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

长波长下的相位相关电离和 CE 相位测量

• 批准号: 281296000
• 负责人: Professor Dr. Gerhard G. Paulus
• 金额: --
• 依托单位: Lehrstuhl Nichtlineare Optik
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2015
• 资助国家: 德国
• 起止时间: 2014-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/281296000?language=en
• 关键词: Phase; dependent; ionization; CE; phase

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.

越来越短的激光脉冲的发展已经达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有一个光周期。少周期脉冲具有波形不对称的显著特性，即在激光偏振轴相反方向上的场强不同。利用所谓的载波包络（CE）相位，可以对短周期脉冲的波形进行定量表征，这在频率计量等领域也具有重要意义。光周期为一到几飞秒。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。为了用激光物理的工具在这个时间尺度上了解一些关于自然的东西，因此有必要关注光周期内的过程。QUTIF优先程序各自的方法是以特定的方式操纵光波形，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。少周期脉冲具有将特定扰动限制在定义良好的光周期内的额外优点。因此，CE相位的测量是非常重要的。我们选择了直观的方法，这种方法建立在不对称激光脉冲将诱导不对称光电子发射的猜想之上，这反过来又可以用来推断CE相位。潜在机制的细节是复杂的。然而，这个概念被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渲染方法遇到了严重的困难：用于CE相位测量的效果随着波长的四次方而降低。尽管如此，我们还是成功地将测量范围扩大到1800nm波长。未来几年，将开放3500nm以内的区域。为此，有必要用红外短周期脉冲研究完全不同的原子和分子体系的CE相依赖的光电离。由于目前还没有合适的方法来测量红外光谱中的CE相，我们面临着一个典型的先有鸡还是先有蛋的困境。