The flat-top beam is required in lots of practical applications. However, the semiconductor laser which is widely used as light source has a Gaussian or Gaussian-like energy distribution. In this work, a beam shaping system consisting of aspherical circular lens, Powell lens and cylindrical lens is proposed to transform the semiconductor laser beam into a collimated flat-top beam. The parameters of the Powell lens are designed based on the energy conservation between the incident and output beams, and the cylindrical lens is used for beam collimation. Simulation and experimental analysis are conducted to investigate the energy distribution of the shaped beam at various distances. The results demonstrate a strong agreement between the theoretical expectations and experimental observations, confirming the feasibility and scientific validity of the shaping system. This approach provides an effective method for shaping Gaussian beams into collimated flat-top beams.
The in-situ investigation of interstellar dust has becoming one of the focuses in deep space exploration. It is of great importance since it provides us with key information about the origin and evolution of planets. To measure the size of a single slow dust particle, a laser-based optical measurement system was designed and calibrated accordingly. In this system, a detection area of 50mm*50mm laser curtain was generated using a diffractive optical element (DOE) and a cylindrical lens, which transform the laser beam in Gaussian profile to a laser sheet with a rectangular uniform profile. When a dust particle passes through the laser curtain, scattered light will be generated and collected by a compound parabolic concentrator (CPC) and then be converted into an electrical signal by a PIN photodiode. The amplitude of electrical signals, which are directly related to the scattered light flux, are used to extract the particle size. Standard spherical SiO2 sample particles of different sizes were used in the calibration activities. Satisfied agreements have been achieved between the theoretical result calculated using the Lorenz-Mie theory and the experimental result.
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