研究了在不同强度的外磁场作用下磁流体的弛豫特性。光束垂直于磁场方向透过磁流体样品盒，记录光强随磁场通、断而上升、下降的重复变化情况。结果表明，在相同强度的磁场作用下，磁流体中磁性颗粒的体积分数越大，则光强的下降弛豫时间越小而上升弛豫时间却越大。对于同一样品，场强越大，透射光强的下降弛豫时间和上升弛豫时间就越大，且随着磁场通、断次数的增加，光强的下降弛豫时间和上升弛豫时间逐渐增大，最后趋于稳定值。对研制和改良新型光子学器件具有一定的指导意义。

The optical relaxation properties of magnetic fluids are investigated in details. In the experiments, the light beam goes through the magnetic fluid samples perpendicularly. Experimental results indicate that the falling relaxation time is shorter for large volume fraction sample, while the rising relaxing time is longer for large volume fraction sample. For a certain sample, the rising relaxation and falling relaxation time increase with the magnetic field and the number of turning magnetic field on and off. Besides, the rising relaxation and falling relaxation time tend to saturate when the number of turning magnetic field on and off is very large. The corresponding physical mechanisms are clarified. These results are convenient for researchers to study optical properties of magnetic fluids deeply. The results provide a guideline for designing the potential photonic devices and are helpful for improving their quality.