Hideki Funamizu

Generation of fractal speckles by means of a spatial light modulator

It was shown in previous studies that, when a diffuser is illuminated by coherent light with an average spatial intensity distribution obeying a negative power function, the scattered field in the Fraunhofer diffraction region exhibits random fractal properties. The method employed so far for producing such fields has a disadvantage in that generated speckle intensities are low due to small transmittance of fractal apertures used in the illumination optics. To overcome this disadvantage, a generation of fractal speckles by means of a spatial light modulator is proposed. The principle is explained and experimental results are also shown.

Effects of spatiotemporal averaging processes on the estimation of spectral reflectance in color digital holography using speckle illuminations.

We present the effects of spatiotemporal averaging processes on an estimation of spectral reflectance in color digital holography using speckle illuminations. In this technique, speckle fields emitted from a multimode fiber are used as both a reference wave and a wavefront illuminating an object. The interference patterns of two coherent waves for three wavelengths are recorded as digital holograms on a CCD camera. Speckle fields are changed by vibrating the multimode fiber using a vibrator, and a number of holograms are acquired to average reconstructed images. After performing an averaging process, which we refer to as a temporal averaging process in this study, using images reconstructed from multiple holograms, a spatial averaging process is applied using a smoothing window function. For the estimation of spectral reflectance in reconstructed images, we use the Wiener estimation method. The effects of the averaging processes on color reproducibility are evaluated by a chromaticity diagram, the root-mean-square error, and color differences.

Estimation of wavelength difference using scale adjustment in two-wavelength digital holographic interferometry.

We propose a method for an estimation of wavelength difference using scale adjustment in two-wavelength digital holographic interferometry. To estimate wavelength difference, two holograms recorded with different wavelengths are reconstructed on the basis of the Fresnel diffraction integral, and pixel sizes in the reconstruction plane, which depend on the wavelength in recording hologram, are analyzed. In the analysis, a zero-padding method and an intensity correlation function are used to adjust pixel sizes in the reconstruction plane and then obtain a wavelength difference given by a difference between the pixel sizes. Theoretical predictions and experimental results are shown to indicate the usefulness of the proposed method in this paper.

Improvement of temporal resolution in blood concentration imaging using NIR speckle patterns

In the imaging of blood concentration change using near infrared bio-speckles, temporal averaging of speckle images is necessary for speckle reduction. To improve the temporal resolution in blood concentration imaging, use of spatial averaging is investigated to measured data in rat experiments. Results show that three frames in temporal averaging with (2×2) pixels in spatial averaging can be accepted to obtain the temporal resolution of ten concentration images per second.

Multifractal analysis of speckle intensities produced by power-law illumination of diffusers

Speckle patterns produced by computer simulations on the assumption of a power-law illumination of scattering objects are investigated on the basis of multifractal analysis. This analysis provides us with more detailed information on a fractal structure than conventional methods yielding a simple dimension. To examine multifractal properties of simulated speckle intensities, their generalized dimensions and singularity spectra are calculated by means of the method of moments. The results show that the multifractal description of the speckles characterizes clustering behaviour of the speckle intensities.

Investigation of temporal response in finger blood flow and concentration change in occlusion test on human arm using bio-speckle patterns

We have developed so far the method for imaging simultaneously blood flow and blood concentration change in skin tissue by using two-wavelength near infrared laser speckle patterns. We conducted experiments for human volunteers to confirm the feasibility of the method for estimating temporal response in the blood flow and blood concentration change in a human finger to occlusion on a human arm with different pressures from 50 to 150 mmHg. The results demonstrated that the response may depend on individual minimum and maximum blood pressure values.

Enhancing spatial resolution of two-wavelength digital holographic microscopy using speckle patterns generated from ring-slit apertures

Digital holographic microscopy (DHM) is actively investigated in the field of bio-imaging as a quantitative phase microscopy. In recent years, digital holographic technique for enhancing the spatial resolution using speckle patterns has been reported by several research groups, and we reported the enhancement of the spatial resolution in DHM using speckle illuminations generated from a ring-slit aperture. In this study, by applying the two-wavelength method to DHM using speckle illuminations, we realize the enhancement of spatial resolution and the extension of measurement range of shape measurement in DHM.

Digital holographic microscopy using speckle illuminations and two-wavelength method

In this study, we propose digital holographic microscopy using speckle illuminations and two-wavelength method. In this method, the spatial resolution is enhanced by speckle illuminations, and the measurement range in depth direction is extended by two-wavelength method. We demonstrate the proposed method experimentally.

Tomographic phase imaging of RBCs in blood coagulation structures using digital holographic microscopy

Blood coagulation is an important role in hemostasis process. In microscopic observation, an aggregation structure of red blood cells (RBCs) indicates the degree of blood coagulation. In this study, we demonstrate a tomographic imaging of phase distributions of aggregation structures of RBCs in blood coagulation using digital holographic microscopy.

Development of skin tissue phantom having a shape of sulcus cutis and crista cutis

There are sulcus cutis and crista cutis on human skin surface. It is known that these affect the light propagation in human skin. To investigate it experimentally, it is desirable to reproduce sulcus cutis and crista cutis in skin tissue phantom. In this study, we made a prototype of skin tissue phantom having a shape of sulcus cutis and crista cutis, and investigated its optical properties and problems to be solved.