We develop an analytical model for the generation of terahertz (THz) fields by the propagation of a higher-order Gaussian laser pulse in a magnetized plasma. A higher-mode Gaussian pulse is utilized for this purpose. The plasma nonlinearity is enhanced due to the modified gradient of the Gaussian spatial intensity profile. THz field generated by the transverse wakefields is significantly larger for this kind of laser pulses. The amplitude of THz fields can be enhanced by the flatness parameter of the higher-order Gaussian laser pulse. The fivefold enhancement of the THz field is reported in this study. Furthermore, the applied axial magnetic field also contributes to enhancing the THz field. For higher-order Gaussian laser pulse, the power conversion efficiency of THz field generation in the presence of a magnetized is four times higher than the ordinary Gaussian pulse case. The production of intense THz field with amplitudes belonging to the GV/m range is helpful in various applications such as THz extreme nonlinear optics and probing remote materials efficiently.
The accelerating structure of the laser wakefield accelerator (LWFA) is dynamic and highly sensitive to the local laser and plasma properties. It can expand and contract as it responds to the evolution of the laser and plasma fields. As a result, the position of, and environment within, the LWFA bubble are usually time dependent, which is not ideal for stable acceleration. Variations can have a negative impact on electron bunch properties, and are deleterious for ion channel lasers and plasma wigglers. We demonstrate how a laser pre-pulse improves the stability of the LWFA, and controls the evolution of the laser group and bubble velocity, which are important for determining LWFA dephasing and ultimately the electron bunch energy.
Generating high-field infrared and terahertz radiation during interaction of a super-intense laser pulse with a complex nanodimensional target consisting of nanowires or nanofoils is studied. During interaction, dense bunches of electrons are extracted out of the target and accelerated in the laser field, generating intense electromagnetic radiation. Depending on the duration and shape of the laser pulse, three interaction modes can be realized. In the first mode, the laser pulse is smooth, and the electrons are only partially displaced from the target. In this case, a unipolar radiation pulse is generated with duration of about that of the laser pulse. In the second mode, the laser pulse is nonadiabatic with the amplitude of the first half-cycle about the maximum pulse amplitude. Here, most of the electrons are extracted from the target at the beginning of interaction, and unipolar and bipolar pulses with duration of dozens of laser periods can be generated. Changing the target geometry allows one to control the period and number of oscillations in the generated radiation. Finally, in the intermediate mode of short laser pulses with an insufficiently steep front, oscillations of the formed electron bunches may occur in the Coulomb field of ions, leading to radiation with a frequency several times lower than that of the laser. Using numerical simulation, the characteristics of infrared and terahertz radiation in three interaction modes are found. It is shown that the amplitude of generated radiation can reach subrelativistic values, and the intensity conversion efficiency can be about one percent. The advantages of using complex nanowire targets are elucidated. Such targets allow to generate a train of terahertz and infrared pulses with controlled delay between them.
We propose the stronger optical guiding of an electromagnetic beam in a plasma by considering the amplitude
modulation of the fundamental beam. With the advent of high power source of electromagnetic radiation, the
electron velocity in a plasma may become quite large (comparable to the light velocity in free space). Thus, the
effect of relativistic mass variation must be taken into account. The relativistic effect of the laser propagation in a
plasma leads to self-focusing because of the dielectric constant of a plasma being an increasing function of the
intensity. The ponderomotive force of the laser beam pushes the electrons out of the region of high intensity, which
reduces the local electron density and increases the plasma dielectric function further, leading to even more selffocusing
of the laser. In this work, we consider a short pulse laser of finite spot size as an amplitude modulation in
time. Our findings show an efficient optical guiding mechanism based on amplitude modulation signal propagation
in plasmas. Medium nonlinearity becomes stronger if an amplitude modulated beam is introduced, which contributes
significantly in laser guiding in plasmas. Furthermore, the rate of laser self-focusing is increased with modulation
index due the fact of stronger Kerr effect. The study related to amplitude modulated optical signal may be useful for
communication technology.
Conference Committee Involvement (1)
Coherent and Incoherent Radiation Sources based on Relativistic Plasma Waves V
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