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Imaging an object embedded in turbid media has become considerably active during the last ten years because of its potential applications including tumor diagnoses in medical and biomedical studies. One method in this area is called transillumination imaging, in which case, image resolution is in the millimeter scale. To increase image resolution, an objective is needed to focus an illumination beam onto a sample. However, the time-gating method, which is usually used in transillumination imaging, becomes less efficient. To solve this problem, we have proposed an angle-grating method for microscopic imaging through a turbid medium. In our experiment, the angle- gating mechanism is implemented by the use of a pair of matched annular filters in the illumination and collection optical paths. The experimental results show that image resolution in a tens-of- micrometer scale is feasible with angle-gating. This new method is then combined with polarization-gating for selecting photons maintaining the incident polarization state, which carry more information of an object embedded in a turbid medium. In the case of a thick turbid medium, the differential polarization intensity can be achieved by subtracting the perpendicular-polarization intensity from the parallel-polarization intensity. Our experimental results on imaging through milk suspension demonstrate that image resolution is significantly improved when differential polarization-gating is employed. Image resolution of tens of micrometer has been achieved in a thick turbid medium, which is 15 times better than that achieved using the transillumination imaging method in a similar medium. With the concept of an effective point spread function derived in a turbid medium, image resolution through a turbid medium may further improve in post image processing.
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