A new method for three-dimensional image formation is proposed in which the distribution of complex amplitude at a plane is measured by phase-shifting interferometry and then Fresnel transformed by a digital computer. The method can reconstruct an arbitrary cross section of a three-dimensional object with higher image quality and a wider viewing angle than from conventional digital holography using an off-axis configuration. Basic principles and experimental verification are described.

A new optical sensor that uses local plasmon resonance is proposed. A peak that is due to the local plasmon resonance appears in the absorption spectrum of a gold colloid suspension in the visible region, and its height and wavelength depend on the refractive index of the suspension. These properties are used for optical sensors. We used gold colloid monolayers in which colloidal gold particles a few tens of nanometers in diameter were immobilized upon a glass slide by a functional organic coupling agent. We measured the absorption spectra of the the gold colloid monolayers, which were immersed in liquid samples or coated with thin films. We observed increases of both the resonance wavelength and the absorbance as the refractive indices of the sample liquids or the thickness of the coated films increased. The proportional constants of the resonance wavelength to the film thickness were 3.6 and 5.7 for a 13.9- and a 20.2-nm gold colloid monolayer, respectively.

In digital holography holograms are recorded by a CCD and image reconstruction is performed by a computer. It is free from tedious photographic processing and delivers three-dimensional distributions of both amplitude and phase quantitatively. Its main limitation that is caused by much lower resolution of CCDs than photographic materials has been substantially overcome by phase-shifting digital holography that reduces the spatial frequency of hologram by employing the inline setup and directly evaluates complex amplitude at the CCD plane to eliminate the conjugate and zero-th order images appearing in the off-axis setup which has been commonly used. In this chapter we first describe its basic principle of image formation. It is followed by applications to microscopy, color holography, and data compression for storage, transmission, and real-time display of holographic data. Then its applications to measurements of shape and deformation of diffusely reflecting surfaces are discussed in comparison with conventional holographic interferometry and electronic speckle pattern interferometry.

We applied phase-shifting digital holography to microscopy by deriving the complex amplitude of light scattered from microscopic three-dimensional objects through a microscope objective by video camera recording, phase-shifting analysis, and computer reconstruction. This method requires no mechanical movement and provides a flexible display and quantitative evaluation of the reconstructed images. A theory of image formation and experimental verification with specimens are described.

The resonance wavelength of the surface plasmon in gold nanoparticles above a gold substrate has been measured using transmission absorption spectroscopy. Gold nanoparticles with diameters in the range of 20-100 nm are immobilized onto a thin gold film deposited onto a glass substrate by a self-assembled monolayer of aminoethanethiol. The resonance wavelength obtained in the experiments shows a large red shift. Its dependence on the particle diameter shows good agreement with theoretical results that are calculated using a static approximation that includes multipole effects.