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The experimental configuration. All the tube lenses were achromatic doublets; focal lengths are in mm.
Tracks written at a depth of in fused silica at a speed of . For each set of tracks a brightfield (left) and a crossed polarizer (centre) image are shown, as well as the phase pattern displayed on the SLM during fabrication (right). The grating period used was (a) 0, (b) 2.4, (c) −2.4, and (d) 7.2 lines per mm. Single headed arrows denote the direction of motion of the substrate for each track.
Calculated and experimental focal intensity distributions for a 150 fs pulse with (a) a “top-hat” pupil illumination (PI) with a blazed phase grating () introducing a PFT of 12.6 fs/mm and (b) a gradient in the PI with a flat phase distribution (, no PFT). The focal intensity is shown at time T corresponding to the centre of the pulse, and at . Each image is individually normalized. The corresponding time averaged intensity is shown both from calculation and experimental measurements. The optical axis is along z.
Control of the pupil illumination using the SLM. (a) and (c) SLM phase distributions used to generate an intensity gradient in the pupil illumination by the zero order beam, as shown in (b) and (d). Brightfield (e) and crossed polarizer (f) images of tracks written where the SLM phase distribution is switched from (a) to (c) at point X during fabrication. Single headed arrows denote the direction of motion of the substrate for each track.
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