Yukio Inoue

UV-Absorbing Substance in the Red Alga Porphyra yezoensis (Bangiales, Rhodophyta) Block Thymine Photodimer Production

The effect of the water-soluble UV-absorbing substance (UVAS) extracted from the marine red alga Porphyra yezoensis Ueda on UV-dependent thymine photodimer production was investigated. The T<>T pyrimidine-pyrimidone 6-4 dimer and the cyclobutane cis-syn T<>T 5-6 dimer produced by UV irradiation with a xenon lamp were analyzed by reverse-phase high-performance liquid chromatography. Although the dimer production was reduced when the irradiation was filtered through a UVAS solution, it decreased more when thymine was mixed with UVAS. Furthermore, UVAS inhibited the degradation of UV-irradiated thymine. The inhibitory effect of UVAS was significantly greater than that of exogenously added adenine or guanine, which forms complementary base pairs with thymine. These data suggest that in addition to its filtering effect against UV radiation, UVAS also protects thymine by a direct molecule-to-molecule energy transfer process. The protective function of UVAS against UV irradiation is advantageous for this alga under strong UV irradiation.

Density of Ar Metastable Atoms on the Discharge Tube Wall Measured by Evanescent Laser Spectroscopy.

In order to measure the density of excited atoms in the metastable state on a discharge tube wall, evanescent wave spectroscopy is applied to a pure Ar discharge. In the experiments, the evanescent laser wave interacts with the Ar metastable atoms. The detection of the evanescent-laser-induced fluorescence and the laser-induced evanescent-mode fluorescence indicates the existence of metastable atoms in the vicinity of the wall within one wavelength of the laser. The absolute value of density is obtained in comparison with the signal for Rb atoms in the same system. The reflectance of metastable atoms at the wall is also estimated.

Collision Broadening and Shift of Cesium D2 Resonance Line Perturbed by Every Rare Gas

Collision broadening and shift of the resonance line 6 2 S 1/2 -6 2 P 3/2 of Cs perturbed by each rare gas at temperature of 293 K were precisely measured with using a single mode diode laser. The broadening and the shift measured at low gas pressures (below 200 mbar) of rare gas showed an excellent linear dependence on atomic density. The broadening and the shift constants are obtained and cross sections of the broadening and the shift are estimated. The broadening and the shift constants are compared with the previously obtained experimental and theoretical results. The cross sections are discussed as a function of atomic parameters of the rare gas.

Injection Locking of a Nitrogen Laser Pumped Dye Laser

Injection locking of a N2-laser pumped dye laser is investigated. The locking efficiency is measured as a function of injecting beam intensity, injecting beam wavelength, and delay time between an injecting laser pulse from a master oscillator and a pumping N2-laser pulse at a forced oscillator. The dye laser output of 1.2 kW with linewidth of 0.2 nm is obtained at locking efficiency ρ=0.8 when the injecting intensity is about 10 kW/cm2.

Dissociation processes of SiCl 4 and plasma parameters measured by transient spectroscopy at the beginning of a SiCl 4 -helium DC discharge

We propose that the excitation or the dissociation mechanism and plasma parameters in a discharge can be estimated by. spectroscopic methods, such as the measurement of the transient behaviour of fluorescences at the beginning of a pulsed de discharge. Fluorescences emitted from excited atoms and dissociated fragments from 270 to 640 nm in wavelength are measured as a function of time at the beginning of a discharge of a He-SiCl4 gas mixture. The transient waveform of fluorescence is calculated by considering the experimental results of discharge current and voltage between electrodes measured as a function of time. From a comparison of the experimental and calculated waveforms of fluorescence it is concluded that the fragment emitting the light, SiCb, is excited in a single-step from SiCl4 by electronic collisions and the fluorescence-emitting fragments of SiCI3, SiCI, C12, CI, Si and CI+ in a discharge can never be excited by electronic collisions in a single step. Furthermore, an average electron energy in the plasma at a steady state is simply estimated from a measurement of the transient behaviour of emission lines from helium excited states. The result is in fair agreement with the value measured by using an electric probe.

Effects of Reabsorption and Xenon on the Lifetime of the Excited Cesium Atom

The effects of the reabsorption of radiation on the lifetime of the Cs 72P3/2 level were measured from the decaying waveform of fluorescence under various experimental conditions. Reabsorption does not have any influence on the lifetime when the experimental condition satisfies k0L<1, where k0 is the peak absorption coefficient and L is the reabsorbing path length. A theoretical calculation based on a simple model agrees with the experimental results.

Electron Swarm Parameters Measured Using Photoelectrons Induced by a Pulse Laser

Electron swarm parameters such as drift velocity and ionization coefficient are measured using photoelectrons induced by a pulse laser. In order to measure parameters in a wide region of E/p, a pulsed dc voltage synchronized with the pulse laser is applied between electrodes with a pure configuration to keep the electric field uniform. Dynamic behavior of electrons is observed as a transient waveform of an induced current. From the analysis of the waveform, the drift velocity and the ionization coefficient in helium gas can be obtained at E/p up to 500 and 4000 V/cmTorr, respectively. Further experiments are performed using an actual discharge tube or a gas mixture of halogen and helium. The results are discussed in comparison with those obtained with a pure configuration of electrodes.