Using a ray matrix method, we analyze theoretically how the r and theta polarizations affect the resonator stability condition of two laser heads with or without thermal birefringence compensation. The resonator stability condition is analyzed graphically for a plane-parallel and a concave-concave resonator. The maximum range of stable region is found for both the short and the long cavity. The characteristics of the laser output power are confirmed experimentally in association with the resonator stability condition. The laser output power of 776 W is obtained with the optical-to-optical efficiency of 45% for a plane-parallel resonator with a short crystal separation.
An optical polishing technology utilizing a line shaped excimer laser beam was introduced to reduce the microroughness of the tungsten films deposited onto the Si wafer surface. The results of the microroughness reduction and the comparisons were made before and after the line beam irradiations for as-grown and post-chemical mechanical planarization (CMP) tungsten films as a function of irradiated laser wavelength, in 248 nm and 308 nm, laser fluence, and the irradiated number of pulses. Characterizations of the microroughness were performed by atomic forced microscopy. The root-mean-square (RMS) roughness and peak-to-valley, R
p-v, roughness of the as-grown tungsten films were decreased by about 30%–40% compared with the initial values. The RMS roughnesses of the post-CMP tungsten films were 25–30 Å for a 5 µm×5 µm measurement. Fluctuations of the reduced microroughness were mainly caused by the beam inhomogeneity and local distributions of the hot (peak energy) spots along or across the line beam. The lowest RMS roughness of 8.0–8.4 Å was obtained for the post-CMP tungsten films by the irradiation of 30 pulses of 308 nm with a fluence of 100 mJ/cm2. Irradiation of the 248 nm and 308 nm homogenized flat-top line beam reduced the peak-to-valley roughness, R
p-v, of the post-CMP tungsten films down to 1/3 of its initial value. It was found that the optimum number of pulses for microroughness diminution of the post-CMP tungsten film is 50 pulses with a fluence of 150 mJ/cm2. The wavelength dependency of the microroughness diminution was not surprising, but 308 nm irradiation showed a slightly better performance with consistent results than the 248 nm irradiation did.
Fast neutrons were generated from a deuterated polystyrene (C8D8) solid target by using an ultraintense Ti:sapphire laser with a 27-fs pulse width and a 260-mJ pulse energy. The dependency of neutron generation on the amplified spontaneous emission (ASE) width was analyzed in terms of the deuteron energy. At a shorter ASE width of 1 ns, neutron tracks of the 3533/pulse were obtained for a target thickness of 80 µm. In addition, the time-of-flight (TOF) neutron signal was analyzed in terms of the X-ray and the neutron signals.
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