Abstract-THz Induced Nonlinear Effects in Materials at Intensities above 26 GW/cm2

A. Woldegeorgis, T. Kurihara, B. Beleites, J. Bossert, R. Grosse, G. G. Paulus, F. Ronneberger, A. Gopal

https://link.springer.com/article/10.1007%2Fs10762-018-0493-3

Nonlinear refractive index and absorption coefficient are measured for common semiconductor material such as silicon and organic molecule such as lactose in the terahertz (THz) spectral regime extending from 0.1 to 3 THz. Terahertz pulses with field strengths in excess of 4.4 MV/cm have been employed. Transmittance and the transmitted spectrum were measured with Z-scan and single shot noncollinear electro-optic pump-probe techniques. The THz-induced change in the refractive index (Δn) shows frequency-dependence and a maximum change of − 0.128$-0.128$ at 1.37 THz in lactose and up to + 0.169$+0.169$ at 0.15 THz in silicon was measured for a peak incident THz intensity of 26 GW/cm2. Furthermore, the refractive index variation shows a quadratic dependence on the incident THz field, implying the dominance of third-order nonlinearity.

Abstract-Vectorial optical field reconstruction by attosecond spatial interferometry

• • 
    
• P. Carpeggiani
• M. Reduzzi
• A. Comby
• H. Ahmadi
• S. Kühn
• F. Calegari
• M. Nisoli
• F. Frassetto
• L. Poletto
• D. Hoff
• J. Ullrich
• C. D. Schröter
• R. Moshammer
• G. G. Paulus
• G. Sansone
• 
  

http://www.nature.com/nphoton/journal/vaop/ncurrent/full/nphoton.2017.73.html

An electrical pulse E(t) is defined completely by its time-dependent amplitude and polarization direction. For optical pulses the manipulation and characterization of the light polarization state is fundamental because of its relevance in several scientific and technological fields. In this work, we demonstrate the complete temporal reconstruction of the electric field of few-cycle pulses with a complex time-dependent polarization. Our experimental approach is based on extreme ultraviolet interferometry with isolated attosecond pulses and on the demonstration that the motion of an attosecond electron wave packet is sensitive to perturbing fields only along the direction of its motion. By exploiting the sensitivity of interferometric techniques and by controlling the emission and acceleration direction of the wave packet, pulses with energies as low as a few hundreds of nanojoules can be reconstructed. Our approach reveals the possibility to characterize completely the electric field of the pulses typically used in visible pump–probe spectroscopy.

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