Development of a refractive plasma lens for focusing attosecond beams

折射透镜广泛用于光的成像和聚焦以及显微镜应用，可用于电磁波谱的许多光谱区域，包括可见光，红外线，太赫兹，紫外线甚至x射线制度。在极紫外（XUV）区域（波长范围从10到124纳米），这是科学和工业应用的高度兴趣，包括纳米级结构的相干衍射成像，阿秒科学和纳米光刻，折射透镜还没有可用。这可以用固体物质对XUV辐射的大量吸收来解释。最近，我们开发了一种气相透镜，使光子能量在原子共振附近聚焦XUV脉冲。这些气相透镜可以在50到124纳米的波长范围内使用，而对于50纳米以下的波长，吸收仍然是一个限制因素。该项目的目标是开发一种等离子折射透镜，使XUV脉冲聚焦在光谱区域在10到50纳米之间。等离子体透镜利用等离子体中自由电子的折射，产生低色差和低色散。因此，等离子体折射透镜非常适合聚焦阿秒脉冲，使人们能够在焦点中保持阿秒脉冲持续时间。随着XUV等离子体透镜的发展，我们将对XUV焦斑进行表征，并将所得结果与模拟结果进行比较。我们将使用阿秒条纹技术进一步测量等离子体透镜焦平面上的XUV脉冲持续时间。与一般用于聚焦XUV光束的反射镜相比，XUV等离子体透镜的重要优点是吸收损耗低，并且可以原位改变焦距。

Refractive lenses, which are widely used for the imaging and focusing of light as well as for microscopy applications, are available in many spectral regions of the electromagnetic spectrum, including the visible, infrared, terahertz, ultraviolet and even X-ray regimes. In the extreme-ultraviolet (XUV) region (covering the wavelength range from 10 to 124 nanometers), which is of high interest for scientific and industrial applications including coherent diffractive imaging of nanoscale structures, attosecond science and nanolithography, refractive lenses have not been available. This can be explained by the large absorption of XUV radiation by solid matter. Recently, we developed a gas-phase lens enabling the focusing of XUV pulses with photon energies in the vicinity of atomic resonances. These gas-phase lenses can be used in the wavelength region between 50 and 124 nanometers, whereas absorption remains a limiting factor for wavelengths below 50 nanometers. The goal of this project is to develop a plasma refractive lens that enables focusing of XUV pulses in the spectral region between 10 and 50 nanometers. The plasma lens exploits the refraction due to free electrons in the plasma, resulting in low chromatic aberration and low dispersion. A plasma refractive lens is therefore ideally suited to focus attosecond pulses, allowing one to maintain an attosecond pulse duration in the focus. Following the development of the XUV plasma lens, we will characterize the XUV focal spot and compare the obtained results with simulations. We will further measure the XUV pulse duration in the focal plane of the plasma lens using the attosecond streaking technique. Compared to mirrors that are typically used to focus XUV beams, important advantages of the XUV plasma lens are the low absorption losses and the possibility to change the focal length in-situ.