Transverse Stimulated Raman Scattering Induced Large Aperture KDP Coating Damages of SG-II Facility

Modeling of transverse stimulated Raman scattering in KDP/DKDP in large-aperture plates suitable for polarization control

“…For a specific plate size and shape, the gain of this transverse stimulated Raman scattering (TSRS) is a function of the crystal cut orientation, which governs the 3D distribution of the spontaneous Raman cross-section and the laser parameters, including the wavelength and polarization state. As the spontaneous Raman cross-section rapidly increases with decreasing laser wavelength, TSRS in ICF-class systems becomes of concern in the ultraviolet section of the laser system, starting with the crystal plate converting the laser energy to the third harmonic [3] . Due to the splitting of the A 1 mode with the introduction of deuterium in the crystal, the peak Raman cross-section is lower in DKDP compared to that in KDP.…”

“…Due to this exponential growth, the fluence level of the TSRS signal reaching the crystal perimeter can vary from harmless levels to ones that cause damage to the crystal or ablation of mechanical components in the vicinity. Methods to manage the TSRS effect have been developed for the THG plate by beveling the edges of the crystal to avoid back-reflections, and thus additional amplification, during the laser pulse [3] . More recently, innovative ideas for TSRS management have emerged and include the introduction of a laser-induced damage array composed of numerous pinpoints inside the plate to form a barrier to prevent signal amplification [7] .…”