Single-cycle Electromagnetic Pulses Research Articles

Design strategies for single-cycle ultrafast electron guns

After the first introduction of ultrafast electron guns for acceleration of particles using single-cycle electro-magnetic pulses, the basic structure has gained increasing interest as promising solutions for high gradient compact electron guns. The significant benefit of using transient ultrashort pulses in this acceleration scheme opens a realistic path towards gigavolt-per-meter acceleration gradients. In this paper, we present an optimized design strategy for these electron guns. The goal is to estimate the THz energy needed for an optimum device to accelerate electrons at rest to a certain energy using materials that endure a pre-determined maximum electric field. We start with designing a gun delivering 400 keV electron beam energy and discuss different techniques to enhance the performance. Throughout this design process, it is implicitly shown that the concept of single-cycle ultrafast electron guns can apply THz beams with energies in the level of 100–400 μJ to accelerate electrons, which is the state-of-the-art technology in THz radiation sources. Subsequently, upgrading the design to an 800 keV device is outlined, to demonstrate the eligibility of this concept to perform as linac injectors in compact accelerator facilities.

Tailoring single-cycle electromagnetic pulses in the 2–9 THz frequency range using DAST/SiO_2 multilayer structures pumped at Ti:sapphire wavelength

We present a numerical parametric study of single-cycle electromagnetic pulse generation in a DAST/SiO2 multilayer structure via collinear optical rectification of 800 nm femtosecond laser pulses. It is shown that modifications of the thicknesses of the DAST and SiO2 layers allow tuning of the average frequency of the generated THz pulses in the frequency range from 3 to 6 THz. The laser-to-THz energy conversion efficiency in the proposed structures is compared with that in a bulk DAST crystal and a quasi-phase-matching periodically poled DAST crystal and shows significant enhancement.

Mobile source of high-energy single-cycle terahertz pulses

The Teramobile laser facility was used to realize the first mobile source of high-power THz pulses. The source is based on a tilted-pulse-front pumping THz generation scheme optimized for application of terawatt laser pulses. Generation of 50-μJ single-cycle electromagnetic pulses centered at 0.19 THz with a repetition rate of 10 Hz was obtained for incoming 700-fs 120-mJ near-infrared laser pulses. The corresponding laser-to-THz photon conversion efficiency is approximately 100%.

Nonstationary time-domain statistics of multiply scattered broadband terahertz pulses

We examine the time-domain statistics of randomly varying electric fields generated by multiple scattering of single-cycle electromagnetic pulses in a random medium. This analysis emphasizes the fact that these measured random fields are not stationary, as is commonly assumed for diffusing photons generated with a narrowband light source. We demonstrate that the nonstationarity is a consequence of the time dependence of the configurationally averaged intensity, and that the statistical properties of the random field can be predicted if this quantity is known. We also discuss an approach for describing the transition from nonstationary to stationary behavior by investigating the degree of stationarity during a short time window. A parameterization of the statistics using a gamma distribution provides a quantifiable measure of the approach to stationarity. Our predictions are in good agreement with experimental observations.

Single-cycle electromagnetic pulses produced by oscillating electric dipoles.

We report an exact analytic solution of the Maxwell equations that is capable of describing single-cycle electromagnetic pulses beyond the slowly varying envelope approximation. The solution is based on the radiation field emitted by oscillating electric dipoles under the complex-source-point model. The spatiotemporal evolution of single-cycle electromagnetic pulses in free space is illustrated and discussed in detail by using the analytic solution obtained.

Spatiotemporal evolution of focused single-cycle electromagnetic pulses

We analyze exact solutions of Maxwell's equations that are capable of describing focused single-cycle electromagnetic pulses. These finite energy solutions are a subset of Ziolkowski's ``modified power spectrum'' pulse solutions [Phys. Rev A 39, 2005 (1989)]. They display substantial temporal reshaping, time reversal, and polarity reversals as they pass through the focus. The temporal profiles at the focus and in the far field are related by a Hilbert transform in time. These results are explained in terms of the Gouy phase shift of focused beams. We also show that these pulse solutions are natural spatiotemporal modes of an open resonator and propose methods for their practical realization.

Gouy shift and temporal reshaping of focused single-cycle electromagnetic pulses:?errata

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text Simin Feng, Herbert G. Winful, and Robert W. Hellwarth, "Gouy shift and temporal reshaping of focused single-cycle electromagnetic pulses:?errata," Opt. Lett. 23, 1141-1141 (1998) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Raman self-conversion of femtosecond laser pulses and generation of single-cycle radiation

Stimulated Raman scattering of light in the regime of laser pulse durations shorter than the period of Raman-active vibrational mode $2\ensuremath{\pi}/{\ensuremath{\Omega}}_{R}$ is investigated. Using full equations for the field and the medium polarization, we obtain an insight into the stage of frequency conversion where the slowly varying amplitude approximation is inapplicable. It is found that the laser pulse experiences a continuous downshift of its spectrum, resulting in the formation of an intense single-cycle electromagnetic pulse. The role of the competing processes is analyzed.

Gouy shift and temporal reshaping of focused single-cycle electromagnetic pulses

We discuss exact solutions of Maxwell's equations that describe the evolution of single-cycle electromagnetic pulses. The solutions are applied to recent observations of the diffraction transformation of terahertz pulses. In particular, we elucidate the role of the Gouy shift in the temporal reshaping and polarity reversals of single-cycle terahertz pulses.

Nonlinear electrodynamics in cuprate superconductors

We present two types of experiments which probe the high-frequency conductivity of BSCCO films in the presence of large superfluid velocities. In the first the superflow is the static velocity field associated with the vortex lattice. In the second the velocity is dynamic, induced by high-intensity single-cycle electromagnetic pulses. We show that intrinsic pair-breaking in a d-wave superconductor can provide a unified explanation for both effects.

Response of grating pairs to single-cycle electromagnetic pulses

The chirp of single-cycle microwave fields after interaction with pairs of parallel diffraction gratings is measured in a phase-sensitive terahertz spectrometer. Novel transmission grating pairs recently proposed by Tournois, which combine diffraction and refraction effects, yield an almost linear group delay over a bandwidth that exceeds that of conventional reflection gratings by a factor of ~3.5. The experimentally measured group delay shows good agreement with theoretical predictions for both types of grating. The applicability of the novel transmission gratings for stretching and compression of 1–2-fs pulses in the optical regime and the limitations set by material dispersion are discussed.