New method for recording digital holograms

Recent noteworthy advancements in the field of incoherent digital holography (the production of 3D images) include optical scanning holography and Fresnel incoherent correlation holography (FINCH) techniques.1, 2 The latter acts as a single channel incoherent interferometer (a device that splits light into two beams and recombines them to produce an interference pattern) and does not require any scanning or mechanical movement, therefore making FINCH fundamentally robust. There is a well-known issue in holography known as the twin image problem. It commonly arises in holograms that are recorded by a single exposure, and where the reference and signal beams hit the camera with the same, or similar, angle. When such holograms are reconstructed, the virtual and real images emitted from the hologram in the same direction cannot be separated. This results in an obtained image that appears as a blurred noisy pattern. With Finch, although a single image contains the complete 3D information of an object, at least three images are required to solve the twin image problem.2 Our new holographic method overcomes the twin image problem through the recording of a Fourier hologram.3 This method, Fourier incoherent single channel holography (FISCH), exploits the beneficial qualities of Fourier holograms over those of Fresnel holograms. These include: increased space-bandwidth performance; enhanced robustness to information loss, as each object point is distributed over the entire hologram plane; and easier filtering ability, since the hologram is captured in the spatial frequency domain.4 By recording a Fourier hologram of a half plane (or space), the twin image problem is avoided and the object can be reconstructed from a single exposure. In addition, our method maintains many of the other advantageous characteristics of FINCH, including its inherent super-resolution property.5 Figure 1. Schematic of a Fourier incoherent single channel holography (FISCH) recorder. BPF: bandpass filter; SLM: spatial light modulator.