Study Of Novel Magneto-optical Modulation Properties Of Magnetic Fluids

Magnetic fluid is a kind of functional composite material with nanosized structure,which has both the magnetism of the solid magnetic materials and the fluidity of liquidbesides the tunable optical properties.As an important application of magnetic fluid, the magneto-optic modulation isalways the interesting point of many researchers. In this work, we develop a newtunable magneto-optic modulation of magnetic fluid under external magnetic fieldachieved by adjusting the polarization direction of incident light. And it is investigatedtheoretically and experimentally. The accompanying mechanisms are clarified by usingthe theory of dichroism of magnetic fluid and the aggregation/disintegration processesof magnetic particles within magnetic fluid when the external magnetic field turnson/off. The corresponding modulation depth and response time are obtained. Under anexternal magnetic field of390Oe, the deepest modulation depth (-52.35%) is obtainedwhen the polarization direction of the incident light is parallel to the field direction. Theresponse time of the process of the magneto-optic modulation does not vary with thepolarization direction of the incident light.The relaxation behavior (including the rising and falling relaxation processes) ofthe transmitted light after the magnetic fluid thin films under longitudinal and transversemagnetic fields is investigated, respectively. The experimental data of the rising andfalling relaxation processes are fitted by using two exponential functions to achieve therising and falling response times. The relationship between the response time and thestrength of applied magnetic field, the concentration of magnetic fluid is studiedexperimentally. In our experiments,0.54389s is obtained to be the shortest responsetime with Sample3(with volume fraction of5.62%) under magnetic field of134Oe atlongitudinal field configuration. The modulation depth of the transmitted light isresearched quantificationally and the deepest modulation depth is obtained to be65.56%with Sample3in our experiments.The results presented in this work give a guideline for designing the potentialphotonic devices based on magnetic fluids are helpful for improving their quality.