Enhanced isotropic etching of quartz with femtosecond laser pre-processing

A laser machining system has been constructed to achieve nanometre precision in devices as large as a few millimetres. The approach exploits a two-step process in which sub-ablation threshold pulses first alter the structure of the transparent material (quartz, glass) to render them more susceptible to a second, chemical etching step. A high-numerical aperature objective lens (0.68) is used to focus the output of a femtosecond oscillator (800 nm, 100 fs pulses, 96 MHz, 450 mW average power; Clark-MXR NJA-5) to a beamwaist of 0.38 μm at the machining surface. High-precision stages translate the substrate relative to the beam. Enhanced selective etching with hydrofluoric acid will allow rapid, repeatable features to be constructed in a variety of substrates.