在探索空间分束法消除椭偏测试中背反杂光干扰的过程中，发现该方案能够使光束在待测样品前表面聚焦，后表面发散，发散的背反光将无法进入到探测器中，从而消除背反光的影响。选用石英玻璃和氧化铌单层膜为实验样品，分为3组，分别采用直接测量、背部打磨和空间分束三种测量模式。实验结果表明，样品未经处理情况下，不同角度直接测量得到石英玻璃折射率值差别较大，经过背部打磨后不同角度下得到石英玻璃折射率趋向一致，而采用空间光学分束处理后，石英玻璃折射率在不同角度下测试获得相同的数据。最后采用空间分束法对氧化铌单层膜进行椭偏测量，获得了较好的拟合数据。

Spatial beam method is explored to eliminate the backside reflection in ellipsometric measurement. The main concept of this program is to focus the beam on the of sample surface, diverge on the bottom, and then the back reflection light will not reach the detector. The quartz glass and niobium oxide monolayer film are chosen as the experimental sample. Quartz glass samples are divided into 3 groups, which are measured directly, after backside grinding, and after the spatial splitting, respectively. For the untreated sample testing, the refractive index values at three incident angles are obviously different. In backside grinding case, the refractive index of the quartz glass appears consistent for three incident angles. After the spatial splitting, the refractive index of the quartz glass appears the same. The spatial splitting method is used for ellipsometric test of anti-niobium oxide monolayer, and good fitting of the experimental data is got.