Controlling the nonadiabatic dynamics of the charge-transfer process with chirped pulses: Insights from a double-pump time-resolved fluorescence spectroscopy scheme.

The manipulation of the ultrafast quantum dynamics of a molecular system can be achieved through the application of tailored light fields. This has been done in many ways in the past. In our present investigation, we show that it is possible to exert specific control over the nonadiabatic dynamics of a generic model system describing ultrafast charge-transfer within a condensed dissipative environment by using frequency-chirped pulses. By adjusting the external photoexcitation conditions, such as the chirp parameter, we show that the final population of the excitonic and charge-transfer states can be significantly altered, thereby influencing the elementary steps controlling the transfer process. In addition, we introduce an excitation scheme based on double-pump time-resolved fluorescence spectroscopy using chirped-pulse excitations. Here, our findings reveal that chirped excitations enhance the vibrational system dynamics as evidenced by the simulated spectra, where a substantial signal intensity dependence on the chirp is observed. Our simulations show that chirped pulses are a promising tool for steering the dynamics of the charge-transfer process toward a desired target outcome.

Temperature-controlled photonic nanojet via VO2 coating.

In this work, a numerical investigation of how temperature can tune the FWHM and working distance (WD) of a photonic nanojet (PNJ) is conducted. Vanadium oxide (VO2), a phase change material, is coated onto the top half-surface of a glass microsphere and illuminated with incident light at a wavelength of 800 nm. As VO2 changes from semiconducting to metallic phase, the refractive index of the VO2 layer changes at its transition temperature of 68°C. It is found that a coating of 75 nm on a 5.0 µm diameter microsphere with a refractive index of 1.50 is the most optimal, as it tunes the FWHM the greatest while remaining thin enough to have a high transmission. When temperature is raised from 20°C to 90°C, the FWHM varies from 0.43 to 0.37 µm, corresponding to a 14.0% change. The WD varies from 0.29 to 0.20 µm, corresponding to a 31.0% change. Tunable PNJs have potential applications in tunable nanolithography and imaging.