CREATION OF A CONDUCTION BAND BY LASER IR RADIATION

ABSTRACT

In this work, the possibility of creating and using a stable conducting channel in a dielectric liquid under the influence of laser radiation is considered. The pattern of breakdown was established. The dependence of the type of breakdown on the radiation power density and frequency is considered. The calculation of the main parameters of the breakdown, such as the breakdown temperature, the calculation of the values of F (intensity) and E (strength) of radiation, the dimensions of the focusing region of laser radiation to achieve the goal of the work, was carried out.

АННОТАЦИЯ

В данной работе рассматривается возможность создания и использования устойчивого проводящего канала в диэлектрической жидкости под действием лазерного излучения. Была установлена закономерность поломки. Рассмотрена зависимость вида пробоя от плотности мощности и частоты излучения. Были проведены расчеты основных параметров пробоя, таких как температура пробоя, расчет значений F (интенсивности) и E (силы) излучения, а также расчёты размеров области фокусировки лазерного излучения для достижения цели работы.

Key words: laser, spectrum, IR radiation, conduction, molecule.

Ключевые слова: лазер, спектр, ИК излучение, проводимость, молекула.

Dissociation of complex (polyatomic) molecules in the field of infrared radiation. In typical cases 30hv. Since the vibrational spectrum of molecules is enharmonic, at first glance it seems that dissociation can occur only at a very high radiation intensity, either due to nonresonant multiphoton absorption of infrared radiation, or when the field strength is so high that the anharmonicity of the vibrational spectrum is compensated by Stark shifts and broadening of the vibrational levels. Estimates show that in both cases we can talk about dissociation at an infrared radiation intensity of the order of 1012 W/m². However, the dissociation of complex molecules is experimentally observed at an infrared radiation intensity many orders of magnitude lower than the intensity given by estimates based on the probability of multiphoton absorption or Stark broadening [3].

Detailed studies of the process of dissociation of complex molecules by IR radiation made it possible to elucidate the nature of this process, explain its relatively high probability and, thus, the possibility of observation at a not very high radiation intensity, and also reveal its isotopic selectivity.

In the lower part of the spectrum, the density of excited states is relatively low. In this region of the spectrum, a multiphoton excitation of a molecule into a fixed discrete excited state occurs. This transition is isotopically selective. The degree of multiphotonity of this transition depends on the particular type of molecule. As a rule, this is a three-photon excitation, less often two-photon, but no more than four - five-photon. Thus, the probability of this transition is relatively high, and its implementation does not require a very high radiation intensity [1].

Higher in the spectrum, at high energies of the excited states, the spectrum acquires the character of a vibrational quasi-continuum. This means that a further increase in the energy of the molecule occurs as a result of a series of successive one-photon quasi-resonance transitions. It is obvious that the probability of each such transition is very high, so that the molecule quickly gains an energy of the order of the dissociation energy. The reason for the emergence of a quasi-continuum is a very rapid increase in the number of transitions that a molecule can make from a given excited state by absorbing a radiation quantum. The increase in the number of transitions is due to the high density of vibrational states of a complex polyatomic molecule, which has a large number of degrees of freedom, and the interaction of these states. The spectrum in the region of the upper levels does not have that sharp resonant character as in the region of the lower levels, the levels broadened, mutually overlap and form absorption bands [2].

A rigorous theoretical description of the kinetics of the absorption of infrared radiation by a complex molecule is in good agreement with both this simplified qualitative model and experimental data [3].

Figure 1. Dependence of energy on the reaction coordinate X for elementary chemical reactions: a - monomolecular reaction: b - bimolecular reaction

An elementary chemical reaction in the gas phase can be understood as overcoming the potential barrier E_a (E_a is the activation energy) along the reaction coordinate x. The rate of the time course of a reaction is determined by the reaction rate constant K.

Figure 1a shows the dissociation of a diatomic molecule (x is the distance between atoms; Ea is the dissociation energy). Figure 1b shows the formation in a bimolecular reaction from the AB molecule through the activated complex A – B – C of the BC molecule. The temperature dependence of the reaction rate constant K is approximately described by the Arrhenius equation in case of thermal excitation:

in the case of photon absorption,

Where C, C' are constants, weakly dependent on temperature.

Due to the increase in the internal energy of the molecules due to absorption, under certain circumstances, it is possible to significantly reduce or completely eliminate the significant costs of thermal energy (high temperatures) to initiate the reaction.

The different absorptive capacities of the molecules provide an opportunity for selective photochemical stimulation as a result of the fact that, for example, only a certain kind of molecules are activated in a mixture by an appropriate selection of the light frequency.

Differences in the absorption spectrum of molecules with the same elemental composition arise due to the spatial structure (cis-, trans-isomerism), different isotopic composition (important for isotope separation), isomerism of atomic nuclei.

There is a possibility of intramolecular selectivity.

The choice of photon energy changes the internal energy of the molecule (regardless of the gas temperature). As a consequence, there is the possibility of various chemical reactions occurring with different activation energies (heating the reaction mixture always leads to an acceleration of the reaction with a minimum activation energy). With the help of lasers, chemical reactions can be initiated or accelerated that do not proceed with thermal excitation.

The internal energy of a molecule can be roughly divided into: electronic energy Еe1: Еe1 is several eV, absorption in the visible and UV regions of the spectrum; vibrational energy Ev1b: Ev1b = 0.1 0.01 eV, absorption in the near-IR region of the spectrum; rotational energy Еrot : Е_rot = 0.001 0.0001 eV, absorption in the far IR region of the spectrum up to submillimeter waves. This results in various possibilities for activating chemical reactions. Based on these, the following conclusions can be drawn:

- An analysis of literary sources showed that the existing works devoted to the breakdown of liquids do not have a complete theory of the breakdown of liquids. The basic electrical properties of liquids seem to be determined by the "short range order", i.e. the nature of the interaction of molecules with their nearest neighbors, as is the case with semiconductors.

- Despite the difficulties associated with the lack of a complete theory of the breakdown of liquids, breakdown patterns were established. The main processes of electrical breakdown of a liquid in the initial stage are multiphoton ionization, cascade, or avalanche ionization. The first electrons appear due to a frequency-dependent tunneling effect, at high frequencies the tunneling mechanism is equivalent to multiphoton ionization.

- It has been established that a breakdown using laser radiation can be obtained using photochemical substances or due to nonlinear ionization of a substance.

- The main parameters that affect the nature of the interaction of laser radiation with matter are: the ionization potential of matter; intensity of laser radiation.

References:

1. Balygin I.E. Electrical strength of liquid dielectrics. M., “Energy”, 1964.-228 p.
2. Grigoryants A.G. Fundamentals of laser processing of materials. - M.: Mashinostroenie, 1989.-304 p.
3. P.P. Napartovich Handbook of laser technology. – M.: Nauka, 1992.- 573 p.