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A laser microphone using the self-coupling effect of laser diodes has a simple optical system, with a wide and flat frequency characteristic. However, due to the structure of the sensor section, detection of spherical sound waves has been difficult until now. In addition, simple miniaturization of the sensor parts of the laser microphone causes a decrease in sensitivity. To address these issues, a laser microphone sensor structure using multiple reflections from a pair of mirrors is considered. By using a multiple reflection sensor, the laser microphone retains sensitivity while achieving the desired miniaturization. When a multiple reflection sensor is used, the sensitivity improves up to approximately seven times, compared to simple miniaturization of the sensor part. When a sound source which generates spherical waves was used for measurement, the sound pressure distribution reconstruction achieved by the multiple reflection type laser microphone was the same as that of a conventional quarter inch sensor condenser microphone. It was found that the multiple reflection type sensor allowed downsizing of the sensor part while still being able to measure spherical sound waves.

We investigated the intermediate formation band and the electronic structures in multi-stacked QDs with different inter dot spacing using theory and experimental techniques: photoluminescence (PL) spectroscopy with 2-color excitation. We observed different behaviors with respect to inter dot spacing of 15nm and 7nm. These results offer an existence of the intermediate band formation and carrier dynamics in the multi stacked QDs.

When a part of the scattering light from the target is entering to the laser cavity, the terminal voltage of semiconductor laser diode slightly fluctuates. This voltage fluctuation has the information related to a distance to the target. However, the terminal voltage fluctuation has many noises. Discrimination of distance signal with many noises is almost impossible. Therefore, a statistical signal processing which utilizes the all information in terminal voltage fluctuation is newly proposed. A system is constructed using Field-Programmable Gate Array (FPGA). This system can measure the distance of 21cm to 45cm with the average error of about 2 %.

In conventional microphone a diaphragm is used for sound wave detection. However, diaphragm limits the detectable frequency range or sound pressure range. A laser microphone which is applying self-coupling effect of LD for sound wave detection is developed. It has flat and wide frequency response by utilizing the self-coupling effect. From experiment results, laser microphone has nearly flat frequency response from 40Hz to 50kHz. However, the SN ratio decreases in low sound pressure. Therefore, actions for sensitivity improvement are subjected. Sound wave collection using parabolic sound reflector improves sensitivity. However, frequency characteristics are arisen in audible band. Light path extension using right angle prism improves sensitivity. Minimum detectable sound pressure decreases from 54dB to 47dB with light path extension.