The commissioning of the Orion laser facility at the Atomic Weapons Establishment (AWE) in the UK has recently been completed. The facility is a twelve beam Nd:glass-based system for studying high energy density physics. It consists of ten frequency-tripled beam-lines operating with nanosecond pulses, synchronized with two beam-lines with subpicosecond pulses, each capable of delivering 500 J to target. One of the short pulse beams has the option of frequency doubling, at reduced aperture, to yield up to 100 J at 527 nm in a subpicosecond pulse with high temporal contrast. An extensive array of target diagnostics is provided. This article describes the laser design and commissioning and presents key performance data of the facility's laser systems.

The Orion laser facility at the atomic weapons establishment (AWE) in the UK has been operational since April 2013, fielding experiments that require both its long and short pulse capability. This paper provides a full description of the facility in terms of laser performance, target systems and diagnostics currently available. Inevitably, this is a snapshot of current capability-the available diagnostics and the laser capability are evolving continuously. The laser systems consist of ten beams, optimised around 1 ns pulse duration, which each provide a nominal 500 J at a wavelength of 351 nm. There are also two short pulse beams, which each provide 500 J in 0.5 ps at 1054 nm. There are options for frequency doubling one short pulse beam to enhance the pulse temporal contrast. More recently, further contrast enhancement, based on optical parametric amplification (OPA) in the front end with a pump pulse duration of a few ps, has been installed. An extensive suite of diagnostics are available for users, probing the optical emission, x-rays and particles produced in laser-target interactions. Optical probe diagnostics are also available. A description of the diagnostics is provided.

This paper describes frequency-doubled operation of a high-energy chirped-pulse-amplification beamline. Efficient type-I second-harmonic generation was achieved using a 3 mm thick 320 mm aperture KDP crystal. Shots were fired at a range of energies achieving more than 100 J in a subpicosecond, 527 nm laser pulse with a power contrast of 10(14).

We present a comparative study on the ultrafast nonlinear optical response of a novel conjugated zinc porphyrin system. The linear optical absorption spectra of these molecules all show the Q-band and B-band transitions of the basic porphyrin unit. We have taken spectrally resolved ultrafast pump–probe measurements on monomer, dimer, and polymer solutions, which allows us to compare their excited state dynamics and relate these to their linear optical absorption. The spectra show several common features, but these features have markedly different decay dynamics. The bleaching is preferential in the Q band for the polymer and the B band for the monomer. The polymer Q-band bleaching shows a two-component decay, of approximately 700 fs and 170±50 ps time constants in a biexponential fit, which we attribute to both exciton–exciton annihilation and exciton diffusion to recombination centers on the polymer chain. The Q band of the dimer also has a two-component decay with 13±5 and 1250±70 ps time constants which we attribute to rotational diffusion of the excited molecule in solution, and decay to the ground state, respectively. The B-band bleaching in the monomer is long lived and has a decay constant of approximately 3.5±0.5 ns; from the absorption recovery of the B band we estimate a triplet yield of 0.8. All molecules exhibit broad π*−π* absorptions in the visible spectral region (between the Q band and the B band). In particular, we show that the monomer has potential as a broadband optical limiter in the visible region from 455 (2.72 eV) to 620 nm (2.00 eV); we estimate that its excited state absorption cross section is 8.5 times that of its ground state cross section at 532 nm (2.33 eV). There is also clear evidence of triplet transitions in the dimer and monomer; the triplet absorption feature ranging from 940 (1.32 eV) to 1000 nm (1.24 eV) rises 10 ps after excitation in the dimer which suggests a short intersystem-crossing time.

The Orion facility at the Atomic Weapons Establishment in the United Kingdom has the capability to operate one of its two 500 J, 500 fs short-pulse petawatt beams at the second harmonic, the principal reason being to increase the temporal contrast of the pulse on target. This is achieved post-compression, using 3 mm thick type-1 potassium dihydrogen phosphate crystals. Since the beam diameter of the compressed pulse is ∼600 mm, it is impractical to achieve this over the full aperture due to the unavailability of the large aperture crystals. Frequency doubling was originally achieved on Orion using a circular sub-aperture of 300 mm diameter. The reduction in aperture limited the output energy to 100 J. The second-harmonic capability has been upgraded by taking two square 300 mm × 300 mm sub-apertures from the beam and combining them at focus using a single paraboloidal mirror, thus creating a 200 J, 500 fs, i.e., 400 TW facility at the second harmonic.