Optical Cherenkov Radiation Research Articles

Feasibility of using optical Cherenkov radiation for non-relativistic ion beam diagnostics

In this paper, we propose to use quasi-monochromatic Cherenkov spectral lines for ion beam diagnostics. As representatives of light and heavy ions, we use C12 and Au197 ions, respectively. First, using the Geant4 toolkit, we determine the ionization lost energy as a function of the radiator penetration depth. After that, we use those data in the polarization currents method to compare the theoretical spectral lines with and without ionization losses. We also use the real-beam polarization currents method to analyze real-beam and setup parameters affecting the accuracy of the beam diagnostics. We emphasize that the precision of refractive index measurement might be a source of inaccuracy in ion beam diagnostics. Nevertheless, according to the provided data, we can expect that the method for measuring Cherenkov quasi-monochromatic spectral lines should be applicable for beam-diagnostics purposes, especially for lighter ions.

Monochromatic Optical Cherenkov Radiation of Moderately Relativistic Ions in Radiators with Frequency Dispersion

Monochromatic Optical Cherenkov Radiation of Moderately Relativistic Ions in Radiators with Frequency Dispersion

Measuring temporal characteristics of the Cherenkov radiation signal from extensive air showers of cosmic rays with a wide field-of-view telescope addendum to the Yakutsk array

A wide field-of-view Cherenkov telescope has been working in the surroundings of the Yakutsk array experiment since 2012. Its main function is to measure the waveform of the optical Cherenkov radiation signal induced by extensive air showers of cosmic rays. Analysis of the dataset collected by the telescope in the vicinity of ${10}^{17}\text{ }\text{ }\mathrm{eV}$ is intended for the reconstruction of the parameters of the development of the showers in addition to the main shower characteristics measured by the rest of the array detectors. In this paper, the observed duration of the Cherenkov radiation signal as a function of the shower core distance is used to estimate the depth of the shower maximum in a different way based on the results of model simulations. The results are in general agreement with those of other works.

First observation of quasi–monochromatic optical Cherenkov radiation in a dispersive medium (quartz)

The present article summarizes the results of a study of optical Cherenkov radiation (ChR) spectral properties both theoretically and experimentally. This type of radiation has a continuous spectral distribution which allows to use it in different fields of physics as for charged particle identification or generation of intense THz radiation. By exploiting the frequency dependency of the target permittivity it is possible to observe quasi–monochromatic radiation. A theoretical model based on a surface current approach is presented which allows to predict angular and spectral properties of ChR. In order to test the model predictions, an experiment was carried out using 855 MeV electrons and a 0.2 mm thick quartz target as radiator which could be rotated with respect to the beam axis. Quasi–monochromatic ChR was observed with a spectrometer placed at a fix observation angle, and tilting the radiator crystal offered the possibility to tune the radiation wavelength. The monochromatization effect is attributed to the frequency dependency of the quartz permittivity, and taking into account the refraction law for emitted ChR crossing the boundary between radiator target and vacuum it is possible to deduce a dispersion relation which connects ChR wavelength and outgoing photon angle - or in an alternative way ChR wavelength and target tilt angle for fixed observation angle. The dispersion relation is clearly confirmed in the experiment, and the model predictions show a satisfactory agreement with the measurements. Exploiting the ChR monochromatization mechanism might offer versatile tools which can find applications for example in beam diagnostics at modern particle accelerators.

CHERENKOV RADIATION OF THE RELATIVISTIC ELECTRON BUNCH IN ION DIELECTRIC MEDIA

The process of wakefields excitation by the relativistic electron bunch in dielectric media with ion type of chemical bond is studied. The spatio-temporal structure of the excited wakefield in ion dielectric waveguide is obtained and investigated. It is shown that the excited wakefield in the infrared and longer wavelength ranges consists of the field of longitudinal optical phonons and Cherenkov radiation as a set of eigen electromagnetic waves of the dielectric waveguide.

Structure of optical Cherenkov radiation in a three-dimensional compound medium with carbon nanotubes

We study the optical Cherenkov radiation in a compound three-dimensional (3D) system with a charge moving over a periodic system of parallel carbon nanotubes. To consider a case of bounded single-walled nanotubes, we apply the numerical finite-difference time-domain technique. We found that, because of the broadband radiation of a charge, the spectrum of the optical field in such a nanosystem is determined by the surface plasmon-polariton excitations. Our study of the field energy spectrum as a function of the plasma frequency detects a nonmonotonic double-well dependency within the area of a surface plasmon-polariton resonance. A well-defined peak that indicates a generation of collective excitations in nanotubes by Cherenkov field is registered.

Optical Cherenkov radiation in overmoded microresonators.

We show that an optical analog of Cherenkov radiation (dispersive wave) is observable in a nonlinear microring resonator generating Kerr frequency comb and containing linearly interacting families of equidistant modes. The radiation results from disruptions in the frequency dependent group velocity dispersion of the pumped cavity modes and is emitted into different mode families of the resonator. This effect reveals itself as a dispersive shaped structure in the spectral envelope of the frequency comb. We found that the dips in the comb spectrum correspond to peaks of the emission of the power in the other mode families of the resonator. The spectrum of the combs that includes both mode families does not have any dips, but peaks and resembles the Cherenkov radiation spectra frequently observed in Kerr comb systems. This Letter shows that a correct description of the Kerr comb in presence of mode anti-crossings should take into account not only the pumped mode family with modified dispersion parameter, but also the modes of the interacting families.

Optical Cherenkov radiation in an As_2S_3 slot waveguide with four zero-dispersion wavelengths

We propose an approach for an efficient generation of optical Cherenkov radiation (OCR) in the near-infrared by tailoring the waveguide dispersion for a zero group-velocity mismatching between the radiation and the pump soliton. Based on an As(2)S(3) slot waveguide with subwavelength dimensions, dispersion profiles with four zero dispersion wavelengths are found to produce a phase-matching nonlinear process leading to a broadband resonant radiation. The broadband OCR investigated in the chalcogenide waveguide may find applications in on-chip wavelength conversion and near-infrared pulse generation.

Efficient frequency shifting of dispersive waves at solitons

We demonstrate frequency redshifting and blueshifting of dispersive waves at group velocity horizons of solitons in fibers. The tunnelling probability of waves that cannot propagate through the fiber-optical solitons (horizons) is measured and described analytically. For shifts up to two times the soliton spectral width, the waves frequency shift with probability exceeding 90% rather than tunnelling through the soliton in our experiment. We also discuss key features of fiber optical Cherenkov radiation such as high efficiency and large bandwidth within this framework.

THz source based on optical Cherenkov radiation

Terahertz (THz) technique has attracted considerable interest due to its broad application prospects. THz source is a crucial part of THz science and technology. Optical Cherenkov radiation in electro-optic crystals is a promising method of THz generation, because phase-matching is automatically satisfied. In this paper, we introduced two types of THz source based on optical Cherenkov radiation: both broadband and tunable monochromatic. The mechanism of radiation was analyzed and recent development was reviewed in detail. The future of THz source based on optical Cherenkov radiation was also forecasted.

Optical Cherenkov radiation by cascaded nonlinear interaction: an efficient source of few-cycle energetic near- to mid-IR pulses

When ultrafast noncritical cascaded second-harmonic generation of energetic femtosecond pulses occur in a bulk lithium niobate crystal optical Cherenkov waves are formed in the near- to mid-IR. Numerical simulations show that the few-cycle solitons radiate Cherenkov (dispersive) waves in the λ = 2.2 - 4.5 μm range when pumping at λ₁ = 1.2 - 1.8 μm. The exact phase-matching point depends on the soliton wavelength, and we show that a simple longpass filter can separate the Cherenkov waves from the solitons. The Cherenkov waves are born few-cycle with an excellent Gaussian pulse shape, and the conversion efficiency is up to 25%. Thus, optical Cherenkov waves formed with cascaded nonlinearities could become an efficient source of energetic near- to mid-IR few-cycle pulses.

Optical Cherenkov radiation in ultrafast cascaded second-harmonic generation

We show through theory and numerics that when few-cycle femtosecond solitons are generated through cascaded (phase-mismatched) second-harmonic generation, these broadband solitons can emit optical Cherenkov radiation in the form of linear dispersive waves located in the red part of the spectrum. The beating between the dispersive wave and the soliton generates trailing temporal oscillations on the compressed soliton. Insertion of a simple short-wave pass filter after the crystal can restore a clean soliton. On the other hand, bandpass filtering around the dispersive wave peak results in near-transform-limited ultrashort mid-IR pulses with pulse durations much shorter than the input near-IR pulse. The Cherenkov radiation for the crystal considered ($\ensuremath{\beta}$-barium borate) is found for pump wavelengths in the range $\ensuremath{\lambda}=0.95--1.45 \mathrm{\ensuremath{\mu}}\mathrm{m}$, and is located in the regime $\ensuremath{\lambda}=1.5--3.5 \mathrm{\ensuremath{\mu}}\mathrm{m}$. For shorter pump wavelengths, the phase-matching point is located in the absorption region of the crystal, effectively absorbing the generated dispersive wave. By calculating the phase-matching curves for typically used frequency conversion crystals, we point out that the mid-IR absorption in the crystal in many cases automatically will filter away the dispersive wave. Finally, an investigation of recent experimental results uncovers a four-wave-mixing phenomenon related to Cherenkov radiation that is an additional generation mechanism of long-wavelength radiation that can occur during soliton compression. We discuss the conditions that lead to this alternative dynamics rather than generation of Cherenkov radiation.

Attenuation of acoustic waves in glacial ice and salt domes

Two classes of natural solid media, glacial ice and salt domes, are under consideration as media in which to deploy instruments for detection of neutrinos with energy ≥1018 eV. Though insensitive to 1011 to 1016 eV neutrinos for which observatories (e.g., AMANDA and IceCube) that utilize optical Cherenkov radiation detectors are designed, radio and acoustic methods are suited for searches for the very low fluxes of neutrinos with energies >1017 eV. This is because owing to the very long attenuation lengths of radio and acoustic waves produced by interactions of such neutrinos in ice and salt, detection modules can be spaced at horizontal distances ∼1 km, in contrast to the 0.12 km distances between strings of IceCube modules. In this paper, I calculate the absorption and scattering coefficients as a function of frequency and grain size for acoustic waves in glacial ice and salt domes and show that experimental measurements on laboratory samples and in glacial ice and salt domes are consistent with theory. For South Pole ice with grain size ∼0.2 cm at depths ≤600 m, scattering lengths are calculated to be 2000 and 25 km at frequencies 10 and 30 kHz, respectively; for grain size ∼0.4 cm at 1500 m (the maximum depth to be instrumented acoustically), scattering lengths are calculated to be 250 and 3 km. These are within the range of frequencies where most of the energy of the acoustic wave is concentrated. The absorption length is calculated to be 9 ± 3 km at all frequencies above ∼100 Hz. For NaCl (rock salt) with grain size 0.75 cm, scattering lengths are calculated to be 120 and 1.4 km at 10 and 30 kHz, and absorption lengths are calculated to be 3 × 104 and 3300 km at 10 and 30 kHz. Existing measurements are consistent with theory. For ice, absorption is the limiting factor; for salt, scattering is the limiting factor. Both media would be suitable for detection of acoustic waves from ultrahigh‐energy neutrino interactions.

Cherenkov energy loss and particle identification

Abstract Particle identification processes are considered in terms of Cherenkov energy loss, i.e. the work done by the particle against the transverse (relative to the wave vector of the Cherenkov photon) component of its electric field in the current particle position. The approach is used for the implementation of G eant 4 electro-magnetic processes responsible for the creation of optical, ultraviolet and X-ray Cherenkov radiation, ionisation energy losses in terms of extended PAI model, and X-ray transition radiation in complex radiators. Simulation results are in satisfactory agreement with experimental data.

Transverse envelope dynamics of a 28.5-GeV electron beam in a long plasma.

The transverse dynamics of a 28.5-GeV electron beam propagating in a 1.4 m long, (0-2)x10(14) cm(-3) plasma are studied experimentally in the underdense or blowout regime. The transverse component of the wake field excited by the short electron bunch focuses the bunch, which experiences multiple betatron oscillations as the plasma density is increased. The spot-size variations are observed using optical transition radiation and Cherenkov radiation. In this regime, the behavior of the spot size as a function of the plasma density is well described by a simple beam-envelope model. Dynamic changes of the beam envelope are observed by time resolving the Cherenkov light.

Emittance meter for time-resolved electron-beam propagation studies

A simple emittance meter is designed which is capable of measuring the temporal evolution of the emittance of a propagating electron beam. The design is based on that of a slit-pinhole emittance meter. A Cherenkov emitter is utilized as the electron detector. A streak camera is used to record the time-resolved optical Cherenkov radiation from the detector. Experimental results with a 700-keV, 4-kA, 100-ns electron beam are presented.

An experiment to detect y-rays of energy above 1000 GeV from Cygnus X-3

High energy y-rays, of energies greater than 10 12 eV, have been detected from Cyg X-3 (Vladimirski et al. 1973; Mukanov et al. 1979). In both experiments, 1.5 m diameter flux collectors were used to detect optical Cherenkov radiation from the small electron showers in the atmosphere. The background radiation due to cosmic ray protons was rejected in both cases by performing drift scans across the position of the object.