Kazuhiko Ishikawa

Measurement of thickness of a thin film by means of laser interference at many incident angles

Abstract An optical method for directly measuring the thickness of a thin transparent film has been proposed by means of multi-wave laser interference at many incident angles, and confirmed experimentally by means of equipment made on an experimental basis. Two methods are available: one can be used when an index of refraction of the film, a wavelength λ , and two successive angles of incidence at which the sinusoidal light intensity has minimum values, are known (Method I), and another can be used without an index of film refraction when three successive angles of incidence and a wavelength are known (Method II). The smallest measurable thickness is 1.43 λ for Method I, and 2.5 λ for Method II. The largest measurable thickness is about 100 λ for both methods. The measurement error by means of numerical calculation is Δ h / h ≒−1.01×10 −2 , and that obtained experimentally with an angular resolution of incident light of 0.3° is Δ h / h ≒7×10 −2 for Method I. The refractive index can also be measured by means of Method II.

Highly Sensitive Optical Sensor System for Blood Leakage Detection

Abstract A highly sensitive method for the detection of blood leakage has been developed, and a practical sensor system for blood concentration measurement has been constructed. The present method is based on the attenuation of laser light by blood cells. The effects of the fluctuations of the incident laser light power are eliminated by normalizing the attenuated light intensity by the incident light intensity. A part of the incident laser light is reflected by a beam splitter mounted at the entrance of the test cell, of which the power is measured to provide base data for normalization. The optical path is extended to enhance sensitivity by using a pair of side mirrors. This multi-reflection method is very effective to increase sensitivity; the maximum sensitivity obtained for blood concentration is about 4 X 10-6 by volume, which is significantly higher than that of the conventional sensors.

Real-time measurement of a thickness of a thin coating by means of sheet laser

An ingenious optical method was developed for measuring the thickness of a coating directly and in real time at a measuring frequency of a few tens of Hz. The basic optical arrangement is very simple, and consists of a semiconductor laser, two cylindrical lenses, and a silicon photodiode array or CCD camera. The range of measurable thickness is roughly between λ and 100λ, where λ is a wavelength of the laser light, and its measuring error is a few percent. The previously developed method for measuring the thin film in air, which can be analyzed theoretically, can also be applied for estimating the thickness of a coating on the substratum within an error of 2%.

An Optical Method for Measuring the Diameter of Polyester Filament in Real Time

An optical method has been proposed and its system has been developed for measuring the change in diameter during the production of polyester filament in a manufacturing plant. The principle of the method is based on the application of scattered light on the filament. The sensor head of the system consisted of a semiconductor laser, two silicon-photodiodes as a light receiver, and a cylindrical lens. It was found from a preliminary experiment that (1) the scattered light intensity was not proportional to the diameter but to the cross section of the filament in the range between a few ?Em and a few tens μm, (2) the measurement error for the diameter of the polyester filament was 8 % for a scattered light intensity measurement error of 15 %, and (3) the system could be used in practical applications.

High Sensitive Optical Sensor for Blood Leak

A method of high sensitive detection for measurement of blood leak has been proposed and demonstrated experimentally. The method was based on multireflection of light at a sidewall mirror of a container and normalization of an output light power to an input power. The obtainable maximum sensitivity for blood concentration was 0.1 ppm which was about 50 times higher than the value of the existing sensors.