Institute on Laser and Information Technologies

On the basis of fundamental research, a method is proposed for improving the quality of laser radiation at Fresnel numbers greater than unity. The method consists in ensuring the generation of a “pure” high-order Laguerre–Gaussian ring mode and subsequent local phase correction, and includes the control of multipass modes, which are the leading cause of deterioration in the laser radiation quality. The proposed approach makes it possible to significantly increase the laser power at a divergence close to that of a Gaussian beam. The beam divergence calculations are performed using an original numerical model. It is shown that during the propagation of a radiation beam having a different number of in-phase rings in the initial intensity distribution, the field distribution evolves to a lowest-order ring mode. New, more advanced polarization-selective optical elements (axicon and diffraction mirror), which form the basis of the proposed method, are developed for high-power lasers.

We obtained the spectra of high optical harmonics produced by subrelativistic femtosecond pulses on the surface of polystyrene, CaF2, BK7, and Al solid targets. High harmonics of up to the 51st order of radiation with central 3.85 µm wavelength were observed. The highest order harmonics were generated from the polystyrene target surface. The harmonics energy versus their numbers is shown to fit well a decaying power law with the exponent ranging from 4 to 8/3.

The possibilities of using oversized slow-wave structures in traveling wave tubes of the submillimeter wave range are investigated. A description of a linear theory developed to analyze the properties of such slow-wave structures is given. The results of the theoretical analysis of the hot dispersion characteristics of oversized diaphragm waveguides at frequencies of 315 and 800 GHz are presented.

In this work, we have experimentally investigated the features of tunneling current-voltage (I-V) curves in the case of 1D-dissipative tunneling in the limit of weak dissipation for various both synthesized (and in the process of synthesis) metallic nanoparticles (NPs) (Ni, Co, Fe) in a combined atomic force microscope/scanning tunneling microscope (AFM/STM) system in an external electric field. It is shown that for individual tunneling I-V curves, a single peak is observed at one of the polarities. In the process of synthesizing metallic nanoparticles with a change in polarity, instead of nanoclusters, it is possible to synthesize toroidal structures (shown by the example of "growing" Ni-NPs). The investigated effects of 1D-dissipative tunneling made it possible to develop the author's method of controlled growth of quantum dots in a combined AFM/STM system. A qualitative agreement was obtained between the experimental and theoretical results, which allows us to assume the possibility of experimental observation of the macroscopic dissipative tunneling effects and thereby confirm the hypothesis expressed in the pioneering works of A.

Terahertz detectors based on two-dimensional Dirac materials offer a new approach for room-temperature terahertz detection with high response and low noise. However, these devices can hardly show high response over a broad frequency range, mainly due to the poor absorption caused by their ultrathin nature. Here we apply metallic gratings to enhance the excitation efficiency of graphene plasmons. When nonzero source-drain bias is applied, graphene plasmons can generate terahertz response orthogonal to the polarization of the incidence. The response is attributed to the orthogonal overdamped plasmon rectification effect, and graphene plasmons-enhanced photo-thermoelectric effect. By comparing the normalized on/off ratio, the metallic gratings are found to effectively enhance the coupling efficiency between graphene plasmons and THz incidence, and thus the absorption and responsivity. The results are beneficial for improving the response of room temperature THz detectors.