In-line digital holography using a quarter wave plate and averaging method

In-line digital holography using a quarter wave plate and averaging technique is described in this paper. In-line digital holographic scheme inherently suffers from DC and conjugate object image noise terms. This problem can be overcome by using phase shifting technique which usually requires four digital holograms. However, it requires four successive holograms, which makes it less robust in relatively poor environment than one-shot off axis scheme. This study is on two-exposure method employing only a quarter wave plate which can produce A/4 phase difference between two successive holograms. The two-exposure method can provide conjugate-free reconstruction capability. Also, the DC terms can be minimized by applying averaging technique for object DC term. Detail explanation on how to reduce the DC term noise and how the intensity level of reference and object wave can affect the reconstructed image quality is discussed. Although the reconstructed image quality has a little undesired background noise compared with the conventional four frame method, it has a benefit in the sense that it requires only two holograms for eliminating the DC and the conjugate terms. The numerically reconstructed results show the feasibility of the two-exposure method and it may be capable of providing more robust approach in on-axis scheme.