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Publications by
Ajay K. Arunachalam

All publications of HI Jena

2018

A. K. Arunachalam, M. B. Schwab, A. Sävert, and M. C. Kaluza
Observation of non-symmetric side-scattering during high-intensity laser-plasma interactions
New Journal of Physics 20, 033027 (2018)

Abstract: Non-symmetric side-scattering has been observed during the interaction between a high-intensity laser pulse and under-dense argon plasma. The angle between the laser's forward direction and the scattered radiation is found to decrease for increasing electron densities ranging from 0.01 to 0.25n c , where n c is the critical density for the laser wavelength. We show that the observed features of the scattering cannot be described by Raman side-scattering but can be explained to be a consequence of the non-uniform density distribution of the plasma with the scattering angle being oriented along the direction of the resulting electron density gradient.

2017

A. K. Arunchalam
Investigation of laser-plasma interactions at near-critical densities
Doctoral thesis
Friedrich-Schiller-Universität Jena, Physikalisch-Astronomische Fakultät (2017)

Abstract: During the high-intensity laser-plasma experiments conducted at the high-power laser system JETI40 at IOQ, the two qualitatively different laser side-scattering processes have been observed. The side-scattering observed during the first experiment was found to be non-symmetric in nature with respect to the laser’s propagation direction and it was estimated to occur from under-dense to quarter critical plasma densities. The scattering angle was found to gradually decrease, as the laser pulse propagates towards regions of higher densities (i.e. the gas jet centre). For increasing nozzle backing pressures, the scattering was also found to gradually change from upward to downward directions. In this thesis, this side-scattering process is shown to a consequence of the laser propagation in non-uniform plasma, where the scattering angle was found to be oriented along the direction of the plasma gradient. In the second experiment, a symmetric side-scattering process with respect to the laser’s propagation direction was observed from the intense central laser-plasma interaction region. This scattering process was found to originate from a longitudinally narrow laser-plasma interaction region and vary over +-50° with respect to the laser’s transverse direction. It was found to primarily occur in the nearcritical plasma density regime (0.09 n_c to 0.25_nc, where n_c is the plasma critical density). In contrast to the previous experiment, Raman scattering has been shown to be the cause of this symmetric scattering process, where the scattering occurs as the result of the wave vector non-alignment between the main laser pulse and the resulting plasma wave.

2014

M. Hornung, H. Liebetrau, A. Seidel, S. Keppler, A. Kessler, J. Körner, M. Hellwing, F. Schorcht, D. Klöpfel, A. K. Arunachalam, G. A. Becker, A. Sävert, J. Polz, J. Hein, and M. C. Kaluza
The all-diode-pumped laser system POLARIS – an experimentalist’s tool generating ultra-high contrast pulses with high energy
High Power Laser Science and Engineering 2, e20 (2014)

Abstract: The development, the underlying technology and the current status of the fully diode-pumped solid-state laser system POLARIS is reviewed. Currently, the POLARIS system delivers 4 J energy, 144 fs long laser pulses with an ultra-high temporal contrast of 5×10^12 for the ASE, which is achieved using a so-called double chirped-pulse amplification scheme and cross-polarized wave generation pulse cleaning. By tightly focusing, the peak intensity exceeds 3.5×10^20 W cm^{−2}. These parameters predestine POLARIS as a scientific tool well suited for sophisticated experiments, as exemplified by presenting measurements of accelerated proton energies. Recently, an additional amplifier has been added to the laser chain. In the ramp-up phase, pulses from this amplifier are not yet compressed and have not yet reached the anticipated energy. Nevertheless, an output energy of 16.6 J has been achieved so far.

2013

M. Hornung, S. Keppler, R. Bödefeld, A. Kessler, H. Liebetrau, J. Körner, M. Hellwing, F. Schorcht, O. Jäckel, A. Sävert, J. Polz, A. K. Arunachalam, J. Hein, and M. C. Kaluza
High-intensity, high-contrast laser pulses generated from the fully diode-pumped Yb:glass laser system POLARIS
Optics Letters 38, 718 (2013)

Abstract: We report on the first generation of high-contrast, 164 fs duration pulses from the laser system POLARIS reaching focused peak intensities in excess of 2×10^20  W/cm2. To our knowledge, this is the highest peak intensity reported so far that has been achieved with a diode-pumped, solid-state laser. Several passive contrast enhancement techniques have been specially developed and implemented, achieving a relative prepulse intensity smaller than 10^−8 at t=−30  ps before the main pulse. Furthermore a closed-loop adaptive-optics system has been installed. Together with angular chirp compensation, this method has led to a significant reduction of the focal spot size and an increase of the peak intensity.