Underwater cutting of 50 and 60 mm thick stainless steel plates using a 6-kW fiber laser for dismantling nuclear facilities

•Underwater laser cutting studies on thick stainless steel plates was performed.•An underwater cutting head was developed by upgrading our previous head.•50 and 60 mm thick stainless steel plates were cut successfully in water.•The cutting performance was the best among the previously reported results.•This work will contribute to dismantling nuclear facilities in the future.