Toru Yoshizawa

Handbook of Optical Metrology: Principles and Applications

Leach, R., (Optical Measurement of Surface Topography), Springer, Berlin (2011). Yoshizawa, T., (Handbook of Optical Metrology: Principles and Applications). Handbook of Optical Metrology: Principles and Applications begins by discussing key principles and techniques before exploring practical applications of optical. Handbook of Optical Systems. Volume 2: Theory, Algorithms, and Applications Introduction to Digital Phase Demodulation in Optical Metrology 1. 1.1.1 The main objective of this book is to present the basic theoretical principles behind.

Generation of achromatic, uniform-phase, radially polarized beams.

Axially symmetric half-wave plates have been used to generate radially polarized beams that have constant phase in the plane transverse to propagation. However, since the retardance introduced by these waveplates depends on the wavelength, it is difficult to generate radially polarized beams achromatically. This paper describes a technique suitable for the generation of achromatic, radially polarized beams with uniform phase. The generation system contains, among other optical components, an achromatic, axially symmetric quarter-wave plate based on total internal reflection. For an incident beam with a constant phase distribution, the system generates a beam with an extra geometrical phase term. To generate a beam with the correct phase distribution, it is therefore necessary to have an incident optical vortex with an azimuthally varying phase distribution of the form exp( + iθ). We show theoretically that the phase component of radially polarized beam is canceled out by the phase component of the incident optical vortex, resulting in a radially polarized beam with uniform phase. Additionally, we present an experimental setup able to generate the achromatic, uniform-phase, radially polarized beam and experimental results that confirm that the generated beam has the correct phase distribution.

Development of a compact inner profile measuring instrument

Inner profile measurement has a lot of request for the applications in field of mechanical industry and even in the medical and dental fields. We proposed measurement method of inner diameters of pipes and/or holes using a ring beam device which consists of a conical mirror and a laser diode. This measurement method is based on optical sectioning of inner wall. This optically sectioned profile is analyzed to calculate the inner diameter and/or profile. Here, an optical instrument with a simple and compact configuration is reported for the inner profile measurement. As experimental results, we show performance of the instrument and some examples for inspection of mechanical components.

Achromatic axially symmetric wave plate.

An achromatic axially symmetric wave plate (AAS-WP) is proposed that is based on Fresnel reflections. The wave plate does not introduce spatial dispersion. It provides retardation in the wavelength domain with an axially symmetric azimuthal angle. The optical configuration, a numerical simulation, and the optical properties of the AAS-WP are described. It is composed of PMMA. A pair of them is manufactured on a lathe. In the numerical simulation, the achromatic angle is estimated and is used to design the devices. They generate an axially symmetric polarized beam. The birefringence distribution is measured in order to evaluate the AAS-WPs.

Uni-axial measurement of three-dimensional surface profile by liquid crystal digital shifter

A uni-axial measurement of three dimensional surface profiles by a liquid crystal digital shifter is proposed using a telecentric optical system. Height information is captured by measuring the contrast in the projected pattern. A shadow less measurement of the objects area is archived by using a uni-axial system. The magnification of the object image captured by a CCD camera is made constant by changing the focus distance. The liquid crystal digital shifter is a powerful tool to make arbitrary intensity and frequency distribution. Surface profiles of mechanical parts were measured to demonstrate this method.

Determination of the polarization states of an arbitrary polarized terahertz beam: Vectorial vortex analysis

Vectorial vortex analysis is used to determine the polarization states of an arbitrarily polarized terahertz (0.1–1.6 THz) beam using THz achromatic axially symmetric wave (TAS) plates, which have a phase retardance of Δ = 163° and are made of polytetrafluorethylene. Polarized THz beams are converted into THz vectorial vortex beams with no spatial or wavelength dispersion, and the unknown polarization states of the incident THz beams are reconstructed. The polarization determination is also demonstrated at frequencies of 0.16 and 0.36 THz. The results obtained by solving the inverse source problem agree with the values used in the experiments. This vectorial vortex analysis enables a determination of the polarization states of the incident THz beam from the THz image. The polarization states of the beams are estimated after they pass through the TAS plates. The results validate this new approach to polarization detection for intense THz sources. It could find application in such cutting edge areas of physics as nonlinear THz photonics and plasmon excitation, because TAS plates not only instantaneously elucidate the polarization of an enclosed THz beam but can also passively control THz vectorial vortex beams.

Small size probe for inner profile measurement of pipes using optical fiber ring beam device

The requirements of inner profile measurement of pipes and holes become recently larger and larger, and applications of inner profile measurement have rapidly expanded to medical field as well as industrial fields such as mechanical, automobile and heavy industries. We have proposed measurement method by incorporating a ring beam device that produces a disk beam and have developed various probes for different inner profile measurement. To meet request for applying to smaller diameter pipes, we tried to improve the ring beam light source using a conical mirror, optical fiber collimator and a laser diode. At this moment a probe with the size of 5 mm in diameter has been realized.

Three-dimensional profilometry based on focus method by projecting LC grating pattern

This paper describes a 3D surface profile measurement based on focus method by an optical sectioning. The optical system is employed uniaxial condition of projection and observation axis. The contrast of projected sinusoidal pattern onto the sample is approximated the Gauss distribution along the distance. The highest contrast indicates at the focused plane. It is possible to analyze the contrast distribution by a grating projected method using a liquid crystal grating. A phase-shifting method is applied to the contrast analysis. The liquid crystal grating is powerful tool to make arbitrary intensity and frequency distribution. Surface profiles of mechanical parts were measured to demonstrate for this method.

Compact camera for three-dimensional profilometry incorporating a single MEMS mirror

To overcome inherent problems with conventional three-dimensional profiling systems based on pattern-projection method, we propose incorporating a digital device, such as a single MEMS mirror in the projection optics. In this system, a projector is controlled to generate a projection pattern with an appropriate periodic structure and sinusoidal intensity distribution. The key aspect to this projection method is that sinusoidal signals are generated by a function generator; that is, the temporal sinusoidal intensity distribution is transformed from the time domain to the spatial domain. This flexible pattern-projection method permits phase-shifting techniques to be applied to industrial measurement and inspection. This apparatus is so compact as to have a dimensional size similar to a conventional digital camera [53  mm(H)×130  mm(W)×38  mm(D)]. Furthermore, it is lightweight (320 g) without a battery or circuit boards. Such a compact system can be used as a palm-top camera and potentially may be used in low cost measurement systems for three-dimensional profilometry.

Development of an inner profile measurement instrument using a ring beam device

Inner profile measurement is an important matter in such fields as medicine, dentistry and anthropology as well as mechanical engineering and other industrial applications. Here we describe recent development of our measurement principle for inner diameter of pipes and/or holes. The key device in this technique is a ring beam device which consists of a conical mirror and a laser diode. And the fundamental principle is based on optical sectioning without using any contact type stylus. The optically sectioned profile of an inner wall of a pipe-like object is analyzed to give the inner profile in addition to the inner diameter. This optical instrument with a simple and small configuration is now under development for practical uses. In our hitherto trial experimental works, the availability of this instrument has been evaluated in many cases and availability for practical applications is expected, especially, for measurement and inspection of mechanical components and elements besides pipes. This ring beam device consisting of a conical mirror and a LD is assembled to form a disk-like light sheet. We show measurement result of pipes and holes, and, at the same time, report a compact inner profile measuring instrument at this point. Both the ring beam device and a miniaturized CCD camera are fabricated into a glass tube. Availability of this instrument is shown by measuring the inner profiles of various pipes. In response to this trial, there appeared a strong request that not only the internal but external profiles should be measured simultaneously. Therefore we propose potentially possible method for measurement of external profile at the same time with internal profile. If one pair of concave mirrors are used in our arrangement, external profile is captured. In combination with inner profile measurement technique, simultaneous measurement of inner and outer profiles becomes attainable. A measurement result on a bevel gear shows availability of here proposed principle. In addition, we are trying to extend our technique to check defects and/or flaws on the inner wall of pipe-like objects.