Inorganic van der Waals bonded semiconductors such as transition metal dichalcogenides are the subject of intense research due to their electronic and optical properties which are promising for next-generation optoelectronic devices. In this context, understanding the carrier dynamics, as well as charge and energy transfer at the interface between metallic contacts and semiconductors, is crucial and yet quite unexplored. Here, we present an experimental study to measure the effect of mutual interaction between thermionically injected and directly excited carriers on the exciton formation dynamics in bulk WS2. By employing a pump–push–probe scheme, where a pump pulse induces thermionic injection of electrons from a gold substrate into the conduction band of the semiconductor, and another delayed push pulse that excites direct transitions in the WS2, we can isolate the two processes experimentally and thus correlate the mutual interaction with its effect on the ultrafast dynamics in WS2. The fast decay time constants extracted from the experiments show a decrease with an increasing ratio between the injected and directly excited charge carriers, thus disclosing the impact of thermionic electron injection on the exciton formation dynamics. Our findings might offer a new vibrant direction for the integration of photonics and electronics, especially in active and photodetection devices, and, more in general, in upcoming all-optical nanotechnologies.

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The nonlinear transformation of fluctuations by frequency broadening is found to produce strong anti-correlations in the spectral output. This effect is investigated by dispersive Fourier transform measurements. We exploit the anti-correlations in order to cancel the intensity noise in a subsequent sum-frequency mixing step. This principle allows for the generation of tunable visible pulses by cascaded nonlinear mixing whilst maintaining the same intensity noise performance as the input pulses. In addition, we demonstrate that the power fluctuations occurring in the process of passive stabilization of the carrier-envelope phase locking via difference frequency generation may be cancelled by an analogous strategy.

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Interface effects in metals-semiconductors heterojunctions are subject of intense research due to the possibility to exploit the synergy between their electronic and optical properties in next-generation opto-electronic devices. In this framework, understanding the carrier dynamics at the metal-semiconductor interface, as well as achieving a coherent control of charge and energy transfer in metal-semiconductor heterostructures, are crucial and yet quite unexplored aspects. Here, we experimentally show that thermionically injected carriers from a gold substrate can drastically affect the dynamics of excited carriers in bulk WS2. By employing a pump-push-probe scheme, where a push pulse excites direct transitions in the WS2, and another delayed pump pulse induces thermionic injection of carriers from the gold substrate into the semiconductor, we can control both the formation and annihilation of excitons. Our findings might foster the development of novel opto-electronic approaches to control charge dynamics using light at ultrafast timescales.