This work investigates the performance of a polyvinyl alcohol/acrylamide-based photopolymer (PVA/AA) under pulsed and continuous-wave (CW) laser exposure for holographic recording. Using a versatile setup that allows direct comparison between both regimes, diffraction efficiency (DE), angular responses, and material parameters were analyzed. Comparable maximum DE was achieved with both CW and pulsed laser exposure; however, the pulsed regime produces stronger attenuation along the grating depth, which emphasizes the need to lower the dye concentration. Furthermore, the temporal evolution of DE reveals a smaller influence of oxygen inhibition under CW exposure. Finally, second-order angular reconstructions confirm that pulsed gratings exhibit a better sinusoidal modulation, especially at low frequency rates. These results enhance the understanding of how pulsed exposure affects holographic recording and open pathways for optimizing photopolymer systems in advanced technologies.

This work introduces a novel computational approach based on Principal Component Analysis (PCA) for dimensionality reduction of the solution space in optimisation problems with known linear interdependencies among solution variables. By creating synthetic datasets with deliberately engineered properties and applying PCA, the solution space’s remapping significantly reduces its dimensionality, leading to faster computation and more robust convergence in optimisation processes. We demonstrate this method by integrating it with a Genetic Algorithm (GA) for solving the optimal director distribution in liquid crystal (LC) devices, specifically addressing 2D and complex 3D spatial light modulator (SLM) structures such as twisted nematic liquid crystals (TN-LC) and parallel-aligned liquid crystal on silicon (PA-LCoS), respectively. The phase profiles obtained from the director vector distributions for horizontal and vertical high-frequency binary phase gratings closely match the theoretical values derived from minimising the traditional elastic Frank–Oseen functional via Euler–Lagrange equations. Beyond this specific application, our method offers a general framework for reducing computational complexity in optimisation problems by directly reducing the dimensionality of the solution space. This approach is applicable across various optimisation scenarios with well-known linear interdependencies among solution variables, enabling significant reductions in computational costs and improvements in robustness and convergence.

Diffractive optical elements (DOEs) are essential components in optical and photonic technologies, motivating the need for rapid mass production with high-precision fabrication methods. Photopolymers are particularly attractive for DOEs production because their optical phase can be modified via both surface and refractive index modulations. In this work, we report the fabrication of DOEs on PVA/AA photopolymers using ultrafast laser direct writing. By combining surface topography measurements with a phase depth model, we extract the surface and bulk phase depth contributions and demonstrate a transition from surface-dominated modulation at 1 kHz to bulk refractive index modification under cumulative conditions at 100 kHz. These outcomes highlight ultrafast laser direct writing as a powerful, rapid and controlled method for the high-quality and rapid fabrication of DOEs.

The control of heat-affected modifications is a major challenge in ultrafast laser processing of polymers due to their low thermal diffusivity and phase transition temperatures. While these effects are typically localized in the vicinity of the ablation region, the interaction may evolve from positive heat-affected deformation to efficient material removal, depending on the irradiation conditions. In this work, we investigate how pulse duration (220 fs – 32 ps), beam radius (40 –118 μm), and repetition rate (100 Hz – 60 kHz) govern the laser-induced response of poly(vinyl chloride) (PVC) under 1030 nm ultrafast laser irradiation. These results reveal that heat accumulation strongly influences the interaction behavior even under fluence conditions above the single-pulse ablation threshold. Under heat accumulation conditions, heat-affected modifications decrease beyond a certain repetition rate, while ablation remains efficient. This behavior suggests that material removal may reduce the fraction of deposited energy contributing to heat diffusion into the surrounding region. These findings suggest that, in polymers with low thermal diffusivity, efficient material removal can contribute to reducing heat-affected modification at repetition rates well below the GHz regime typically discussed in the context of ablation cooling. This enables the investigation of this regime under conditions where the influence of additional effects, such as plasma or particle shielding is reduced. This work provides new insights into the interplay between heat accumulation and material removal in ultrafast laser processing, offering guidelines for the controlled fabrication of surface structures and the optimization of laser processing conditions.