精确测量孔径光阑面积的光学方法

Optical method for accurate measurement on the area of aperture diaphragm

精确测量孔径光阑的面积对降低辐射测量和光度测量的不确定度具有重要的意义。根据辐射照度与面积的基本关系E=Ф/A,采用制造覆盖孔径光阑恒定的照度区域方法,使等间距的激光束阵列叠加后可以形成覆盖孔径光阑的空间均匀的照度区域,通过孔径光阑的辐射通量与辐射照度的比值即为孔径光阑的面积。对该方法进行了理论分析和实验验证,得到形成均匀照度场允许的最大光束间隔,由于实际使用的光束并非理想高斯光束,因此光束间隔应小于允许间隔,对直径3mm光阑面积测量的不确定度达到3.24×10-4。该方法优越之处在于:可以不接触光阑边缘而直接测量光阑面积,无需任何已测定面积的辅助光阑,测量装置简单。

Accurate measurement of the area of the aperture diaphragm to reduce uncertainty of radiometric calibration and photometric calibration is of great significance. According to the basic relation of irradiance E and area A,E=Ф/A, a direct optical method, which was based on formation of constant and known irradiance over the aperture, for measurement of aperture area was provided. A known spatial uniform irradiance was formed over the aperture by overlapping an array of equal spacing laser beams. The aperture area was gived through the ratio of the throughput power and irradiance. The method was analyzed theoretically and verified experimentally. The maximal permissible beam spacing of the formed uniform irradiance field was obtained. The beam spacing should be smaller than permissible spacing because the actually used beam was not ideal Gaussian. The uncertainty of the measured aperture area for an aperture of 3 mm diameter was about 3.24 ×10^- 4. Compared with conventional ones, the direct measurement method has advantages of non-contact with aperture edge, no requirement of reference aperture known its area, and simple calibration setup.