Observation of Gigawatt-Class THz Pulses from a Compact Laser-Driven Particle Accelerator

A. Gopal^1,2,*, S. Herzer^1,2, A. Schmidt¹, P. Singh^1,†, A. Reinhard¹, W. Ziegler¹, D. Brömmel³, A. Karmakar^3,‡, P. Gibbon³, U. Dillner⁴, T. May⁴, H-G. Meyer⁴, and G. G. Paulus^1,2 
1Institute of Optics and Quantumelectronics, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany
²Helmholtz Institute Jena, Fröbelstieg 3, 07743 Jena, Germany
³Forschungzentrum Jülich GmbH, Institute for Advanced Simulation, Jülich Supercomputing Centre, D-52425 Jülich, Germany
⁴Institut für Photonische Technologien, Postfach 100239, 07702 Jena, Germany
http://prl.aps.org/abstract/PRL/v111/i7/e074802

We report the observation of subpicosecond terahertz (T-ray) pulses with energies ≥460  μJ from a laser-driven ion accelerator, thus rendering the peak power of the source higher even than that of state-of-the-art synchrotrons. Experiments were performed with intense laser pulses (up to 5×10¹⁹  W/cm²) to irradiate thin metal foil targets. Ion spectra measured simultaneously showed a square law dependence of the T-ray yield on particle number. Two-dimensional particle-in-cell simulations show the presence of transient currents at the target rear surface which could be responsible for the strong T-ray emission.

© 2013 American Physical Society

synopsis:

http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.111.074802

Terahertz (THz) radiation—the band of frequencies falling between the microwave and visible range—can pass through materials that block light and couple to important rotational, vibrational, or electronic degrees of freedom of solids and molecules. Many applications could take advantage of these properties, from wireless communications to imaging of biomolecules or semiconductor wafers. But a key stumbling block for THz technologies is the development of sufficiently powerful sources. Now, as reported in Physical Review Letters, Amrutha Gopal at the Friedrich Schiller University Jena, Germany, and co-workers have demonstrated a laser-based source that emits short THz pulses with the highest peak power ever recorded in a laboratory.

Presently, the most powerful THz sources are at expensive, large-scale accelerator facilities, which generate THz radiation by bending a beam of relativistic electrons with a magnet. Gopal et al.’s solution instead exploits a high-power laser available at the Friedrich Schiller University Jena. The authors focus the laser’s femtosecond pulses onto micrometer-thick metallic foils. The intense pulses ionize the material, creating hot plasma that emits THz radiation. The setup delivers ten THz pulses per second with a broad spectrum ($03$–$30$ THz). Since the energy is concentrated in pulses only about half a picosecond long, their peak power is close to a gigawatt.

The scheme also generates a synchronous beam of energetic ions, which suggests an intriguing medical application: the THz beam could be used for detecting cancerous cells on human skin (which reflect THz wavelengths differently than normal cells), while the ions could be directed selectively at such cells for simultaneous treatment. – Matteo Rini