Observation of Photoinduced Terahertz Gain in GaAs Quantum Wells: Evidence for Radiative Two-Exciton-to-Biexciton Scattering

Abstract

We have observed photoinduced negative optical conductivity, or gain, in the terahertz frequency range in a GaAs multiple-quantum-well structure in a strong perpendicular magnetic field at low temperatures. The gain is narrow band: it appears as a sharp peak (linewidth < 0.45 meV) whose frequency shifts with applied magnetic field. The gain has a circular-polarization selection rule: a strong line is observed for holecyclotron-resonance-active polarization. Furthermore, the gain appears only when the exciton 1s state is populated, which rules out intraexcitonic transitions to be its origin. Based on these observations, we propose a possible process in which the stimulated emission of a terahertz photon occurs while two free excitons scatter into one biexciton in an energy and angular-momentum conserving manner.

Terahertz spin dynamics in rare-earth orthoferrites

“…THz time-domain spectroscopy is a useful technique to reveal fundamental excitations in solids [124][125][126][127][128][129][130][131][132][133][134][135][136][137] . Its most common layout is in transmission geometry, as depicted in Fig.…”

Broadband and High‐Sensitivity Time‐Resolved THz System Using Grating‐Assisted Tilted‐Pulse‐Front Phase Matching

“…Time‐resolved terahertz (THz) spectroscopy is an optical characterization technique now routinely used in the spectral range between 0.5 and 3 THz to monitor microscopic interactions and resolve key signature resonances in diverse materials such as superconductors, [ 1–4 ] semiconductors, [ 5,6 ] topological insulators, [ 7–10 ] heavy fermions, [ 11–13 ] ferroelectrics, [ 14,15 ] antiferromagnets, [ 16 ] and metal‐organic compounds. [ 17,18 ] One configuration commonly used for these experiments relies on a near infrared (NIR) ultrafast source and a pair of second‐order nonlinear crystals to generate and detect phase‐locked THz transients.…”