Multiphoton ionization (MPI) is a fundamental first step in high-energy laser-matter interaction and is important for understanding the mechanism of plasma formation. With the discovery of MPI more than 50 years ago, there were numerous attempts to determine the basic physical constants of this process in direct experiments, namely photoionization rates and cross-sections of the MPI; however, no reliable data was available until now, and the spread in the literature values often reaches 2–3 orders of magnitude. This is due to the inability to conduct absolute measurements of plasma electron numbers generated by MPI, which leads to uncertainties and, sometimes, contradictions between MPI cross-section values utilized by different researchers across the field. Here, we report the first direct measurement of absolute plasma electron numbers generated at MPI of air, and subsequently we precisely determine the ionization rate and cross-section of eight-photon ionization of oxygen molecule by 800 nm photons σ8 = (3.3 ± 0.3)×10−130 W−8m16s−1. The method, based on the absolute measurement of the electron number created by MPI using elastic scattering of microwaves off the plasma volume in Rayleigh regime, establishes a general approach to directly measure and tabulate basic constants of the MPI process for various gases and photon energies.
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机译:多光子电离(MPI)是高能激光与物质相互作用的基本第一步,对于理解等离子体的形成机理非常重要。随着50多年前MPI的发现,人们在直接实验中进行了很多尝试来确定该过程的基本物理常数,即光电离速率和MPI的横截面;但是,到目前为止,尚无可靠的数据,而且文献中的值通常会达到2-3个数量级。这是由于无法对MPI生成的等离子体电子数进行绝对测量,这导致不确定性,有时还会导致跨领域的不同研究人员使用的MPI横截面值之间存在矛盾。在这里,我们报告了首次直接测量在空气中MPI产生的绝对等离子体电子数的方法,然后我们通过800 nm光子σ8=(3.3±0.3)精确确定氧分子的电离速率和八光子电离截面。 ×10 −130 sup> W −8 sup> m 16 sup> s -1 sup>。该方法基于对MPI产生的电子数的绝对测量,该测量是利用瑞利政权下的微波从血浆体积中弹性散射微波而产生的,建立了一种直接测量和制表MPI过程中各种气体和光子能量基本常数的通用方法。
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