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We have developed a signal amplifier for the detection of weak repetitive pulsed signals superimposed on a large background. It is based on a double gated integrator principle with two channels locked to a sequence of alternate signal and background pulses. The circuit is compact and cost effective, and thus suitable for use in large numbers with detector arrays, for example in terahertz imaging. The performance was verified in terahertz time-domain spectroscopy based on an amplified femtosecond laser and found to be better than that of a commercial lock-in amplifier.

We have developed a real-time THz imaging system based on the two-dimensional (2D) electro-optic (EO) sampling technique. Employing the 2D EO-sampling technique, we can obtain THz images using a CCD camera at a video rate of up to 30 frames per second. A spatial resolution of 1.4 mm was achieved. This resolution was reasonably close to the theoretical limit determined by diffraction. We observed not only static objects but also moving ones. To acquire spectroscopic information, time-domain images were collected. By processing these images on a computer, we can obtain spectroscopic images. Spectroscopy for silicon wafers was demonstrated.

Undoped and Ga-doped (3 wt %) n-type ZnO thin films were grown by a reactive plasma deposition method on glass substrates at 200 °C under an oxygen flow rate from 0 to 50 SCCM. In this paper, we report on the defect and band edge related signals in the optical absorption spectra for ZnO thin film by using a piezoelectric photothermal (PPT) spectroscopy, which is effective in observing a nonradiative transition process. The PPT peak around 2.5 eV was observed only for the undoped ZnO samples grown under a low oxygen flow rate. This signal is considered to be related to the oxygen vacancies, because it disappears with the increase of the oxygen flow rates. No corresponding peak was found for the Ga-doped samples. This result indicates that Ga doping inhibits the generation of the oxygen vacancies, and it agrees with that from the first-principle electronic band structure calculations. We have also carried out the theoretical calculation for the optical absorption edge of degenerated ZnO as a function of the carrier concentration. Burstein-Moss effect and band-gap-narrowing effect in ZnO should be considered in the case of high carrier concentration. Comparing the experimental results with the theoretical predictions, we found out that the proposed PPT edge energy coincides well with the Fermi level EF. [ABSTRACT FROM AUTHOR]

We developed a novel dynamic light scattering system to observe elastic relaxation phenomena with hyper frequency resolution. The principle of the measurement is based on the theory, which describes the dynamic structure factor of fluid under the condition of the frequency dependent compressibility. The dynamic structure factor, which is usually composed of the Brillouin and Rayleigh triplet, is modulated and shows an additional central component that directly reflects the whole aspect of the relaxation. In the experiment, the output from a frequency-doubled cw-YAG laser was incident into the liquid sample and the power spectrum of the light scattered into the backward direction was analyzed by the optical beating spectroscopy technique. The sample is liquid acetic acid that is known to show a strong ultrasonic relaxation around 1 MHz due to the molecular association process. We could find in the observed spectrum, the central component introduced by the phenomenon, whose relaxation frequency and the strength can be obtained from the width and the intensity of the observed central peak, respectively. The results show very good agreement with those previously obtained by the conventional ultrasonic spectroscopy technique. © 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The chemical structures of SiO2/Si interfaces were studied by photoelectron spectroscopy using high-brilliance soft X-ray with photon energy ranging from 500 to 1500 eV at Super Photon ring 8 GeV(SPring-8) and it is able to probe a depth of about 1.2 to 3 nm with energy resolution of 100 meV. On the other hand, high-brilliance hard X-ray with photon energy ranging from 6 to 10 keV is able to probe a depth of about 8.5 to 12.5 nm with energy resolution of 100 meV. Hard photoelectron spectroscopy are particularly useful for studying the composition and the chemical structure of transition layer at high-k dielectric/silicon interface. [ABSTRACT FROM AUTHOR]

A new light scattering system for the ripplon spectroscopy with the time resolution better than 1 ms was developed. Remarkably improved sensitivity to detect weakly scattered light from the thermal fluctuation in the liquid surface displacement enables the digital detection and spectrum analysis of the ripplon propagation. The dynamic adsorption process of the surfactant molecules onto the surface was observed for aqueous solutions of sodium myristic-acid and the results are interpreted in terms of the physical model of diffusion controlled molecular adsorption. [ABSTRACT FROM AUTHOR]

Abstract: Undoped and Ga-doped (3wt.%) n-type ZnO thin films were grown by a reactive plasma deposition method on glass substrates at 200°C under oxygen flow rate from 0 to 50sccm. Piezoelectric photothermal spectroscopy (PPTS) was measured for characterizing the ZnO films from the viewpoint of nonradiative recombination processes. Strong peak due to the band edge transition was observed around 3.3eV in all the samples at room temperature. Furthermore, a broad band of the PPT signal at 2.5eV was observed for the undoped ZnO samples grown under low oxygen flow rate. This signal disappeared with increasing the oxygen flow rates and did not appear in the Ga-doped samples. Therefore, it is considered that this PPT signal at 2.5eV was due to the electron transition from the oxygen vacancies. [Copyright &y& Elsevier]

This paper investigates through experimental methods the dynamic characteristics of a farm tractor by changing the forward velocity from 0.63 m/s to 4.50 m/s. Nonlinear time series, frequency spectrum and continuous wavelet transform were used in the analysis. From the nonlinear time series analysis, a nonlinear resonance of the tractor vibration occurred at forward velocity of 2.15 m/s. The existence of a subharmonic frequency at 4.32 m/s indicated chaotic dynamics that was confirmed by the trend of the Lyapunov exponent analysis with a positive exponent indicating chaos. Continuous wavelet transform analysis results, presented graphically, called coefficient plots showed patterns composed of large and fine feature distribution in both time and scale. Quasi-periodic velocities of 1.95 m/s and 2.15 m/s were estimated by these coefficient plots. At forward velocity of 2.88 m/s, the coefficient plots showed dominant features that varied periodically and were estimated to be a period-doubling vibration. The coefficient plots during chaotic vibration at 3.52 m/s, 4.02 m/s and 4.32 m/s showed various feature distributions. At forward velocities of 0.95 m/s and 1.42 m/s, the existence of features with scale values of almost equal and half of the dominant feature was due to the influence of the gravel road surface and not to the artificial test track profile. Experimentally obtained bifurcation was observed clearly from the coefficient plots that showed three different patterns from quasi-periodic vibration at 2.15 m/s, period-doubling at 2.88 m/s and chaos at 3.52 m/s. [ABSTRACT FROM AUTHOR]

The deep defect levels in n-type 4H-SiC single crystals were investigated by using a photoluminescence (PL) and a piezoelectric photo thermal (PPT) spectroscopies. Three peaks at 2.10, 2.35, and 2.80 eV in the PL spectra and two peaks at 2.2 and 2.7 eV in the PPT spectra were observed. Since the PPT spectrum gives the insight from the nonradiative electron transition, the relations for these observed peaks were discussed in terms of a configuration coordinate model. [Copyright &y& Elsevier]

The deep defect levels in n-type 4H-SiC single crystal were investigated from the two physical viewpoints of nonradiative and radiative recombination by using piezoelectric photothermal and photoluminescence spectroscopy, respectively. Three peaks at 2.1, 2.4, and 2.8 eV in the PL spectra and two peaks at 2.2 and 2.7 eV in PPT spectra were observed. The origins of these peaks were explained by the electron transitions through impurity and defect levels in terms of a configuration coordinate model. [Copyright &y& Elsevier]

A system of optical beating spectroscopy has been newly developed for hyper-resolution Brillouin scattering. Frequency resolution as high as 1 kHz was obtained, far beyond the limit of the classical Fabry-Perot interferometer which is commonly used in ordinary experiments. This system is useful over the frequency range from 10[sup 4] to 10[sup 9] Hz at present. Experiments for Rayleigh and/or Brillouin spectra were performed in water, toulene, and carbon disulfide to demonstrate the performance of this system. [ABSTRACT FROM AUTHOR]

A new light scattering system was developed to investigate the propagation of liquid surface waves over a wide wave-number range 4×104–3×106 m-1 (or 10 kHz–6 MHz in frequency). Thermal fluctuation of liquid surface displacement excites a surface tension wave called a ‘‘ripplon’’ whose behavior yields information on the dynamics of the liquid surface. The transmission diffraction method and some optical and electrical improvements are successfully applied to the light scattering system and the upper limit of the frequency measured was extended about two orders higher than the conventional one. The wave-number dependence of the ripplon frequency and damping constant was measured for several kinds of liquids and the results agreed well with the classical hydrodynamic theory. [ABSTRACT FROM AUTHOR]

The energy spectrum of cosmic-ray antiprotons (¯p's) from 0.17 to 3.5 GeV has been measured using 7886 ¯p's detected by BESS-Polar II during a long-duration flight over Antarctica near solar minimum in December 2007 and January 2008. This shows good consistency with secondary ¯p calculations. Cosmologically primary ¯p's have been investigated by comparing measured and calculated p spectra. BESS-Polar II data show no evidence of primary ¯p's from the evaporation of primordial black holes. [ABSTRACT FROM AUTHOR]

Analysis of chlorpyrifos using UV was performed to assess the possibility of nondestructive detection of pesticides on agricultural products. Absorbance of chlorpyrifos dissolved in acetonitrile was positively proportional to its concentration at 229 and 290 nm at limits of detection (LOD) of 0.0233 and 0.0113 mg kg-1 and limits of quantification (LOQ) of 0.0778 and 0.0378 mg kg-1 respectively. This suggested that a UV method is suitable for detection and quantification of chlorpyrifos. UV reflectance changes were used to estimate the amount of chlorpyrifos dried on apple skin. Differences between reflectance at 280 and 300 nm were positively proportional to the amount of chlorpyrifos standard dried on apple skin, and the LOD was 0.0849 mg cm-2. Reflectance differences between 260 and 290 nm were positively proportional to the amount of chlorpyrifos included in water-dispersible Dursban dried on apple skin, and the LOD was 0.000214 mg cm-2 These LOD values were below the amount required for acute intoxication in mammals resulting from oral dosage. This UV optical method is practical for 100% nondestructive inspection and detection of chemicals present on product surfaces and thus may be suitable for use in sorting lines. However, it may not be effective for detecting chemicals in products' internal tissues as can be achieved through immunochemical techniques and gas chromatography with mass spectrometry, which, while more sensitive than this UV method, are destructive and therefore not suitable for 100% inspection of shipping products. [ABSTRACT FROM AUTHOR]

Abstract: Interatomic Coulombic decay (ICD) in Ar2, ArKr and Kr2 following Ar 2p or Kr 3d Auger decay has been investigated by means of momentum-resolved electron–ion–ion coincidence spectroscopy. This sequential decay leads to Coulombic dissociation into dication and monocation. Simultaneously determining the kinetic energy of the ICD electron and the kinetic energy release between the two atomic ions, we have been able to unambiguously identify the ICD channels. We find that, in general, spin-conserved ICD, in which the singlet (triplet) dicationic state produced via the atomic Auger decay preferentially decays to the singlet (triplet) state, transferring the energy to the other atom, is faster than spin-flip ICD, in which the Auger final singlet (triplet) dicationic state decays to the triplet (singlet) state. However, spin-flip ICD may take place when spin-conserved ICD becomes energetically forbidden. Dipole-forbidden ICDs from (B=Ar or Kr) to are also observed. [Copyright &y& Elsevier]

Abstract: The optical absorption spectra of hydrogenated microcrystalline silicon (μc-Si:H) films deposited on glass and transparent conductive oxide (TCO) covered glass substrates were measured by using the piezoelectric photothermal (PPT) technique. The effects of the deposition rate on the optical absorption of μc-Si:H thin films were investigated from the nonradiative transition point of view. It was found that increasing the deposition rate resulted in a decrease of optical absorption and a shift of effective energy gap to the higher photon energy side. These changes in the optical properties of μc-Si:H cause the decrease of the number of carriers optically generated by absorbing sunlight, and results in a reduction in the photovoltaic conversion efficiency of the solar cells for high deposition rate samples. The usefulness of the PPT method for investigating the optical properties of thin and transparent μc-Si:H films was also demonstrated. [Copyright &y& Elsevier]