High Damage Threshold Ultrafast Laser Nanostructuring in Silica Glass

A new type of birefringent modification (oblate nanopores or type X) with high optical transmission (>99%) was recently reported in silica glass using ultrafast laser writing [1] . This enables low-loss geometric phase (GP) flat optical elements with controlled phase shift by birefringence patterning. Here, high damage threshold of type X modification is demonstrated and compared with type II modification (nanograting type).