ИСТИНА

The physical phenomenon of filamentation has been known for more than 60 years, receiving even more attention from researchers in the mid-1990s when the first experiments on the propagation of high-power ultrashort laser pulses in media appeared, and, for example, extended thin plasma channels (“filaments”) were obtained in air with a high concentration of energy in them. Such interaction in gases, liquids, and dielectrics is accompanied by various physical processes, such as the generation of plasma channels, conical emission, and supercontinuum generation. The unique properties of filamentation find applications in microoptics, micromachining of materials, atmospheric optics, generation of terahertz radiation, and laser spectroscopy. The control parameter of self-focusing of high-power laser pulses of (sub)nanosecond duration, which determines the possibility of their filamentation, is the critical power that depends on the laser wavelength. In the case of femtosecond laser pulses, the nonlinear optical interaction with the medium is determined by the Kerr nonlinearity (the real component of the nonlinear susceptibility) and the laser plasma generated by the nonlinear photoionization of the medium in a strong laser field (the imaginary component of the nonlinear susceptibility). As for longer (sub) picosecond laser pulses, an increase in the nonlinear polarization of the medium due to coherent lattice processes, including those induced in solid dielectrics by photogenerated electron-hole plasma, can act as an additional stabilizing factor for filamentation. In this case, the formation and stabilization of a nonlinear focus is a complex and insufficiently studied process. To date, most studies of the filamentation of ultrashort laser pulses in air and transparent media have been carried out in the form of scattered experiments and calculations for certain sets of wavelengths in the ranges of 248–1064 nm and 1.6–2.2 μm. Theoretical studies of filamentation, including a nonlinear optical model, for example, of an air medium, are most developed for a wavelength of 800 nm, while for other wavelengths and other media there is a lack of experimental data and the parameters are often taken from qualitative considerations. In this regard, there is a need for a systematic study of a wider range of wavelengths and durations of laser radiation with the same parameters (intensity, polarization, focusing) to determine the parameters of the nonlinear optical interaction of radiation with dielectrics and refine existing theoretical models. Modern laser systems with parametric amplifiers and laser pulse compression make it possible to cover the wavelength range of 0.35–2.7 μm and durations from 30 fs to 20 ps using one experimental setup. Such a system will be used within the current project to study the processes and parameters of monofilamentation in isotropic transparent condensed media (water, fused silica).

1. Будут экспериментально исследованы важные характеристики спектрального (0.35-2.7 мкм) управления параметрами монофиламентов – диаметром, пороговой мощностью образования, плотностью плазмы и энергии (оценки) – в изотропных диэлектриках (вода, плавленый кварц); 2. Будет проведен анализ условий баланса керровской самофокусировки и плазменной дефокусировки в данном широком спектральном диапазоне при монофиламентации в изотропных диэлектриках (вода, плавленый кварц) с учетом сильных дисперсионных зависимостей нелинейного показателя преломления и сечения многофотонной ионизации; 3. Будет выполнен анализ условий баланса керровской самофокусировки и плазменной дефокусировки при монофиламентации в изотропных диэлектриках (вода, плавленый кварц) в зависимости от длительности ультракоротких лазерных импульсов (0.03-20 пс) с учетом вкладов мгновенной и задержанной керровской нелинейности. В результате, в рамках данного проекта будут получены основополагающие зависимости параметров одиночных филаментов для идентичных условий возбуждения изотропных диэлектриков (вода, плавеный кварц) от длины волны (350 – 2700 нм) и длительности (30 фс – 20 пс) ультракоротких лазерных импульсов, которые не только позволят провести систематическое моделирование, но и, вполне возможно, обнаружат новые физические эффекты нелинейно-оптического взаимодействия.