The potential for miniaturised optical systems to be printed onto integrated circuits and mass manufactured like consumer electronics has remained tantalisingly just out of reach for decades. The major challenge has been combining the vast array of fundamentally different elements into a fully functional system. This talk will present an overview of recent breakthroughs to achieve true integrated circuits that combine the mass manufacture of silicon, the ultra-low loss of nitride and active semiconductors through hybrid integration. Emphasis will be placed on the resurgence of lithium niobate and its potential to unlock the electromagnetic spectrum linking the visible, infrared, Terahertz and microwave regimes. The talk will conclude with a vision for the diverse applications that could be transformed by harnessing these fully integrated photonic circuits.

Femtosecond lasers are a powerful tool for micro-machining, while various parameters such as irradiation paths and pulse energies must be optimized. We have developed a method to simulate three-dimensional shapes after femtosecond pulse irradiation at arbitrary locations with arbitrary pulse energies using a difference equation for laser ablation based on deep learning. The deep-neural-network-based simulator successfully predicted the processing results for various materials such as semiconductors, glass, and polymers.

This presentation was prepared for SPIE LASE 2023.

Energy transfer from laser pulses to electrons in solids is a key quantity to understand laser materials processing. We have been developing a first-principles computational approach based on ab initio time-dependent density functional theory (TDDFT) that has been made public as a software SALMON. Combining microscopic calculation of electronic motion by TDDFT and mesoscopic light-propagation calculation by Maxwell equations, ab initio evaluation of energy transfer is feasible in nanometer and femtosecond spatio-temporal resolution. Using the method, systematic calculations are under way for several distinct materials including metals, semiconductors, and large-gap insulators, for a wide range of laser intensities.

A study of the of laser peen forming of thin stainless steel metal foils (50 μm thick) using a solid-state ps-pulsed laser, emitting at a wavelength of 1064 nm was conducted. The dependence of the bending angle and the radius of curvature on the energy per pulse, the treated area, the distance between lines, and the repetition rate of the treatment is presented. The study also shows that the bending effect is local, and it cannot be scaled by increasing the repetition rate, because the increase in temperature relaxes the superficial stresses previously induced.

Laser direct write with ultrashort pulses allows high-resolution, high-precision modification inside transparent materials. In diamond, and other wide bandgap semiconductors such as silicon carbide, this provides many opportunities to engineer devices for use in quantum technology. A single ultrashort laser pulse can induce vacancies in the diamond lattice, that may then be mobilized to form stable colour centre defects, which can then be employed as quantum bits. The laser write process can additionally be used to manufacture electrically conductive wires in 3D in the substrate, providing options for control over the qubits.

We investigated femtosecond laser inscription of IG2 waveguides and photonic structures for mid-infrared applications. 1 x 4 beamsplitters are realized, achieving normalized splitting ratios of more than 90% among the four arms. In addition, both fundamental mode and multimode guiding in the mid-IR regime at 4.55 µm are demonstrated. The Mid-IR waveguiding properties at 4.55 µm will be presented for both single-mode and multimode waveguides with as low as 0.8 dB/cm propagation loss for the single-mode guiding and controllable mode field diameter. This work is supported by the US National Aeronautics and Space Administration under STTR Contracts 80NSSC20C0027, 80NSSC21C0638, and 80NSSC22PA936.

We demonstrate laser-fabrication of length-controlled channels in the bulk of dielectrics with a spatial periodicity down to 0.7 µm and moderate aspect ratio (1:10), by single-shot ablation using different (fs/ps) pulse durations. We take advantage of beam shaping technique using an axicon and annular aperture to generate a Bessel beam with an extra control of the so-called “non-diffracting” length. The dimensions and pitch attained are suitable to envision the writing of NIR nanophotonic components. As a proof-of-principle demonstration, we fabricate patterns whose arrangements mimic photonic-crystal devices like waveguide, Y-coupler, and structures with square and triangular lattices as their basic units.

Recently, we started a new project toward data-driven laser processing, in which real-time monitoring data are delivered to AI system for high-speed optimization. Then, the optimized laser parameters are transferred to the ultrafast laser processing system. To follow the optimized parameters instantly, it’s important to develop a new laser processing system with high-speed modulation as well as wide-range variable parameters. In this work, effect of ultrafast laser parameters including high-speed modulation on ablation volume was discussed for micro-drilling of glass materials. The drilling of silica glass was performed under three types of modulation conditions with the same total input power and number of pulses: monotonic increase in the pulse energy, constant energy, monotonic decrease. As a result, the holes drilled with monotonic decrease became much deeper compared to samples drilled under monotonic increase. The usefulness of the high-speed laser modulation was demonstrated.

Femtosecond GHz-burst mode laser processing has attracted much attention in the last few years. Very recently, we reported first results on percussion drilling and the process dynamics in this new regime. In this contribution, we present our latest results on top-down drilling in different dielectric materials. Holes of very high quality with a smooth and glossy inner surface and with aspect ratios up to 70 were obtained in fused silica. Moreover, we investigated the drilling depth and speed as a function of burst number and show a three-stage behavior in the drilling mechanism.

Ultrafast laser interference ablation leads to deterministic, strictly periodic patterns on metals and semiconductors with periods down to a few 100 nm. Manipulation of the interfering partial beams enable a variety of surface patterns with applications in photonics, fraud protection, electronics, fluidics, tribology, and medicine. Under suitable excitation conditions, a single beam may generate a surface plasmon polariton (SPP) and their interference may create a periodic surface pattern as well. Specific beam shaping may compensate the strong SPP attenuation leading to homogeneous patterns with a single laser pulse.

The nature of transparent materials makes their laser-based functionalisation more complex, highly material dependant and often characterised by process throughputs too low to be considered competitive for an industrial uptake. In this frame, direct laser interference patterning (DLIP) appears to be the right compromise to achieve 100s-nm surface features while running at competitive throughputs. A state-of-the-art DLIP processing setup is employed to shape the 100s-nm nanostructure features to obtain highly homogeneous morphologies in different regimes of interaction on polycarbonate, fused silica and sapphire, including a DLIP-tailored f-theta lens connected to a 30-mm aperture high-speed galvanometric scanning head.

In the last several years, femtosecond laser processing using GHz burst mode, which consists of the ultrashort laser pulse (intra-pulse) trains with the pulse-to-pulse interval of several hundred ps, has attracted much attention, as it can achieve higher-processing quality with enhanced processing efficiency than the conventional femtosecond laser irradiation scheme (single-pulse mode). However, most of the research using the GHz burst mode was aimed at ablation. In this study, we extend the GHz burst mode femtosecond laser processing to the formation of laser-induced periodic surface structures (LIPSS) to explore the possibility of novel nanostructuring, over the single-pulse mode.

Refractive index engineering is critical for fabrication of refractive optical elements directly inside transparent materials. Such three-dimensional optical engineering is only emerging for the technologically important material, silicon. Here we show the first analysis of refractive index and birefringence observations written with a beam other than Gaussian inside Si. Exploiting a Bessel-type beam, we created laser-written structures with average refractive index as high as 6 ✕ 10-^3 and retardance on the order of 20nm. These properties are studied as function of laser modulation and other relevant parameters, including writing geometry, and compared with results of Gaussian beam written structures.

A relatively new consumer electronics market is active eyewear, which includes virtual reality (VR) and augmented reality (AR) glasses. AR glasses present the challenge of combining the functionality of conventional eyeglasses with that of projected graphics, leading to the use of glasses with higher than typical indices of refraction. Infrared (IR) picosecond pulse lasers are commonly used for cutting conventional glasses. We present results using a 50 W IR picosecond laser to cut high-index glass for AR eyewear applications, demonstrating excellent quality at with high throughput. Straight line as well as curved contour cutting are demonstrated.

Several methods have recently been proposed for improving the speed of the popular two-photon polymerization process. One such method makes use of a spatiotemporal focusing technique to achieve a planar projection printing strategy. This works uses a projection two-photon polymerization process in a continuous fashion to fabricate complex 3D structures at a large print rate while maintaining smooth surface features. Fabrication of millimeter scale structures are achievable with this continuous, layer-by-layer projection two-photon lithography system.

This presentation was prepared for SPIE LASE 2023.

Femtosecond laser direct write (fs-LDW) is a promising technique for fine 3D printing of biomaterials such as protein due to nonlinear multiphoton absorption processes facilitating microfabrication along a designated laser light path. Proteinaceous microstructures fabricated by fs-LDW are reported to retain their native protein function. Combined with submicron feature sizes, they might offer diverse biomedical or biochip applications. Here, we show the pulse energy dependence of free-form pure proteinaceous line segments fabricated by fs-LDW. To utilize fs-LDW for arbitrarily created complex shapes, it is important to minimize line segment mismatches and assure sufficient connectivity by carefully selecting the appropriate parameters.

Optical vortex possesses unique physical properties, such as a ring-shaped spatial form, and an orbital angular momentum, associated with its helical wavefronts. Optical vortex materials processing enables the fabrication of a variety of nano/micro-scale chiral structures and the direct print of solids and even ultrahigh viscosity liquids at high spatial and pointing resolutions. Going beyond the conventional laser materials processing technologies, the optical vortex materials processing opens the door towards advanced materials science and technology, such as chiral and printed photonics, plasmonics and metamaterials. In this presentation, we review the state-of-art of the optical vortex materials processing and optical vortex laser induced forward transfer technologies.

The first successful nano-photonics element deep inside the silicon is created. This was achieved by creating nanoscale and high-aspect-ratio laser-written modifications inside Si, without altering the wafer surfaces. We exploit Bessel beams, in order to create 700-nm thick subsurface planes of 250 µm axial length, arrayed and layered to increase device efficiency. The length of modifications is controlled by precise axial stitching of individual subsurface lithographic layers. The maximum efficiency at the incident angle, satisfying the Bragg condition, is measured 85% for the two-layer grating, and its angular sensitivity is recorded, with a strong agreement between experiment and theory.

Femtosecond lasers are available with an increasing energy per pulse. Their efficient exploitation without any decrease of quality is key. It could be done with beam-splitting and parallel processing. We present a fully reflective CANUNDA-SPLIT module used with a 100W 1030nm 500fs laser and a 100mm F-theta. The uniformity of the beams over the Field of View is presented. The drilling of stainless steel and Nickel cavities matrices, designed for tribological properties improvement, has been performed. The homogeneity of the cavities and the circularity are analyzed. These results paves the way to meter-scale area processing with a reduced processing time.

We have demonstrated surface plasmon polaritons excited on Si transiently metalized with an intense femtosecond laser pulse by measuring the reflectivity of a Si grating changed in the incident angle of the fs pulse. We observed that the incident angle where the sharp dip of the reflectivity appeared was changed by the thickness of SiO2 films. The result demonstrates that the plasmon wavelength is controlled through SiO2 film deposited on Si.

Ultrafast laser processing of glass material was investigated to address the need for precise, flexible figuring and finishing tools with minimal thermal effects. A dynamic pulse propagation model was established and used to predict the spatial and temporal distribution of surface temperature, through which a set of optimum laser processing conditions was determined. The impact of laser parameters on material removal and surface quality was experimentally investigated for Borofloat glass. Linearly controllable material removal is achieved with the determined laser parameters, and the processed area maintains the optic-quality surface roughness for various material removal depths. This research was supported by the US National Science Foundation I/UCRC Center for Freeform Optics (IIP-1822049 and IIP-1822026).

Our laboratory has reported that periodic micro swelling structures on silicone rubber surfaces are photochemically formed, and the surface has superhydrophobicity. At the conference, the formation of capsule structures on the top of periodic micro swelling structures on silicone rubber surface by 193 nm ArF excimer laser irradiation will be reported. The microcapsule structure is formed by irradiating the silicone rubber with silica microspheres aligned in a single layer with the 193 nm ArF excimer laser. The formation method and the nature of the microcapsule structure will be discussed.

Crystalline silicon (c-Si) solar cells are the dominant PV technology today. The production volume is bound to tenfold in the next decade. Upcoming c-Si solar cells are increasingly sensitive semiconductor devices demanding higher quality materials, more precise yet sustainable processing at low cost. We discuss the history and current status of laser processing in PV production. New laser process routes can enable higher quality PV devices while remaining compatible with a sustainable scaling of production. The processes include mask-free direct writing techniques delivering almost photolithography quality results, micro joining of metal foils as electrodes and annealing for defect passivation of crystalline silicon solar cells.

Transition metal oxide (TMOs) layers have interesting properties as selective contacts for novel semiconductor devices. Especially, oxides of molybdenum (MoO3), vanadium (V2O5), and tungsten (WO3) show good behaviour acting as front hole-selective contacts for n-type crystalline silicon heterojunction solar cells. Laser scribing has been widely used for thin-film ablation and seems the appropriate technology for device manufacturing with such non-conventional materials. In this work, we study the laser scribing of non-stoichiometric evaporated WOx, VOx, and MoOx films with three different wavelengths (1064, 532, and 355 nm) with pulse duration in the ns and ps regimes. The selection of the proper laser source allows a wide parametric window, with complete removal of the TMO films and no alteration of the silicon substrate. The results on the isolation of diodes and their electrical characteristics show the quality of the laser scribing processes.

Calcium phosphate coatings were employed for medical implants such as dental or orthopedic for bone bonding. Essentially, these layers were dissolved by osteoclast and replaced with newly formed bone by osteoblast. Finally, the implant is fixed with bone without a gap in vivo, which is called “osseointegration”. In this situation, the implant and bone are fixed only by an anchor effect, therefore they aren’t fixed microscopically. If this coating layer isn’t dissolved easily, enhances bone formation, and adheres strongly with implants, implants will be expected much stronger bone bonding than osseointegration. We reported that dense without holes, high purity, and high crystallinity hydroxyapatite coating layer was fabricated on zirconia substrate by droplets eliminated type pulsed-laser deposition scheme, which was similar geometric configuration with the solar eclipse. Pressed and sintered -Tricalcium phosphate target was irradiated by a 4th harmonic of YAG laser in H2O gas at 0.1 T

The performance of lithium-ion-batteries at high current charging rates can be enhanced through laser structuring of the electrode coatings. Using picosecond laser pulses, various structures in the cathode coating were created. The manufactured pouch cell batteries were formed and cycled at different current rates. The discharge capacity was measured for each cycle and compared with non-structured reference cells. The results of batteries with hole patterns show an improvement of the specific discharge capacity, depending on the hole diameter and distance. A significant increase in the discharge capacity was measured for line structures, plus an enhanced ageing over the first cycles.