On-target contrast diagnostic via specular reflectivity measurement

Pirozhkov, A. S. and Choi, I. W. and Sung, J. H. and Lee, S. K. and Yu, T. J. and Jeong, T. M. and Kim, I. J. and Hafz, N. and Kim, C. M. and Pae, K. H. and Noh, Y. C. and Ko, D.-K. and Lee, J. and Robinson, A. and Foster, P. and Hawkes, S. and Streeter, M. and Spindloe, C. and McKenna, P. and Carroll, D. C. and Wahlström, C.-G. and Zepf, M. and Dromey, B. and Markey, K. and Kar, S. and Li, Y. T. and Xu, M. H. and Nagatomo, H. and Mori, M. and Yogo, A. and Kiriyama, H. and Ogura, K. and Sagisaka, A. and Orimo, S. and Nishiuchi, M. and Sugiyama, H. and Esirkepov, T. Zh. and Okada, H. and Kondo, S. and Kanazawa, S. and Nakai, Y. and Akutsu, A. and Motomura, T. and Tanoue, M. and Shimomura, T. and Ikegami, M. and Daito, I. and Kando, M. and Kameshima, T. and Bolton, P. and Bulanov, S. V. and Daido, H. and Neely, D.; (2009) On-target contrast diagnostic via specular reflectivity measurement. In: Laser-Driven Relativistic Plasmas Applied to Science, Industry and Medicine - The 2nd International Symposium. AIP, JPN, pp. 7-15. ISBN 9780735406902 (https://doi.org/10.1063/1.3204560)

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Abstract

High-power laser contrast is challenging to measure, especially in the real target irradiation conditions. We present a convenient and relatively simple contrast diagnostic technique based on the measurement of target specular reflectivity at full laser power. The reflectivity remains high even at intensities above l019W/cm2 in the case of a high-contrast prepulse-free laser. On the contrary, the specular reflectivity drops in the case of lower contrast, due to the beam break-up and increased absorption caused by the preformed plasma. The technique was demonstrated using three different laser systems with several contrast conditions: Astra (CLF, RAL), TiS laser at APRI, GIST, and J-KAREN (APRC, JAEA).