Production of submicrometre fused silica gratings using laser-induced backside dry etching technique

Laser micromachining of transparent materials is a promising technique for producing micro-optical elements. Several types of both direct ( e. g. ablation) and indirect ( e. g. laser-induced backside wet etching: LIBWE) procedures have already been developed and presented in the last two decades. Here we present a new method (laser-induced backside dry etching (LIBDE)) in the analogy of LIBWE for the micro and nanoprocessing of transparent materials. In our experiments 1 mm thick fused silica plates were used as transparent work pieces. The plates were covered with 100 nm thick silver layers. The metal absorbing films were irradiated through the fused silica by a KrF excimer laser beam (lambda = 248 nm, FWHM = 30 ns). The illuminated area was 1.05 mm(2) and the fluence on the silver - quartz interface varied in the range 0 - 1800 mJ cm(-2). We have provided evidence that LIBDE is more effective and simple than LIBWE, its etch rate being much higher at a given laser fluence. Our interference experiments proved that the LIBDE etching technique is suitable to fabricate gratings displaying submicrometre periods in transparent materials. On the basis of all these, it is suggested that this method may be useful to produce other nano and microoptical elements, too.