研究了不同浓度磁流体薄膜样品的厚度对其场致双折射的影响。结果表明，固定磁流体浓度时，其双折射随样品厚度的增加而减小，且厚度不同的样品，其双折射随磁场的增加的变化趋势不同。对于薄样品，其双折射随磁场的增加而逐渐增加直至趋于饱和，而对于厚样品，其双折射随磁场的增加呈现非单调或“振荡”变化的现象。磁流体的浓度对其双折射的厚度依赖特性具有明显的影响，浓度越高，其双折射随磁场的增加开始呈现非单调或“振荡”变化时所对应的样品厚度就越小。详细分析了薄膜样品厚度和磁流体浓度对其双折射影响的有关物理机制，并定义了转折磁场的概念进行了定量的研究。

The influence of sample thickness of different concentration magnetic fluid on the magnetic-field-induced birefringence is studied. Experimental results show that the birefringence of magnetic fluid sample decreases with the thickness of magnetic fluid with certain concentration. The variation of birefringence with the externally magnetic field strength is different for samples with different thicknesses. For the thin sample, its birefringence increases gradually with the magnetic field and then saturates at relatively high magnetic field. For the thick sample, the birefringence varies non-monotonously or oscillates with the externally magnetic field. The magnetic fluid concentration has obvious influence on the thickness-dependence of the birefringence. The higher the concentration, the smaller the thickness of the sample for the occurrence of non-monotonous or oscillating variation of birefringence with magnetic field. The underlying physical mechanisms are clarified. The transition magnetic field is defined and employed to analyze the corresponding phenomena quantitatively.