u02dc 0 37 fig1 shows a weld feature in fused silica with images taken both before and after breaking the two silica plates apart the first image a shows the intact weld feature exhibiting regions of smooth melted glass and the subsequent images b and c show the two glass surfaces after the weld was fractured exhibiting facets of fractured glass welding speeds ranged from 0 1 to 1 0 mm s though speeds greater than 5 mm s are possible and the maximum speed could be increased with an increased pulse repetition rate the nominal fluence range for the process is 5 15 j cm 2 and the nominal pulse duration range is 10 1000 fs within these fluence and pulse duration ranges the nominal pulse repetition rate range is 1 50 mhz with rigorous process optimization these ranges may be extended to 1 100 j cm 2 1 fs 500 ps and 100 khz 100 mhz for the fluence pulse duration and repetition rate respectively the high repetition rate is required for sufficient thermal accumulation for the onset of melting in the fused silica with the availability of higher energy pulses at similar repetition rates looser focusing is possible to generate a larger focal volume with the required fluence the size and shape of this welding focal volume can be tailored based on the region to be welded fig1 shows a glass sample with the arrow mark illuminated by a green light source from the side here the arrow pattern is clearly visible the illustrations in fig8 and 9 show the details of the arrow pattern where lines at different depths perpendicular to the.