Nanofabrication of tailored surface structures in dielectrics using temporally shaped femtosecond-laser pulses

Arbitrary spectro-temporal pulse-shaping algorithm

Measurement applications in optical fields require arbitrary spectro-temporal pulse shaping. However, conventional pulse-shaping algorithms are limited to controlling only the shape of the temporal intensity waveform. To overcome this limitation, we introduce the concept of short-time Fourier transformation into the conventional iterative Fourier transform algorithm, enabling it to introduce spectro-temporal constraints using a spectrogram image as a target. We numerically demonstrate that the proposed algorithm can find an appropriate spectral phase modulation pattern to realize arbitrarily controlled spectro-temporal pulse waveforms by testing the algorithm with different spectro-temporal multi-pulse waveforms. The algorithm benefits from reducing computational costs for generating spectro-temporal waveforms.

Nanopatterning of silicon via the near-field enhancement effect upon double-pulse femtosecond laser exposure

Utilizing the near-field enhancement effect of a polystyrene microsphere, direct ablation of nanohole arrays by a temporal-shaping femtosecond (fs) laser pulse is presented. The nanohole arrays, which are circular, regular, and free of cracks, were processed without extra post-processing, and their average diameter decreased gradually, as the double-pulse delay increased until 2500 fs. The simulated results by a plasma model and finite difference time domain solution demonstrate that the size decrease of the structure is attributed to the increase of the ablation threshold of silicon. Through fs laser near-field fabrication, the FWHM of nanoholes can be reduced to approximately 50 nm (λ/16) and even to 23 nm when using the second harmonic laser at a wavelength of 400 nm.

3D Manufacturing of Glass Microstructures Using Femtosecond Laser

The rapid expansion of femtosecond (fs) laser technology brought previously unavailable capabilities to laser material processing. One of the areas which benefited the most due to these advances was the 3D processing of transparent dielectrics, namely glasses and crystals. This review is dedicated to overviewing the significant advances in the field. First, the underlying physical mechanism of material interaction with ultrashort pulses is discussed, highlighting how it can be exploited for volumetric, high-precision 3D processing. Next, three distinct transparent material modification types are introduced, fundamental differences between them are explained, possible applications are highlighted. It is shown that, due to the flexibility of fs pulse fabrication, an array of structures can be produced, starting with nanophotonic elements like integrated waveguides and photonic crystals, ending with a cm-scale microfluidic system with micro-precision integrated elements. Possible limitations to each processing regime as well as how these could be overcome are discussed. Further directions for the field development are highlighted, taking into account how it could synergize with other fs-laser-based manufacturing techniques.

Energy adjustment pulse shaping algorithm part I: accuracy improvement of phase retrieval IFTA

Techniques to generate a targeted temporal waveform with high accuracy are desirable to extend the application range for pulse shapers. In this study, a target energy adjustment mechanism is applied to the input-output iterative Fourier transform algorithm (IFTA). It is numerically demonstrated that, considering multi-pulse temporal waveforms, the developed algorithm provides a suitable spectral phase modulation pattern and improves the shape of the temporal waveform compared to that of the input-output IFTA.

Energy adjustment pulse shaping algorithm part II: realization of a spectral intensity design

An accurately controlled arbitrary temporal waveform is required for many applications. To realize accurate pulse shaping, many optimization algorithms have been proposed to design spectral phase modulation patterns. However, as far as the authors know, no intensity optimization algorithm has been proposed. Therefore, in this paper, an algorithm is proposed to design an optimal spectral intensity modulation pattern for shaping short laser pulses. Consequently, it is numerically demonstrated that the proposed algorithm provides suitable spectral intensity modulation patterns, which create more accurate shapes of temporal waveform than those of spectral phase-only modulation.

The Fabrication of Micro/Nano Structures by Laser Machining

Micro/nano structures have unique optical, electrical, magnetic, and thermal properties. Studies on the preparation of micro/nano structures are of considerable research value and broad development prospects. Several micro/nano structure preparation techniques have already been developed, such as photolithography, electron beam lithography, focused ion beam techniques, nanoimprint techniques. However, the available geometries directly implemented by those means are limited to the 2D mode. Laser machining, a new technology for micro/nano structural preparation, has received great attention in recent years for its wide application to almost all types of materials through a scalable, one-step method, and its unique 3D processing capabilities, high manufacturing resolution and high designability. In addition, micro/nano structures prepared by laser machining have a wide range of applications in photonics, Surface plasma resonance, optoelectronics, biochemical sensing, micro/nanofluidics, photofluidics, biomedical, and associated fields. In this paper, updated achievements of laser-assisted fabrication of micro/nano structures are reviewed and summarized. It focuses on the researchers' findings, and analyzes materials, morphology, possible applications and laser machining of micro/nano structures in detail. Seven kinds of materials are generalized, including metal, organics or polymers, semiconductors, glass, oxides, carbon materials, and piezoelectric materials. In the end, further prospects to the future of laser machining are proposed.

Adaptive optics in laser processing

Adaptive optics are becoming a valuable tool for laser processing, providing enhanced functionality and flexibility for a range of systems. Using a single adaptive element, it is possible to correct for aberrations introduced when focusing inside the workpiece, tailor the focal intensity distribution for the particular fabrication task and/or provide parallelisation to reduce processing times. This is particularly promising for applications using ultrafast lasers for three-dimensional fabrication. We review recent developments in adaptive laser processing, including methods and applications, before discussing prospects for the future.

Single shot laser writing with sub-nanosecond and nanosecond bursts of femtosecond pulses

A method is proposed for efficient laser modification of fused silica and sapphire by means of a burst of femtosecond pulses having time separation in the range 10-3000 ps. Modification enhancement with the pulse separation increase in the burst was observed on the tens picoseconds scale. It is proposed that accumulated transient tensile strain in the excitation region plays a crucial role in modification by a sub-nanosecond burst.

Laser Synthesis and Processing of Colloids: Fundamentals and Applications

Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials, thereby enabling the fabrication of bioconjugates and heterogeneous catalysts. Accurate size control of LSPC-synthesized materials ranging from quantum dots to submicrometer spheres and recent upscaling advancement toward the multiple-gram scale are helpful for extending the applicability of LSPC-synthesized nanomaterials to various fields. By discussing key reports on both the fundamentals and the applications related to laser ablation, fragmentation, and melting in liquids, this Article presents a timely and critical review of this emerging topic.