This p a p er p resents the recent p ro g ress in the develo p ment of lar g e-area hydro p hobic silica aero g els for use as radiators in the aero g el-based rin g -ima g in g Cherenkov (A RICH) counter that will be installed in the forward end ca p of the Belle II detector. The p roximity-focusin g A-RICH counter is desi g ned to identify char g ed p ions and kaons and to have a se p aration ca p ability of more than 40" at momenta u p to 4 GeV/c.In a focusin g -dual-layer radiator with different refractive indices, a p rototy p e A-RICH counter satisfied the required p erformance usin g our conventional aero g el tiles with refractive indices n of 1.045 and LOSS, transmission len g ths AT of 3�0 mm, and desi g ned final dimensions of 18 x 18 x 2 cm 3 • Moreover, we achieved better 1[/ K se p aration p erformance usin g n rv 1.06 aero g els with relatively small dimensions but lon g transmission len g th (AT> SO mm) produced by a novel p in-dryin g method.We need to fill the lar g e end ca p area of 3.5 m 2 with two layer aero g el tiles and to minimize the number of tiles with realistic dimensions to reduce the tile boundaries, at which the number of detected p hotoelectrons decreases. Therefore, we studied lar g e area aero g el p roduction by both conventional and p in-dryin g methods as a key to achievin g hi g h p erformance over the actual detector. This p a p er discusses the crack-free yield, o p tical trans p arency, and uniformity in refractive index within a monolith of recently p roduced large area aerogels.
I. INT RODUCTIONT HE aerogel-based ring-imaging Cherenkov (A-RICH) counter is one of the particle identification devices for the Belle II experiment [1] that will be performed using the SuperKEKB accelerator at KEK, Japan. The Belle II is a super B factory experiment to search for new physics beyond the standard model of particle physics through flavor physics and C P violation measurements. Because the forward end cap of the Belle II detector has a limited space, the A-RICH system is designed as a proximity-focusing RICH counter. To