The Orion laser facility at AWE provides multiple beams to target delivering synchronized pulses at both nanosecond and sub-picosecond duration. In the latter, the peak power approaches the petawatt level. This paper presents a conceptual design for potential development of these beamlines. This would deliver a significant enhancement of performance at the fundamental level. In addition, a new approach is described for the management of frequency conversion at high intensity, which may allow significantly enhanced performance at the second harmonic also.

An all-solid-state single-frequency 1064 nm laser with a $100~{\rm\mu}\text{s}$ pulse width, 500 Hz repetition rate and 700 mJ single pulse energy is designed using seed injection and a three-stage master oscillator power amplifier (MOPA) construction. Using this as a basis, research on long-pulse laser frequency doubling is carried out. By designing and optimizing the lithium triborate (LBO) crystal, the theoretically calculated maximum conversion efficiency ${\it\eta}_{\max }$ reaches 68% at $M^{2}=1$, while ${\it\eta}_{\min }$ is 33% at $M^{2}=3$. Generation of 212 mJ pulses of green light with a repetition rate as high as 500 Hz is obtained from a fundamental energy of 700 mJ. The experimental conversion efficiency reaches 31% and the power stability is better than $\pm 1\%$.