Phonon Absorption And Stimulated Emission Of So Called Longitudinal Optical Phonons (IMAGE)
Caption
(a) Phonon (wavy lines) absorption and (b) stimulated emission of so called longitudinal optical (LO) phonons schematically explained in the conduction band structure (black parabola: electron energy vs. its momentum) of the semiconductor gallium arsenide (GaAs). (a) The blue circles of different size represent a thermal electron distribution at room temperature. A phonon is absorbed (removed) by lifting an electron from a state with a higher occupation probability to one with a lower. (b) A strong THz field (green double arrow) shifts the electron distribution to an inversion situation. Now, stimulated emission of a phonon increases the number of phonons by the inverse electron transition. (c) Sketch of the sample architecture covered by an array of metallic dogbone resonators (orange). The latter enhance electric fields (along the dashed lines) close to the electrically charged arms of the resonators. (d) Measured amplitude (area under peaks) of coherent phonons as a function of time showing a 10-fold increase within a period of 1.5 picoseconds.
Credit
MBI Berlin
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