Abstract |
Terahertz (THz) beam profile shaping has an essential role in an extensive spectrum of
scientific, industrial, and technological applications, among them high-resolution imaging,
spectroscopic analysis, advanced communication systems, and material processing. Classical
methods for modifying the THz beam profile, such as diffractive optical elements,
metasurfaces, and wavefront phase manipulation, have proven beneficial; nevertheless, they
tend to be associated with supplementary system complexity or losses of power. In this present
study, we suggest a novel approach for controlling the shape and the energy distribution of a
broadband THz beam by manipulating the THz source directly. In our experimental setup,
ultrashort laser pulses (800 nm, 35 fs, 2 mJ/pulse, 1 kHz) and their second harmonic deliver a
typical two – cοlor laser filamentation process in air, which produces THz radiation. To shape
the THz beam, we use a Spatial Light Modulator (SLM) that operates at the initial laser
frequency and produces diverse laser energy distributions. By creating off-axis spherical
phases, the SLM allows the development of different laser filaments across multiple spatial
arrangements. This technique enables us to alter the classical doughnut – shaped THz beam
profile that results from a single filament, leading to additional complicated beam profiles when
two or more filaments are positioned in varied geometries. The method we developed provides
the entire electronic control of the beam profile by employing phase masks on the SLM,
resulting in dynamic and adaptable THz beam shaping. When the filaments are significantly
separated, the resulting beam profiles can be attributed to either linear interference effects or
nonlinear energy redistribution through Kerr cross – talk when the filaments are sufficiently
close to one another. This all – optical approach, recognized for its straightforwardness and
simplicity of execution, presents promising applications in THz imaging and beam engineering,
notably in the field of telecommunications. Our outcomes illustrate that by directly controlling
the laser – induced filamentation process, we can obtain flexible and efficient manipulation of
THz beam shaping, setting up potential opportunities for the development of advanced THz
technologies.
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