To verify the superoscillatory optical diffraction focusing characteristics of multiannular metasurfaces (MAMs), we propose an experimental detection method. It consists of two parts, the reflection positioning optical system and transmission detection imaging system. The best focal plane of the superoscillatory optical diffraction focus for the MAM can be precisely positioned through the reflection positioning optical system, which is the core part of the experimental detection method and is based on the structured illumination optical sectioning principle. A typical MAM is designed using vectorial angular spectrum (VAS) theory and a genetic algorithm. It was fabricated by focused ion-beam milling. The three-dimensional finite-difference time-domain method is used to verify the intensity distribution of the focus predicted by the VAS theory. For the designed 14-μm-diameter MAM at a wavelength of 640 nm, the simulation result broadly agrees with the experimental result obtained from the transmission microscopic imaging system. The proposed detection method can be used in fields such as optical diffraction focusing and subwavelength resolution imaging.
Stressed lap, compared to traditional polishing methods, has high processing efficiency. However, this method has disadvantages in processing nonsymmetric surface errors. A basic-function method is proposed to calculate parameters for a stressed-lap polishing system. It aims to minimize residual errors and is based on a matrix and nonlinear optimization algorithm. The results show that residual root-mean-square could be >15% after one process for classical trefoil error. The surface period errors close to the lap diameter were removed efficiently, up to 50% material removal.
During the development of the Lunar Rover, a posture tracking measurement scheme was designed to verify its movement control ability and path planning performance. The principle is based on the indoor GPS measurement system. Four iGPS transmitters were set around the test site. By tracking the positions of four receivers that were installed on the rover, the position and orientation of the rover can be acquired in real time. The rotation matrix and translation vector from the Lunar Rover coordinate system to the test site coordinate system were calculated by using the software. The measurement precision reached 0.25mm in the range of 30m2. The real time position and posture datum of the rover was overlaid onto 3-D terrain map of the test site. The trajectory of the rover was displayed, and the time-displacement curve, time-velocity curve, time-acceleration curve were analyzed. The rover’s performances were verified.
Through modulating the Bessel–Gaussian radially polarized vector beam by the cosine synthesized filter under a reflection paraboloid mirror system with maximum focusing semi-angle of π/2 , arbitrary-length super-Gaussian optical needles are created with consistent beam size of 0.36λ (full width at half maximum) and the electric field being pure longitudinally polarized (polarization conversion efficiency greater than 99%). Numerical calculations show that the on-axis intensity distributions are super-Gaussian, and the peak-valley intensity fluctuations are all within 1% for 4λ , 6λ , 8λ , and 10λ long light needles. The method remarkably improves the nondiffraction beam quality, compared with the subwavelength Gaussian light needle, which is generated by a narrow-width annular paraboloid mirror. Such a light beam may suit potential applications in particle acceleration, optical trapping, and microscopy.
Focusing of the plane wave with radially polarized electric field by an arbitrary opening paraboloid mirror is analyzed
using a rigorous vectorial diffraction theory, i.e., Stratton-Chu integral. In the vicinity of the focus, far-field
approximation conditions are used to simplify the derived integrals with sufficiently high accuracy. It is found that a
noticeable deviation of the approximate integral, as characterized by a phenomenon of focal shift, from the exact integral
can be observed when the maximum focusing semi-angle α below π/9. For α=π/2, the radial spot size reduces to below
0.40λ if cutting off the central segment, larger than π/4, of the paraboloid mirror. The sharp focusing property of the
paraboloid mirror has the potential application in super-resolution confocal scanning microscopy. Specific confocal
scanning arrangements are provided and remarked.