Research on table-top plasma soft x-ray lasers

1994年，我们在19.6 nm波长的类氖锗J=0-1谱线上用双脉冲抽运得到了激光性能的显著改善。单个脉冲宽度为100ps，间隔为300ps，总能量为300j的双脉冲抽运产生的软x射线束峰值强度是1.1 kJ能量为1ns的单脉冲抽运产生的软x射线束峰值强度的12倍，束散度仅为2 mrad。1995年，我们展示了类镍镧系元素（Nd, Sm, Gd， Tb和Dy）的有效软x射线激光，其光谱范围在6 nm到8 nm之间。采用1.053 μ m波长多脉冲泵浦曲面靶；在7.97 mn条件下，在2.5 cm长的靶上以250 J的抽运能量获得了增益系数为3.1 cm-1和增益长度乘积为7.8的增益系数。讨论了进一步降低抽运能量的可能性。我们还展示了在类镍元素（即Ag到Ta）中有效的软x射线激光，其光谱范围在14.3nm到4.4 nm之间。采用1.053 μ m波长四重激光脉冲泵浦曲面靶；前3个脉冲的脉冲间隔为400 ps，第3个和第4个脉冲的脉冲间隔为1.6 ns。低原子序数元素的脉冲持续时间和辐照度分别为100 ps和-7 * 10^<13> W/cm^2，高原子序数元素的脉冲持续时间和辐照度分别为-2 * 10^<14> W/cm^2。在11 nm和14 nm波长处，Te和Ag激光器的增益系数为2 cm^<-1>，增益长积为5。

In 1994, we have obtained the significant improvement of a lasing performance using double pulse pumping with a curved slab target at 19.6 nm wavelength of neon-like germanium J=0-1 line. The double pulses of 100 ps individual pulse width separated by 300 ps with a total energy of 300 J results in a soft x-ray beam of 12 times higher peak intensity with a smaller beam divergence of 2 mrad compared with those produced by the 1 ns single pulse pumping with 1.1 kJ energy.In 1995, we have demonstrated efficient soft x-ray lasing in nickel-like lanthanide elements (Nd, Sm, Gd, Tb and Dy) covering the spectral range between 6 nm and 8 nm. A curved slab target was pumped by 1.053 mum-wavelength multiple laser pulses ; two or three 100 ps duration pulses separated by 400 ps. A gain coefficient of 3.1 cm-1 and a gain-length product of 7.8 have been achieved at 7.97 mn in the Nd ions with 250 J pumping energy on a 2.5 cm length target. Possibility for further reduction of the pumping energy is discussed. We have also demonstrated efficient soft x-ray lasing in nickel-lik-elements i.e., Ag through Ta covering the spectral range between 14.3nm and 4.4 nm. A curved slab target was pumped by 1.053 mum-wavelength quadruple laser pulses ; the pulse to pulse separation for the first 3 pulses was 400 ps and that between the third and the fourth pulses was 1.6 ns, respectively. Each pulse duration and irradiances on a target were 100 ps and -7 * 10^<13> W/cm^2 for low atomic number elements and -2 * 10^<14> W/cm^2 for high atomic number elements, respectively. A gain coefficient of 2 cm^<-1> and a gain-length product of 5 have been achieved at 11 nm and 14 nm wavelengths for the Te and Ag lasers.