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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.

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.

A low-cost laser disdrometer (LLD), which is a type of high-speed line-image scanner, has been developed and calibrated for raindrops. The disdrometer measures hydrometeor's particle-size distribution (PSD) and fall velocities, as well as record hydrometeor images. Hydrometeor imaging is advantageous for hydrometeor classification. All hydrometeor types, raindrops, graupels, snowflakes, and ice crystals, can mix with snowfall. Snowfall sensing requires a wide sensing light sheet to capture large-sized snowflakes. Accordingly, a new LLD equipped with a 35-mm sensing light sheet has been developed. This paper demonstrates and evaluates the new drisdrometer's snowfall-evaluation performance. The wide sensing light sheet captures images of large-sized (14 mm) snowflakes reasonably well, and the PSD and the fall velocities correlate with those measured with the commercially available Parsivel laser disdrometer. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

We report the effect of a poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl fluorene)] (PFN) interlayer on the performance of PTB7:PC71BM-based organic thin-film solar cells (OTFSCs) prepared using the spray-coating method. The active layer shows a broad absorption, but the effective contact area in the bulk hetrojunction (BHJ) is small because of the formation of aggregates on the surface. The surface aggregates dissolved by the addition of 1,8-diiodooctane (DIO) to the PTB7:PC71BM matrix, which results in an increase in the contact area between the donor and acceptor in the active layer and, thereby , an improvement in the device performance. The PFN interlayer enhances the charge-transport properties and suppresses exciton-recombination processes. This results in increases in the short-circuit current density (Jsc = 13.87 mA/cm2), open-circuit voltage (Voc = 0.747 V), and fill factor (FF = 57.97%), as a result of a high power conversion efficiency (PCE, η = 6.01%) compared ...

The PTB7 : PC71BM polymer based solar cells have been successfully fabricated by spin and spray coating technique using chlorine-free solvent (xylene), which are desirable to reduce environmental issues. The surface morphology of fabricated film characterized by AFM reveals that the surface morphology of the film is uniform and smooth when xylene is used as compared with chlorobenzene. The highest power conversion efficiency (PCE) (5.07 ± 0.6) was achieved using spray-coating technique than that of spin coating technique (PCE of 4.47 ± 0.6). The enhancement in the performance of the polymer solar cell could be attributed to the improved charge carrier transportation due to additive. The combination of chlorine-free solvent and spray-coating method minimize the waste material and reduce the environmental problem in large-area production of organic solar cells (OSCs).

Recently, a new low-cost disposable laser disdrometer with the capacity for hydrometeor imaging was proposed by the authors. The laser disdrometer has the drawback of detecting false raindrops, which are splashed droplets and pooled water drops on the housing. Actual raindrops can be sorted from false raindrops by their different fall speeds, but the large size and slow falling speed of false raindrops induce significant observational dead time, affecting the raindrop capture rate and the number density of the raindrops. The ratio between the actual number of raindrops and the total number of drops including the false raindrops provides a reasonable rain intensity correction. This report describes the performance of a laser disdrometer with rain intensity correction in heavy rainfall. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

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.

Organic thin film solar cells (OTFSCs) were fabricated with blended active layers of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7)/[6,6]-phenyl-C71-butyric (PC71BM). The performances of active layers are prepared in chlorobenzene (CB) with different additives of 1-chloronaphthalene (CN) and 1,8-Diiodooctane (DIO) by a wet process with spin coating technique. The effects of different solvent additives on photovoltaic parameters such as fill factor, short circuit current density, and power conversion efficiency of active layers are reported. The absorption and surface morphology of the active layers are investigated using UV-visible spectroscopy and atomic force microscopy, respectively. The results indicate that structural and morphological changes were induced by the additives with solvent. The current density-voltage (J-V) characteristics of photovoltaic cells were measured under the illumination of simulated solar light with 100 mW/cm2(AM 1.5 G) by an Oriel 1000 W solar simulator. The OTFSCs of PTB7/PC71BM prepared with organic solvent additives of DIO+CN show more improved PCE of 4.96% by spin coating method.

In this paper, signal processing using a statistical algorithm for vibration measurement is reported. The algorithm uses the statistical features of the standard deviation of sinusoidal vibration and is capable of accuracy superior to the peak-to-peak method. Additionally, the algorithm achieves accuracy as good as or better than the FFT method with less hardware. This method gave good results in simulations and actual measurement values. The method is widely applied in self-coupling effect sensors and other vibration sensors. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(3): 9–16, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11454.

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.

Precision of microwave precipitation remote sensing is ensured by studying different hydrometeor classes (raindrops, snowflakes, graupel, and so on), shapes, and drop size distribution (DSD). Recently, DSD estimates and hydrometeor classification algorithms using polarimetric radars were proposed. These algorithm developments require a validation tool providing in situ hydrometeor measurement. We are working toward the development of a low-cost, light-weight, and disposable ballooning hydrometeor imaging probe with DSD measurement capabilities. This paper describes the performance of a new line-scanning laser hydrometeor imaging probe (called PROBE) and validates the DSD using a commercially available impact-type disdrometer. PROBE captures raindrop images with 0.125 mm horizontal resolution and more than six slices at the 33-kHz slice rate, providing a reasonable raindrop diameter. DSD validation shows that PROBE acquires adequate DSD shapes during every 2-min interval. These results demonstrate PROBE's performance in hydrometeor imaging and DSD measurement capabilities in a rainfall. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

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

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 our 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. And also an output signal is needed at maximum sensitivity. This output signal is generated 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 10nm, and a small vibration is able to be measured irrespective of the frequency in the range between 500 Hz and 3000 Hz.

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.

A thermoionic energy conversion is one of the methods of direct electricity generation. The space charge effect, which limits the space emission, is relaxed by enclosing cesium in the converter. In general, the converter is operated at high emitter temperature because of the production of cesium ion by contact thermal ionization. The high operating temperature causes short emitter lifetime which becomes a problem in terms of practical use. The converter is irradiated with the resonance light so that cesium ion is produced by photoionization. It is seen that the output resulting from the resonance light irradiation is much higher than that resulting from the visible light. Many cesium ions can be produced in the space between the electrodes since most of the resonance light is absorbed by cesium atoms. The maximum value of the short circuit current density is about 1kA/m2. It is found that resonance light irradiation is one of the effective methods suitable for practical application. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(1): 14–21, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10250

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.

The organic thin film solar cells (OTFSCs) have been successfully fabricated using PCDTBT : PC71BM with different mixing ratios (1 : 1 to 1 : 8) and the influence of hole transport layer thickness (PEDOT : PSS). The active layers with different mixing ratios of PCDTBT : PC71BM have been fabricated using o-dichlorobenzene (o-DCB). The surface morphology of the active layers and PEDOT : PSS layer with different thicknesses were characterized by AFM analysis. Here, we report that the OTFSCs with high performance have been optimized with 1 : 4 ratios of PCDTBT : PC71BM. The power conversion efficiency (PCE = 5.17%) of the solar cells was significantly improved by changing thickness of PEDOT : PSS layer. The thickness of the PEDOT : PSS layer was found to be of significant importance; the thickness of the PEDOT : PSS layer at 45 nm (higher spin speed 5000 rpm) shows higher short circuit current density (Jsc) and lower series resistance (Rs) and higher PCE.

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.