Terahertz spectroscopy and technology

Consequently, THz spectroscopy on semiconductors is relevant in revealing both new technological potentials of nanostructures as well as in exploring the fundamental properties of many-body systems in a controlled fashion.

Obviously, the combination of ultrafast duration and strong peak ETHz(t) provides vast new possibilities to systematic studies in semiconductors.

Besides the strength and duration of ETHz(t), the THz field's photon energy plays a vital role in semiconductor investigations because it can be made resonant with several intriguing many-body transitions.

For example, one can propagate a THz pulse through a semiconductor sample and measure the transmitted and reflected fields as function of time.

Therefore, one collects information of semiconductor excitation dynamics completely in time domain, which is the general principle of the terahertz time-domain spectroscopy.

Due to their analog to the hydrogen atom, excitons have bound states that can be uniquely identified by the usual quantum numbers 1s, 2s, 2p, and so on.

At resonance, the dipole d1s,2p defines the Rabi energy ΩRabi = d1s,2p ETHz(t) that determines the time scale at which the 1s-to-2p transition proceeds.

[4] Using this technique one can follow the formation dynamics of excitons[7][8] or observe THz gain arising from intraexcitonic transitions.

As a result, the Rabi oscillations become strongly distorted by the non-RWA contributions, the multiphoton absorption or emission processes, and the dynamic Franz–Keldysh effect, as measured in Refs.

[23] Terahertz transitions in solids can be systematically approached by generalizing the semiconductor Bloch equations[9] and the related many-body correlation dynamics.

At this level, one realizes the THz field are directly absorbed by two-particle correlations that modify the quantum kinetics of electron and hole distributions.