Improving depth-of field in broadband THz beams using nondiffractive Bessel beams

As a kind of special beams, Bessel beams are always a research hot spot in optics due to its non-diffractive and self-healing properties. Here, zero-order terahertz (THz) Bessel beams with linear and circular polarizations are generated by using a THz quarter wave plate and Teflon axicons with different opening angles. By applying a THz digital holographic imaging system, the evolutions of the transverse (E x, E y) and longitudinal (E z) electric fields are coherently measured and analyzed during the propagation processes of the THz Bessel beams. The vectorial Rayleigh diffraction integral is used to accurately reproduce the amplitude, phase, and non-diffractive feature of each polarization component for the THz Bessel beams. With varying opening angles of the axicons, the focal spots, diffraction-free ranges, and Gouy phase shifts of the THz Bessel beams are compared and discussed. The experiment and simulation results provide a comprehensive view for exactly understanding peculiar features of THz Bessel beams.

“…In 2012, Bitman et al . demonstrated that a pulsed THz Bessel beam can enhance the ability of obtaining depth information in a THz imaging system 11 . In 2015, Knyazev et al .…”

Section: Introductionmentioning

confidence: 99%

Vector characterization of zero-order terahertz Bessel beams with linear and circular polarizations

Wang

Feng

et al. 2017

“…Recently, studies of terahertz (THz) Bessel beams properties began, and Bessel beams of narrow and broadband THz radiation have already found their application in several fields. For example, usage of Bessel-like beams in THz imaging results in significantly improved depth of focus 8 . Another actively developing application based on THz radiation is THz communications, where the Bessel beam’s potential for wireless communications was studied 9 .…”

Section: Introductionmentioning

confidence: 99%

On terahertz pulsed broadband Gauss-Bessel beam free-space propagation

Kulya

Semenova

Bespalov

et al. 2018

Terahertz pulse time-domain holography is the ultimate technique allowing the evaluating a propagation of pulse broadband terahertz wavefronts and analyze their spatial, temporal and spectral evolution. We have numerically analyzed pulsed broadband terahertz Gauss-Bessel beam’s both spatio-temporal and spatio-spectral evolution in the non-paraxial approach. We have characterized two-dimensional spatio-temporal beam behavior and demonstrated all stages of pulse reshaping during the propagation, including X-shape pulse forming. The reshaping is also illustrated by the energy transfer dynamics, where the pulse energy flows from leading edge to trailing edge. This behavior illustrates strong spatio-temporal coupling effect when spatio-temporal distribution of Bessel beam’s wavefront depends on propagation distance. The spatio-temporal and spatio-spectral profiles for different spectral components clearly illustrate the model where the Bessel beam’s wavefront at the exit from the axicon can be divided into radial segments for which the wave vectors intersect. Phase velocity via propagation distance is estimated and compared with existing experimantal results. Results of the phase velocity calculation depend strongly on distance increment value, thus demonstrating superluminal or subluminal behavior.

“…Currently, investigations of THz special beams have gradually become an important development orientation, because it is possible that distinctive features of these light beams are applied to broaden the scope of THz application. In 2012, a broadband Bessel THz beam was introduced into a THz scanning imaging system for enhancing the capability of obtaining depth information 15 . In 2015, the longitudinal component of a THz vector vortex beam was utilized to realize the linear acceleration of electrons 16 .…”

Section: Introductionmentioning

confidence: 99%

Vector measurement and performance tuning of a terahertz bottle beam

Wang

et al. 2018

A terahertz (THz) bottle beam is realized by adopting the combination of a Teflon axicon and a silicon lens. By using a THz imaging system with a focal-plane array, the vector characteristics of the THz bottle beam are coherently measured and detailedly analyzed, including the transverse (Ex) and longitudinal (Ez) components. The experimental phenomena vividly reveal the distribution characteristics and the formation origin of the THz optical barrier. A vectorial diffraction integral algorithm of a focusing optical system are utilized to exactly simulate the measured results. Besides, the features of the THz bottle beam are effectively tuned by varying the parameters of the Teflon axicon and the silicon lens. This work gives a full view to understand the evolution characteristics of the THz bottle beam and provide a solid experimental foundation for guiding the future applications of this type of THz beam.