ИСТИНА

The present paper demonstrates the possibility of simultaneous generation of X-ray and THz radiation in a gas cluster jet of argon. The concept of developing of “X-ray-optical-THz” source of ultrashort pulse duration. We demonstrated that optimal conditions for THz and characteristic X-ray radiation in gas-cluster jets are different. This allows to control the ratio of values of simultaneously generated signals at THz and X-ray frequencies by means of changing the temporal delay between laser pulses and the moment of cluster stream formation, and also when changing chirp parameters of the exciting laser pulses. The diagram showing the direction of the generated THz radiation in the near-axial area represents the cone with semiapex angle of 3.7 degrees and the minimal value in the near-axial area of the beam. The angular area less than 15 degrees was studied. The THz radiation, generated in the laser-induced cluster plasma excited by linearly polarized optical radiation is also linearly polarized. The dependence of THz signal value on excessive gas pressure, which creates a stream, in the dichromatic system has a nonlinear character and demonstrates saturation in high pressure. The absence of saturation of the volume of THz radiation signal with the growth of energy of exciting pulses at the main frequency observed up to 25 mJ in the pulse, agrees with the published earlier data for both monochromatic and dichromatic systems of optical excitation, and in our experiments up to 80-100 mJ saturation doesn’t take place either. Absence of saturation will allow in perspective get THz pulses of higher energy by means of increasing the energies of exciting optical pulses. The comparative analysis of the obtained experimental data showed that given equal average atom concentrations, THz radiation generation in static gas takes place with a higher optical-THz conversion coefficient than in gas-cluster streams. This effect can be connected with a relatively small volume of plasma waist and accordingly, with a considerably smaller number of atoms/molecules taking part in the interaction in the latter case. It has been demonstrated that argon clustering leads to the power decrease of THz signal in the near-axial area in the case of dichromatic pumping. One of the possible explanations is the formation of hyper critical cluster plasma. It has been demonstrated experimentally that by means of through changing the ratio of buffer and cluster gases in the gas mixture one can effectively change the value of THz radiation generated in the cluster stream. In the carried out experiments the highest efficiency of THz radiation generation was observed when the gas mixture of Ar (argon) + He (helium) was used with the 1:10 ratio. It seems productive to carry on research in this direction and proceed in the future to mixed clusters, formed at supersonic discharge from the nozzle of double, triple mixtures of multiatomic molecules with inert gases. For the purpose of correct interpretation of of the experimental data a model was made which took into consideration the frequency of the cluster own oscillation in the shape of an ellipse. A hypothesis was suggested that widening the resonance in THz radiation observed in a number of experiments of other research groups is connected with the spread in sizes and shapes of clusters. The power of dipole and quadrapole cluster radiation at THz range frequency is the result of action of ponderomotive Miller force and the power of radiation pressure. It has been established that the calculated dependence of the power of THz radiation on the power of laser radiation agrees with the experimental results.