反射式椭圆高斯光束平顶整形系统

为了将椭圆高斯光束整形为圆形平顶光束,设计了一种无中心遮拦反射式两镜整形系统。根据能量守恒思想,选择匀化洛伦兹函数作为出射光束平顶分布函数,建立了入射面和出射面之间的坐标变换关系;采用光程守恒原理和矢量形式的反射定律,推导了积分形式的整形系统两反射镜面形方程。利用数值解法计算出两反射镜的面形数据,经过光学设计软件仿真与系统参数分析,得到的圆形平顶光束在目标区域的照度均匀性大于95%。结果表明,这种整形系统可以明显提高椭圆高斯光束的平顶性,具有现实可行性。     

平顶光束和平顶涡旋光束对金属瑞利粒子的光学俘获

 使用聚焦平顶光束和平顶涡旋光束,以金为例,对金属瑞利粒子辐射力和俘获稳定性进行了分析,着重研究了拓扑电荷和光束阶数对辐射力的影响。结果表明,随着拓扑电荷和光束阶数的增大,最大光强和辐射力随之减小;平顶光束可以俘获金瑞利粒子,俘获微粒的牢固性和俘获范围随着光束阶数增大而减小,而平顶涡旋光束的梯度力不能作为回复力,因此不能俘获。最后,还讨论了不同光强分布下,俘获金属瑞利粒子时复介电常数需满足的必要条件。     

平顶光束和平顶涡旋光束对金属瑞利粒子的光学俘获

使用聚焦平顶光束和平顶涡旋光束,以金为例,对金属瑞利粒子辐射力和俘获稳定性进行了分析,着重研究了拓扑电荷和光束阶数对辐射力的影响。结果表明,随着拓扑电荷和光束阶数的增大,最大光强和辐射力随之减小;平顶光束可以俘获金瑞利粒子,俘获微粒的牢固性和俘获范围随着光束阶数增大而减小,而平顶涡旋光束的梯度力不能作为回复力,因此不能俘获。最后,还讨论了不同光强分布下,俘获金属瑞利粒子时复介电常数需满足的必要条件。     

平顶高斯光束的相关概念和对称化变换

对平顶高斯光束有关的一些重要概念,例如场分布和束宽等作了物理分析。进一步将二维平顶高斯光束推广到三维情况,并且对三维平顶高斯光束的对称化变换,包括在X和Y方向束宽相等和ｚ平面处曲率半径相等,进行了详细的研究。     

平顶高斯光束的相关概念和对称化变换

对平顶高斯光束有关的一些重要概念,例如场分布和束宽等作了物理分析。进一步将二维平顶高斯光束推广到三维情况,并且对三维平顶高斯光束的对称化变换,包括在X和Y方向束宽相等和ｚ平面处曲率半径相等,进行了详细的研究。     

平顶高斯光束的相关概念和对称化变换

 对平顶高斯光束有关的一些重要概念,例如场分布和束宽等作了物理分析。进一步将二维平顶高斯光束推广到三维情况,并且对三维平顶高斯光束的对称化变换,包括在X和Y方向束宽相等和ｚ平面处曲率半径相等,进行了详细的研究。     

椭圆平顶高斯光束及其传输特性

 用张量光学方法定义了三维不可分离变量的椭圆平顶高斯光束(EFGB),导出了这种光束经过非轴对称光学系统的传输公式及相应的张量ABCD定律, 并对EFGB经过自由空间的传输作了数值计算。结果表明, EFGB的传输特性依赖于阶次, 而且耦合EFGB的光强分布在传输过程中会发生旋转。     

椭圆平顶高斯光束及其传输特性

用张量光学方法定义了三维不可分离变量的椭圆平顶高斯光束(EFGB),导出了这种光束经过非轴对称光学系统的传输公式及相应的张量ABCD定律, 并对EFGB经过自由空间的传输作了数值计算。结果表明, EFGB的传输特性依赖于阶次, 而且耦合EFGB的光强分布在传输过程中会发生旋转。     

平顶高斯光束与超高斯光束传输特性的比较研究

对平顶高斯光束与超高斯光束的传输特性作了研究和比较,并给出了典型的数值计算例．所得的主要结论是有相同M²因子和束宽的平顶高斯光束与超高斯光束在通过光学系统时,具有非常相似的包括光强分布和光阑衍射效应在内的传输变换特性． 关键词：     

高阶模高斯光束整形方法研究

研究了高阶模高斯光束的整形方法.在高阶模高斯光束和平顶光束理论模型的基础上,分别选择了平项洛仑兹函数和费米狄拉克函数作为平顶光分布函数,利用能量守恒定律,分别推导针对拉盖尔-高斯光束和厄米特-高斯光束整形系统中入射光与出射光的映射函数.最后利用ZEMAX软件设计了针对TEM01模高斯光束进行整形的非球面透镜元件.结果表...     

大气湍流对部分相干平顶高斯光束的影响

采用相屏近似处理方法对激光通过湍流大气的传输进行了数值模拟。从数值模拟的结果拟合出两个公式：一是通过湍流前后部分相干平顶高斯光束的束宽平方比随阶数、传输距离和湍流强度的变化关系式;一是通过湍流后的相干长度随初始光束相干长度、湍流相干长度的变化关系式。研究发现：部分相干平顶高斯光束分解为相互独立的厄米-高斯光束的叠加;相干性越差的光束受到湍流的影响程度就越小;湍流对光束传输的影响与光束自身相干特性对其传输的影响之间是不相关的。     

大气湍流对部分相干平顶高斯光束的影响

采用相屏近似处理方法对激光通过湍流大气的传输进行了数值模拟。从数值模拟的结果拟合出两个公式:一是通过湍流前后部分相干平顶高斯光束的束宽平方比随阶数、传输距离和湍流强度的变化关系式;一是通过湍流后的相干长度随初始光束相干长度、湍流相干长度的变化关系式。研究发现:部分相干平顶高斯光束分解为相互独立的厄米-高斯光束的叠加;相干性越差的光束受到湍流的影响程度就越小;湍流对光束传输的影响与光束自身相干特性对其传输的影响之间是不相关的。     

Coupling efficiency of laser beam to multimode fiber

The coupling efficiency of laser beam to multimode fiber is given by geometrical optics, and the relation between the maximum coupling efficiency and the beam propagation factor M² is analyzed. An equivalent factor for the multimode fiber is introduced to characterize the fiber coupling capability. The coupling efficiency of laser beam to multimode fiber is calculated in respect of the ratio by the overlapping integral theory. The optimal coupling efficiency can be roughly estimated by the ratio of M² to but with a large error range. The deviation comes from the lacks of information on the detail of phase and intensity profile in the beam factor M².     

Method for converting a Gaussian laser beam into a uniform beam

The use of a phase filter to convert a gaussian laser beam into a beam with more uniform irradiance distribution is discussed. This phase filter is calculated by employing an iterative procedure on a computer. A computer-generated hologram of this phase function is used to experimentally verify the feasibility of this method.     

Fiber-optic beam shaper based on multimode interference

A new method of fiber-optic based beam shaping is investigated both numerically and experimentally. A cylindrically symmetric method of lines (MoLs) is developed to simulate the device. The device is fabricated by fusion splicing a predetermined length of multimode fiber (MMF) to a single-mode fiber. The multimode interference (MMI) effects create ring-shaped field profiles at certain positions inside the MMF. The shaped beam can be used in medical applications requiring particular irradiation patterns.     

Single-mode Raman fiber laser based on a multimode fiber

Single-mode operation of a Raman fiber laser based on a multimode fiber has been demonstrated for what is to our knowledge the first time. Single-mode operation was achieved through the beam cleanup effect of stimulated Raman scattering in multimode fibers. The Raman laser, consisting of a 50-microm-core multimode fiber and a multimode Nd:YAG laser pump, produced an output beam corresponding to the fundamental mode of the fiber.     

Single fiber dual-functionality optical tweezers based on graded-index multimode fiber

We propose and demonstrate single fiber dual-functionality optical tweezers based on a graded-index multimode fiber. By using the multi-angle fiber grinding and polishing technology, we fabricate the multimode fiber tip to be a special tapered shape, contributing to focus the outgoing beam with a large intensity gradient for the first functionality—three-dimensional contactless trapping of a microparticle. By adjusting the radial direction offset between the lead-in single mode fiber and the graded-index multimode fiber, we perform the second functionality—axial shift of the trapped microparticle with respect to the fiber tip without need of moving the fiber probe itself. It is convenient for practical applications. The theoretical and experimental results about the relationship between the radial offset and the equilibrium positions of the microparticle have the good consistency. Tailoring the trap and axial shift of the microparticle based on the graded-index multimode fiber provides convenient avenues for fiber optical tweezers applied in practical researches.     

Generation of a hollow laser beam by a multimode fiber

A simple method to generate a hollow laser beam by multimode fiber is reported. A dark hollow laser beam is generated from a multimode fiber and the dependence of the output beam profile on the incident angle of laser beam is analyzed. The results show that this hollow laser beam can be used to trap and guide cold atoms.