Micro-ablation at the front and rear surfaces of a fused silica window by using a femtosecond laser pulse in air

The ablation induced by a single shot and multi-shots of a femtosecond laser pulse at the front (entrance) and rear (exit) surfaces of a fused silica window in air was studied under a tight focusing condition (NA = 0.4). It was found that the ablation at the front and rear surfaces was quite different. The quality of the ablation at the rear surface was dramatically improved compared with that at the front surface. Cavities at the rear surface were well-defined and clean, and debris was avoided. Ablation at the rear surface is expected to be a powerful method for high quality surface ablation of a transparent medium by a pulsed laser in air.