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Time-resolved Two-Photon Photoelectron (2PPE) spectroscopy is a time-resolved spectroscopy technique which is used to study electronic structure and electronic excitations at surfaces. The technique utilizes femtosecond to picosecond laser pulses in order to first photoexcite an electron. After a time delay, the excited electron is photoemitted into a free electron state by a second pulse, as shown in Figure 1. The kinetic energy and the emission angle of the photoelectron are measured in an electron analyzer. To facilitate investigations on the population and relaxation pathways of the excitation, this measurement is performed at different time delays. This technique has been used for many different types of materials to study a variety of exotic electron behaviors, including image potential states at metal surfaces,〔Fauster, Thomas, and Wulf Steinmann. "Two-photon photoemission spectroscopy of image states." Electromagnetic Waves: Recent Developments in Research 2 (1995): 347-411.〕〔Weinelt, Martin. "Time-resolved two-photon photoemission from metal surfaces." Journal of Physics: Condensed Matter 14.43 (2002): R1099.〕 and even electron dynamics at molecular interfaces.〔Zhu, X-Y. "Electron transfer at molecule-metal interfaces: a two-photon photoemission study." Annual review of physical chemistry 53.1 (2002): 221-247.〕 == Basic physics == The final kinetic energy of the electron can be modeled by the following equation: EB = Epump + Eprobe - Ekin - Φ Where the EB is the binding energy of the initial state, Ekin is the kinetic energy of the photoemitted electron, Φ is the work function of the material in question, and Epump, Eprobe are the photon energies of the laser pulses, respectively. Without a time delay, this equation is exact. However, as the delay between the pump and probe pulses increases, the excited electron may relax in an energy. Hence the energy of the photoemitted electron is lowered. With large enough time delay between the two pulses, the electron will relax all the way back to its original state. The timescales at which the electronic relaxation occurs, as well as the relaxation mechanism (either via vibronic coupling or electronic coupling) is of interest for applications of functional devices such as solar cells and light-emitting diodes. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Two-photon photoelectron spectroscopy」の詳細全文を読む スポンサード リンク
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