Research On LED Based Low-coherence Phase-shifting Digital Holographic Microscopy And Phase-shifting Calibration

Digital holographic microscopy, as an important branch of digital holography, plays asignificant role in micro-structure detection, and has a broad development prospects. It recordsamplitude and phase information simultaneously, so that it can reconstruct the original object inthree dimensions. The reconstruction is numerically done based on the spatial-filter orphase-shifting techniques. And its numerical reconstruction is more flexible for imaging processof original object image. The phase-shifting technique can eliminate zero-diffraction and twinimage effectively. It is not only suitable for off-axis holography, but also on-axis holography. Butthere are still some issues in phase-shifting technique, for example, the calibration of phase shifts.It is hard to achieve accurate phase shifts in actual detection environment, because the phaseshifts is influenced by both the phase-shifter and ambient vibration. So the self-calibrationphase-shifting method is worth trying. At present stage, digital holographic microscopy usuallychoose laser as source. But phase-shifting digital holographic microscopy usually needscomplicated interference light path, so the multiple reflections among optical elements areinevitable. Moreover, laser is high coherence light, so there will be much speckle noise andparasitic interference fringe in recorded holograms. Choosing low-coherence source caneliminate this noise effectively, so a phase-shifting digital holographic microscopy based on LEDsource is demonstrated in this paper. The main work includes:1. Propose a self-calibration phase-shifting digital holographic microscopy based on Fouriertransform phase shifts determination technique. The sample is USAF-1975-1X resolutiontarget. The comparison between self-calibration and traditional phase-shifting digitalholographic microscopy verifies that the former has a better reconstruction quality.2. Propose a phase-shifting digital holographic microscopy based on LED source. Firstly,analyze the coherence of LED source. Then build the LED low-coherence source baseddigital holographic microscopy system, and choose USAF-1975-1X resolution target assample to test the reconstruction quality of the proposed method. The results verify that it caneliminate the speckle noise and parasitic interference fringe effectively, and the max resolution is128lp/mm.3. The actual application of LED based low-coherence phase-shifting digital holographicmicroscopy is done. In this experimental, we choose AlGaN/GaNelectron mobility transistorintegration as the sample, then reconstruct the circular transmission line model in theintegration and achieve its high-quality3-D image.