Showing papers in "Japanese Journal of Applied Physics in 2007"
TL;DR: In this paper, a β-Ga2O3 thin film was grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy, which exhibited a sharp absorption edge at around 5.0 eV, which is in the deep-ultraviolet region.
Abstract: (201)-oriented β-Ga2O3 thin films were grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. In-plane X-ray diffraction measurements revealed the inclusion of α-Ga2O3 and rotational domains. However, the film grown under the optimized growth conditions exhibited a sharp absorption edge at around 5.0 eV, which is in the deep-ultraviolet region. An ohmic-type metal–semiconductor–metal photodetector showed a high resistance of around 6 GΩ with a small dark current of 1.2 nA at the 10 V bias voltage. Under 254 nm light illumination and 10 V bias voltage, the photoresponsivity was 0.037 A/W, which corresponded to a quantum efficiency of 18%.
468 citations
TL;DR: In this paper, the authors developed ultra high efficiency green organic light-emitting devices (OLEDs) using a novel electron transport material containing dipyridylphenyl moieties and green phosphorescent emitter.
Abstract: We developed ultra high efficiency green organic light-emitting devices (OLEDs) using a novel electron transport material containing dipyridylphenyl moieties and green phosphorescent emitter, fac tris(2-phenylpyridine)iridium, Ir(ppy)3. An OLED with a simple structure of glass/indium–tin oxide/polymer buffer layer/arylamine derivative as a hole transport layer/Ir(ppy)3-doped dicarbazolylbiphenyl as an emitter layer/dipyridylphenyl derivative as an electron transport layer/LiF/Al exhibited low drive voltages, which were 2.5 V at 100 cd/m2 and 2.9 V at 1000 cd/m2. High external quantum efficiencies of 29% at 100 cd/m2 and 26% at 1000 cd/m2 were also observed, which lead to the ultra high power efficiencies of 133 lm/W at 100 cd/m2 and 107 lm/W at 1000 cd/m2.
344 citations
TL;DR: In this article, high power and high efficiency nonpolar m-plane (1100) light emitting diodes (LEDs) have been fabricated on low extended defect bulk mplane GaN substrates.
Abstract: High power and high efficiency nonpolar m-plane (1100) nitride light emitting diodes (LEDs) have been fabricated on low extended defect bulk m-plane GaN substrates. The LEDs were grown by metal organic chemical vapor deposition (MOCVD) using conditions similar to that of c-plane device growth. The output power and external quantum efficiency (EQE) of the packaged 300 ×300 µm2 was 23.7 mW and 38.9%, respectively, at 20 mA. The peak wavelength was 407 nm and <1 nm redshift was observed with change in drive current from 1–20 mA. The EQE shows a minimal drop off at higher currents.
314 citations
TL;DR: The first nonpolar m-plane (1-100) nitride laser diodes have been realized on low extended defect bulk mplane GaN substrates in this article, using conditions similar to that of c-plane device growth.
Abstract: The first nonpolar m-plane (1-100) nitride laser diodes (LDs) have been realized on low extended defect bulk m-plane GaN substrates The LDs were grown by metal organic chemical vapor deposition (MOCVD) using conditions similar to that of c-plane device growth Broad area lasers were fabricated and tested under pulsed conditions Lasing was observed at duty cycles as high as 10% These laser diodes had threshold current densities (Jth) as low as 75 kA/cm2 Stimulated emission was observed at 4055 nm, with a spectral line-width of 1 nm
297 citations
TL;DR: In this article, a high Poisson's ratio σ= 0.38 was determined from the ratio of overtone frequency and resonant frequency in the planar mode, which is most likely the origin of the high d33 of the ceramics.
Abstract: Barium titanate (BaTiO3) ceramics with a density of more than 98% of the theoretical value were fabricated by two-step sintering method from hydrothermally synthesized BaTiO3 nano-particles of 100 nm. The average grain size was around 1.6 µm and the biggest one was controlled less than 3 µm. Dielectric constant er33T of the poled samples was 5000 and electromechanical coupling factor kp was 42%. Large piezoelectric constants d33 = 460 pC/N and d31 = -185 pC/N were measured by a d33-meter and the resonance–antiresonance method, respectively. A high Poisson's ratio σ= 0.38 was determined from the ratio of overtone frequency and resonant frequency in the planar mode. The high Poisson's ratio and the large dielectric constants are most likely the origin of the high d33 of the ceramics. The discovery of high d33 in non-lead-based BaTiO3 ceramics with low cost process has important practical consequences in addition to scientific interest.
290 citations
TL;DR: In this article, a continuous-wave (CW) operation of nonpolar m-plane InGaN/GaN laser diodes with the lasing wavelengths approximately 400 nm was demonstrated.
Abstract: Continuous-wave (CW) operation of nonpolar m-plane InGaN/GaN laser diodes (LDs) with the lasing wavelengths approximately 400 nm was demonstrated. The threshold current was 36 mA (4.0 kA/cm2) for the CW operation [28 mA (3.1 kA/cm2) for pulsed mode], being comparable to that of conventional c-plane violet LDs. Both the LDs with the stripes parallel to a- and c-axes showed TE mode operation, according to the polarization selection rules of the transitions in strained InGaN. The c-axis stripe LDs exhibited lower threshold current density, since the lowest energy transition is allowed. As is the case with the m-plane light emitting diodes fabricated on the free-standing m-plane GaN bulk crystals [Okamoto et al.: Jpn. J. Appl. Phys. 45 (2006) L1197], the LDs shown in this paper did not have distinct dislocations, stacking faults, or macroscopic cracks. Nonpolar m-plane GaN-based materials are coming into general use.
257 citations
TL;DR: In this paper, the authors have developed hydrogen-doped In2O3 films on glass with high mobility and high near-infrared transparency by using sputtering process performed at room temperature, followed by post-annealing treatment at 200 °C.
Abstract: We have developed hydrogen (H)-doped In2O3 films on glass with high mobility and high near-infrared transparency by using sputtering process performed at room temperature, followed by post-annealing treatment at 200 °C. To incorporate H-donor into In2O3 matrix, H2O vapor has been introduced into a chamber during the deposition. In the post-annealing of the films, phase transition from amorphous to polycrytalline was confirmed to occur. The resulting In2O3 films containing 1.9–6.3 at. % H show quite large mobility as high as 98–130 cm2/(V s) at carrier density of (1.4–1.8)×1020 cm-3. We attributed the high mobility in the film to suppression of grain boundary defects as well as multicharged and neutral impurities.
225 citations
TL;DR: In this article, a parametric study of super growth of single-walled carbon nanotubes (SWNTs) was done by using combinatorial libraries of iron/aluminum oxide catalysts.
Abstract: A parametric study of so-called "super growth" of single-walled carbon nanotubes (SWNTs) was done by using combinatorial libraries of iron/aluminum oxide catalysts. Millimeter-thick forests of nanotubes grew within 10 min, and those grown by using catalysts with a thin Fe layer (about 0.5 nm) were SWNTs. Although nanotube forests grew under a wide range of reaction conditions such as gas composition and temperature, the window for SWNT was narrow. Fe catalysts rapidly grew nanotubes only when supported on aluminum oxide. Aluminum oxide, which is a well-known catalyst in hydrocarbon reforming, plays an essential role in enhancing the nanotube growth rates.
209 citations
TL;DR: In this paper, an improved nonpolar m-plane (1100) light emitting diode (LED) with a thick InGaN active layer of 8 nm and a thick GaN barrier layer of 37.5 nm for multi-quantum-well (MQW) structure have been fabricated on low extended defect bulk mplane GaN substrates using metal organic chemical vapor deposition (MOCVD).
Abstract: Improved nonpolar m-plane (1100) light emitting diode (LED) with a thick InGaN active layer of 8 nm and a thick GaN barrier layer of 37.5 nm for multi-quantum-well (MQW) structure have been fabricated on low extended defect bulk m-plane GaN substrates using metal organic chemical vapor deposition (MOCVD). The peak wavelength of the electroluminescence (EL) emission from the packaged LED was 468 nm. The output power and external quantum efficiency (EQE) were 8.9 mW and 16.8%, respectively, at a DC driving current of 20 mA.
207 citations
TL;DR: A thin-film solar cell based on a Cu2ZnSnS4 (CZTS) absorber layer deposited by pulsed laser deposition has been fabricated with an Al:ZnO (n-type) window layer and a CdS buffer layer.
Abstract: A thin-film solar cell based on a Cu2ZnSnS4 (CZTS) absorber layer deposited by pulsed laser deposition has been fabricated with an Al:ZnO (n-type) window layer and a CdS buffer layer. Some peaks attributed to (112), (200), (220), and (312) planes of CZTS appeared in an X-ray diffraction pattern of a thin film. The composition of the film was Sn-rich and the band gap energy was approximately 1.5 eV. A CZTS film annealed at 500 °C in an atmosphere of N2 had optical characteristics suitable for use in an absorber layer of a thin-film solar cell and was used for a solar cell. The CZTS thin-film solar cell with an active area of 0.092 cm2 showed an open-circuit voltage of 546 mV, a short-circuit current of 6.78 mA/cm2, a fill factor of 0.48, and a conversion efficiency of 1.74%.
180 citations
TL;DR: In this article, the output power and external quantum efficiency at a driving current of 20 mA were 20.58 mW and 33.91% respectively, with peak electroluminescence emission wavelength at 411 nm.
Abstract: We report the fabrication of violet InGaN/GaN light-emitting diodes (LEDs) on semipolar (1011) GaN bulk substrates. The LEDs have a dimension of 300 ×300 µm2 and are packaged in an epoxy resin. The output power and external quantum efficiency (EQE) at a driving current of 20 mA were 20.58 mW and 33.91% respectively, with peak electroluminescence (EL) emission wavelength at 411 nm. The LEDs show minimal shift in peak EL wavelength with increasing drive current along with a high EQE.
TL;DR: In this article, the authors demonstrate spin injection into a graphene thin film with high reliability by using non-local magnetoresistance (MR) measurements, in which the electric current path is completely separated from the spin current path.
Abstract: We demonstrate spin injection into a graphene thin film with high reliability by using non-local magnetoresistance (MR) measurements, in which the electric current path is completely separated from the spin current path. Using these non-local measurements, an obvious MR effect was observed at room temperature; the MR effect was ascribed to magnetization reversal of ferromagnetic electrodes. This result is a direct demonstration of spin injection into a graphene thin film. Furthermore, this is the first report of spin injection into molecules at room temperature.
TL;DR: In this paper, [110]-oriented barium titanate (BaTiO3) ceramics were prepared by templated grain growth (TGG) method using [110-oriented BaTiOO3 plate-like particles as a template and hydrothermal BaTaO3 sphere particles with different particle sizes as a matrix, and the degree of orientation along the [110] direction was measured using an X-ray diffraction (XRD) pattern by the Lotgering method.
Abstract: [110]-oriented barium titanate (BaTiO3) ceramics were prepared by templated grain growth (TGG) method using [110]-oriented BaTiO3 platelike particles as a template and hydrothermal BaTiO3 sphere particles with different particle sizes as a matrix. The degree of orientation along the [110] direction, F110, was measured using an X-ray diffraction (XRD) pattern by the Lotgering method. To obtain both a high density and a high F110, the preparation conditions were optimized as functions of matrix particle size, volume fraction of the template to the matrix, and sintering temperature. As for the results, BaTiO3-grain-oriented ceramics with a high density of more than 96% were successfully prepared despite various F110 values from 0 to 98%. Scanning electron microscopy (SEM) revealed that their average grain sizes were always approximately 75 µm despite various F110 values and there were no anisotropic microstructures. These grain-oriented BaTiO3 ceramics were poled at 100 °C, and their piezoelectric properties were measured using a resonance–antiresonance method and a piezo d33 meter for d31 and d33 piezoelectric constants. As for the results, the d31 values were almost constant at -50 pC/N despite various F110 values, while the d33 values increased with increasing F110 values, and at around an F110 of 85%, d33 reached a maximum of 788 pC/N.
TL;DR: In this paper, a nonstoichiometric hafnium oxide (HfOx) resistive-switching memory with low power operation has been demonstrated, where polycrystalline HfOx (O:Hf=1.5:1) films with a thickness of 20 nm are grown on a titanium nitride (TiN) bottom electrode by commercial atomic layer deposition.
Abstract: Nonstoichiometric hafnium oxide (HfOx) resistive-switching memory devices with low-power operation have been demonstrated. Polycrystalline HfOx (O:Hf=1.5:1) films with a thickness of 20 nm are grown on a titanium nitride (TiN) bottom electrode by commercial atomic layer deposition. Platinum (Pt) as a top electrode is used in the memory device. Voltage-induced resistance switching is repeatedly observed in the Pt/HfOx/TiN/Si memory device with resistance ratio is greater than 10. During the switching cycles, the power consumptions for high- and low-resistance states are found to be 0.25 and 0.15 mW, respectively. At 85 °C, the memory device shows stable resistance switching and superior data retention with resistance ratio is greater than 100. In addition, our memory device shows little area dependence of resistance-switching behavior. The anodic electrode containing noble metal Pt serves an important role in maintaining stable resistance switching. The resistance switching in the HfOx films is thought to be due to the defects that are generated by the applied bias. The nonstoichiometric HfOx films are responsible for the low SET and RESET currents during switching. Our study shows that the HfOx resistive-switching memory is a promising candidate for next-generation nonvolatile memory device applications.
TL;DR: In this article, a vertical insulated gate AlGaN/GaN heterojunction field effect transistor (HFET) was fabricated using a free-standing GaN substrate, which exhibited a specific on-resistance of as low as 2.6 mΩ·cm2 with a threshold voltage of -16 V.
Abstract: We fabricated a vertical insulated gate AlGaN/GaN heterojunction field-effect transistor (HFET), using a free-standing GaN substrate. This HFET has apertures through which the electron current vertically flows. These apertures were formed by dry etching the p-GaN layer below the gate electrodes and regrowing n--GaN layer without mask. The HFET exhibited a specific on-resistance of as low as 2.6 mΩ·cm2 with a threshold voltage of -16 V. This HFET would be a prototype of a GaN-based high-power switching device.
TL;DR: Two-step sintering was applied to manufacture fine-grain barium titanate (BaTiO3) piezoelectric ceramics from hydrothermally synthesized 100 nm particles as discussed by the authors.
Abstract: Two-step sintering was applied to manufacture fine-grain barium titanate (BaTiO3) piezoelectric ceramics from hydrothermally synthesized 100 nm particles Scanning electron microscopy (SEM) revealed a small and irregular domain structure in the samples The sintering condition dependences of density, dielectric constants, and piezoelectric properties were investigated Under the optimal conditions, dense specimens had an average grain size of approximately 16 µm, and showed large dielectric constants and excellent piezoelectric properties The large piezoelectric constant of d33=460 pC/N was measured using a d33 meter The Curie and orthorhombic-to-tetragonal phase transition temperatures were 126 and 24 °C, respectively These results indicated the possibility of applying non-lead-based BaTiO3 ceramics manufactured by a low-cost process to ultrasonic generators, actuators, piezoelectric vibrators, and sensors working at room temperature
TL;DR: In this article, a blue laser diodes based on m-plane gallium nitride (GaN) was demonstrated by using mplane GaN substrates and the lasing wavelength and the threshold current under pulsed operation were 4518 nm and 134 mA (223 kA/cm2), respectively.
Abstract: Blue laser diodes (LDs) based on m-plane gallium nitride were demonstrated by using m-plane GaN substrates The lasing wavelength and the threshold current under pulsed operation were 4518 nm and 134 mA (223 kA/cm2), respectively The device structures consisted of InGaN-based multi-quantum wells, InGaN guiding layers, and Al-containing cladding layers The InGaN guiding layers play two roles; as appropriate optical waveguides for longer lasing wavelengths and for the prevention of macroscopic cracks parallel to the c-plane The latter is an indispensable technology in order to fabricate nonpolar LDs for longer wavelengths beyond the blue region
TL;DR: In this paper, the solidification pressure of Daphne 7373 was examined at room temperature and it was shown that it can hold hydrostatic pressure even in the newly developed BeCu-NiCrAl clamp-type pressure cell, which exceeds the limit of 1.5 GPa generated by a conventional BeCu cell.
Abstract: The solidification pressure of Daphne 7373, which is widely used as a pressure medium in high pressure studies, was examined at room temperature. Using a new generation clamp-type pressure cell, we found that Daphne 7373 solidifies at 2.2 GPa at room temperature. This is exactly on the natural extrapolation of the melting curve obtained at lower pressures and temperatures in our previous report. The solidification pressure of Daphne 7373 is twice as high as that of another well-known medium Fluorinert 77/70 (0.9 GPa). This allows us to hold hydrostatic pressure even in the newly developed BeCu–NiCrAl clamp-type pressure cell, which exceeds the limit of 1.5 GPa generated by a conventional BeCu cell.
TL;DR: In this paper, a blue organic light-emitting devices (OLEDs) were constructed by using a phosphorescent emitter, iridium(III) bis[(4,6-di-fluorophenyl)-pyridinate-N,C2']picolinate and high triplet energy materials as the host and the carrier transport materials.
Abstract: We succeeded to fabricate highly efficient blue organic light-emitting devices (OLEDs) by using a phosphorescent emitter, iridium(III) bis[(4,6-di-fluorophenyl)-pyridinate-N,C2']picolinate, and high triplet energy materials as the host and the carrier transport materials. A high power efficiency of 39 lm/W and external quantum efficiency of 21% were obtained at 100 cd/m2.
TL;DR: In this paper, the first semipolar nitride laser diodes have been realized on low extended defect density semipolar (1011) GaN bulk substrates by conventional metal organic chemical vapor deposition (MOCVD).
Abstract: The first semipolar nitride laser diodes (LDs) have been realized on low extended defect density semipolar (1011) GaN bulk substrates. The LDs were grown by conventional metal organic chemical vapor deposition (MOCVD). Broad area lasers were fabricated and tested under pulsed conditions. Lasing was observed at a duty cycle of 0.025% with a threshold current density (Jth) of 18 kA/cm2. Stimulated emission was observed at 405.9 nm with a full width at half maximum (FWHM) of less than 0.3 nm.
TL;DR: In this article, the authors reported the reduction of threshold voltage, Vth, of twisted nematic liquid crystal devices by doping the nanoparticles of MgO and SiO2, where both of these quantities decrease due to the existence of these nanoparticles.
Abstract: We report the reduction of threshold voltage, Vth, of twisted nematic liquid crystal devices by doping the nanoparticles of MgO and SiO2. The results are well explained by inserting the experimentally determined values of elastic constants and dielectric anisotropy in the formula Vth = π√Keff/e0Δe, where both of these quantities decrease due to the existence of these nanoparticles. The Vth decrease approximately as √S, where S being the order parameter. The S is also shown to decrease by doping nanoparticles.
TL;DR: In this paper, three types of high luminous efficiency white light emitting diodes (LEDs) were fabricated from the high power blue LED with high output power (e) of 42.2 mW and a high external quantum efficiency (ηex) of 75.5%.
Abstract: We fabricated three types of high luminous efficiency white light emitting diodes (LEDs). The first is the white LED, which had a high luminous efficiency (ηL) of 161 lm/W with the high luminous flux (v) of 9.89 lm at a forward-bias current of 20 mA. The blue LED had a high output power (e) of 42.2 mW and a high external quantum efficiency (ηex) of 75.5%. The second is the high luminous efficiency white LED with a low forward-bias voltage (Vf) of 2.80 V, which was almost equal to the theoretical limit. ηL and wall-plug efficiency (WPE) were 169 lm/W and 50.8%, respectively, at 20 mA. They were approximately twice higher than those of a tri-phosphor fluorescent lamp (90 lm/W and 25%). The third is the high power white LED fabricated from the high power blue LED with high e of 651 mW at 350 mA. v, ηL, and WPE of the high power white LED were 145 lm, 134 lm/W, and 39.6% at 350 mA, respectively.
TL;DR: In this paper, a green phosphorescent organic light-emitting devices (OLEDs) with high quantum and luminous efficiencies were developed, which exhibited an external quantum efficiency (EQE) of 27% (95 cd/A) and high power efficiency of 97 lm/W at 100 cd/m2 at 3.1 V.
Abstract: We have developed green phosphorescent organic light-emitting devices (OLEDs) with high quantum and luminous efficiencies. A green phosphorescent metal complex, fac-tris(2-phenylpyridine) iridium [Ir(ppy)3], was used as an emitter material. Wide-energy-gap materials with high triplet excited energy levels were used as host materials for Ir(ppy)3 and as carrier transport materials. Hole injection and electron injection from the electrodes were balanced by placing chemically doped layers at the interface between the electrodes and the organic layers. In addition, a highly reflective Ag cathode was employed as an anode, instead of a conventional Al cathode to enhance the reflectivity of the cathode metal. An optimized device exhibited an external quantum efficiency (EQE) of 27% (95 cd/A) and a high power efficiency of 97 lm/W at 100 cd/m2 at 3.1 V.
TL;DR: In this article, a lead-free piezoelectric K0.5NbO3 (KNN) single-phase thin film with good leakage current properties was successfully prepared by optimizing the KxNaxNbOn3 (x0.55Nb On3) composition of the precursor solution.
Abstract: Lead-free piezoelectric K0.5Na0.5NbO3 thin films for microelectromechanical systems were fabricated via chemical solution process using metal alkoxide. Perovskite K0.5Na0.5NbO3 (KNN) single-phase thin films with good leakage current properties were successfully prepared by optimizing the KxNaxNbO3 (x0.5) composition of the precursor solution. The KNN thin films prepared from the solution with K0.55Na0.55NbO3 composition showed typical ferroelectric P–E hysteresis and field-induced strain loops. The 2Pr and 2Ec values of the K0.55Na0.55NbO3 films were 14 µC/cm2 and 140 kV/cm, respectively. From the slope of the field-induced butterfly loop, the effective d33 was found to be 46 pm/V.
TL;DR: In this paper, electron and hole injection processes in a forward biased p-n junction electrically induced in a graphene heterostructure with split gates were studied under the conditions of population inversion.
Abstract: We study electron and hole injection processes in a forward biased p–n junction electrically induced in a graphene heterostructure with split gates and calculate the ac conductivity associated with the interband and intraband transitions under the conditions of population inversion. It is shown that the net conductivity can be negative in the terahertz range of frequencies, so that the electrically induced p–n junctions in graphene heterostuctures might be used in sources of coherent terahertz radiation.
TL;DR: In this article, the flat band voltage in metal/HfLaOx/SiO2/Si capacitors has been investigated as a function of La concentration in HfLa Ox.
Abstract: The flat band voltage in metal/HfLaOx/SiO2/Si capacitors has been investigated as a function of La concentration in HfLaOx. We have found that with an increase of La concentration, the flat band voltage shifts to the negative direction. Furthermore, we demonstrate that the flat band voltage in this system is determined by the La concentration at HfLaOx/SiO2 interface. This result suggests that the flat band voltage shift is due to the dipole layer formed at the HfLaOx/SiO2 interface rather than the Fermi-level pinning at the metal/HfLaOx interface.
TL;DR: In this paper, the authors studied the effect of bubble defects on the removal of the bubble defects using pentafluoropropane, which has a vapor pressure of 0.15 MPa at 25 °C.
Abstract: We studied UV nanoimprint in air and the elimination of bubble defects using pentafluoropropane, which has a vapor pressure of 0.15 MPa at 25 °C. Bubble defects are unavoidable when UV nanoimprint is carried out in air. Pillars fabricated in thin resin film by UV nanoimprint in air contain bubble defects since bubbles are not eliminated by resin squeezing and only a small amount of air is dissolved in the resin. By introducing pentafluoropropane under such experimental condition, bubble elimination by gas condensation was separately investigated. The bubble elimination phenomenon is completed within a few seconds under an imprint pressure of 0.5 MPa in a sufficiently high concentration of pentafluoropropane. No bubble defects are generated in the entire imprint area of 10×10 mm2 with an imprint pressure of 0.5 MPa at a hold time longer then 20 s and a pentafluoropropane flow higher than 150 sccm.
TL;DR: In this paper, continuous-wave (CW) operation of nonpolar m-plane InGaN/GaN laser diodes without Al-containing waveguide cladding layers was demonstrated, achieving peak output powers of more than 25 mW with threshold current densities and voltages of 6.8 kA/cm2 and 5.6 V, respectively.
Abstract: We demonstrate continuous-wave (CW) operation of nonpolar m-plane InGaN/GaN laser diodes without Al-containing waveguide cladding layers. Thick InGaN quantum wells (QWs) are used to generate effective transverse optical mode confinement, eliminating the need for Al-containing waveguide cladding layers. Peak output powers of more than 25 mW are demonstrated with threshold current densities and voltages of 6.8 kA/cm2 and 5.6 V, respectively. The unpackaged and uncoated laser diodes operated under CW conditions for more than 15 h.
TL;DR: In this paper, a dual-wavelength optical parametric oscillator (OPO) with two KTP crystals pumped by a frequency-doubled Nd:YAG laser was constructed and the OPO is tunable at 1300-1900 nm, giving an ultra-broad tunable range of the THz wave.
Abstract: Random frequency accessible, ultra-broad-band (1.5–37 THz) THz-wave generation was demonstrated using difference frequency generation (DFG) in an organic 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal. Such DAST crystals are promising materials for efficient and high-power THz-wave generation because of their very high nonlinearity and low refractive index dispersion between the near-infrared region and the THz-wave region. We can use the highest nonlinear component of DAST, d11 (about 230 pm/V), to generate THz waves using DFG because the collinear phase-matching condition of the Type 0 configuration is satisfied. We constructed a dual-wavelength optical parametric oscillator (OPO) with two KTP crystals pumped by a frequency-doubled Nd:YAG laser. Each KTP crystal was set on a galvano scanner. The angle of each crystal was controlled independently. The OPO is tunable at 1300–1900 nm, giving an ultra-broad tunable range of the THz wave. We generated an ultra-broad tunable THz wave using only one DAST crystal without any change of the experimental setup aside from the computer-controlled galvano-scanner angle change. The highest THz-wave energy of 10 nJ was obtained at around the 26 THz region under 2 mJ of pumping energy. Also, the THz-wave source can access a desired THz frequency at every pulse (50 Hz at present). The galvano scanner has 1 kHz of response, with 1-ms frequency access speed.
TL;DR: In this article, the optical constants of vanadium dioxide (VO2) films were determined at visible and near-infrared wavelengths at various temperatures during a semiconductive-metallic phase transition by ellipsometric analysis with Lorentz-oscillator formulae.
Abstract: The optical constants of vanadium dioxide (VO2) films were determined at visible and near-infrared wavelengths at various temperatures during a semiconductive–metallic phase transition by ellipsometric analysis with Lorentz-oscillator formulae. The reversible changes in optical constants against temperature due to thermochromism were observed at around 70 °C. The wavelength dispersions of the optical constants were well expressed by the sum of three oscillators and their oscillating energies were attributed to photon-excited transitions. The variation in band structure during the phase transition was monitored, and the relationship between the band structure and optical properties was discussed.