Due to their high resonant third-order nonlinear response, lead sulfide quantum dots (QDs) are potential materials for applications in the field of nonlinear optics. In this paper, we implement the Z-scan method to study the resonant nonlinear response of lead sulfide QDs in colloidal solutions. We managed to measure the purely intrinsic resonant nonlinear response, free of thermal contribution. We report that the lead sulfide QD third-order nonlinear response per QD shows an unconventional increase. A figure of merit for QD nonlinearity grows as a power function with a factor of 2.9.

Emerging laser plasma-based technologies require new knowledge on the optical pump optimization and underlying physics of laser–matter interaction. Plasma in liquid jets is still largely unexplored, although this configuration is actively used as a part of optical devices. Hereby, in this work, we report on the reflectivity-based approach to study the optical properties of the induced plasma and quasi-free electron temporal dynamics. The single-shot experiments provide plasma characteristics relative to the laser pump parameters. A strong angular dependence of the plasma absorptivity, which affects rigorously the reflectivity curve, is demonstrated. Furthermore, twofold higher plasma reflectivity in ethanol is revealed and explained through the theoretical model of ultrashort laser pulse interaction with a thin dielectric surface layer. Finally, the time-resolved fundamental and third harmonic reflection measurements and associated analytical study provide the new insight into the electron density dynamics in the case of optical breakdown in water and ethanol. We believe that these findings are of particular significance for the development of highly efficient plasma-based x rays and THz radiation sources.

In this work we tested two reagent kits developed by us for detecting SARS-CoV-2 RNA using a fragment of the ORF1ab gene in digital PCR and real-time PCR formats. Data were obtained on the detection of SARS-CoV-2 virus RNA in nasopharyngeal swabs of patients with COVID-19 and asymptomatic carriers. The developed reagent kits provided 100% sensitivity and a detection limit of 103 GE / ml for qPCR, and at least 200 copies / ml of viral RNA when performing digital PCR. These methods were tested using a panel of 1,328 samples collected from patients with suspected COVID-19 at the beginning of 2020 in the Russian Federation. It has been shown that dPCR is more sensitive and can be used to analyze samples with low viral load, including those from patients without clinical symptoms. dPCR significantly improves the accuracy of laboratory research and significantly reduces the number of false negative results in the diagnosis of SARS-CoV-2. Determination of the concentration of SARS-CoV-2 RNA in patients with different clinical course of the disease showed that the concentration of viral RNA can sharply decrease in the first days of the disease. A low concentration of viral RNA in samples from patients is also characteristic of asymptomatic disease. Digital PCR provides a higher detection rate for asymptomatic cases, which is approximately 75% of those infected, as opposed to 45% for real-time PCR. The results obtained on the use of the digital PCR method for detecting SARS-CoV-2 RNA showed that this method is especially suitable for detecting RNA in case of its low concentration in contacts, as well as for monitoring changes in viral load in convalescent patients.