50 J discharge-pumped XeCl laser

An X-ray preionized XeCl laser with a wide aperture of 10×10 cm² is described. The density for preionization electrons is estimated from an X-ray energy distribution to be greater than 6×10⁹ cm^-3 under operational gas conditions. In high pressure operation at 4500 torr, sufficient preionization has led to successful discharge-breakdown at a low E/N of 6.4×10^-17 V-cm², resulting in a high electrical efficiency of 3.1% with an output energy of 17.6 J. An output energy of 50 J in an 85-ns (FWHM) optical pulse has been extracted from an active volume of about 10:1 for a pulse-forming-line (PFL) voltage of 400 kV. The effects of impedance transformation of a pulse-transmission-line (PTL) following the PFL have been investigated using two types of PTL with output impedances of 0.26 and 0.48 Ω     

Ultrafast refractive-index dynamics in a multiquantum-well semiconductor optical amplifier

We investigate ultrafast refractive index dynamics in a multiquantum-well InGaAsP-InGaAs semiconductor optical amplifier that is operated in the gain regime by using a pump-and-probe approach. The pump-and-probe pulses are cross-linearly polarized. We observe a phase shift of 200/spl deg/ if the amplifier is pumped with 120 mA of current, but find that the phase shift vanishes if the injection current is increased to 160 mA. Our results indicate a contribution of two-photon absorption to the nonlinear phase shift that opposes the phase shift introduced by the gain. Finally, we observe that the phase shift comes up and disappears within a picosecond.     

Intersubband all-optical switching in submicron high-mesa SCH waveguide structure with wide-gap II-VI-based quantum wells

An all-optical switch using intersubband transition in wide-gap II-VI-based quantum wells in an improved waveguide structure is presented. The waveguide exhibits a separate confinement heterostructure (SCH) and submicron high-mesa waveguide for stronger optical confinement. A reduction of 39% is achieved in control pulse energy for a 10 dB switching extinction ratio while maintaining a subpicosecond response     

Generation of single short tunable UV pulses using a simple short-cavity dye laser

Generation of single, short, tunable UV pulses using a short-cavity dye laser (SCDL) with a novel simple cavity structure is described. A single 80-ps pulse has been obtained at the 616-nm wavelength from a rhodamine 640 dye laser pumped with a 2-ns N2 laser pulse. By amplifying and subsequent frequency-doubling, a 90-ps 308-nm pulse was generated, which can be used as a short-duration XeCl excimer laser source. The temporal characteristics coupled rate equations.     

Decay characteristics of expiratory aerosol in various diffuser-induced airflow patterns using large-eddy simulation

This paper presents the decay characteristics of expiratory aerosol using large-eddy simulations coupled with Lagrangian particle tracking for evaluating the prevention of pathogen infection in a typical indoor environment. Ten cases of enclosed-rooms with five different diffuser-induced airflow patterns were investigated. For particles about 10 μm in diameter, which closely approximates the mean diameter of expiratory aerosol, the decay characteristics of each case with no obstacles proved that the most efficient case was the floor-supplied displacement type, followed by the ceiling-mounted line diffuser, floor-mounted diffuser, and ceiling-mounted square diffuser. The least effective case was the ceiling-mounted four-way cassette-type air diffuser under the same air changes per hour. However, in the situation of obstacles representing human bodies, the floor- supplied displacement type showed worse decay characteristics because of preventing the “piston flow-like” one-direction flow. On the other hand, the diffuser cases of the ceiling-mounted square type and the ceiling-mounted four-way cassette-type showed improved decay speed by exhaust and deposition. In particular, the ceiling-mounted square diffuser showed the most effective removal performance. These results imply that the flow configurations that induce small circulation caused by the inlet-outlet layout tend to improve the decay characteristics in terms of “the robust flow design” in a situation of complex flow field.     

1-ns high-power high-repetitive excimer laser oscillator

A 1-ns high-power high-repetitive excimer laser oscillator has been developed for which the peak power obtained was more than 1 MW with 1-ns pulse width for both XeCl and KrF gas mixtures. The characteristic output power per unit active volume is calculated to be more than 2 GW/L, which is nearly one order larger than that extracted from usual discharge devices. It is inferred that the gain depletion in the active medium under such an extremely large output power condition has led to successful pulse shortening. The device can be operated at a repetition frequency of at least 500 Hz without a gas circulation system. The beam divergence was reduced to near the diffraction limit, although the oscillated-pulse width is only 1 ns