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Andrzej Szczepkowicz

Publications and source records attributed to Andrzej Szczepkowicz.

10 recordsLinked to original sources
arXiv2025

Monochromatic Cherenkov diffraction radiation from continuous coupling of an electron beam to a thin dielectric slab waveguide

A scheme for generation of monochromatic Cherenkov radiation in a thin dielectric layer is proposed. The electrons travel in vacuum parallel to a dielectric, exciting a single synchronous electromagnetic waveguide mode. The proposed scheme is studied quantitatively for near-infrared radiation in silicon induced by a 100-keV electron beam, using time-domain and frequency-domain numerical simulations, with material absorption and dispersion taken into account. This method of radiation generation can be scaled from ultraviolet to terahertz radiation by changing the thickness of the dielectric layer and choosing a material with low loss at the desired wavelength. Comparison with conventional Cherenkov Radiation and Cherenkov Diffraction Radiation is also presented.

physics.optics↗
arXiv2023

Efficiency of gratings for silica fiber-coupled internal Smith-Purcell radiation and Cherenkov diffraction radiation -- a quantitative numerical study

We propose a setup for measuring visible and near-visible internal Smith-Purcell radiation and Cherenkov Diffraction Radiation, based on silica and silicon, and perform quantitative numerical analysis of its radiation efficiency. We calculate the total radiated energy per electron and the spectral distribution of different radiation orders, taking into account material dispersion and absorption. For an optimized silica grating of 200 micrometer length, the total radiated energy reaches 2~eV per electron for 2 MeV electrons. Above the Cherenkov threshold, in most cases the energy of Cherenkov diffraction radiation is several times higher than the energy of internal Smith-Purcell radiation, but for some geometries and frequency ranges first or second order radiation may dominate over Cherenkov radiation (zeroth order). Radiation up to the 4th order is detected in the simulation. The spectrum of Cherenkov radiation is highly resonant, with local minima for frequencies where maxima of the other radiation orders occur. The spectrum of Cherenkov radiation takes a frequency comb-like shape for a uniform layer of Si on SiO2 substrate, due to a Fabry-Perot effect occurring for the evanescent field of the moving electron. The proposed setup could become a prototype of a non-invasive particle beam monitor for both conventional and laser particle accelerators.

physics.optics↗
arXiv2021

Internal Smith-Purcell radiation and its interplay with Cherenkov diffraction radiation in silicon -- a combined time and frequency domain numerical study

We consider radiation generated by an electron travelling parallel to a planar rectangular silicon grating: Smith-Purcell radiation to the vacuum side, internal Smith-Purcell radiation into the dielectric, and Cherenkov radiation into the dielectric. Internal Smith-Purcell radiation dominates over the other two radiation mechanisms in the range where conventional Smith-Purcell radiation is forbidden. This observation may lead to improved design of contactless particle beam monitors.

physics.optics↗
arXiv2020

Frequency-domain calculation of Smith-Purcell radiation for metallic and dielectric gratings

The intensity of Smith-Purcell radiation from metallic and dielectric gratings (silicon, silica) is compared in a frequency-domain simulation. The numerical model is discussed and verified with the Frank-Tamm formula for Cherenkov radiation. For 30 keV electrons, rectangular dielectric gratings are less efficient than their metallic counterpart, by an order of magnitude for silicon, and two orders of magnitude for silica. For all gratings studied, radiation intensity oscillates with grating tooth height due to electromagnetic resonances in the grating. 3D and 2D numerical models are compared.

physics.acc-ph↗
arXiv2018

Electron dynamics in grating-type dielectric laser accelerators: particle transfer function, generalized acceleration/deflection gradients and Panofsky-Wenzel theorem

The notions of acceleration gradient and deflection gradient are generalized to phasor quantities (complex-valued functions) in the context of dielectric laser acceleration (DLA). It is shown that the electromagnetic forces imparted on a near-resonant particle traversing a unit cell of a grating-type DLA can be conveniently described by generalized acceleration and deflection gradients. A~simple formulation of the Panofsky-Wenzel theorem in terms of the generalized gradients is given. It is shown that all particle transfer properties of a DLA unit cell can be derived from a single, complex-valued function, the generalized acceleration gradient.

physics.acc-ph↗
arXiv2017

Application of transfer matrix and transfer function analysis to grating-type dielectric laser accelerators: ponderomotive focusing of electrons

The question of suitability of transfer matrix description of electrons traversing grating-type dielectric laser acceleration (DLA) structures is addressed. It is shown that although matrix considerations lead to interesting insights, the basic transfer properties of DLA cells cannot be described by a matrix. A more general notion of a transfer function is shown to be a simple and useful tool for formulating problems of particle dynamics in DLA. As an example, a focusing structure is proposed which works simultaneously for all electron phases.

physics.acc-ph↗
arXiv2011

Oxygen-covered tungsten crystal shape: time effects, equilibrium, surface energy and the edge-rounding temperature

The equilibrium crystal shape (ECS) of oxygen-covered tungsten micricrystal is studied as a function of temperature. The specially designed ultrafast crystal quenching setup with the cooling rate of 6000 K/s allows to draw conclusions about ECS at high temperatures. The edge-rounding transition is shown to occur between 1300 K and 1430 K. The ratio of surface free energies $γ(111)/γ(211)$ is determined as a function of temperature.

cond-mat.stat-mech↗
arXiv2009

Image deformation in field ion microscopy of faceted crystals

We perform detailed numerical simulations of field ion microscopy images of faceted crystals and compare them with experimental observations. In contrast to the case of crystals with a smooth surface, for a faceted topography we find extreme deformations of the ion image. Local magnification is highly inhomogeneous and may vary by an order of magnitude: from 0.64 to 6.7. Moreover, the anisotropy of the magnification at a point located on the facet edge may reach a factor of 10.

cond-mat.mes-hall↗
arXiv2008

Optimal geometry for efficient loading of an optical dipole trap

One important factor which determines efficiency of loading cold atoms into an optical dipole trap from a magneto-optical trap is the distance between the trap centers. By studying this efficiency for various optical trap depths (2--110 mK) we find that for optimum dipole trap loading, longitudinal displacements up to 15 mm are necessary. An explanation for this observation is presented and compared with other work and a simple analytical formula is derived for the optimum distance between the trap centers.

physics.atom-ph↗