The ignition condition and fusion gain for isochoric implosion with off-centre ignition are evaluated based on 2D hydrodynamic simulations. We show that the ignition energy can be reduced by increasing the compressed fuel density, although it is accompanied by a reduction in the fusion gain. Experimental results on channel formation in an overdense plasma are presented. It is shown that the laser beam propagates in a channel over a 200 μm distance in an overdense plasma and deposits its energy close to the original target surface. For the study of fast ignition, ultrashort-pulse high-energy lasers are constructed with GEKKO MII and GEKKO XII at ILE.