[OPTICAL REVIEW Vol. 7, No. 3 (2000) 216-220]

Two-Dimensional Multi-Lens Array with Circular Aperture Spherical Lens for Flat-Top Irradiation of Inertial Confinement Fusion Target

Noriaki NISHI,* Takahisa JITSUNO, Koji TSUBAKIMOTO, Shinichi MATSUOKA, Noriaki MIYANAGA and Masahiro NAKATSUKA

Institute of Laser Engineering, Osaka University, 2-6, Yamada-oka, Suita, Osaka, Japan

(Received October 20, 1998; Accepted November 17, 1998; Revised manuscript received February 28, 2000)

A two-dimensional multi-lens array 350 mm in diameter with spherical element lenses has been tested to improve the irradiation uniformity of a high power glass laser for inertial confinement fusion (ICF). A circular shape for the element lens aperture is chosen to eliminate azimuthally asymmetric intensity distribution. An approximate flat-top intensity distribution is obtained with a lens array of 37 lenses. Beam patterns of a coherent laser and partially coherent light (PCL) with the random phase plate (RPP) and the multi-lens array (MLA) are measured in a GEKKO XII glass laser system. Spherical mode structure of the irradiation nonuniformity of 5.6% with MLA is estimated with cos3 θ distribution of absorption coefficient in the target plasma.

Key words : multi-lens array, circular aperture, irradiation nonuniformity, low-mode, flat-top