Terahertz (THz) radiation, which lies in the far-infrared region, is at the interface of electronics and photonics. Narrow-band THz radiation can be produced by free-electron lasers and fast diodes. Broadband THz radiation can be produced by thermal sources and, more recently, by table-top laser-driven sources and by short electron bunches in accelerators, but so far only with low power. Here we report calculations and measurements that confirm the production of high-power broadband THz radiation from subpicosecond electron bunches in an accelerator. The average power is nearly 20 watts, several orders of magnitude higher than any existing source, which could enable various new applications. In particular, many materials have distinct absorptive and dispersive properties in this spectral range, so that THz imaging could reveal interesting features. For example, it would be possible to image the distribution of specific proteins or water in tissue, or buried metal layers in semiconductors; the present source would allow full-field, real-time capture of such images. High peak and average power THz sources are also critical in driving new nonlinear phenomena and for pump-probe studies of dynamical properties of materials.

/pdf/high-power-terahertz-radiation-from-relativistic-electrons-26oaegosvh.pdf

High-power terahertz radiation from relativistic electrons

Electromagnetic waves centred at a frequency of 1 THz lie between photonics on the one hand and electronics on the other, and are very hard to generate and detect. However, since the THz part of the spectrum is energetically equivalent to many important physical, chemical and biological processes including superconducting gaps and protein dynamical processes, it is of great interest to facilitate experimental research in this region. This has stimulated major steps in the past decade for filling this gap in the usable spectrum. In this review paper we describe the evolution of a new generation of sources that boost the average power available in the THz region by more than a million-fold, making this region routinely accessible for the first time. This is achieved using two enhancement factors, namely relativistic electrons and super-radiance. We will also point to the scientific potential for discovery that is now enabled in this region.

https://iopscience.iop.org/article/10.1088/0034-4885/69/2/R01/pdf

Filling the THz gap—high power sources and applications

The AILES Infrared Beamline on the third generation Synchrotron Radiation Facility SOLEIL

Electron beams can generate radiation spanning a wide range of the electromagnetic spectrum. Creating temporal structure in the beam density results in intense radiation emission proportional to the square of the particle number as compared to the linear dependence on particle number from a randomly distributed electron beam. In this article various coherent radiation emission processes are discussed including spontaneous emission, coherent spontaneous superradiance, and stimulated superradiance.

Superradiant and stimulated-superradiant emission of bunched electron beams

High-Resolution Infrared Spectroscopy with Synchrotron Sources

We report the observation of multiparticle coherent emission in the very far infrared from bunched electrons in an electron storage ring. The emission occurs in quasi-periodic bursts, and only when the electron beam current exceeds a threshold value, suggesting an instability-driven modulation of the electron bunch density. For the operating conditions reported, the spectral content of the coherent emission is peaked near a wavelength of 7 mm. This wavelength is much shorter than the nominal electron bunch length, indicating the presence of a density modulation within the bunch.

/pdf/observation-of-coherent-synchrotron-radiation-from-the-nsls-3eptbqgfki.pdf

Observation of coherent synchrotron radiation from the NSLS VUV ring

The lifetime in the NSLS VUV ring is limited by intra-bunch scattering (Touschek scattering). A second RF cavity was added to lengthen the electron bunch, thereby reducing the Touschek loss rate. Initially, the cavity was operated in a “passive” mode. This provided significant lifetime enhancement at higher currents, but also created larger than normal bunch length variations over the range of operating currents. In October 1993, a generator was added to the system to provide greater bunch length control and added lifetime at all operating currents. Recent studies have also been done on bunch shortening with encouraging results. This paper provides a summary of the system, including results from studies and operations.

Bunch length control in the NSLS VUV ring

Philosophy for NSLS II Design with Subnanometer Horizontal Emittance

NSLS-II at Brookhaven National Laboratory is a new third-generation storage ring light source, whose construction is on the verge of being approved by DOE. When completed, NSLS-II with its ability to provide users with a wide range of spectrum, ranging from IR to ultra-high brightness hard X-ray beams will replace the existing two (20+ years old) NSLS light sources. While presenting an overview of the NSLS-II accelerator system, this paper focuses on the strategy and development of a novel <1 nm emittance light source.

/pdf/philosophy-for-nsls-ii-design-with-sub-nanometer-horizontal-3kte9xh3t4.pdf

Philosophy for NSLS-II design with sub-nanometer horizontal emittance

We describe a major paradygm shift in in the approach to the production of synchrotron radiation This change will considerably improve the scientific capabilities of synchrotron light sources. We introduce plans for an upgrade of the National Synchrotron Light Source (NSLS). This upgrade will be based on the Photoinjected Energy Recovering Linac (PERL). This machine emerges from the union of two technologies, the laser-photocathode RF gun (photoinjector) and superconducting linear accelerators with beam energy recovery (Energy Recovering Linac). The upgrade will bring the NSLS users many new insertion device beam lines, brightness greater than 3rd generation light-source's and ultra-short pulse capabilities, not possible with storage ring light sources.

/pdf/photoinjected-energy-recovery-linac-upgrade-for-the-national-24ver0f01j.pdf

S.L. Kramer

Papers

Observation of coherent synchrotron radiation from the NSLS VUV ring

Bunch length control in the NSLS VUV ring

Philosophy for NSLS II Design with Subnanometer Horizontal Emittance

Philosophy for NSLS-II design with sub-nanometer horizontal emittance

Photoinjected energy recovery linac upgrade for the National Synchrotron Light Source