A digital in-line holographic microscope is presented using Fresnel zone plate. The light impinging on the Fresnel zone plate is divided into a number of diffraction orders. We use the Ord light, which propagate along the original direction, as the reference beam. And the first order focus is used as a virtual point source after which the sample is placed. The light transmitted through the sample is scattered by the object and the structure information is carried by the light. The interference fringes created by the first and zero order diffraction are recorded by a digital camera. Afterwards, the object information is retrieved using reconstruction algorithm. With the aid of the Fresnel zone plate, an image with higher lateral resolution and lower noise could be obtained. This holographic microscope is tested with several samples and the results show that the lateral resolution is good, and for the phase object, the measured phased difference is accurate compared with the AFM test result.
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