Kaho Watanabe

Simultaneous measurement of refractive index and thickness distributions using low-coherence digital holography and vertical scanning

The simultaneous measurement method of a refractive index distribution and a thickness distribution using low-coherence digital holography with a vertical scanning is proposed. The proposed method consists of a combination of digital holography and low-coherence interferometry. The introduction of a datum plane enables the measurement of both a refractive index distribution and a thickness distribution. By the optical experiment, the potential of the proposed method is confirmed.

Refractive index & physical thickness distributions measurement and consideration of dependence of measurement accuracy on scanning interval using low-coherence digital holography

The measurement method of a refractive index distribution and a physical thickness distribution using digital holography with a low-coherent light source is proposed. The introduction of a datum plane enables the simultaneous measurement of a refractive index and a physical thickness distributions. By the optical experiments, the potential of the proposed method is confirmed. For the reduction of measurement time, the relation between stepping intervals of a reference mirror and measurement results are also discussed.

Spatially incoherent Fourier digital holography

The possibility of incoherent digital holography has been widely studied because it is free from coherent light sources. Here spatially incoherent Fourier digital holography is described. The incoherent hologram is obtained by a rotational shearing interferometer. The hologram obtained by the interferometer is a cosine transform of a spatially incoherent object. After describing the principle of a rotational shearing interferometer, methods to obtain Fourier transform of an object presented.

Incoherent holography by a Michelson type interferometer with a lens for a radial shear

The modified Michelson type interferometer with lenses for a radial shear to record incoherent holograms is proposed. It enables us to record a hologram by self-interference without coherent illumination such as a laser. The interferometer has two wave plates which can realize phase-shifting incoherent holography. The feature can avoid a very large bias term and the twin image, which are the inherent problem of incoherent holography by self-interference. The advantages of the proposed method using lenses and wave plates are easy adjustment of the zone plate and simplification of the optical system. A preliminary experiment using an LED as an incoherent object was performed to confirm the four step phase-shifting by wave plates.

Recording spatially incoherent hologram using rotational shearing interferometer with a lens for the parallel shear

Incoherent holography enables us to use a spatially incoherent illumination for recording holograms. In this paper, we describe incoherent holograms which can be recorded by the optical setups based on the rotational shearing interferometer. The experiment in which a LED was used an incoherent object confirms obtaining the holograms as the figures of a cosine transformation and a Fresnel zone-like pattern.

Reconstruction of incoherent Fresnel-like hologram by a rotational shearing interferometer

The systems to record incoherent holograms using a rotational shearing interferometer is demonstrated. The systems can record incoherent holograms by self-interference of the two coherent object points created by the beam splitter from one object point. In general, the rotational shearing interferometer cannot reproduce any depth information. The proposed rotational shearing interferometer has the advantage of obtaining depth information by the reconstruction owing to lenses for the shear which is parallel to the optical axis. A preliminary experiments were performed. The object images at some reconstruction distances were reconstructed numerically. The experimental results confirm the proposed system.

Incoherent holography to obtain depth information by a rotational shearing interferometer

The system to record incoherent holograms using a rotational shearing interferometer is proposed. It enables us to record a hologram without coherent illumination such as a laser. The systems can record an incoherent hologram by self-interference. A rotational shearing interferometer to record incoherent cosine hologram is described. Furthermore, a rotational shearing interferometer with lenses to record incoherent hologram is described. It has the advantage of obtaining depth information by the reconstruction owing to lenses for the shear which is parallel to the optical axis. The preliminary experiments were performed. An LED and a liquid crystal display with an LED backlight were used as incoherent objects. The incoherent holograms were recorded. The object images were reconstructed numerically. The experimental results confirm the proposed incoherent holography using a rotational shearing interferometer.