency parameter in cosine function.     

Tight focusing of double ring shaped radially polarized beam with high NA lens axicon

A method is presented for generation of a sub wavelength (0.45λ) longitudinally polarized beam, which propagates without divergence over lengths of about 8λ in free space. This is achieved by tight focusing of double ring shaped radially polarized beam with a high NA lens axicon that utilizes spherical aberration to duplicate the performance of an axicon and to create an extended focal line. The intensity distributions were calculated based on the vector diffraction theory and it was observed that in the case of high numerical aperture (NA) lens axicon, the distribution of the total intensity near the focus had little effect on the degree of truncation of the incident beam by the pupil.     

Pattern generation using axicon lens beam shaping in two-photon polymerisation

The fabrication of three-dimensional microstructures by two-photon polymerisation has been widely reported as a viable route to the development of photonic crystals, rotors, bridges and other complex artefacts requiring nanoscale resolution. Conventionally, single point serial writing is used to write the structures but recently multipoint beam delivery using beam division optics has been reported as a method of introducing parallel processing. In this paper we present an alternative and novel approach using an axicon lens to give profiled beam delivery. This enables complete three-dimensional annular structure fabrication without the use of scanning stages. In addition, the concept of axicon delivery is developed further to investigate three-dimensional structure as a function of axicon geometry.A Ti:sapphire laser, with wavelength 795 nm, 80 MHz repetition rate, 100 fs pulse duration and an average power of 700 mW, was used to initiate two-photon polymerisation. The axicon was used, in combination with a 100× microscope objective, to form representative three-dimensional structures based on the annular cell with varying diameter. The structures were written in a Zr-loaded resin prepared on a glass substrate using dip coating deposition of a Zr/PMMA hybrid prepared by the sol-gel method. Annuli with diameters up to 50 μm were characterised in terms of topography and surface roughness using SEM and Zygo interferometer. The writing technique was also extended to fabrication of stacked structures.     

Generation of sub wavelength super-long dark channel using high NA lens axicon

We investigate the focusing properties of a double-ring-shaped azimuthally polarized beam by a high numerical aperture (NA) lens axicon based on vector diffraction theory. We observe that our proposed system generates a sub wavelength focal hole of 0.5λ having large uniform focal depth of 48λ without any annular aperture. We also observed that the distribution of the total intensity near the focus has little variation with the degree of truncation β of the incident beam by the pupil. The authors expect such a super-long dark channel may find applications in optical, biological, and atmospheric sciences.     

Tight focusing of circularly polarized beam over high NA lens axicon with a diffractive optical element

We propose to use diffractive optical element in combination with high NA lens axicon to achieve a high depth of focus when illuminated by a circularly polarized beam. With this kind of system, the focal depth is increased to 12.816λ and the magnetic spot size is reduced to 0.3764λ. However, in the conventional lens with same NA, the FWHM of the magnetic spot is found to be 0.4308λ and its corresponding magnetization depth is only 0.888λ. The author expects that such a high focal depth strong longitudinal magnetic field with large magnetization depth can be widely used in high density magneto optic recording, laser machining, laser cutting and the scanning near-field magnetic microscope.     

Generation of spirally polarized propagation-invariant beam using fiber microaxicon

We present here a fiber microaxicon (MA)based method to generate spirally polarized propagation-invariant optical beam. MA chemically etched in the tip of a two-mode fiber efficiently converts the generic cylindrically polarized vortex fiber mode into a spirally polarized propagation-invariant (Bessel-type) beam via radial dependence of polarization rotation angle. The combined roles of helico-conical phase and nonparaxial propagation in the generation and characteristics of the output beam from the fiber MA are discussed.     

应用无衍射贝塞尔光束的固体线膨胀系数测量系统

测量固体线膨胀系数是工程设计中的一项重要工作。这套非接触固体线膨胀系数测量系统利用激光三角法进行了设计。通过采用线阵CCD作为信号传感器来实现自动化测量。通过采用无衍射贝塞尔光束来提高测量精度和增大测量范围。     

Generation of radially polarized Ti:sapphire laser beam using a c-cut crystal

First, it is demonstrated that with a c-cut Ti:sapphire crystal the generation of a nonpolarized laser beam is possible, in contrast to the conventional a-cut Ti:sapphire crystal, which produces a linearly polarized beam. Second, the generation of a radially polarized Ti:sapphire laser beam is demonstrated in combination with a c-cut YVO(4) crystal used as a selector of radial polarization.     

Generation of an axially super-resolved quasi-spherical focal spot using an amplitude-modulated radially polarized beam

An axially super-resolved quasi-spherical focal spot can be generated by focusing an amplitude-modulated radially polarized beam through a high numerical aperture objective. A method based on the unique depolarization properties of a circular focus is proposed to design the amplitude modulation. The generated focal spot shows a ratio of x:y:z=1:1:1.48 for the normalized FWHM in three dimensions, compared to that of x:y:z=1:0.74:1.72 under linear polarization (in the x direction) illumination. Moreover, the focusable light efficiency of the designed amplitude-modulated beam is 65%, which is more than 3 times higher than the optimized case under linear polarization and thus make the amplitude-modulated radial polarization beam more suitable for a wide range of applications.     

Generation of sub wavelength multiple focal hole segments using azimuthally polarized annular multi-Gaussian beam

We propose a new approach for generating multiple focal hole segment of sub wavelength size, by tight focusing of phase modulated annular multi-Gaussian beam. The focusing properties are investigated theoretically by vector diffraction theory. We observed that focal segment with multiple focal rings structure separated with different axial distance can be generated by properly tuning the phase of the incident azimuthally polarized annular multi-Gaussian beam. Potential applications of this focal shaping technique are also discussed.     

用线偏振光产生可调矢量椭圆空心光束

提出了利用π相位板产生矢量空心光束的新方案,两个偏振方向互相垂直的线偏振光波分别通过π相位板调制后进行强度叠加,得到椭圆空心光束,用矩形光阑调节相位板的几何尺寸,可以实时调节椭圆的离心率;调节π相位板的方位,能够实现径向矢量空心光束到角向矢量空心光束的转换。分析、讨论了方案的可行性和在原子光学中的潜在应用,结果表明:本方案在原子光学中有很好的应用前景。     

Generation of sub wavelength super long dark channel using azimuthally polarized annular multi-Gaussian beam

We investigate the interesting focal properties of phase modulation azimuthally polarized annular multi Gaussian beam employing a high numerical aperture (NA) lens on the basis of vector diffraction theory. We observe that our proposed system generates a sub wavelength focal hole of \(0.43 \uplambda \) having large uniform focal depth of \(84 \uplambda \) . This kind of nondiffracting focal hole is called dark channel, which may have applications in atom optical experiments, such as with atomic lenses, atom traps, and atom switches.     

Calculation of the vectorial field distribution of an axicon illuminated by a linearly polarized Guassian beam

An analytical expression describing the vectorial field distribution of Gaussian light beams diffracted by an axicon is obtained. The theoretical analysis and simulation calculation show that for the linearly x-polarized light incident on an axicon, the y-component of the diffraction field is very small and the x-component dominates. The intensity of the z-component along the propagation direction is related with the open angle and index of axicon. The open angle plays the more important role in determining the polarization than does the index. For a small open angle, the z-polarized effect can be neglected and the scalar method is simple and valid to evaluating the diffraction field distribution of axicon. However, the vectorial method has to be used for great open angle.     

Generation of high quality tunable Bessel beams using a liquid-immersion axicon

By immersing a conventional glass axicon in index-matching liquid, we generated high quality, tunable, quasi-non-diffracting Bessel beams. The aberrations resulting from the roundness of the axicon tip are minimized when a large base angle is used in liquid-immersion. This configuration also allows coarse and fine tunability through changing the liquid and adjusting the temperature, respectively. Our experimental results match very well with calculated intensity profiles. We succeeded to generate two-meter long plasma channels in air by focusing femtosecond laser pulses with the liquid-immersion axicon.     

Generation of azimuthally and radially polarized beams by coherent polarization beam combination

A new architecture for generating pure azimuthally and radially polarized beams is presented. It involves coherent polarization beam combination of two orthogonally polarized LP(11) fiber modes. Experimental results reveal that high purely polarized (polarization purity of 95% or better) azimuthal and radial beams can be generated.     

Experiments with longitudinally polarized electrons in a storage ring using a siberian snake

We report on first measurements with polarized electrons stored in a medium-energy ring and with a polarized internal target. Polarized electrons were injected at 442 MeV (653 MeV), and a partial (full) Siberian snake was employed to preserve the polarization. Longitudinal polarization at the interaction point and polarization lifetime of the stored electrons were determined with laser backscattering. Spin observables were measured for electrodisintegration of polarized 3He, with simultaneous detection of scattered electrons, protons, neutrons, deuterons, and 3He nuclei, over a large phase space.