Research On Center Axis Positioning Technology Of Point Diffracted Beam Based On Photosensitive Defection Array

In the construction of a practical point diffraction interferometry system,alignment errors will inevitably arise due to the presence of human operating errors,causing the shape and position of the spot emitted from the small aperture to deviate from the ideal,thus directly affecting the subsequent optical path arrangement and the final measurement accuracy of the system.Therefore,accurate measurement of the diffracted spot size and accurate positioning of the diffracted beam centre axis are essential in the research of point diffraction interferometer.This project proposes a method to accurately locate the centre of the diffracted spot of a small aperture with the aid of a wide range of photosensitive detection arrays,and relevant technical research is carried out.Firstly,based on the design requirements of small-aperture diameter,detection position and accuracy,the size and characteristics of the 2.5-μm small-aperture diffraction spot are theoretically analysed,and on this basis,a method is proposed to construct a large-area detection array with a diameter of not less than 330 mm based on a 1.6-mm SMD small-face element phototransistor.The system consists of a linear array of multiple phototransistors arranged at equal intervals to form eight independent light-sensitive units in a metre-shaped arrangement.The main microcontroller receives the eight spot edge coordinates B1 to B8 sent by the photoreceptors,and the actual diffracted spot centre O’ is fitted by an algorithm in the computer.The centre of the probe array is equipped with a point laser pointing vertically at the small aperture plate,whose function is to indicate the beam for the coincidence adjustment of the ideal optical axis of the small aperture with the central axis of the self-made probe array.Secondly,the hardware circuit design is carried out,including the design of the photosensitive circuit board and the control circuit board.The photosensitive circuit board consists of a photosensitive array module,minimum system of STM32F103ZET6 and interface circuit,while the control circuit board contains the power supply circuit,minimum system of STM32F103C8T6 and interface circuit.The function of the photosensitive circuit is to collect the 96-way level and collect the coordinates of the triode from high level to low level,and send them to the main control circuit through the interface circuit;the function of the main control board is to power the light-sensitive circuit and the auxiliary laser,and receive the coordinates of the spot boundary sent from the photosensitive circuit,and then send them to the software through the serial port of HC-12.Thirdly,the software design was carried out.The host computer is based on the QT development environment and uses Python as the development language.The eight spot boundary coordinates B1 to B8 sent from the main control board are fitted to a circle by a least squares algorithm to calculate the spot centre coordinates and radius,and the auxiliary laser is switched on and off by the software.Finally,the spot measurement device was built and the spot is measured.The centre axis of the small-aperture diffraction beam is calibrated with an auxiliary laser based on the actual measured spot centre position.The measurement results are analysed and then verified by comparison experiments,which show that the small-aperture diffraction beam centre-axis positioning system meets the design specifications.