A MONTE CARLO CALCULATION OF LENS ABBERATION EFFECT ON THE SIZE OF SOURCE EFFECT IN RADIATION PYROMETRY

摘要

The size of source effect (SSE) is one of the most serious components of uncertainty sources in the primary pyrometry and the radiometry. The SSE is originated from aberration, diffraction, and scattering. To optimize design of pyrometers and improve the uncertainty of the temperature scales, a calculation of the aberration effect on the SSE is necessary. We have calculated effect of objective lens aberrations on the SSE by the Monte Carlo method. The source was assumed uniform and Lambertian. Random numbers determined positions on the source rays emerged from and the direction the rays traveled. Trajectories of rays were calculated by the ray tracing until the ray struck a screen after passing through the lens. The number of rays that struck each annulus predefined on the screen was counted to give an amplitude distribution of radiance level on the image plane. The distributions were calculated as increasing the dimension of the source to yield the SSE. The defocus effect of the SSE was also calculated by changing the screen distance from the best focus. The results were discussed with comparison to measurement of the KRISS standard pyrometer of which the minimum target size is 0.8 mm in diameter. Aberrations of the objective lens in the KRSS pyrometer gave the most critical effect to SSE in the range where the source size is less than 2 times of the minimum target size in diameter.