Kinetic study of terahertz generation based on the interaction of two-color ultra-short laser pulses with molecular hydrogen gas

Abstract

In this work, using a two dimensional particle in cell-Monte Carlo collision simulation scheme, interaction of two-color ultra-short laser pulses with the molecular hydrogen gas (H2) is examined. The operational laser parameters, i.e., its pulse shape, duration, and waist, are changed and, their effects on the density and kinetic energy of generated electrons, THz electric field, intensity, and spectrum are studied. It is seen that the best pulse shape generating the THz signal radiation with the highest intensity is a trapezoidal pulse, and the intensity of generated THz radiation is increased at the higher pulse durations and waists. For all the operational laser parameters, the maximum value of emitted THz signal frequency always remains lower than 5 THz. The intensity of applied laser pulses is taken about 1014 w/cm2, and it is observed that while a small portion of the gaseous media gets ionized, the radiated THz signal is significant.

THz radiation generation via the interaction of two‐colour ultra‐short laser pulses with SO2 and NH3 gases

“…This is due to the fact that the trapezoidal pulse shape has the capability to generate much higher current densities (see Figure ). For the considered laser pulse shapes, the temporal variation of the generated THz electric field is in good agreement with the experimental and theoretical findings by other researchers . On the other hand, the spectra of generated THz radiation with all the considered laser pulse shapes are presented in Figure .…”

“…Babushkin et al reported the generation of more efficient THz radiations with rectangular pump pulses similar to THz signals using the trapezoidal laser pulses. Similarly, in the THz radiation generation from molecular hydrogen and water vapour as narrow slabs, it was observed that the trapezoidal pulse shape was able to create THz signals with the highest efficiencies . This is the main reason for choosing trapezoidal laser pulse shape in all the performed simulations in this work.…”

“…For NH 3 and SO 2 , SFIE is 25.1 and 21.16 eV, respectively . This is higher than that of other atoms and molecules such as Ar (11.87 eV), Xe (9.08 eV), diatomic hydrogen molecules (0.824), and triatomic water molecules (1.88 eV) . This is reflected in the increased laser energy required for the electron tunnelling ionization.…”

“…The used two‐colour laser parameters are listed in Table . On the other hand, in previous works on THz generation from hydrogen and water molecules, it was confirmed that a trapezoidal pulse shape has the capability of generating THz pulses with higher intensities than with other pulse shapes. Thus, in this work, the trapezoidal laser pulse shape is considered.…”

“…Their findings show that the efficiency of THz signal generation by water vapour is about 50% higher than that of the diatomic molecule nitrogen . Moreover, using a 2D particle‐in‐cell Monte Carlo collision (PIC‐MCC) simulation, the effects of the laser parameters, including different pulse shapes, pulse durations, and beam waists, on the THz signal radiation based on the interaction of two‐colour ultra‐short laser pulses with a simple linear diatomic molecule (H 2 ) were examined . In addition, the developed 2D PIC‐MCC simulation scheme was used to study the broadband THz signal generation from the irradiated diatomic oxygen molecules by two‐colour laser pulses …”