Transient Electron Impact Excitation 19.6nm X-ray Laser In Ne-like Ge

Since the first demonstration of soft x-ray laser in 1984 in LLNL, extensive experimental and theoretical work has been done and significant advances have been made. The recently proposed TCE (Transient Collisional Excitation) scheme greatly reduces the driving energy and lasing wavelength down to 7.3 nm x-ray laser has been obtained .In this thesis, we introduced the newly developed serie codes for TCE Ne-like Ge in the IAPCM, and modeled the x-ray laser experiment done by the RAL in 2000, comparing our results with experimental data shows agreement within experimental uncertainty. And with this serie codes we simulated Ne-like Ge 19.6 nm X-ray laser driven by two 250 ps Nd:glass laser pulses with 10 J total energy and after some delay time a 1ps pulse at 1.053μm under different pumping parameters producing a focus line 1cm length and 100μm width, and simulations indicate that under the optimized pumping condition, the local gain greater than 60cm^-1 could be obtained. Calculations of the propagation of X-ray laser, including refraction effects, shows small signal gain of ¹9.5 cm^-1, and the deflection angle is ⁶.8 mrad which suggests that refraction is an important factor that affects the x-ray laser output. And x-ray laser pumped by double-frequency laser is modeled and simulations show that the electron density in the gain region moves from less than ⁰.6×l0²¹cm^-3 to near the critical density surface where the electron density is ¹Ã—10²¹cm^-3 , and the small signal gain increases to 33cm^-1, with ¹2 mrad deflection angle which again means that refraction effect can not be neglected . One possible way to suppress the effect of refraction is to sharply reduce the distance that x-ray laser propagates in plasmas, but on the other hand, to obtain saturation, one must have much higher gain in the gain region. Previous simulations and experiments show that gain for the Ne-like Ge 19.6nm x-ray laser driven by Nd:glass laser peaks at critical density for the pumping laser, one problem arises that whether it is possible to produce higher gain above this electron density region. We have designed and simulated a series of experiments for Ne-like Ge 19.6nm x-ray laser to study gain above this electron density region, we adopt 3ω2ω pumping scheme, and the short pulse incidents with a 45° angle relative to the normal of the target surface, with less than 2.5J total pumping energy, simulations predict high gain up to 111cm^-1, and a ¹0 μm width narrow flat region with electron density larger than 1.7×10²¹cm^-3, the gain's life time is very short, it is only lps. Looking back at the development of QSS scheme, one can find that the prepulse pumping technique has experienced the following stages: The prepulse with almost the same intensity as that of the main pulse, was firstly adopted to produce plasma with proper ionization, and later it was found that a 10% or even less than 1% prepulse was more advantageous, in the later method, the low intensity prepulse produce plasma with low ionization, the main pulse not only heats but ionizes the plasma to produce high gain. Recent TCE experiments have obtained amplified x-ray laser with only one single short pulse, their analysis indicates that the pedestal of the short pulse produces preplasma with low ionization and low electron temperature, the short pulse bothionizes and heats preplasma to proper ionization with proper electron temperature to produce nigh gain, which suggests that there appears the same tendency in TCE scheme as in QSS, and according to this idea, we designed a series of experiments expecting to get high gain? hydrodynamic simulation was made and analysis show that as for the TCE Ne-like Ge 19.6 nm x-ray laser , it is possible to get high gain by this pumping method.