High-resolution nonlinear laser spectroscopy of heavy-hole excitons in GaAs/AlGaAs quantum-well structures: A direct measure of the exciton line shape

Population pulsation resonances of excitons in monolayer MoSe2 with sub-1 μeV linewidths

Monolayer transition metal dichalcogenides, a new class of atomically thin semiconductors, possess optically coupled 2D valley excitons. The nature of exciton relaxation in these systems is currently poorly understood. Here, we investigate exciton relaxation in monolayer MoSe_{2} using polarization-resolved coherent nonlinear optical spectroscopy with high spectral resolution. We report strikingly narrow population pulsation resonances with two different characteristic linewidths of 1 and <0.2  μeV at low temperature. These linewidths are more than 3 orders of magnitude narrower than the photoluminescence and absorption linewidth, and indicate that a component of the exciton relaxation dynamics occurs on time scales longer than 1 ns. The ultranarrow resonance (<0.2  μeV) emerges with increasing excitation intensity, and implies the existence of a long-lived state whose lifetime exceeds 6 ns.

Near-field coherent spectroscopy and microscopy of a quantum dot system

We combined coherent nonlinear optical spectroscopy with nano-electron volt energy resolution and low-temperature near-field microscopy with subwavelength resolution (<lambda/2) to provide direct and local access to the excitonic dipole in a semiconductor nanostructure quantum system. Our technique allows the ability to address, excite, and probe single eigenstates of solid-state quantum systems with spectral and spatial selectivity while simultaneously providing a measurement of all the various time scales of the excitation including state relaxation and decoherence rates. In analogy to scanning tunneling microscopy measurements, we can now map the optical local density of states of a disordered nanostructure. These measurements lay the groundwork for studying and exploiting spatial and temporal coherence in the nanoscopic regime of solid-state systems.

High-resolution nonlinear laser spectroscopy of room-temperature GaAs quantum-well structures: observation of interference effects

We describe frequency-domain four-wave mixing spectroscopy measurements near the fundamental band edge in room-temperature GaAs multiple quantum wells. The line-shape information gives a measure of the dynamical behavior of the material and what is to our knowledge the first observation of an interference line shape due to a dominant slow contribution to the nonlinear response.