The paper discusses the effect of the initial electron bunch distribution on the angular and spectral parameters of the radiation the bunch produces when passing periodic structures. The realistic electron bunch distributions in the vicinity of the photocathode are obtained with the use of the dedicated numerical code PhDyn. The beam dynamics for electron bunches in the radio-frequency photogun and the linear accelerator following it are calculated using the BEAMDULAC_BL-photogun code. The electron phase space distributions obtained with this code are subsequently used to simulate spiral undulator and channeling radiations. The results reveal significant deviations in the spectral-angular distributions when realistic initial distributions are used, highlighting the importance of accurate modeling of the photocathode emission process.
The paper considers the possibility of using synchrotron radiation as a source of photons carrying OAM. We derive a simple formula describing the spectral-angular distribution of photons as a function of their OAM and polarization. This formula describes the general properties of synchrotron radiation regardless of the specific field configuration or particle energy. We show that the radiation properties are symmetric under the simultaneous reversal of the signs of the OAM and the photon spin. As a result, the total OAM per photon in synchrotron radiation is zero. We numerically show how much energy corresponds to radiation with definite values of OAM and polarization. More than 86% of the total energy emitted in synchrotron radiation is in the form of twisted photons. We determine the frequencies and angles at which the maximum energy loss occurs for given values of OAM and polarization. In addition, the paper provides the corresponding values of the radiated energy at these maxima.
We investigate “quantum vortices” (QV) in the amplitude of the ionization of polarized atoms by few-cycle circularly polarized (CP) pulses. These are zeros of the ionization amplitude, which are seen as swirls in the amplitude’s velocity field. By analyzing results of numerical simulations of the ionization of polarized atoms by left- and right-hand CP (LCP and RCP) pulses, we have found that positions of QVs in the momentum space exhibit some regularities when ionization is performed in the multiphoton regime. Namely, QVs in the emission plane perpendicular to the pulse propagation direction occur in points with the same momentum p but different emission angles φ for both, RCP and LCP pulses. Based on the parametrization of the ionization amplitude within the non-stationary perturbation theory (PT), we present arguments explaining the vortex position rule. Apart from that, by representing the multipole terms of the ionization amplitude as vectors on a complex plane, we demonstrate that QVs can be associated with polygonal figures, which are topologically equivalent in the cases of the ionization by RCP and LCP pulses.
In a multi-ion magnetoplasma with two different ion species (p and q) and kappa-distributed electrons, the Rayleigh–Taylor (RT) instability, a fundamental plasma instability causing equatorial plasma bubbles (EPBs) in the ionospheric F-region, is examined. The dispersion relation for electrostatic perturbations in a density-stratified plasma under gravity is derived using a linear fluid model. In line with the susceptibility of EPB occurrence to bottomside F-region preconditioning documented during the 2022 Tonga volcanic eruption and the July 2022 geomagnetic storm, the unstable threshold and growth-rate curve fluctuate systematically with the inverse density scale length. By using the reductive perturbation method to extend to the nonlinear regime, we obtain a Korteweg–de Vries (KdV) equation whose soliton solutions show amplitudes and widths that are sensitive to plasma parameters, such as the kappa index and ion mass ratio. Numerical results demonstrate that ion composition and electron superthermality can substantially modify the amplitude, width, and localization of the weakly nonlinear structures. A distinguishing feature of the present study is the treatment of composition-dependent ion inertia and a non-Maxwellian electron response within one linear-to-weakly nonlinear framework, together with an explicit parameter set that permits numerical reproduction of the plotted branches. The resulting dependencies provide reduced-order diagnostics for interpreting composition-sensitive structures measured by satellites, ionosondes, airglow imagers, coherent radars, and Global Navigation Satellite System receivers. They can also be used as benchmarks for multi-ion ionospheric simulations and as physically interpretable inputs to EPB occurrence and scintillation-risk studies. The one-dimensional solitary structures are, therefore, presented as local nonlinear plasma diagnostics rather than as complete models of mature, three-dimensional plasma bubbles. In this article we obtain a Korteweg–de Vries (KdV) equation whose soliton solutions show amplitudes and widths that are sensitive to the following plasma parameters such as: Kappa index, Ion to mass ratio, Numerical results demonstrate that ion composition and electron super thermality can substantially modify the amplitude, width, and localization of the weakly nonlinear structures as shown in the below figure. Fig Shows Normalized solitary-wave profiles at m_p/m_q=16 for κ =3 , κ =5 , and the Maxwellian limit, with α _p=0.90 , α _q=0.10 , and U=0.1 . The curves have smooth, sharp peaks and use solid lines throughout. A distinguishing feature of the present study is the treatment of composition-dependent ion inertia and a non-Maxwellian electron response within one linear-to-weakly nonlinear framework, together with an explicit parameter set that permits numerical reproduction of the plotted branches.
In this experimental work, we address the issue of quantum interference-assisted optical offset frequency switching through a combination of ladder 5S_1/2⟶_780nm^5P_3/2⟶_776nm^5D_5/2 + Vee ( 5S_1/2⟶_780nm^5P_3/2 ) connections in a Doppler-broadened medium of Rb atoms using three excitation fields in the first part of the study. The system exhibits electromagnetically induced transparency. However, ultra-narrow electromagnetically induced absorption appears as a fine structure within the transparency lineshape when the Vee system is reduced to a degenerate two-level connection by addressing 5S1/2(F=2) →5P3/2(F/=3) cyclic transition. The blue fluorescence due to the decay of atoms through the channel 5D_5/2⟶_5.2μ m^6P_3/2⟶_420nm^5S_1/2 , indicating the double resonance optical pumping signal starts to get weakened under the influence of Vee-type electromagnetically induced transparency, compared to the same obtained under a pure ladder system. However, the blue light signal becomes almost obscured in the current atom–field picture when the electromagnetically induced absorption signal appears around the closed transition F=2→F/=3. Very high extinction ratio of blue light at this particular condition paves the way for offset frequency switching at 420 nm by modulating the intensity of one of the excitation channels, satisfying a two-level double-degenerate connection in the 5S→5P hyperfine manifold. In the second part of the investigation, we used phase-correlated beams from a single laser to execute degenerate two-level coupling and left the third laser connecting the 5P→5D transition domain intact. By switching ON and OFF one of the near infrared (780 nm), we obtain switching in the blue fluorescence at 420 nm, thereby establishing offset frequency switching. This may lead to important technical applications like obtaining higher modulation depth in coherence-assisted intensity switching, logic gate construction, etc., in the field of optical communication.
