Abstract-Spatiotemporal visualization of the terahertz emission during high-power laser-matter interaction

A. Gopal, A. Woldegeorgis, S. Herzer, and M. Almassarani

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.100.053203

Single-cycle pulses with multimillion volts per centimeter field strengths and spectra in the terahertz (THz) band have attracted great interest due to their ability to coherently manipulate molecular orientations and electron spins resonantly and nonresonantly. The tremendous progress made in the development of compact and powerful terahertz sources have identified intense laser-thin foil interaction as a potential candidate for high-power broadband terahertz radiation. They are micrometers in size and deliver radially polarized terahertz pulses with millijoule energy and gigawatt peak power. Although several works have been carried out to investigate the terahertz generation process, their origin and angular distribution are still debated. We present here an indisputable study on their spatiotemporal characteristics and elaborate the underlying physical processes via recording the three-dimensional beam profile along with transient dynamics. These results are substructured with the quantitative visualization of the charge particle spectra.

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Abstract-Modeling terahertz emission from the target rear side during intense laser-solid interactions

A. Woldegeorgis, S. Herzer, M. Almassarani, S. Marathapalli, and A. Gopal

https://journals.aps.org/pre/accepted/b207eNd9R751152c60cb192029efcb45add52c9d0

Relativistic laser-solid target interaction is a powerful source of terahertz radiation where broadband terahertz radiation is emitted from the front and rear surfaces of the target. Even though several experimental works have reported the generation of sub-picosecond duration gigawatt (GW) peak power terahertz pulses from the target rear surface, the underlying physical process behind their origin is still a question at large. Here we discuss a numerical model which can accurately reproduce several aspects of the experimental results. The model is based on the charged particle dynamics at the target rear surface and the evolution of the charge separation field. We identify the major contributors which are responsible for broadband terahertz emission from the rear surface of the target.

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.