G. D. Shandybina

Simulation of the absorption of a femtosecond laser pulse in crystalline silicon

The effect of the nonlinearity of the absorptivity and absorption coefficient on the process of the intense photoexcitation of silicon is studied on the basis of a model of the two-photon excitation of a semiconductor with consideration for external emission. Correlation between the results of simulation of the absorption of a femtosecond laser pulse in single-crystal silicon and experimental data under conditions of the femtosecond excitation of surface plasmon polaritons makes it possible to refine the mechanism of changes in the absorptivity and to make an inference regarding the necessity of considering these changes when assessing the conditions of the laser treatment of semiconductors. Avenues for further improvement of the theoretical model are discussed.

Dynamics of the permittivity of a semiconductor acted on by a femtosecond laser

A theoretical analysis of how the permittivity of a broad-band semiconductor varies while it is being acted on by a femtosecond laser pulse is presented, taking into account various types of emission phenomena. The spatial permittivity distribution considered here is modelled experimentally, using surface plasmon resonance on the corresponding multilayer structures and is compared with the data of femtosecond microstructuring of silicon at a wavelength of 1.25 µm.

Electrophysical phenomena accompanying femtosecond impacts of laser radiation on semiconductors

The space–time concentration distribution of nonequilibrium charge carriers is numerically modelled under the action of ultrashort laser radiation pulses on semiconductors, taking into account the external emission of electrons. The results are compared with the experimental conditions for the excitation and propagation of waveguide modes in silicon under the action of femtosecond pulses with a quantum energy of about 0.98 eV.

Role of the heat accumulation effect in the multipulse modes of the femtosecond laser microstructuring of silicon

The results of quantitative evaluation of the heat accumulation effect during the femtosecond laser microstructuring of the surface of silicon are presented for discussion. In the calculations, the numerical–analytical method is used, in which the dynamics of electronic processes and lattice heating are simulated by the numerical method, and the cooling stage is described on the basis of an analytical solution. The effect of multipulse irradiation on the surface temperature is studied: in the electronic subsystem, as the dependence of the absorbance on the excited carrier density and the dependence of the absorbance on the electron-gas temperature; in the lattice subsystem, as the variation in the absorbance from pulse to pulse. It was shown that, in the low-frequency pulse-repetition mode characteristic of the femtosecond microstructuring of silicon, the heat accumulation effect is controlled not by the residual surface temperature by the time of the next pulse arrival, which corresponds to conventional concepts, but by an increase in the maximum temperature from pulse to pulse, from which cooling begins. The accumulation of the residual temperature of the surface can affect the microstructuring process during irradiation near the evaporation threshold or with increasing pulse-repetition rate.

Laser-pulse microstructuring of a silicon surface*

Laser microstructuring of a silicon surface usually results from the development of instabilities and the effects of self-organization. This paper shows that this is a multistage process, consisting of successive rapid transitions of the system from some quasi-stationary states into others. The following classification of the observed changes is proposed:

Influence of multi-pulse action on the evolution of silicon microrelief under femtosecond laser irradiation

The results of numerical modeling of the process of multi-pulse femtosecond laser photoexcitation and heating of monocrystalline silicon are presented. It is shown that starting from a certain level of irradiance at pulse repetition rates of 10–1000xa0Hz, the structural changes in the surface that occur between pulses influence the spatiotemporal distribution of the electron plasma in the near-surface layer of the semiconductor at the time of irradiation with a subsequent pulse and thus accumulate, forming a stable surface microstructure in the irradiated region. A mechanism is proposed for the formation of a two-dimensional periodic microrelief on a silicon surface, which is based on a change in the type of a surface excited by electromagnetic waves with an increasing number of irradiating femtosecond pulses.

The contribution of the polariton mechanism of the surface microstructuring of silicon by picosecond laser pulses

This paper discusses the experimental results of a study of the polariton mechanism of the microstructuring of silicon in the near-IR region when it is irradiated with picosecond laser pulses. The results are presented of a numerical model analysis of the excitation conditions of surface polaritons in a semiconductor when it is irradiated by a single picosecond pulse. It is determined that the polariton microstructuring mechanism of silicon has low probability when a picosecond laser pulse acts on it.

Investigation of the properties and structure of the field of surface electromagnetic excitations of the optical range

This paper discusses the localization processes of optical radiation when surface electromagnetic waves (SEWs) are excited in ordered arrays of scattering inhomogeneities whose size is much less than the wavelength of light. The features of the SEW excitation when ultrashort laser pulses act on the surface of a semiconductor are also investigated. The possibility of spatial and temporal localization of optical radiation in an SEW is analyzed.