Two-photon lithography (2PL) enables high-resolution 3D nanoprinting of complex, functional microdevices. This review examines 2PL fundamentals, resolution and throughput improvements, and emerging applications in various fields.

Nanoelectrospray laser deposition (NELD) of nanoparticles (NPs) on various substrates has attracted considerable attention as a fast, cost-effective, and scalable technique for precise control of heating time and zone. In this work, NELD-assisted sintering of titanium dioxide (TiO2) NPs on borosilicate glass and quartz substrates is addressed. A 10.6μm CO2 laser was used for patterning and sintering titania nanoparticles in ambient air. The effects of laser dose and deposition process parameters on the morphological, structural, and optical characteristics of the sintered TiO2 patterns were characterized using optical microscopy, scanning electron microscopy, and x-ray diffraction. The results point out that the anatase phase was preserved after laser sintering, without the appearance of any TiO2 rutile traces. We show that the improvement in the morphological properties of TiO2 patterns is due to the laser sintering of a dense layer of ceramic with enhanced interconnectivity and connection between single nanoparticles. A theoretical model was developed to select the temperature required to sinter TiO2 nanoparticles and to correlate it with the laser power and scanning speed to prevent cracking on the substrate and sintered nanoparticles and also to get transparent TiO2 films. An optical transmittance of ∼91% was achieved. The experimental data were in accordance with the theoretical model, predicting the success of the model.

Laser doping of n-type 4H-silicon carbide (SiC) semiconductor substrates with boron (B) using a pulsed Nd:YAG laser (λ = 1064 nm) is reported. An aqueous boric acid solution was used as a boron precursor. A simple theoretical heat transfer model was employed to select the laser processing parameters, i.e., laser power and laser-substrate interaction time, and determine the appropriate temperature to dope 4H-SiC substrates. The selected processing parameters ensured that the temperature at the laser-substrate interaction zone was below the SiC peritectic temperature to prevent any crystalline phase transformations in SiC. Fourier-transform infrared spectrometry was conducted to determine the optical properties of both undoped and boron-doped 4H-SiC substrates within the mid-wave infrared (MWIR) wavelength range (3–5 μm). Boron atoms create an acceptor energy level at 0.29 eV above the valence band in the 4H-SiC bandgap, which corresponds to λ = 4.3 μm. Boron-doped 4H-SiC substrate exhibited reduced reflectance and increased absorptance for the MWIR range. An absorption peak at λ = 4.3 μm was detected for the doped substrate. This confirmed the creation of the acceptor energy level in the 4H-SiC bandgap and, thus, doping of 4H-SiC with boron. A notable decrease in the refractive index, i.e., from 2.87 to 2.52, after laser doping of n-type 4H-SiC with boron was achieved.

A novel Additive Manufacturing (AM) process is presented for depositing inorganic glasses with sufficient quality and precision for fused multi-component and gradient index (GRIN) optics. The CO 2 laser is used to evaporate and sinter the suspension of oxide nanopowder and to produce inorganic glasses.

Semi-insulating (SI) 4H-polytype of silicon carbide (SiC) is a highly desirable wide bandgap semiconductor material for various applications in challenging environments owing to its exceptional characteristics such as high melting point, remarkable thermal conductivity, strong breakdown field, and excellent resistance to oxidation. This study investigates the critical laser processing parameters to operate a pulsed UV 355 nm laser to dope high-purity (HP) SI 4H-SiC substrates with boron. The doping process parameters are examined and simulated for this UV laser doping system using a liquid precursor of boron. Boron atoms create a dopant energy level of 0.3eV in the doped HP 4H-SiC substrates. Diffusion of boron atoms into 4H-SiC substrates modifies the hole density at 0.3eV energy level, and causing a variation in the dynamic refraction index, and absorption index. Consequently, the optical properties of boron doped samples, namely, transmittance, reflectance, and absorbance, can be modified. The current simulation reported in this study explains the motivation of UV optical doping strategy to dope SiC substrates. A beam homogenizer was used to control the laser spot used to generate doping process. The advantage of the beam homogenizer is demonstrated by producing flat-top beams with uniform intensity over a certain area defined by the focusing lens choice. A simple theoretical model is used to select the laser processing parameters for doping SiC substrates. These modeled parameters are used to determine the efficient laser processing parameters for our doping experiments.

Multilayer thin films of sintered TiO2 and SiO2 nanoparticles (NPs) are frequently used as antireflection coatings (ARCs) due to their excellent optical properties. We report CO2 laser-assisted deposition, i.e., spin-coating of wet films followed by laser processing, of multilayer transparent films using a mixture of TiO2 and SiO2 NPs. A simple heat transfer model is presented to optimize laser processing parameters for effective sintering while preventing the anatase-to-rutile phase transformation of TiO2. To minimize the reflectance, and enhance the transmittance, an ARC model is utilized to select the film material and determine the thickness of each layer. UV/Vis spectrophotometry was carried out to measure the optical reflectance. UV/Vis/NIR spectrophotometry analysis shows that the sintered homogenous films are highly transparent, with an average transmittance of above 90% in a certain range of wavelength. Due to the porosity of the films, an effective medium model was utilized to determine the optical constants, i.e., the refraction and absorption indices, of just the solid phase, which is formed by the sintered NPs in the nanocomposite TiO2/SiO2 coatings. The results demonstrate that the effective refraction or absorption index can be smaller than that of the solid phase. The effect of TiO2 and SiO2 concentrations on the optical properties of multilayer homogenous TiO2/SiO2 coatings is also investigated. The effect of laser processing on the microstructural properties was investigated using SEM and XRD techniques. Optical profilometry was conducted to determine the thickness of the sintered films.