All-Optical Attosecond Technology

点击翻译按钮获取中文摘要

Summary of the Proposal: An attosecond is one millionth of one millionth of one millionth of a second. To make such a small number more real, one attosecond is to one second as a second is to the age of the universe. As incredible as it may seem, today we can make light flashes that last less than 100 attoseconds and over the next five years, I predict that we will reach 25 attoseconds. Imagine how different the world seems when it is observed on this fast time-scale. We could “freeze-frame” any valence electron orbiting atoms or molecules. To appreciate the importance of the issues that attosecond science will be able to address recall that electrons form the bonds that hold all molecules and solids together. Therefore, electrons power chemical reactions. Consider a few examples: (1) Through electron excitation in the molecule “rhodopsin” and the very rapid relaxation of the excited electron, we see the world. (2) Solar cells function by fast and efficient electron transport. (3) In some materials (called “correlated materials) two or more of the molecule’s electrons respond synchronously. These are examples of the issues that attosecond science will help us understand. This proposal involves three sub-themes: • Measuring how intense light drives very rapid electron excitation in small molecules, • Developing a powerful new technique to follow how energy is exchanged between different electronic excitations in molecules or solids,• Transferring attosecond technology from atomic molecular gases (where they were developed) to solids (where technological applications lie). The proposal focusses on “all-optical methods” because “all-optical” allows simple and flexible measurement. In fact, many measurements will only be practical if they are “all-optical”. An analogy might help a non-scientific reader understand the underlying technology. He/she might think of a cork and a water wave. The cork responds like an electron in this analogy. For the analogy of the water wave, please think of a light wave. As the wave goes through peaks and valleys, the cork (or the electron) bobs in response. Now imagine that the electron is a part of an atom. For an analogy, think of the cork tethered to a rock near the shore. If a strong wave comes, the electron can be pulled from the atom. In the analogy, the tether can break. Once free, the electron moves in the wave, but it can re-collide with its parent ion -- the cork hits the rock as the wave recedes. Just like in the cork-rock collision we might hear a noise in the electron-ion collision an attosecond pulse is born. With this analogy you will not be surprised to learn that attosecond pulses can be shaped and controlled through the light wave that creates the pulse. For this “all-optical” control we might, for example, add a different wavelength light or a wave travelling in a slightly different direction for control or measurement. Let me conclude by commenting on the last aim. So far, gases have been used for attosecond technology. However, if we could transfer the technology to solids, then we could use attosecond science to study how solid-state electronics – especially the electronics of correlated materials -- responds on this new time scale and we would have a material that can be used to create “practical attosecond devices”.