## 1 Introduction
For mass-market, the process is suitable for the manufacturing of diffractive structured surfaces such as holograms [39]. Temperature control challenges within the process have resulted in the evolution of the process whereby ultrasonic hot embossing has been developed. Within this process configuration, a sonotrode and pressure are applied to soften the plastic to allow flow into the micropattern of the mould. Further advantages of the US hot embossing process include its ability to be conducted at room temperature [40]. [PERSON] et al. created a robust method to manufacture and characterise the optical performance of transparent 3D-printed, high-quality bulk optics using a consumer-grade printer and commercially available resin [41]. Contact lenses have been manufactured using the direct laser printing (DLP) technique, and nanopatterns were textured on the surface of the contact lenses with the help of direct laser interference patterning (DLIP) [42]. Stereolithography (SLA) 3D-printing of transparent resin lens was performed where the surface roughness, light transmittance, and morphologies of SLA-fabricated lens were examined by atomic force microscopy, UV spectrophotometer, and scanning electron microscopy [43]. SLA printing of Fresnel lenses exhibited over 90% of optical transmittance and the printed lenses confirmed the feasibility of the 3D printing process for the fabrication of optical devices [44]. [PERSON] et al. reported a comparison between a commercially available straight cylindrical lens and custom 3D-printed, curved cylindrical lenses [45]. [PERSON] et al. discussed additive manufacturing (AM) processes like Fused Deposition Modelling (FDM), SLA, material jetting, and binder jetting, highlighting their applications in radar/sensing, communications, EMI shielding, and electromagnetic absorption. They identified that the challenges include optimising material properties, intricate structural design, manufacturing precision, and performance validation [46]. Acrylonitrile Butadiene Styrene (ABS) is a widely used commercial polymer for demanding engineering applications [47; 48; 49]. However, for the HE of ABS, only limited research has been conducted [20]. In a study by [PERSON] and [PERSON], it identified that ABS is made up of strongly entangled polymeric chains, and thus has a high activation energy [20]. Further studies also concluded that when using ABS, high activation energy is required by molecules to move against the frictional forces, and thus polymer flow is two to three times higher than those of the other polymers [50]. To initiate flow in moulds, the applied energy must be greater than the internal flow resistance of the polymer. To achieve flow, higher T\({}_{\text{e}}\) can be used to reduce the resistance of flow into a mould cavity. Typically, temperatures higher than the T\({}_{\text{g}}\) are required [51; 52; 53; 54]. However, increases in temperature result in excessive thermal shrinkage when cooling, which can distort the replicas [13]. To address this challenge, [PERSON] and [PERSON] used a viscous embossing strategy for surface micropatterning of ABS products. This process used a T\({}_{\text{e}}\) far above T\({}_{\text{g}}\) and demoulded shortly after, with the polymer in the viscous state. The absence of cooling resulted in the replication of 1 \(\upmu\)m structures over a large surface area. This proposed strategy exhibits several advantages such as highly precise and more productive replication, which are not observed in the conventional HE of ABS [20]. Many researchers have dedicated their efforts to improve the surface finish and dimensional accuracy of Fused Deposition Modelling (FDM) prototypes. The research has concluded that the surface finish of FDM parts can be greatly enhanced through exposure to specific chemicals. One notable advancement in this area is Stratasys, Inc.'s vapour smoothing (VS) process. This method creates a controlled environment for vaporising specialised chemicals, allowing hot chemical vapours to react with the upper surface of FDM parts.