Microstructured Grayscale Optics with Direct Laser Writing for Structured Light

This thesis develops a platform for the fabrication of diffractive optical elements in fused silica for structured light generation in high-energy ultrafast regimes. For this purpose, a direct laser writing grayscale lithography process, followed by inductively coupled plasma reactive ion etching transfer into fused silica, was established. Different blazed diffractive axicons were fabricated to be used in ultrafast two-dimensional spectroscopy (27 μm- period), synthetic motion experiments (27 μm- period), and light spring (spatio-temporal beams) generation for laser-plasma interaction (9 and 12 μm- period), the latter using a narrowband 1030 nm laser.

The fabrication process optimization included the AZ 1518 photoresist dose-height curve calibration, the selection of the development time, and the use of a temporary thermoplastic adhesive layer during etch transfer, to limit photoresist thermal degradation. The axicons were characterized by profilometry, scanning electron microscopy, and first-order diffraction efficiency measurements.

The axicons with a period of 27 μm achieved efficiencies of 62.6% and 65%, whereas the more demanding periods of 9 and 12 μm achieved 29.9% and 38.2%, respectively. This reduction reflects the increased flattening and top rounding of the axicons' blazed profiles observed at smaller periods.



A spatiospectral hologram matched to the axicon with period of 12 μm was fabricated with a transferred silica depth of 2.22 μm, close to the 2.29 μm target for full 2π phase modulation, at 1030 nm. This work establishes the optical architecture required for future light spring generation and spatio-temporal characterization, using a system in fused silica scalable towards high-energy structured light applications.