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This paper describes a Multiangle Snowflake Imager (MSI) designed to capture the pseudo-three-dimensional (3D) shape and the fall velocity of individual snowflakes larger than 1.5 mm in size. Four height-offset line-image scanners estimate fall velocities and the four-angle silhouettes are used to reconstruct the 3D snowflake shapes. The 3D shape reconstruction is tested using reference objects (spheres, spheroids, cubes, and plates). The four-silhouette method of the MSI improves the representation of the particle shape and volume compared to two-silhouette methods, such as the two-dimensional video disdrometer (2DVD). The volume (equivolumetric diameters) of snowflakes estimated by the four-silhouette method is approximately 44% (13%) smaller than that estimated by the two-silhouette method. The ability of the imager to measure the fall velocity and particle size distributions based on the silhouette width and the equivolumetric diameter of 3D-shaped particles is verified via a comparison with the 2DVD in three snowfall events.

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.

Quantum dots (QDs) are widely used for enhancing the performance of optical devices. Intermediate-band solar cells that use multistacked QDs can surpass the conversion efficiency of conventional silicon cells. We performed the optical characterization of In0.4Ga0.6As/GaAs multistacked QDs without strain compensation. We used the theoretical and experimental techniques prescribed for intermediate-band solar cells, i.e., photoluminescence (PL) spectroscopy and two-color excitations spectroscopy. The interdot spacings were not uniform and were found to be 15 nm and 7 nm. The results verify the formation of intermediate bands by the multistacked QDs. Using the theoretical studies and experimental results, we performed an in-depth study on the mechanism underlying the formation of intermediate bands by the multistacked QDs and the effect of different interdot spacings.

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.

The demand for noncontact and nondestructive internal defect detection is increasing. Using the photoacoustic effect, internal defects can be detected by a low-power semiconductor laser and an ultrasonic sensor. But the sensitivity of ultrasonic sensors is low in detecting photoacoustic signals. Thus, an internal defect detection using the photoacoustic and self-coupling effect of a semiconductor laser has been studied. To generate photoacoustic signals, a semiconductor laser with an output power of 20 mW is focused by a lens and is directed toward the sample at an angle of 45°. To detect the photoacoustic signal by the self-coupled effect, another laser with an output power of 10 mW is directed against the sample at a right angle. Sample defect can be detected by directing these laser beams at the same point on the sample. The self-coupling sensor can detect internal defects with greater sensitivity than an ultrasonic sensor. The edge effect and the frequency characteristic have also been observed. The device proved able to detect a very small defect of 0.07 mm. © 2010 Wiley Periodicals, Inc. Electron Comm Jpn, 93(7): 17–23, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10307

We report on the electronic properties and band structure of multistacked quantum dots (QDs) fabricated without a strain compensation technique. It is possible to realize a small interdot spacing and introduce a strong quantum mechanical coupling. From the using temperature dependence, polarized photoluminescent spectra, and photoluminescent excitation experiments, we observe a markedly different behavior depending on the interdot spacing. These results evidence that minibands of electrons and holes are formed with interdot spacings of 7 and 3.5 nm, respectively. In addition, thise results are in good agreement with numerical calculations. We describe in detail the miniband formation and electronic structure of multistacked QDs with various interdot spacings of 10 nm or less.

In this paper peak count correction methods for a self-coupling distance sensor with a Vertical-Cavity Surface-Emitting Laser (VCSEL) are reported on. The distance to the target in these distance sensors is usually calculated by determining the frequency of power fluctuations that are produced by the self-coupling effect. In this study it is proposed that the peak count correction method using statistical feature with little computational effort than Fast Fourier Transform (FFT) and higher accuracy than traditional peak count methods. The counting error is reduced to less than 1/100 with the peak count correction methods under adverse condition.

Small vibration sensors with the laser interferometer have been developed. However, there are some disadvantages, for example, weakness to external vibration, difficulty in optical alignment, and so on. These disadvantages are improved by making use of a self-coupling effect of a semiconductor laser, because this sensor is composed of only a laser diode and a lens. When a small vibration, whose amplitude is less than half-wavelength of the laser, is measured, a reference signal is needed. The reference signal is generated by moving the sensor head quickly. Also an output signal should be measured at maximum sensitivity. This output signal is observed by moving the sensor head slowly. The signal is controlled by a microcomputer. The vibration amplitude is evaluated from the ratio of the output signal to the reference one by the microcomputer. This sensor can detect a small vibration with minimum amplitude of about 3 nm, and a small vibration is able to be measured irrespective of the frequency in the range between 0.5 kHz and 3.0 kHz, and the target color.

Recently, laser radar has been widely studied as a sensor to measure the distance from a car ahead. Laser radar has the characteristic that the received signal becomes buried in noise with increasing distance. It is difficult to measure long distances at low laser power. Thus, a new type of chaos laser radars has been studied. This laser radar is relatively resistant to noise and can perform processing simply because it uses only addition operations. However, the distance resolution of chaos laser radars is limited by the clock cycle of the FPGA which is used for signal processing of the laser radar. Therefore, a new method of improving distance resolution by means of a phase delay circuit has been developed. As a result, the distance resolution of chaos laser radars has been improved to 1/10 using phase delay circuitry. © 2011 Wiley Periodicals, Inc. Electron Comm Jpn, 94(6): 59–65, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10177

In recent years, as a result of a large amount of greenhouse gas emission, atmosphere temperature at ground level gradually rises. Therefore the Kyoto Protocol was adopted to solve the matter in 1997. By the energy-saving law amended in 1999, it is advisable that an escalator is controlled to pause during no user. Now a photo-electric sensor is used to control escalator, but a pole to install the sensor is needed. Then, a new type of approach detection sensor using laser diode, CCD camera and CPLD, which can be built-in escalator, has been studied. This sensor can derive the irradiated area of laser beam by simple processing in which the laser beam is irradiated in only the odd field of the interlace video signal. By second order derivative of laser irradiated area, this sensor can detect only the approaching target but can not detect the target which crosses and stands in the sensing area.

In developing an automation in processes, a demand for compact and simple distance measurement is increasing. A compact distance meter based on self-coupling effect of semiconductor laser has been studied. It is a compact and simple sensor with high accuracy as it consists of only a laser and a lens. However, a measurement error of this distance meter increases due to mode hop of FP type semiconductor laser. In this paper, a distance meter based on self-coupling effect using VCSEL is studied. It is confirmed that the mode hop for VCSEL does not happen and the distance meter using VCSEL can measure a distance. Furthermore, the distance meter using VCSEL with less optical output power can measure longer distance than that using FP laser.

Many laser radars have been studied as in-car radar. Generally, a distance is measured from delay time using either a periodic signal or a single pulse. But the received signal becomes to be buried in noise with increasing distance. Recently a chaos has been paid an attention and a chaos laser radar has been suggested. When a received signal is correlated with a transmitted one, it takes long processing time to perform repeatedly multiplications and integrations. A new type of chaos laser radar which processes by only an addition is proposed. It can quickly process and is comparatively strong for noise. A proto type of chaos laser radar is produced, in which a semiconductor laser with low output power below 1mW is used. This laser radar is able to measure the distance up to 80m. It is confirmed that the chaos laser radar is effective.

A safety area sensor for automatic guided vehicles using a semiconductor laser and a CCD camera has been studied. But this detection system, which depends on the light intensity, has the weak point for disturbance light. A new detection method is proposed which is called beam width selection method. This method is able to select a laser light from the beam width difference between a laser light and a disturbance light. The edge component of the video signal is selected by a differentiation circuit, and the pulse signals are produced from the positive differentiation signal and negative one. The laser light signal can be obtained from the product of these pulse signals. The detected distance is 3 m and the detected width is 1 m under the disturbance light of 10000lx. The repetition error for various color obstacles is below 0.2 percent.

When a XeCl excimer laser beam was focused in a high-pressure argon gas up to 150 atm, a hot and dense plasma was produced at the focal spot. The plasma developed not only backward but also forward, which differed from one produced by a visible laser. The radius of the forward plasma became smaller beyond the focal spot. There had been no explanation for the development mechanism of the forward plasma. A new model for the forward development mechanism called a forward breakdown wave was proposed. The forward plasma was calculated assuming that the laser beam transmitted through the plasma was further focused by the plasma. This model could predict the forward development behavior considerably well.

We propose a quantum dot (QD) laser with the half-etched mesa distributed feedback (HEM DFB) structure fabricated by single-step dry etching. The HEM DFB structure provides several advantages, such as low scattering loss and wavelength stability. In this study, we demonstrated a low threshold current of 23 mA and a high thermal stability of 0.077 nm/K for 1.3 µm ground state emission. We also improved the performance of the slope efficiency of HEM DFB lasers by using Cl2 dry etching.

When a XeCl excimer laser beam was focused in a high-pressure gas of up to 100 atm, a hot and dense plasma was produced at the focal spot. The plasma developed not only backward but also forward. The forward plasma developed by means of a forward breakdown wave. The radius of the forward plasma becomes smaller further from the focal spot because the laser beam transmitted through the plasma was further focused by the plasma. The radiation intensity from plasma produced by an ultraviolet laser was observed using a spectrometer. The temporal spectral intensity signal had two peaks. The first peak was a signal from the plasma produced at the observed point, but the second peak was that diffused from the back. The electron temperature was measured from the ratio of the spectral intensity of Ar II lines. The electron temperature on the order of 105 K was obtained.