Takeki Sakurai

Pseudomomentum transfer from evanescent waves to atoms measured by saturated absorption spectroscopy

Abstract We perform saturated absorption spectroscopy using counterpropagating evanescent waves at different incident angles. The experimental results show that a crossover resonance splits into two resonant peaks, and the separation increases with an increase in the difference between the incident angles of the pump and the probe evanescent waves. This indicates that the pseudomomentum of the evanescent wave, which is the wave vector along the surface multiplied by ℏ and is larger than the momentum in vacuum, is actually transferred to the atoms as a real recoil momentum.

Quantum efficiency and thermal stability of organic dye vapors

Abstract Organic dyes, POPOP, perylene and pyren, in the vapor phase are excited by a N 2 laser. The quantum efficiency is measures as a function of temperature up to 450°C. Optical properties such as the radiative transition probability are also estimated from the experimental results. It is found that the decrease in the vapor density by the thermal dissociation can be neglected during several tens of hours.

Measurement of Ar metastables near a dielectric surface in barrier and plasma display panel discharges

The density of Ar 1s5 metastable excited atoms in the vicinity of a surface in barrier and display panel discharges was measured by the laser-induced evanescent-mode fluorescence technique. The temporal and spatial distributions of excited atoms were also measured by conventional spontaneous emission and laser absorption methods. From these measurements at various pressures, the behavior of the metastable atoms is clarified and the flux of the metastable atoms on the barrier surface is estimated.

Properties of Rhodamine 6G in vapor phase

Basic parameters of optical interaction in Rhodamine 6G in vapor phase are measured from the experimental result that the intensity of emission saturates with increasing intensity of pumping argon laser light. The quantum yield of fluorescence obtained in 0.13 and the cross section of absorption is 2.1×10−16 cm2 at a wavelength of 488 nm. The maximum vapor density obtained is in the order of 1015 cm−3 at a temperature of about 450 °C, the vapor pressure seems to saturate. From the results it is concluded that laser action of Rhodamine 6G in vapor phase requires pumping conditions that are not readily available.

Decay of Metastable Argon Atoms in the Afterglow Plasma

Time-dependent studies of the particle density in 1s5 state of Ar plasma are performed using single-frequency laser absorption probing. The applied voltage on the 400 Pa striated plasma (current: 0.01–20 mA DC) is cut off, and from the decay curve studies of the density, the following rates are obtained: the rate of collision between 1s5–1s5 metastable atoms α (cm3 s-1)=(2.0±0.5)×10-8, the rate of collision between 1s5 metastable atoms and electrons Fe (cm3 s-1)=3.8×10-7 and the electron loss rate in the afterglow γe (s-1)=250+1.0×10-7×ne, where ne (cm-3) is the electron density. We also present the time-dependent ne behavior in one striation peak using values obtained here.

Excited atoms in the vicinity of a surface in a barrier discharge measured by evanescent-wave laser spectroscopy

The density of metastable excited Ar atoms in the vicinity of a surface in a barrier discharge was measured by the laser-induced evanescent-mode fluorescence technique. The temporal and spatial distributions of excited atoms in the barrier discharge were also measured by conventional spontaneous emission and laser absorption methods in order to clarify the behavior of the excited species. It was also found that a technique using an evanescent wave spectroscopy makes it possible to measure the density distribution of the atoms in the vicinity of a surface.

Mode‐transition characteristics and tunability of an AlGaAs laser

The wavelength characteristics of a transverse‐junction‐stripe AlGaAs laser were precisely measured for a wide range of diode temperatures and injection currents. A very simple rule was found in the mode transition characteristics. Typical features of mode competition, such as mode‐competition noise, mode hopping with and without hysteresis phenomenon, and a tristable state of the lasing wavelength, were successively observed for a single diode sample. The characteristics were analyzed theoretically by using a two‐mode intensity equation of laser oscillation under the assumption of a homogeneously broadened gain spectrum. The results were in good agreement with the experiment.

Ar lowest excited state densities in Ar and Ar-Hg hot cathode discharge

The densities of the Ar lowest excited levels in Ar and Ar–Hg gas-filled discharge lamps were measured using the absorption and laser-induced fluorescence methods from the positive column to the vicinity of the cathode. The lamp current was between 20 to 200 mA. A contour of the density distributions was obtained. Near the cathode, the exponential decay of these densities was observed within a distance of 20 mm from the cathode. This spatial decay characteristic can be explained by the result that the main deexcitation of the lowest excited atoms is caused by three-body and electron collision depopulation processes. In the Ar discharge, time-dependent density oscillations were observed in the positive column. High as well as very low (close to zero) densities were observed alternately. No density oscillations existed in the vicinity of the cathode. The behavior of the densities in such oscillations is also reported.

Characteristics of the discharge current in the nanosecond‐pulse breakdown

The rise time and the peak of a pulsed discharge current are measured under various experimental conditions such as the change in capacitances of both storage and peaking condensers. It is shown that the peak of the discharge current can be determined by the law of the second voltage‐time area. The relation between the rise time and the peak is also made clear.

Decaying mechanism of a pulsed opto-galvanic signal in helium in a positive column

Abstract The pulsed opto-galvanic (og) signal in helium is measured under various conditions of a direct-current discharge. The decay rate of the og signal is strongly dependent on gas pressure p 0 and tube diameter and almost independent of discharge current. The transient change in population density in the excited levels of helium produced by the pulsed laser is also measured. It is concluded from these experiments that the decay of the og signal is mainly determined by the change in electronic ionization probability caused by the perturbation of the electric field E and the decay rate depends on only E/p 0 .