Masataka Toda

Virtual interferogram-generation algorithm for phase measurement using two interferograms

Phase-shifting digital holography is a technique for phase measurement with high spatial resolution and applied to many fields. This technique typically requires four phase-shifted interferograms between a signal beam and a reference beam. We focused on the two-step phase shifting algorithm, which needs only two phase-shifted interferograms and an intensity distribution of the reference beam to reduce the number of required interferograms. However, in this algorithm, the intensity of the reference beam must be much greater than that of the signal beam because this algorithm uses the quadratic formula and the inside of square root must be positive. This leads to the saturation of the dynamic range of the image sensor and the degradation of accuracy. In this paper, we propose a virtual interferogram-generation algorithm (VIGA) to improve the performance of phase-shifting digital holography only using two interferograms. This algorithm virtually generates a π phase-shifted interferogram by the intensity distribution of the signal beam and that of the reference beam with an observed interferogram. Therefore, capturing two real interferograms and generating two virtual interferograms, the four-step phase shifting algorithm can be used for this method. Comparing to the conventional algorithm, the VIGA has no limitation in terms of the magnitude of the intensity. This means that the intensity of the reference beam and that of the signal beam can be equalized and the dynamic range saturation of the image sensors can be prevented. Therefore, the VIGA makes highly accurate phase measurement possible owing to the effective utilization of the dynamic range of the image sensors.

Digital confocal microscopy using a virtual 4f-system based on numerical beam propagation for depth measurement without mechanical scanning

We propose a digital confocal microscope using a virtual 4f-system based on numerical beam propagation for depth measurement without mechanical scanning. In our technique, the information in the sample target along the depth direction is obtained by defocusing the virtual 4f-system, which consists of two virtual lenses arranged in a computer simulation. The principle of our technique is completely different from that of the mechanical scanning method used in the conventional confocal microscope based on digital holography. By using the virtual 4f-system, the measurement and exposure time can be markedly reduced because multilayered tomographic images are generated using a single measurement. In this study, we tested the virtual depth imaging technique by measuring cover glasses arranged along the depth direction.

Improvement of measurement-speed by virtual optical-system for confocal laser scanning microscope

We propose a virtual optical-system for the confocal laser scanning microscope, which enables to measure tomographic images with the high acquisition rate. In our technique, by utilizing the virtual optical-system based on complex-amplitude detection, multi-layered tomographic images can be measure collectively without mechanical scanning.

Expansion method for depth measurement range based on number theory using two wavelength light sources

The expansion method for the depth measurement range is proposed. After capturing two wavelength phase images, the depth information is reconstructed by estimating the number of phase discontinuity in these images. The measurable depth-range can be expanded to hundreds times of wavelength.

Virtual interferogram-generation algorithm for phase-shifting digital holography

A virtual interferogram-generation algorithm is proposed to improve the performance of phase-shifting digital holography. Combining the intensity distribution of a signal and that of a reference beam with two observed interferograms, this algorithm generates four interferograms with different phases. Simulation results confirmed the basic operation of this algorithm.

Model shape oriented robust matching of dot cloud data based and its application to defect recognition

We propose a robust algorithm for matching three-dimensional dot cloud data in an effort to detect defects during manufacturing processes. We apply our proposed method to inspect a complex three-dimensional die-cast product. Our approach recognizes the difference between two data sets as a defect after matching the data sets. Moreover, our method improves matching accuracy by detecting geometrical features such as edge points, and by using such property values as gradients. Fundamental experiments using real three-dimensional dot cloud data show that the method is effective as a defect inspection system.

Defect inspection system by dot data

We successfully develop a defect inspection method based on a robust method for matching the distance between points in three dimensions. The three-dimensional distance data of an object is measured by means of a laser range finder. The data is compared with the measured data of a high-quality item. Then, we examine the differences between two sets of data in order to detect defects in the target object. The three-dimensional distance data is matched with high robustness by using the proposed method. Furthermore, we attach labels to sets of points corresponding to a detected defect. By performing an experiment with real data, we show that a high-quality object and a defect object can be distinguished on the basis of the features of each label.