A novel method to amplify laser pulses in inertial confinement fusion (ICF) facilities is presented, in which twin pulses are employed to propagate along the amplifier in opposite directions. The resulting bidirectional propagation provides a substantially higher extraction efficiency of the amplifier than the conventional multipass architecture for an equal B limit, while keeping the laser fluence at a low level that is beneficial to system reliability and stability. It is shown that an extraction efficiency of ∼61% is achievable under a laser fluence of 10 J cm−2 (1ω, one pulse) in an 18-slab amplifier with the bidirectional amplifying design (slab thickness: 4 cm, small signal gain coefficient: 0.0525 cm−1), while the extraction efficiency is only ∼40% under a fluence of 13 J cm−2 (1ω) for the conventional multipass architecture.

A unique 'double-lung' laser-induced damage pattern of a large-aperture potassium dihydrogen phosphate (KDP) crystal is observed during a damage experiment carried out on a large-aperture laser system, which has not been predicted by damage tests on small-aperture laser systems. Investigations show that 'double-lung' damage results from transverse stimulated Raman scattering (SRS) and the non-uniform fluence and intensity distribution of transverse SRS leads to the 'double-lung' damage pattern.