Kyu Yoshimori

Interferometric spectral imaging for three-dimensional objects illuminated by a natural light source

A phase-space analysis of a rotational-shear volume interferometer is presented. It is shown that, in a fairly general condition of this interferometer and by using a Fourier transform method to retrieve spectrodirectional images, a defocus region of the source location exists near the interferometer. This indicates that the usual Fourier transform method has its focal point at an infinite distance. By focusing on finite-depth sources located in the defocus region, a new interferometric method to obtain both three-dimensional spatial information and spectral information of a stationary, quasi-homogeneous, polychromatic source distribution is developed. A key element of this method is the use of a filter function that acts on the volume interferogram of the rotational-shear volume interferometer. This filter function realizes, for a particular position of a monochromatic point source located within the defocus region, a diffraction-limited resolution of the interferometer for the spectrodirectional image.

Digital holographic three-dimensional imaging spectrometry.

A fully interferometric technique for obtaining hypermultispectral components of three-dimensional (3D) images has been tested for a polychromatic object that consists of spatially incoherent, planar light sources of different shapes. Each planar source has different continuous spectra, located at different 3D positions. The method is based on measurement of a five-dimensional (5D) interferogram. By applying synthetic aperture technique and spectral decomposition to that 5D interferogram, one obtains a set of complex holograms of different spectral components. From these holograms, 3D images of multiple spectral components have been retrieved. A decomposed continuous spectrum of each planar light source is also shown to demonstrate the potential applicability to identify materials of a particular part of an object under illumination by white light.

Interferometry and radiometry

A general connection between interferometry and radiometry is studied on the basis of a new relationship between Walther’s first generalized radiance function and the mutual coherence function for polychromatic fields. New results include a definition of the generalized radiance function that is valid even for nonstationary fields and a principle of novel radiometry that retrieves three-dimensional radiance in the direction-frequency domain from the three-dimensional mutual coherence function. Radiometric interpretations of interferometric multispectral imaging are given as illustrative examples of this new principle.

First Experimental Report on Fully Passive Interferometric Three-Dimensional Imaging Spectrometry

A fully passive interferometric technique for obtaining a set of spectral components of three-dimensional (3D) images for a spatially incoherent, polychromatic object is experimentally verified. The method is based on the measurement of a five-dimensional (5D) interferogram using a suitably designed interferometer. By applying signal processing, including aperture synthesis, spectral decomposition, and image recovery, the method yields a set of 3D images of different spectral bands. In this paper, we report the first experimental verification of the method in which a monochromatic point source is used as the measured object. The 3D image and the spectrum obtained agree well with the experimental situation.

Fully interferometric three-dimensional imaging spectrometry using hyperbolic-type volume interferogram

A signal-processing method is proposed in the fully interferometric three-dimensional (3D) imaging spectrometry. This processing computes a 3D interferogram, in which recorded fringe patterns do not directly reflect wavefront forms propagated from a polychromatic light source under measurement. This paper presents a procedure for signal processing including a synthesis of the 3D interferogram and retrieval of a set of spectral components of 3D images. We demonstrate retrieving 3D images for spectral components of two planar light sources by means of the proposed method. The procedure to synthesize the 3D interferogram in this method suggests the possibility of direct measurement of the 3D interferogram.

Passive digital multispectral holography based on synthesis of coherence function

An interferometric method, called digital multispectral holography, to obtain three-dimensional (3D) multispectral images of spatially incoherent, polychromatic source distributions is presented. Each 3D spectral image is retrieved separately from a 3D spatial coherence function that is synthesized from interferograms measured with a two-axes wavefront folding interferometer. Numerical demonstration incorporated with spatially extended polychromatic source distribution, located at nearfield positions, shows that the 3D information of each spectral component is successfully retrieved by the method.

3D spatial resolution and spectral resolution of interferometric 3D imaging spectrometry.

Recently developed interferometric 3D imaging spectrometry (J. Opt. Soc. Am A18, 765 [2001]1084-7529JOAOD610.1364/JOSAA.18.000765) enables obtainment of the spectral information and 3D spatial information for incoherently illuminated or self-luminous object simultaneously. Using this method, we can obtain multispectral components of complex holograms, which correspond directly to the phase distribution of the wavefronts propagated from the polychromatic object. This paper focuses on the analysis of spectral resolution and 3D spatial resolution in interferometric 3D imaging spectrometry. Our analysis is based on a novel analytical impulse response function defined over four-dimensional space. We found that the experimental results agree well with the theoretical prediction. This work also suggests a new criterion and estimate method regarding 3D spatial resolution of digital holography.

Sub-nanometre double shearing heterodyne interferometry for profiling large scale planar surfaces

A novel interferometric method, called double shearing interferometry, is presented for profiling large-scale quasi-planar surfaces, such as semiconductor wafers, optical flats and x-ray mirrors. The surface profile is measured even if there is an inclination in the scanning stage. By adopting the common-path optical configuration and heterodyne detection, the proposed method achieves excellent resolution at the subnanometre scale and allows a robust measurement in the presence of unwanted disturbances in the measurement environment. A height resolution of 0.1 nm was achieved experimentally. The standard deviation of the analytical surface profiles was found to be 1.3 nm, even when using a conventional screw-lead scanning stage. The measured results show that the surface profile and stage inclination are determined separately. We confirmed that the resultant profile was quite consistent with that measured with a Fizeau interferometer.

Application of digital holographic three-dimensional imaging spectrometry to a spatially incoherent, polychromatic object

A fully interferometric method to obtain spectral components of 3-D images has been applied to a polychromatic object composed of planar light sources, located at different positions, having different continuous spectra and shapes.

Systematic study of synthetic aperture processing in interferometric three-dimensional imaging spectrometry

We have recently proposed a method of obtaining many spectral components of complex holograms under incoherent illumination. This method is based on the measurement of five-dimensional interferograms and signal processing including synthetic aperture processing. In this paper, we report the relationship between the selection rules used for synthetic aperture processing and the generated volume interferograms. As a result of our systematic study, we find six types of selection rule and generate volume interferograms that are the most important and basic. We discuss the benefits of using each selection rule and the three-dimensional (3D) imaging properties of retrieval imaging obtained from these volume interferograms. A new noise reduction method based on these six types of selection rules is also proposed.