Katsuhiko Asada

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.

Realtime densitometer for glass wool using solar cells

Abstract An optical method to measure the weight density of raw glass wool has been developed for use in a manufacturing plant. The method is based on the light attenuation theory. The system consists of the usual white light as a light source, a solar cell as a light-sensitive receiver, an amplifier, a personal computer with an A/D converter for data acquisition and a monitor for display of the data. The accuracy of the system was found to be above 98% and the system can be effectively applied to practical use in the factory. The system may be further applied for quality control in manufacturing raw glass wool.

An optical system for monitoring torsion in a power transmission shaft in realtime

An optical system has been proposed and verified experimentally for monitoring the torsion of a power transmission shaft in realtime. The system consists of a pair of lasers, mirrors and light receivers as a sensor head, and logic circuit, high-frequency oscillator, and computer as a data processing system. The smallest measurable angle of torsion can be expressed by co/f, where co is the rotational frequency of the power transmission shaft andfis the frequency of the oscillator. The experimental error was found to be a few percentage points.

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.

An Optical Sensor for Measuring the Degree of a Parched Coffee Berry

An optical sensor system has been proposed for measuring the degree of parched coffee berry. The principle of the method is based on a scattering intensity of the light on parched coffee berry. The system consists of a sensor head including light source and light receiver, an amplifier, an A/D converter, a computer and a display. The results show that the optimum degree of coffee berry can be obtained when the scattering intensity is about 83% of the maximum intensity and that the scattering intensity depends only on the degree of parched coffee berry and does not depend on the wavelength of the light source.