Abstract
A simple and flexible method is presented for the generation of optical focal field with prescribed characteristics. By reversing the field pattern radiated from a uniform line source, for which the electric current is constant along its extent, situated at the focus of a 4Pi focusing system formed by two confocal high-NA objective lenses, the required illumination distribution at the pupil plane for creating optical focal field with desired properties can be obtained. Numerical example shows that an arbitrary length optical needle with extremely high longitudinal polarization purity and consistent transverse size of ~0.36λ over the entire depth of focus (DOF) can be created with this method. Coaxially double-focus with spot size of ~0.36λ in the transversal direction and ~λ in the axial direction separated by a prescribed spacing is illustrated as another example. The length of optical needle field and the interval between double-focus are determined by the length of uniform line source. These engineered focal fields may found potential applications in particle acceleration, optical microscopy, optical trapping and manipulations.
Highlights
In recent years, three-dimensional (3D) focus engineering with cylindrical vector (CV) beams [1, 2] has received increasing interests due to its novel properties and potential applications in many areas such as optical trapping and manipulation [3, 4], particle acceleration [5, 6], microscopy [7,8,9], and high-density optical data storage [10]
A simple and flexible method is presented for the generation of optical focal field with prescribed characteristics
By reversing the field pattern radiated from a uniform line source, for which the electric current is constant along its extent, situated at the focus of a 4Pi focusing system formed by two confocal high-numerical aperture (NA) objective lenses, the required illumination distribution at the pupil plane for creating optical focal field with desired properties can be obtained
Summary
Three-dimensional (3D) focus engineering with cylindrical vector (CV) beams [1, 2] has received increasing interests due to its novel properties and potential applications in many areas such as optical trapping and manipulation [3, 4], particle acceleration [5, 6], microscopy [7,8,9], and high-density optical data storage [10]. A large number of methods for creating specific focusing patterns, such as optical needle [11], optical tunnel [12, 13], and optical chain [14], have been reported both theoretically and experimentally. These methods can be roughly classified into four categories. A novel method for 3D focus engineering was developed more recently through reversing the electric field radiated from a dipole antenna or a dipole array [22,23,24,25]. The transverse size of the optical needle realized with this method is 10% (0.36λ vs. 0.405λ) smaller than that reported with the previous method using dipole array
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