Dark Hollow Gaussian Beam Research Articles

Terahertz emission with remarkable efficiency through spherical nanoparticles using dark-hollow-Gaussian beams

Simultaneous tuning of Terahertz (THz) radiation with respect to its frequency, power and focus is still a challenge for the scientific community, because of which its use is lacking in several areas. To achieve such properties, the present work proposes monodisperse graphite nanoparticles (NPs) of spherical shape dispersed in two orthogonal directions with normal vector of their basal planes parallel and perpendicular to the electric field of the dark-hollow-Gaussian beams (DHGBs) used for the generation of THz radiation. The NPs are impinged upon by two DHGBs of slightly different frequencies, which exert a ponderomotive force on the conduction electrons of the NPs. The motion of these electrons under the action of high intensity laser beams constitutes a macroscopic nonlinear current that produces the THz radiation. The well-structured THz emission occurs with the efficiency reaching 10−2 when the NPs resonate with the beating frequency, and they are arranged in their parallel orientations with respect to the electric field of the lasers. The proposal and the obtained results will contribute to the THz science and technology along with their use in medical science and THz time-domain spectroscopy.

THz radiation generation in axially magnetized collisional pair plasma

We investigate the electron-positron plasma for terahertz radiation generation by two Dark Hollow Gaussian beams (DHGBs), which result in multifocal radiations quite useful for various modern applications. In this process, the ponderomotive force acts as a driver for the generation of terahertz field and the realistic situation of collisional plasma under the application of axial magnetic field reveals an efficient radiation generation. An appreciable efficiency of more than 2% is achieved for the process.

Focusing properties of partially coherent dark hollow Gaussian beams through a thin lens system

This paper investigated the focal shift of partially coherent dark hollow Gaussian beams through a thin lens system. An analytic expression of the irradiance distribution of the focusing partially coherent dark hollow Gaussian beams in the back focal plane has been given by using the Collins formula. The focus shift of focused partially coherent dark hollow Gaussian beams in different parameters is studied in detail by numerical calculations. It is found that the absolute value of the focal shift of partially coherent dark hollow Gaussian beams decreases as the transverse coherence width or the order of the dark hollow Gaussian beams or a parameter of the dark hollow Gaussian beams increases.

Hollow Gaussian beam generated by beam shaping with phase-only liquid crystal spatial light modulator

Based on the refractive beam shaping system, the transformation of a quasi-Gaussian beam into a dark hollow Gaussian beam by a phase-only liquid crystal spatial light modulator (LC-SLM) is proposed. According to the energy conservation and constant optical path principle, the phase distribution of the aspheric lens and the phase-only LC-SLM can modulate the wave-front properly to generate the hollow beam. The numerical simulation results indicate that, the dark hollow intensity distribution of the output shaped beam can be maintained well for a certain propagation distance during which the dark region will not decrease whereas the ideal hollow Gaussian beam will do. By designing the phase modulation profile, which loaded into the LC-SLM carefully, the experimental results indicate that the dark hollow intensity distribution of the output shaped beam can be maintained well even at a distance much more than 550 mm from the LC-SLM, which agree with the numerical simulation results.

Spectral Anomalies of Polychromatic DHGB and Its Applications in FSO

This paper contains some interesting experimental results of the study carried out on anomalous spectral behavior due to coherence and polarization change on polychromatic focused dark hollow Gaussian beam (DHGB). On the basis of experimental and numerical analysis, the possibility and significance of DHGB based free-space optical (FSO) links for indoor and outdoor optical communications are explored.

Relativistic and ponderomotive effects on evolution of dark hollow Gaussian electromagnetic beams in a plasma

AbstractNonlinear parabolic partial differential equation governing the evolution of complex envelope in slowly varying envelope approximation is solved using variational approach. The basic nonlinear phenomena of relativistic and ponderomotive self-focusing in a plasma are taken into account. Self-focusing, self-phase modulation as well as self-trapping of dark hollow Gaussian beam is studied for higher orders of hollow Gaussian beam (n).

The effect of spherical aberration on the phase singularities of focused dark-hollow Gaussian beams

The phase singularities of focused dark-hollow Gaussian beams in the presence of spherical aberration are studied. It is shown that the evolution behavior of phase singularities of focused dark-hollow Gaussian beams in the focal region depends not only on the truncation parameter and beam order, but also on the spherical aberration. The spherical aberration leads to an asymmetric spatial distribution of singularities outside the focal plane and to a shift of singularities near the focal plane. The reorganization process of singularities and spatial distribution of singularities are additionally dependent on the sign of the spherical aberration. The results are illustrated by numerical examples.

Phase singularities of the transverse field component of high numerical aperture dark-hollow Gaussian beams in the focal region

By using the vectorial Debye diffraction theory, phase singularities of high numerical aperture (NA) dark-hollow Gaussian beams in the focal region are studied. The dependence of phase singularities on the truncation parameter δ and semi-aperture angle α (or equally, NA) is illustrated numerically. A comparison of phase singularities of high NA dark-hollow Gaussian beams with those of scalar paraxial Gaussian beams and high NA Gaussian beams is made. For high NA dark-hollow Gaussian beams the beam order n additionally affects the spatial distribution of phase singularities, and there exist phase singularities outside the focal plane, which may be created or annihilated by variation of the semi-aperture angle in a certain region.

Nonparaxial Dark-Hollow Gaussian Beams

The concept of nonparaxial dark-hollow Gaussian beams (DHGBs) isintroduced. By using the Rayleigh–Sommerfeld diffraction integral, theanalytical propagation equation of DHGBs in free space is derived. Theon-axis intensity, far-field equation and, in particular, paraxialexpressions are given and treated as special cases of our result. It isshown that the parameter f = 1/kw0 with k beingthe wave number and w0 being the waist width determinesthe nonparaxiality of DHGBs. However, the parameter range, within whichthe paraxial approach is valid, depends on the propagation distance.The beam order affects the beam profile and position of maximum on-axisintensity.