Ultrafast Dynamics

Light, or electromagnetic radiation, influences our life every second. It is absorbed by plants or solar cells and used for data transmission in fibers. Light becomes harmful to our DNA as UV light, but is used in skin therapy as near-infrared light. Chemical products can be produced using light as well.

There are many more examples for the large interest in the interaction of light with matter, because it governs our well-being like no other relationship. The interest in understanding the ultrafast relationship is based on the origin of light-induced processes that are found in femto- to picoseconds. If we want to gain a deep understanding of how the microcosmos dictates our life when light is involved, we do not want to miss out on the beginning.

On these time scales, energy packages and charges are transported between molecules, the fundamental requirement for fast data transmission or harvesting of the sun's energy. A typical tool for investigation is laser-based optical spectroscopy that provides us with femtosecond laser pulses of all kinds. 

In laser-based optical spectroscopy, ultrashort laser pulses are overlapped for example in an organic solar cell. The very first pulse activates the solar cell's molecules, which can use the energy for transporting charges to generate electricity. The following pulses pass the sample slightly after the process was initiated. The interaction between molecules and laser pulses depends on the progression of the reaction and since every pulse has a different time delay, it carries a precise signature of the reaction at that particular time. In other words, only specific parts of the colors get absorbed or modified at each time step, imprinting a special signature into the spectrum. Analyzing each pulse signature and combining the information gives a global picture of the light-induced reaction on ultrafast time scales. In this sense, the ultrafast light-induced process is like a story written by the molecules and we can read the story word by word looking at the spectral imprint of the pulses. Because one pulse activates or pumps the reaction and the other probes it, such a technology is commonly called ultrafast pump probe spectroscopy.