super-Gaussian Laser Research Articles

Strong Terahertz Generation by Beating of Two Super Gaussian Laser Beams in Axially Magnetized Plasma

THz generation by nonlinear mixing of two coaxial Super-Gaussian laser beams, propagating in rippled density plasma with an axially applied static magnetic field, is investigated. The ponderomotive force which arises due to nonuniform spatial intensity profiles of laser beams, imparts a nonlinear oscillatory velocity at beat wave frequency to electrons. This oscillatory velocity couples with the preformed density ripple to generate a nonlinear current density driving a radiation. Frequencies of lasers are chosen such that the beat frequency lies in the terahertz region. The density ripple provides the phase matching for resonant excitation and the axial static magnetic field is utilized to enhance the nonlinear coupling. Numerical results show that the yield of the generated THz amplitude enhances with increase in index of super-Gaussian lasers as well as the magnitude of the axially applied static magnetic field.

Comparison of Gaussian and super Gaussian laser beams for addressing atomic qubits

We study the fidelity of single qubit quantum gates performed with two-frequency laser fields that have a Gaussian or super Gaussian spatial mode. Numerical simulations are used to account for imperfections arising from atomic motion in an optical trap, spatially varying Stark shifts of the trapping and control beams, and transverse and axial misalignment of the control beams. Numerical results that account for the three dimensional distribution of control light show that a super Gaussian mode with intensity $I\sim e^{-2(r/w_0)^n}$ provides reduced sensitivity to atomic motion and beam misalignment. Choosing a super Gaussian with $n=6$ the decay time of finite temperature Rabi oscillations can be increased by a factor of 60 compared to an $n=2$ Gaussian beam, while reducing crosstalk to neighboring qubit sites.

High-intensity terahertz generation by nonlinear frequency-mixing of lasers in plasma with DC magnetic field

AbstractWe propose a mechanism of highly focused, tunable and high-intensity terahertz (THz) radiation generation by frequency-mixing of two super-Gaussian lasers with frequencies ω1, ω2 and wave numbers k1, k2 (laser profile index p > 2) in a corrugated plasma in the presence of external static magnetic field ${B_0}\hat z$. In this process, a strong nonlinear ponderomotive force is offered to the plasma electrons at frequency ω′ = ω1 − ω2 and wave number k′ = k1 − k2 by laser beams. The ponderomotive force results in a strong, controllable nonlinear transverse oscillatory current, which can be optimized by optimizing the external magnetic field, ripple parameters, and laser indexes. This controllable current produces focused and intense THz radiation of tunable frequency and power along with a remarkable efficiency ~25%.

Publisher's Note: Tunable and efficient terahertz radiation generation by photomixing of two super Gaussian laser pulses in a corrugated magnetized plasma [J. Appl. Phys. 117, 193303 (2015)

First Page

Enhancement of terahertz emission in magnetized collisional plasma

We carry out analytical calculations for the electric field amplitude and efficiency of the mechanism of terahertz (THz) radiation generated due to interaction of super-Gaussian lasers with collisional plasma. The contribution of magnetic field and the role of index of lasers for enhancing the field amplitude are uncovered under the effect of laser beam width and collision frequency between electrons and neutrals. Terahertz radiation with larger electric field is realized when lasers of higher index and lower beam widths interact with the plasma in the presence of an external static magnetic field. Under optimized parameters, THz field amplitude of about 107 kV m−1 and 6% efficiency of the mechanism can be realized using the lasers with field 5.0 × 1010 V m−1.

Self-focusing of super-Gaussian laser beam inmagnetized plasma under relativistic and ponderomotive regime

In this paper, we have investigated the propagation characteristics of super-Gaussian laser beam in magnetized plasma. Self-focusing of short pulse laser propagating along the direction of ambient magnetic field in plasma is studied. The nonlinearity arises through the combined effect of relativistic mass variation and ponderomotive force induced electron cavitation. An appropriate nonlinear Schro¨dinger equation has been solved analytically using variational approach. Self-phase modulation is also studied under variety of parameters. Further, the effect of magnetic field on self-focusing of the beam have been explored.

Tunable and efficient terahertz radiation generation by photomixing of two super Gaussian laser pulses in a corrugated magnetized plasma

A scheme of terahertz (THz) radiation generation is investigated by photo-mixing of two super Gaussian laser beams having different frequencies (ω1, ω2) and wave numbers (k→1, k→2) in a performed corrugated plasma embedded with transverse dc magnetic field. Lasers exert a nonlinear ponderomotive force, imparting an oscillatory velocity to plasma electrons that couples with the density corrugations (n′=nα0eiαz) to generate a strong transient nonlinear current, that resonantly derives THz radiation of frequency ∼ωh (upper hybrid frequency). The periodicity of density corrugations is suitably chosen to transfer maximum momentum from lasers to THz radiation at phase matching conditions ω=ω1−ω2 and k→=k→1−k→2+α→. The efficiency, power, beam quality, and tunability of the present scheme exhibit high dependency upon the applied transverse dc magnetic field along with q-indices and beam width parameters (a0) of super Gaussian lasers. In the present scheme, efficiency ∼10−2 is achieved with the optimization of all these parameters.

Generation and pointing stabilization of multi-GeV electron beams from a laser plasma accelerator driven in a pre-formed plasma waveguidea)

Laser pulses with peak power 0.3 PW were used to generate electron beams with energy >4 GeV within a 9 cm-long capillary discharge waveguide operated with a plasma density of ≈7×1017 cm−3. Simulations showed that the super-Gaussian near-field laser profile that is typical of high-power femtosecond laser systems reduces the efficacy of guiding in parabolic plasma channels compared with the Gaussian laser pulses that are typically simulated. In the experiments, this was mitigated by increasing the plasma density and hence the contribution of self-guiding. This allowed for the generation of multi-GeV electron beams, but these had angular fluctuation ≳2 mrad rms. Mitigation of capillary damage and more accurate alignment allowed for stable beams to be produced with energy 2.7±0.1 GeV. The pointing fluctuation was 0.6 mrad rms, which was less than the beam divergence of ≲1 mrad full-width-half-maximum.

High energy protons generation by two sequential laser pulses

The sequential proton acceleration by two laser pulses of relativistic intensity is proposed to produce high energy protons. In the scheme, a relativistic super-Gaussian (SG) laser pulse followed by a Laguerre-Gaussian (LG) pulse irradiates dense plasma attached by underdense plasma. A proton beam is produced from the target and accelerated in the radiation pressure regime by the short SG pulse and then trapped and re-accelerated in a special bubble driven by the LG pulse in the underdense plasma. The advantages of radiation pressure acceleration and LG transverse structure are combined to achieve the effective trapping and acceleration of protons. In a two-dimensional particle-in-cell simulation, protons of 6.7 GeV are obtained from a 2 × 1022 W/cm2 SG laser pulse and a LG pulse at a lower peak intensity.

Comparison between illumination model and hydrodynamic simulation for a direct drive laser irradiated target

AbstractA spherical target irradiated by laser beams located at 49o and 131° with respect to the polar axis has been considered. The illumination model has been used to evaluate the irradiation non-uniformity assuming circular and elliptical super-Gaussian laser intensity profiles and the irradiation scheme has been optimized by means of the polar direct drive technique. A parametric study has been performed providing the irradiation non-uniformity as a function of the polar direct drive displacement and of the laser intensity profile parameters. Moreover, two-dimensional axis-symmetric hydrodynamic simulations have been performed for a plastic sphere irradiated by laser beams characterized by a constant flat temporal power pulse. In these simulations, the front of the inward shock wave has been tracked providing the time-evolution of any non-uniformity. The results provided by the two methods — illumination model and hydrodynamic data — have been compared and it is found that the illumination model reproduces the main behavior exhibited by the hydrodynamic data. The two models provide compatible values for the optimum polar direct drive parameter and similar optimal super-Gaussian profiles.

Terahertz generation by mixing of two super-Gaussian laser beams in collisional plasma

Considering a realistic situation, where electron-neutral collisions persist in plasma, analytical calculations are carried out for the Terahertz (THz) radiation generation by beating of two Super-Gaussian (SG) lasers of index p. The competency of these lasers over Gaussian lasers is discussed in detail with respect to the effects of collision and beam width on the THz field amplitude and efficiency of the mechanism. A critical transverse distance of the peak of the THz field is defined that shows a dependence on the index of SG lasers. Although electron-neutral collisions and larger beam width lead to the drastic reduction in the THz field when the SG lasers are used in the plasma, the efficiency of the mechanism remains much larger than the case of Gaussian lasers. Moreover, the higher index SG lasers produce stronger and focused THz radiation.

Numerical analysis of the direct drive illumination uniformity for the Laser MegaJoule facility

The illumination uniformity provided during the initial imprinting phase of the laser foot pulse in a direct drive scenario at the Laser MegaJoule facility has been analyzed. This study analyzes the quality of the illumination of a spherical capsule and concerns the uniformity of the first shock generate in the absorber of an Inertial Confinement Fusion capsule. Four configurations making use of all or some of the 80 laser beams organized in the 20 quads of the cones at 49° and 131° with respect to the polar axis have been considered in order to assemble the foot pulse. Elliptical and circular super-gaussian laser intensity profiles taking into account beam-to-beam power imbalance (10%), pointing error (50 μm), and target positioning (20 μm) have been considered. It has been found that the use of the Polar Direct Drive technique can in some cases reduce the irradiation non-uniformity by a factor as high as 50%. In all cases, elliptical profile provides better results in comparison with the circular one and it is shown that the minimum of the non-uniformity is also a function of the capsule radius.

Polar direct drive illumination uniformity provided by the Orion facility

The ten long-pulse laser beams of the Orion facility have been considered as a direct driver for the irradiation of a spherical capsule. The intrinsic root-mean-square illumination non-uniformity σ 0 has been evaluated assuming circular and elliptical super-Gaussian laser intensity profiles. Calculations accounting for nominal uncertainties in power imbalance, pointing error and target positioning have shown a degradation of the irradiation uniformity. Non-uniformity of the irradiation as a function of the capsule radius has been calculated and it has been shown that the use of the polar direct drive technique significantly improves the quality of the irradiation. Finally, it is found that an elliptical focal shape provides better symmetry results in comparison to circular ones, whilst the laser-capsule coupling is reduced.

Effects of laser pulse shape and carrier envelope phase on pair production

For different fields of supercycle and subcycle laser pulses, the effects of laser pulse shape and carrier envelope phase on pair production are investigated by solving quantum Vlasov equation. By changing the pulse width and shape, the nonlinear behaviors of momentum distribution function and number density of created electron–positron pairs are obtained. It is found that there exist the multiphoton processes and stabilization phenomenon in pair production for supercycle situation. Our study may shed a light on optimizing the form of applied laser field to enhance the created pairs number, for example, when other conditions are fixed, the flat-top super-Gaussian laser pulse has advantage on pairs production.

Wakefield generation and electron acceleration by intense super-Gaussian laser pulses propagating in plasma

AbstractEvolution of longitudinal electrostatic wakefields, due to the propagation of a linearly polarized super-Gaussian laser pulse through homogeneous plasma has been presented via two-dimensional particle-in-cell simulations. The wakes generated are compared with those generated by a Gaussian laser pulse in the relativistic regime. Further, one-dimensional numerical model has been used to validate the generated wakefields via simulation studies. Separatrix curves are plotted to study the trapping and energy gain of an externally injected test electron, due to the generated electrostatic wakefields. An enhancement in the peak energy of an externally injected electron accelerated by wakes generated by super-Gaussian pulse as compared to Gaussian pulse case has been observed.

Effects of pulse transverse profile on electron bow-wave injection of electrons in laser wakefield acceleration

In this paper we study the effects of transverse profile of incident laser on trapping of electrons in an electron bow-wave injection regime. By using the particle-in-cell code, we find that the super-gaussian profile laser pulse can drive more energetic electrons of the electron bow-wave into the bubble with higher longitudinal injection velocity. At last, the total number of trapped electrons increases almost 5 times. And the quality of electron beam is also improved obviously.

Nonlocal Ponderomotive Force in a Super Gaussian Laser Beam and the Conditions for Long Time Scale Interaction

Nonlocal Ponderomotive Force in a Super Gaussian Laser Beam and the Conditions for Long Time Scale Interaction

Strong and collimated terahertz radiation by super-Gaussian lasers

We propose two super-Gaussian laser beams with frequency difference for obtaining more collimated terahertz (THz) radiation at a desired position based on their order/index and for enhancing the efficiency of the scheme by realizing stronger transient transverse current due to the spatial variation of their fields. For the laser intensity of ∼1014 W/cm2 and along with the application of a periodic density structure, a resonant excitation of the THz radiation is achieved together with the efficiency of scheme as ∼0.006.

Self-focusing of super-Gaussian laser beams propagating in an array of carbon nanotubes

Propagation of a monochromatic laser beam in an array of carbon semiconductor nanotubes is considered. Initial distribution of the field intensity in the beam incident on the system is chosen in the form of a super-Gaussian profile in the plane perpendicular to the wave vector. The electromagnetic field of laser radiation in the nanotube array is described semiclassically by the Maxwell equations. In the approximation of slowly varying amplitudes and phases, the effective equation is derived and solved numerically that allows the intensity distribution of the beam field in the system to be determined. The phenomenon of laser beam self-focusing onto a waist region with increased field intensity is revealed. Dependences of the characteristics of the waist region on the amplitude and frequency of the laser radiation field incident on the system are obtained.

Relativistic self-focusing of super-Gaussian laser beam in plasma with transverse magneticfield

AbstractThis paper presents an investigation of a self-consistent, theoretical model, which explains the ring formation in a super-Gaussian laser beam propagating in plasma with transverse magnetic field, characterized by relativistic nonlinearity. Higher order terms (up to r4) in the expansion of the dielectric function and the eikonal have been taken into account. The condition for the formation of a dark and bright ring has been used to study focusing/defocusing of the beam. It is seen that inclusion of higher order terms does significantly affect the dependence of beam width parameter on the distance of propagation. Self-focusing of super-Gaussian beam is studied at various values of super-Gaussian coefficient, m and magnetic field. Further, we have studied some distinct features of critical power curves for varying values of magnetic field.