Time-Resolved Two Photon Photoemission Schematic

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 Photoexcitation is the production of an excited state of a quantum system by photon absorption. The excited state originates from the interaction between a photon and the quantum system. Photons carry energy that is determined by the wavelength ...

an electron. After a time delay, the excited electron is photoemitted into a free electron state by a second pulse. The

kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its a ...

and the emission angle of the photoelectron are measured in an electron energy 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, and electron dynamics at

molecular A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

interfaces.

Basic physics

The final kinetic energy of the

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary partic ...

can be modeled by :

E_\text= E_\text+E_\text-E_\text-\Phi

where the E_B is the binding energy of the initial state, E_kin is the kinetic energy of the photoemitted electron, Φ is the work function of the material in question, and E_pump, E_probe 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 diode A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light ( ...

Experimental configuration

Time-resolved two-photon photoelectron spectroscopy usually employs a combination of ultrafast optical technology as well as ultrahigh vacuum components. The main optical component is an ultrafast (femtosecond) laser system which generates pulses in the near infrared. Nonlinear optics are used to generate photon energies in the visible and ultraviolet spectral range. Typically, ultraviolet radiation is required to photoemit electrons. In order to allow for time-resolved experiments, a fine adjustment delay stage must be employed in order to manipulate the

time Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, t ...

delay between the pump and the probe pulse.

References

{{reflist Emission spectroscopy Ultrafast spectroscopy Electron spectroscopy

Basic physics

Experimental configuration

See also

References