光弹性圆偏振场中测定非整数(2m+1)/4级等差线条纹的方法

On the determination of isochromatics of(2m+1)/4 order in a photoelastic model in Circular polariscope

在平面偏振场中,加入四分之一波片,作为一个均匀的光载波,与实验模型中的等差线相叠加,可得到n+1/4和n+3/4级等差线。但这样所得到的条纹要受0°等倾线的干扰,使得相应点位的条纹难以直接观测。虽然同步旋转光路系统的各元件可以消除这种干扰,但在暗室中操作既麻烦又容易出错。理论推导和实践结果表明:在光弹性圆偏振场的明视场或暗视场中,在待测模型之前(或后),另加一个四分之一波片,形成一种非明暗的混合视场;使另加入的四分之一波片的快、慢轴与起偏振片和分析片的光轴平行或成45°,可消除等倾线的干扰,获得清晰的非整数(2m+1)/4级条纹。

By inserting a quarter-wave plate. used as a light wave carrier, in front of or behind the photoelastic model in the plane polariscope. isochromatics of n +1/4 and n+3/4 order may be obtained, n being any integer. The loci of these isochromatics, however, are disturbed by the isoclinics of 0 degree, rendering their determination to be difficult at the corresponding point in the model. By rotating synchronously the elements of the optical system the disturbance might be eliminated, but this operation is rather troublesome and apt to cause error. It has been proved both theoretically and experimentally that the superimposition of an additional quarter-wave plate with the photoelastic model in the circular polariscope (either dark field or light field), with the axis of the interposed quarter-wave plate set at 0 or 45 degrees with the polarizing axis as well as the analysing axis, the disturbance due to the isoclinics can be got rid of,and sharp images of the isochromatic of n +1/4 and n+3/4 order can be obtained.