Incoherent digital holographic microscopy with coherent and incoherent light

Holography is an attractive imaging technique as it offers the ability to view a complete three-dimensional volume from one image. However, holography is not widely applied to the regime of fluorescence microscopy, because fluorescent light is incoherent and creating holograms requires a coherent interferometer system. We review two methods of generating digital Fresnel holograms of threedimensional microscopic specimens illuminated by incoherent light. In the first method, a scanning hologram is generated by a unique scanning system in which Fresnel zone plates (FZP) are created by a coherently illuminated interferometer. In each scanning period, the system produces an on-axis Fresnel hologram. The twin image problem is solved by a linear combination of at least three holograms taken with three FZPs with different phase values. The second hologram reviewed here is the Fresnel incoherent correlation hologram. In this motionless holographic technique, light is reflected from the 3-D specimen, propagates through a spatial light modulator (SLM), and is recorded by a digital camera. Three holograms are recorded sequentially, each for a different phase factor of the SLM function. The three holograms are superposed in the computer, such that the result is a complexvalued Fresnel hologram that does not contain a twin image. When these two types of hologram are reconstructed in the computer, the 3-D properties of the specimen are revealed.