The Study On The Measurement Of Near-field Intensity Distribution With Rotary Canister For CW Laser

As one of the most important parameters of laser beam, intensity distribution is of great importance for evaluating laser beam quality. The measurement of near-field intensity distribution is urgently required during the research of infrared laser. Since 2D array detectors of certain wave bands are not commercially available, a two-dimensional beam profile measuring device using cell detector and rotary canister is studied in this dissertation.Main methods for measuring laser intensity distribution are introduced in this paper. The principles, errors and characters of scanning method that are in common use are analyzed. Rotary canister scanning is selected considering the measuring requirements.The traditional rotary canister scanning method is improved by adding a slot on the canister using for triggering and the precision vertical translation stage is introduced to improve the space resolution. The parameters of the device are calculated and main factors that would affect measuring result are discussed. Corresponding methods for reducing measuring error are proposed. A rotary canister scanning measurement device that can measure two-dimensional intensity distribution is designed and fabricated.Three experiments are carried out. The first experiment is carried out to elementarily validate the measurement with this device. Second, to compare the result obtained by using the rotary canister scanning measurement system with that obtained by using laser beam analyzer(LBA). Third, to compare the results with and without precision vertical translation stage. The intensity distribution profile is obtained by the experimental data digital processing, in which Zernike polynomial surface fitting and FFT de-noising are used. The measurement of small spot is compared with its counterpart measured by laser beam analyzer(LBA). The horizontal width of spot measured by rotary canister scanning measurement system has 13.16% difference from the result measured by LBA. The vertical width of spot has 5.93% difference from the result measured by LBA. The correlation coefficient of the two groups of data in horizontal direction is 99.18%. The correlation coefficient of the two groups of data in vertical direction is 98.66%. The factors that cause measuring errors are analyzed considering the result of measurements. And the result of measuring wide laser beam with and without precision vertical translation stage is also compared. The result shows that using vertical translation stage can improve the precision of measurement effectively. The experiments show that the results obtained by the device proposed in this dissertation for measuring laser beam intensity distribution are exact and credible.