As an example, Archerjee et al. investigated laser welding of PMMA to ABS via a diode laser at 809.4 nm wavelength . In their study, the transparent PMMA was placed at top and the opaque ABS with 0.1 wt% of CB pigments was placed at the bottom. The laser power, area of the beam spot, and welding speed are the parameters that should be optimized in laser welding to achieve the best efficiency. Moreover, high clamping pressure and good surface finish of the substrates are required in order to eliminate any air gaps in between, which may cause a weak bond. 0.40 wt% of CB was also melt blended in polystyrene in Juhl et al.'s study, allowing for laser bonding to another polystyrene layer 116 . The CB can also be added only at the interface between the two layers 117 . Nowadays, with advancements in laser beam sources, it is possible to generate lasers at the wavelengths of around 2 µm, namely, by using thulium fibre lasers. This avoids the necessity for an additional absorbent layer as thermoplastic polymers are already absorbent in this range.