400 TW operation of Orion at ultra-high contrast

• Published in: High power laser science and engineering 2018, Vol.6, Article e47
• Main Authors: Parker, Stefan, Danson, Colin, Egan, David, Elsmere, Stephen, Girling, Mark, Harvey, Ewan, Hillier, David, Hussey, Dianne, Masoero, Stephen, McLoughlin, James, Penman, Rory, Treadwell, Paul, Winter, David, Hopps, Nicholas
• Format: Article
• Language: English
• Subjects: Special Issue for HPLSE 2018
• ISSN: 2095-4719; 2052-3289
• DOI: 10.1017/hpl.2018.44

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 ${\sim}600$  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 $\times$ 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.