Radiative decay of optically excited coherent plasmons in a two-dimensional electron gas

Abstract

We report on the observation of coherent submillimeter-wave emission from optically excited plasmons in a two-dimensional electron gas. Phase-synchronous plasma oscillations are induced by femtosecond optical pulses generating electron-hole pairs in the accumulation channel of an AlGaAs͞GaAs heterostructure. The radiative decay of the grating-coupled plasmons is traced in time by terahertz-emission spectroscopy. An analysis of the data suggests that ultrafast thermalization and current surges are the plasmon-driving mechanism.

Dynamical Properties of a Terahertz Driven Two-dimensional Electron Gas

“…ω p ∼ q 1 2 , see equation 20), it is much easier to measure experimentally the optical spectrum than to measure directly the plasmon modes. At present, optical studies have been popularly and widely used to measure the free electron density in inhomogeneous systems and to verify the dependence of the plasmon dispersion on electron density and wavevector in electronic systems (Voβebürger et al 1996). Theoretically, the optical spectrum of an electron gas system can be obtained from the imaginary part of the inverse dielectric function, E(Ω) =Im −1 (Ω), which measures the energy loss of fast electrons via absorption of the probing field with frequency Ω (Glicksman 1971).…”

Grating-coupler assisted infrared spectroscopy on anisotropic multilayer systems: A comparative study

“…This fact has been exploited to realize high-performance output couplers for semiconductor bandgap lasers [28] as well as to achieve tunable terahertz emitters, based on the light emission of quasi-two-dimensional (Q2D) plasmons due to gratings [29][30][31][32][33]. In such modulation-doped semiconductor nanostructures the electrons form a quasi-two-dimensional electron gas (Q2DEG) due to size quantization.…”

Improved coherent terahertz emission by modification of the dielectric environment

“…Two basic principles are commonly employed to generate coherent THz radiation in this frequency range: ͑a͒ optical downconversion using nonlinear optical materials 1,2 and ͑b͒ acceleration of photogenerated charge carriers by built-in and/or externally applied bias fields in semiconductor structures. [3][4][5][6][7] Regardless of the approach, however, conversion efficiency from optical input to usable coherent THz output power is usually very low and losses up to 50 dB are common. This lack of efficient coherent sources severely limits a more widespread application of coherent THz time domain spectroscopy and imaging.…”