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ISSN: 1023-5086

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ISSN: 1023-5086

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Opticheskii Zhurnal

A full-text English translation of the journal is published by Optica Publishing Group under the title “Journal of Optical Technology”

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DOI: 10.17586/1023-5086-2024-91-04-16-25

УДК: 535

Second-harmonic generation of a circularly polarized laser pulse ionizing atoms and molecules in the presence of a static electric field

Silaev A.A., Romanov A.A., Vvedenskii N.V.

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For Russian citation (Opticheskii Zhurnal):

Силаев А.А., Романов А.А., Введенский Н.В. Генерация второй гармоники циркулярно-поляризованного лазерного импульса, ионизующего атомы и молекулы в присутствии постоянного электрического поля // Оптический журнал. 2024. Т. 91. № 4. С. 16–25. http://doi.org/10.17586/1023-5086-2024-91-04-16-25

 

Silaev A.A., Romanov A.A., Vvedenskii N.V. Second-harmonic generation of a circularly polarized laser pulse ionizing atoms and molecules in the presence of a static electric field [in Russian] // Opticheskii Zhurnal. 2024. V. 91. № 4. P. 16–25. http://doi.org/10.17586/1023-5086-2024-91-04-16-25

For citation (Journal of Optical Technology):
-
Abstract:

Subject of study. We study the generation of the second harmonic of a circularly polarized laser pulse during the tunneling ionization of atoms or molecules in the presence of a static electric field. Aim of study. The aim of the study is to obtain the analytical expression for the free-electron current density at the second harmonic of the laser pulse in the presence of static electric field and to compare the efficiency of second harmonic generation for circular and linear polarizations of the laser pulse. Method. To calculate the electron current density we use the classical equation of cold plasma hydrodynamics with a variable number of particles determined by the probability of tunneling ionization under the action of the laser pulse and static field. The analytical solution is obtained using the expansion of the ionization probability in a Taylor series in small constant field. Main results. Based on the comparison with the results of numerical calculations, we demonstrate high accuracy of the obtained analytical expression. We show that the excited current density consists of the circularly polarized second harmonic with the amplitude linear in the static field, while the amplitude of the third harmonic is proportional to the square of the static field and is much less than the amplitude of the second harmonic. For a fixed final degree of gas ionization (both much smaller and of the order of unity), the second-harmonic has the same order of amplitudes for linear and circular pulse polarization. For an arbitrary ellipticity of the laser pulse the duration of the second harmonic is determined by ionization duration, which is much shorter than the duration of the laser pulse. Practical significance. The linear dependence of the amplitude of the second harmonic on the constant field opens up the possibility of measuring pulses in the terahertz and mid-infrared ranges using the sampling method with high temporal resolution.

Keywords:

second harmonic generation, laser pulse, ionization, plasma, detection of terahertz and mid-infrared radiation

Acknowledgements:

second harmonic generation, laser pulse, ionization, plasma, detection of terahertz and mid-infrared radiation.

OCIS codes: 020.0020, 190.0190

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