With the improvement of the performance of electro-optical sensors and computer performance, lensless digital in-line holography has been studied and applied widely. However, the resolution of the digital in-line holography system are limited by pixel size and influenced by the twin image. To solve the problem, we proposed a resolution enhancement method, which collects two holograms with different sample-to-sensor distance. The reconstruction is based on Gerchberg–Saxton iteration algorithm, using two normalized and interpolated holograms. We used two prior constraints in the iteration process according to the iteration algorithm for phase retrieval: intensity of the two normalized holograms and the non-negative absorption of the sample. In this method, the interpolation operation before phase retrieval can digitally reduce the sampling interval, and the interpolation point will be optimized with the iteration process. We simulated the resolution enhancement method, and the results of the simulation show that the resolution and image quality of lensless digital in-line holography can be effectively improved.
Unlike traditional imaging, the light field imaging can obtain location and direction information by one shot, which makes the dynamic three-dimensional shape measurement possible. Firstly, this paper establishes a pixel light field model, and calibrates the measurement system, which lays the foundation for light field refocus. Then proposes light field 3-D shape measurement method based on digital focus distance measurement and appropriate sharpness evaluation function. Meanwhile, hardware module used in dynamic three-dimensional shape measurement based on light field imaging is designed, which is responsible for real-time collection and processing of the light field images and greatly improves the reconstruction speed of the images. Finally achieve light field 3-D shape measurement. The experimental results are present to demonstrate the feasibility of this technique.
Proc. SPIE. 9685, 8th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Design, Manufacturing, and Testing of Micro- and Nano-Optical Devices and Systems; and Smart Structures and Materials
KEYWORDS: Lithography, Control systems, Semiconducting wafers, Clocks, Photomasks, Process control, Stepper motor drivers, Data communications, Telecommunications, Camera shutters
Three-dimensional wafer stage is an important component of lithography. It is required to high positioning precision and efficiency. The closed-loop positioning control system, that consists of five-phase step motor and grating scale, implements rapid and precision positioning control of the three-dimensional wafer stage. The MCU STC15W4K32S4, which is possession of six independent PWM output channels and the pulse width, period is adjustable, is used to control the three axes. The stepper motor driver and grating scale are subdivided according to the precision of lithography, and grating scale data is transmitted to the computer for display in real time via USB communication. According to the lithography material, mask parameter, incident light intensity, it's able to calculate the speed of Z axis, and then get the value of PWM period based on the mathematical formula of speed and pulse period, finally realize high precision control. Experiments show that the positioning control system of three-dimensional wafer stage can meet the requirement of lithography, the closed-loop system is high stability and precision, strong practicability.