| Stimulated Brillouin scattering(SBS)is an important topic in the field of laserdrive inertial confinement fusion(ICF).SBS can reduce the laser-target energy coupling efficiency,spoil implosion symmetry and degrade target gain.In order to study the SBS process in the integration experiment of Double Cone Ignition[J.Zhang,et al.,Trans.R.Soc.A-Math.Phys.Eng.Sci.,378(2020)11],an angle-resolved full-aperture backscatter diagnostic system is developed for the Shenguang-ⅡU(SG-ⅡU)facility.The design of the system is guided with the time characteristics of the backward reflection signals on the SG-ⅡU.It is found that both SBS signals from target and stray lights from the surfaces of the frequency-conversion crystals propagate along the same direction but with a fixed time delay which depends on the geometry of the final optical assembly.The level of stray lights is proportional to the incident laser energy,and is rather stable so that it can be used as references to infer SBS energies.An optical fiber array is designed to collect the angle-resolved signals reflected from the servo mirror of the SG-ⅡU facility.The signals are then split into two beams and recorded with two intensified charge-coupled devices,respectively.The time delay between the two ICCDs is determined with that between SBS signals and stray lights.In order to make sure the ICCDs record accurate signals energy and verify the timing and intensity ratio between the SBS signals and stray lights,the temporal features of the ICCDs gating process are tested and the total signals are also recorded with a streak camera coupled with a spectrometer in some shots.With the assumption that the level of stray lights is known,the SBS level can be inferred.which is in reasonable agreement with that obtained from other diagnostics.With the system,it is the first time for us to find that the angular distribution of the backward SBS depends on the focal location of the laser pulse on the target surface. |
