Phase-dependent ionization and CE-phase measurement at long wavelengths

越来越短的激光脉冲的发展已经到了几乎不可能取得进一步进展的地步：所谓的少周期脉冲实际上只包括一个光学周期。少周期脉冲具有显著的特性，即它们的波形可以是不对称的，即在激光偏振轴的相反方向上的场强不同。利用所谓的载波包络（CE）相位可以定量表征几个周期脉冲的波形，这在以下方面也具有突出的意义，例如，光学周期持续一到几飞秒。然而，原子、分子和固体中的电子动力学是在阿秒时间尺度上进行的。为了用激光物理学的工具来了解这个时间尺度上的自然界，因此有必要关注光学周期内的过程。QUTIF优先计划的相应方法是以特定的方式操纵光学波形，并观察量子动力学的后续反应。当使用少周期脉冲时，这显然可以通过改变CE相位来实现。少周期脉冲的另一个优点是可以将特定的微扰限制在一个明确定义的光周期内，因此CE相位的测量非常重要。我们已经选择了直观的方法，建立在推测，不对称的激光脉冲将诱导不对称的光电子发射，反过来，可以用来推断CE阶段。潜在机制的细节是错综复杂的。然而，这一概念已证明是非常富有成效的。不幸的是，由于分子共振而特别感兴趣的红外光谱区域的方法遇到了严重的困难：用于CE相位测量的效应随着波长的四次方而减小。尽管如此，我们成功地将测量范围扩展到了1800 nm。未来几年，将开放3500 nm的区域。为此，将有必要研究CE相位依赖的光电离的完全不同的原子和分子系统与红外几个周期的脉冲。由于目前还没有合适的方法来测量CE相在红外区，我们面临着一个典型的鸡和蛋的困境，我们必须解决。

The development towards shorter and shorter laser pulses has reached the point, where further progress is hardly possible: So-called few-cycle pulses consist of virtually only one optical cycle. Few-cycle pulses have the remarkable property that their waveform can be asymmetric, i.e. the field strength in the opposing directions of the laser polarization axis is different. A quantitative characterization of the waveform of few-cycle pulses is possible with the so-called carrier-envelope (CE) phase, which is of outstanding significance also in, e.g., frequency metrology.An optical period lasts one to a few femtoseconds. Electronic dynamics in atoms, molecules and solids, however, proceeds on the attosecond time scale. In order to learn something about nature on this time scale with the tools of laser physics, it is therefore necessary to focus on processes within an optical cycle. The respective approach of the QUTIF priority program is to manipulate the optical waveform in specific ways and to observe the subsequent reactions of the quantum dynamics. When few-cycle pulses are used, this can obviously be achieved by varying the CE phase. Few-cycle pulses have the additional advantage of confining the specific perturbation to a well-defined optical cycle.The measurement of the CE phase is consequently of huge importance. We have chosen the intuitive approach that builds on the conjecture that asymmetric laser pulses will induce asymmetric photoelectron emission which, in turn, can be used to infer the CE phase. The details of the underlying mechanisms are intricate. However, the concept has proven very fruitful. Unfortunately, rendering the method for the infrared spectral region, which is of particular interest because of molecular resonances, encounters serious difficulties: The very effects that are exploited for CE phase measurement decrease with the forth power of the wavelength.Nevertheless, we succeeded to expand the measurement range to wavelengths up to 1800nm. In the next years, the region up to 3500nm shall be opened up. To this end, it will be necessary to investigate CE phase-dependent photoionization of entirely different atomic and molecular systems with infrared few-cycle pulses. Since there are no suitable methods for measuring the CE phase in the infrared regime at present, we are confronted with a typical chicken-egg dilemma which we have to resolve.