Long-working-distance synthetic aperture Fresnel off-axis digital holography.

An aperture synthesis approach of digital holography for microscopy imaging at long working distance is proposed. Firstly, for an oblique object, a series of Fresnel off-axis holograms are recorded with different tilted plane wave illuminations without using lens for pre-magnification. Then the complex amplitudes are reconstructed and magnified from these holograms by the double-step Fresnel reconstruction method respectively. Finally, the synthesized image of the resolution enhanced and the speckle suppressed is obtained by incoherent superposition of these reconstructed complex amplitudes. The important advantage of the proposed approach is that the working distance of the system isn't constrained and the reconstructed image doesn't subject to lens aberrations. The experimental results with a die and an USAF-1951 resolution test target are shown and demonstrated that the resolution of both intensity and phase image can be effectively enhanced with simple set-up and procedure. The proposed approach can improve the capabilities of digital holography in three-dimensional in-situ microscopy at long working distance.