Short Wavelength Side Research Articles

感温液晶による温度測定に関する研究

We describe the investigation of the optical characteristics of four thermosensitive liquid crystals. Spectral characteristics are measured using a spectrometer, and their optical properties are evaluated using a CIE 1931 standard calorimetric system, XYZ. The peak position of the spectrum moves from the long-wavelength side to the short-wavelength side with temperature increase. The wavelength of maximum intensity does not show hysteresis for the temperature increase and decrease. The wavelength of maximum intensity and the hue value are well correlated with temperature. The spectrum distribution moves to the short-wavelength side with increase of the measuring angle. The wave change is not dependent on temperature.

Persistent Spectral Holeburning of Frenkel Exciton System with Large Coherence Length: PIC(Br) J-Aggregates

Abstract We found unique burning power dependence in the hole formation of linear Frenkel exciton system, J-aggregates of pseudo-isocyanine bromide, in water-ethylene glycol glasses at 4.7 K. With DC-laser light for burning, clear zero-phonon hole was formed with the width of 0.36 cm−1. Once switching the laser for burning to the pulse mode operation, on the other hand, nano-second pulses e.g. can give rise to novel feature of dispersive lineshape of spectral change from the initial stage of burning: a broad and red-shifted (∼3 cm−1 from the laser frequency ωB) non-resonant hole accompanied by antihole with similar size at shorter wavelength side. We consider the appearance of red-shifted nonresonant hole is essential in the present situation and is due to the two-exciton excitation through one-exciton transition by two-photon absorption. Based on this model, the shift of the hole is equal to half of the difference of k = 2 and k = 1 exciton energy, from which we can estimate the coherence length of N = 5...

Sol-gel synthesis of Pr-doped silica glasses

Pr-doped silica gels with Pr-content up to 10 wt.% have been prepared using a colloidal—polymeric as well as polymeric sol-gel method. The gels densified at 1150°C show absorption and fluorescence spectra similar to that of melt or CVD prepared Pr-doped silica glasses. Structural properties of the densified gels have also been studied. Al co-doping increases the fluorescence intensitiy of Pr 3+ ions and shifts the maxima to the shorter wavelength side.

Coupling characteristics of photo-induced Bragg gratings in depressed- and matched-cladding fibre

Experimental transmission spectra of ultraviolet (u.v.)-written Bragg gratings in depressed- and matched-cladding fibre are characterized and compared. In particular, we discuss how the location and strength of the spectral features vary with the degree of blazing, or angular tilt of the grating. The fine-structure detail on the short-wavelength side of the fundamental Bragg line is attributed to power coupling between the forwardpropagating fundamental (LP01) mode and discrete, backward-propagating cladding modes. Resonances corresponding to backward-propagating LP0n and LP1n modes are identified, and their relative strengths are compared with theoretical overlap calculations. Physical arguments are presented that explain the pronounced ‘ghost’-grating notch that appears in the transmission spectra of blazed, fibre Bragg gratings in depressed-cladding fibre.

QUANTUM WELL LASERS AND THEIR APPLICATIONS

Quantum well lasers have attracted a great deal of attention by their many advantages such as low threshold current density, excellent temperature feature, high modulation rate and wavelength adjustability etc. The investigation on quantum well laser in mainland China started in the early 80s. AlGaAs/GaAs QW laser diode and InGaAs/GaAs strained layer QW laser diode have been developed using MBE technology with extremely low threshold current and high T0. Now the growth technologies for QW structure have been expanded to MOCVD technology. Emission wavelengths, on longer wavelength sides have been expanded up to 1.3 µm and 1.55 µm with InGaAsP/InP material system for application in optical fiber communication. On shorter wavelength sides, the emission wavelength has been expanded to lower than 670 nm, for applications in optical information processing. The characteristics of these devices will be demonstrated in this paper. The QW-DFB LD and low-dimension quantum wire and quantum dot lasers are under investigation.

Photoisomerization dynamics of DODCI studied by spectrally resolved fluorescence decay measurements

Abstract The organic dye DODCI (3,3′-diethyloxadicarbocyanine iodide) in methanol and ethylene glycol is excited with picosecond light pulses at 527 nm (dominant N-isomer excitation) and the time dependence of the N-isomer and P-isomer fluorescence is monitored with a spectrometer-streak camera system. The slowed-down non-exponential N-isomer fluorescence and the time-delayed P-isomer fluorescence indicate S1-state photoisomerization via an intermediate state (M). The energetic position of this intermediate state is determined. The formation of a further photoisomer (P2-isomer) emitting at the short wavelength side of the N-isomer is observed. Additionally the molecular reorientation is analysed by time-dependent fluorescence anisotropy measurements.

Influence of resonant absorption on the propagation of femtosecond pulses in an Er-doped optical fibre

By making numerical simulations the influence of resonant absorption in Er-doped fibres on the propagation characteristics of femtosecond pulses has been examined. It is shown that when the fibre background dispersion is relatively small compared to the dispersion caused by absorption, the pulses propagating in an unpumped Er-doped fibre can be either compressed or broadened, depending on whether the spectrum of the launched pulse is on the longer or shorter wavelength side of the absorption center. The phase distortion due to absorption has a more severe impact on the temporal profile of a propagating pulse than the corresponding amplitude attenuation. A switching of the sign of the actual fibre dispersion on one side of the absorption center occurs and this can lead to a change of pulse propagation characteristics from a soliton regime to a non-solitonic regime.

Strongly directed single mode emission from organic electroluminescent diode with a microcavity

The strongly directed spontaneous emission along the optical axis of an organic electroluminescent (EL) diode with a typical emitting material, tris(8-quinolinolato) aluminum, is realized with a planner microcavity structure. The structure of the microcavity EL diode is designed to have a resonance condition in which the total optical length is 3/2λ and the resonance wavelength λ is located at shorter wavelength side of a natural emission spectrum of a noncavity EL diode.

Instabilities and nonlinear L-I characteristics in complex-coupled DFB lasers with antiphase gain and index gratings

Complex-coupled DFB lasers can be designed to provide large bandwidths and low chirp by adjusting the strength and phase of their index and gain gratings. In this paper we develop a self-consistent method of calculating the coupling coefficient of complex-coupled DFB lasers with a corrugated active region. Basic geometrical and structural parameters are used as inputs to the model. We show that antiphase coupling implies lasing on the short-wavelength side of the Bragg wavelength which in turn leads to instabilities and/or nonlinearities in the light-current characteristic. The critical output power for onset of instabilities is typically in the order of a few milliwatts. Time-domain simulations are used to assess the potential effects of these instabilities on optical communication systems. We find that transitions from a state of equal output powers from the facets to a state of dramatically different output powers occur within a few nanoseconds of turn-on. The origin of these instabilities is explained using a simple physical model and possible ways of increasing the critical power for instabilities are discussed. For example, we clearly show that the critical power for instability increases when the carrier lifetime is decreased.

Temperature dependent ultraviolet absorption cross sections of propylene, methylacetylene and vinylacetylene

Abstract The temperature dependence of the UV absorption cross sections of propylene (CH3CHCH2) and methylacetylene (CH3CCH) from 160 to 200 nm and vinylacetylene (CH2CHCCH) from 160 to 240 nm have been measured in the gas phase, for temperatures ranging from about 220 to 330 K. The propylene spectrum, exhibits a broad absorption band with a maximum at 172.0 nm with some structure to the short wavelength side of the broad band. At the absorption peaks a small increase (about 5%) in the cross sections has been observed with decreasing temperature from 333 to 233 K. At the long wavelength tail of the absorption band the cross sections are found to decrease with decreasing temperature. The absorption spectrum of methylacetylene in the region of 160 to 200 nm consists of a broad continuum with a maximum at 172.4 nm. The cross section values, for methylacetylene, near the absorption peak are found to remain nearly independent of temperature. However, at the long wavelength side of the absorption band the cross sections increase with increasing temperature. The spectrum of vinylacetylene consists of a very strong and structured absorption in the 160 to 170 nm region and strong diffuse bands between around 190 and 230 nm. The cross section values at the absorption peaks, determined at low temperatures, are significantly higher than those at higher temperatures. A sharp absorption feature at 168.2 nm shows the most pronounced temperature effect, with an increase in cross section from 35.86 × 10−18 to 63.54 × 10−18 cm2 for a temperature change of 333 to 223 K.

X-RAY SPECTROSCOPIC ANALYSIS OF BORON-NITRIDE CLUSTERS DEPOSITED BY ION-PLATING METHOD

Cubic boron-nitride (c-BN) films were deposited on a silicon substrate by varying the deposition time, using a reactive ion-plating method. In order to investigate the growth mechanism of c-BN films, these c-BN films were characterized by x-ray emission spectra of boron (B K x-ray emission spectra), infrared absorption spectra, selected area diffraction patterns, and TEM microstructures. It was found that the BN film with sp2 bonding formed initially on the substrate and subsequently c-BN film formed. The c-BN film was composed of fine crystallites with a size of about 10 nm and with random orientation. In the case of the B K x-ray emission spectrum from the BN film with sp 2 bonding, the intensity of the satellite peak at the short-wavelength side was extremely stronger than that of sp 2-bonded BN-like turbostratic or hexagonal BN. As a result of calculation of the B K x-ray emission spectrum of BN using the discrete variational Hartree-Fock-Slater (DV-Xα) method, it was found that the satellite peak intensity increased with formation of the fine BN cluster having two-coordinated boron (which has a dangling bond) and with decreasing size of the cluster. Therefore, it is considered that the BN film with sp 2 bonding was composed of the very fine BN cluster having two-coordinated borons, and became the precursor of c-BN film at the interface between the substrate and c-BN film.

Asymmetrical Longitudinal Mode Spectrum of Fabry-Perot Semiconductor Lasers

Quantitative analysis has been given to account some asymmetric features observed on the mode spectrum of the F-P semiconductor lasers detected at the end facets of the diodes. Using ray trace method, the spontaneous emission spectrum generated by the illuminating centers inside the diode has been extracted from the mode spectrum obtained at the end facet. After the wavelength difference between the peaks of the gain and spontaneous emission has been experimentally determined, the output powers P p and P v at the resonant and antiresonant wavelengths of the mode and the asymmetric distribution of the modulation index on the output spectrum have been studied. Employing the implicit analytical solutions to the multimode rate equations, the variation of the mode intensity with wavelength has been simulated. The theory predicts that the mode intensity is larger at the shorter wavelength side than that at the longer wavelength side, and the experiments have quantitatively confirmed this conclusion.

MAD Phasing Strategies Explored with a Brominated Oligonucleotide Crystal at 1.65Å Resolution

The crystal structure of a brominated oligonucleotide d(CGCG(Br)CG), chemical formula C(114)N(48)O(68)P(10)Br(2), has been analysed by multiwavelength anomalous dispersion (MAD) methods. The oligonucleotide crystallizes in space group P2(1)2(1)2(1) with a = 17.97, b = 30.98, c = 44.85 A, alpha = beta = gamma 90 degrees . Data to a resolution of 1.65 A were collected at four wavelengths about the K-absorption edge of the bromine atom (lambda(1) = 0.9323 A, a reference wavelength at the long-wavelength side of the edge; lambda(2) = 0.9192 A, at the absorption-edge inflection point; lambda(3) = 0.9185 A, at the ;white line' absorption maximum; lambda(4) = 0.8983 A, a reference wavelength at the short-wavelength side) using synchrotron radiation at Station PX9.5, SRS, Daresbury. Multiwavelength data could be collected on a single-crystal as the sample was radiation stable. Anomalous and dispersive Patterson maps were readily interpretable to give the bromine anomalous scatterer positions. Phase calculations to 1.65 A, resolution, using all four wavelengths, gave a figure of merit of 0.825 for 2454 reflections. The electron-density map was readily interpretable showing excellent connectivity for the sugar/phosphate backbone and each base was easily characterized. The two nucleotide strands paired up as expected in an antiparallel Watson-Crick-type manner. The structure was refined to 1.65 A using all the data (R-factor = 17.0% based on 3151 reflections, with a data-to-parameter ratio of 2.6). In addition to the four-wavelength analysis, a variety of other phasing strategies, and the associated quality of the resulting electron-density maps, were compared. These included use of either of the reference wavelength data sets in the two possible three-wavelength phasing combinations to assess their relative effectiveness. Moreover, the time dependence upon measuring the Bijvoet differences and its effect upon phasing was also investigated. Finally, the use of only two wavelengths, including Friedel pairs, is demonstrated (the theoretical minimum case); this is of particular interest when considering overall beam time needs and is clearly a feasible experimental strategy, as shown here.

Effect of pseudo-phonon side hole in laser-induced hole filling

Abstract Multiple hole-burning processes have been studied in a photon-gated donor-acceptor electron-transfer system. Zinc-tetraphenylbenzoporphyrin (Zn-TPBP_ and zinc-tetraphenyl(4-phenyl-acetylamino)benzotribenzoporphyrin (Zn-TPBTP) were used together as the electron donors, while phydroxybenzaldhyde (PHBA) was the electron acceptor, and they are doped in the matrix poly(methyl)methacrylate (PMMA). It is more effective to form multiple holes from the shorter wavelength side to the longer side in such a system than the other way round. This wavelength-dependent phenomenon of laser-induced hole filling is mainly due to the effect of the pseudo-phonon side band, which leads to a smaller absorption loss at the zero-phonon holes previously burned, but to a larger absorption loss in the region that was not previously burned. Then, the previously burned holes, especially those holes located at the longer wavelength side of the new burning hole, seem to be filled. A theoretical simulation based on this assumption shows fairly good agreement with the experimental results.

The observation of photoproducts and multiple photon-gated spectral hole burning in a donor-acceptor and a donor 1 + donor 2-acceptor system

Multiple photon-gated spectral hole burning and photoproducts were observed in two systems: zinc-tetrabenzoporphyrin/crotonic acid/phenoxy resin film and zinc-tetraphenyl-benzoporphyrin+zinc-tetraphenyl(4-phenyl-acetylamino)benzotribenzoporphyrin/phydroxybenzaldehyde/poly(methyl)metacrylate film. The hole burning sequence, whether burned successively from the shorter wavelength side to the longer side or the opposite, and the selection of suitable intensities of burning and gating laser were proved to be important in high quality multiple hole formation. Their photoproducts after hole burning are cation radicals of their corresponding electron donors. The photon-gated spectral hole burning processes are determined to be donor-acceptor electron-transfer reactions.

Characteristics of MgO-doped LiNbO 3 crystals

Congruent MgO:LiNbO 3 (MLN) single crystals doped with 0, 2.5, 5.0, 7.5 and 10.0 mol% of MgO contents were grown by the Czochralski method. The grown crystals were water clear without any precipitation. The density and Curie temperature ( T C ) for MLN crystals were measured. The Curie temperature increased first with the MgO concentration and decreased again when the concentration of MgO went beyond the threshold limit ([Mg] C, 5.0–7.5 mol%). We also measured optical absorption edge and IR absorption spectra at room temperature for MLN crystals. The threshold concentration of nearly 6.0 mol% was estimated. The IR absorption peak appeared at 3470 cm −1 in 0–5.0 mol% and at 3534 cm −1 in 7.5–10.0 mol%; the peak shifted about 60 cm −1 toward the shorter wavelength side.

Simultaneous and consecutive two-photon excited fluorescence detection in conventional-size liquid chromatography

The applicability of two-photon excitation (TPE) for fluorescence detection in flow dynamic systems was explored. Emphasis was on conventional-size liquid chromatography (LC) and a direct comparison was made with one-photon excitation (OPE) by the use of standard laser- and lamp excitation. Simultaneous two-photon excitation (STPE) with visible laser light was used for fluorescence detection of UV-absorbing analytes; in consecutive two-photon excitation (CTPE) fluorescence from higher excited states was detected. In both TPE modes fluorescence is measured at the short-wavelength side of the laser light, a spectral region with relatively low background signals. STPE fluorescence will only have potential if the background measured in real samples is sufficiently low; this was investigated for the LC analysis of urine spiked with indole-3-acetic acid. The relative intensities of signals from the urine matrix and indole-3-acetic acid were not improved; that is, no extra selectivity was gained by applying STPE. In CTPE, one photon is sufficient to bring the analyte in an excited electronic state so that in this mode, in principle, both normal and short-wavelength fluorescence can be measured. CTPE fluorescence has a distinct potential; it was observed for aminoanthraquinones, one of them has a very low fluorescence quantum yield in protic eluents. Detection limits were at the nM level. Mitoxantrone, a potent anti-tumour drug, could be detected in urine at a similar level by applying excitation at 625 nm and detecting higher excited state emission in a 290–400 nm window; sample treatment prior to LC was very simple.

Cladding-mode coupling characteristics ofBragg gratings in depressed-cladding fibre

Experimental transmission spectra of UV-written Bragg gratings in depressed-cladding fibre are characterised. The fine-structure features on the short-wavelength side of the fundamental Bragg line are shown to be due to coupling between the LP01 and higher-order LP0n and LP1n modes.

Pulse characteristics of passively mode-locked diode lasers

For the first time to our knowledge, asymmetric pulse shapes and the linear and nonlinear chirp from a passively mode-locked semiconductor laser are directly measured. For the laser tuned to various center wavelengths, fall-time-to-rise-time ratios of 2.0 to 2.5 are measured. With the laser tuned to the shorter-wavelength side of its tuning range, a significant quadratic chirp of -60 fs/nm(2) is measured, along with a linear chirp of -800 fs/nm. The nonlinear chirp is responsible for the asymmetrically shaped compressed pulses that produce long-tailed autocorrelations.

Exciton dynamics in circular aggregates: application to antenna of photosynthetic purple bacteria

A theoretical model of exciton dynamics in circular molecular aggregates of light-harvesting bacteriochlorophyll of photosynthetic bacteria is proposed. The spectra and anisotropy of photoinduced absorption changes in the femto- and picosecond time domain are under its scope. The excited state of aggregate was treated due to the standard exciton theory, taking into account a pigment inhomogeneity. Dephasing processes via the exciton-phonon interactions were described by means of the Haken-Strobl equation. It was shown that only two exciton levels are dipole-allowed in the case of homogeneous circular aggregate. The pigment inhomogeneity results in the appearance of several weak transitions to higher exciton levels. It was proposed that the minor band (B896) in an absorption spectrum of the B875 complex as well as the similar minor band in spectra of B800-850 complex correspond to electron transition from the ground to the lowest exciton level, whereas the major band corresponds to transition to the higher exciton level. The proposed model shows the subpicosecond decay of anisotropy at the short-wavelength side of absorption band and a high degree of anisotropy at the long-wavelength side, even at high temperatures.