Current activities on our research of soft x-ray lasers and higher harmonic generations using intense, subpicosecond lasers are reviewed. Especially for soft x-ray lasers we experimentally demonstrate that by longitudinally pumping 2-mm-long molybdenum preformed plasma with high-intensity 475 fs duration laser pulse, a highly directive soft x-ray laser at 18.9 nm wavelength is generated. The divergence of the beam is evaluated to be of the submillirad order, and only requires pump laser energy of 150 mJ. Simulations show that the pedestal in the main pump pulse can generate electron density and gain profiles with large spatial gradients, which result in the selective amplification of low-order transverse modes. The present result is the demonstration of an efficient and alternative method of improving the spatial coherence of x-ray lasers with amplified spontaneous emission medium, with possibilities of becoming an excellent tool to explore various application experiments. In higher harmonic generation, topics related to observation of blue shift due to collisionless absorption process is described. We demonstrate the generation of high harmonics (up to the 65
th order, λ=12.24 nm) of a Ti:sapphire laser radiation after the propagation of femtosecond laser pulses through the low-excited boron plasma produced by a prepulse radiation on the surface of different targets. High-order harmonics generated from the surface plasma of most targets showed a plateau pattern. The harmonic generation in these conditions assumed to occur due to the interaction of femtosecond pulses with ions. The conversion efficiencies in the plateau region were varied between 10
-7 to 8×10
-5 depending on the target. The main contribution to the limitation of harmonic generation efficiency and cutoff energy was attributed to the free-electrons-induced self-defocusing of main pulse.
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