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Multi-photon lithography -a powerful laser nanoscale additive-manufacturing method- is employed for structuring micro-ring traveling-wave resonators onto micrometric diameter, optical fiber tapers. These weakly guided, micro-ring resonating structures achieve light circulation with Q-factors of the order of ∼2.0 × 103, for typical diameters of tens of micrometers, in the spectral band of 1550 nm. The parametrization of the fabrication process, the characterization of these structures in TE and TM polarization, and the numerical simulation of their spectral performance is presented and analyzed. Moreover, these micro-ring resonators are exemplified into the demonstration of an ethanol vapor sensor, readily achieving detectivities of 0.5 ppm, based on reversible physisorption effects. Our demonstration aims at developing a new type of photonic platforms, based on a versatile, laser based prototyping approach onto micrometric size, optical fiber tapers, while exhibiting unique guiding and modal interaction characteristics, for departing the laboratory bench, while being implemented into diverse types of sensing and actuating devices.

Optics manufacturing technology is predicted to play a major role in the future production of integrated photonic circuits. One of the major drawbacks in the realization of photonic circuits is the damage of optical materials by intense laser pulses. Here, we report on the preparation of a series of organic–inorganic hybrid photoresists that exhibit enhanced laser-induced damage threshold. These photoresists showed to be candidates for the fabrication of micro-optical elements (MOEs) using three-dimensional multiphoton lithography. Moreover, they demonstrate pattern ability by nanoimprint lithography, making them suitable for future mass production of MOEs.

Since the global energy demand increases annually, a great need is arising in energy-related technologies. Photocatalysis plays a major role in these technologies, as it exploits one of the renewable types of energy, solar energy. For this reason, there is a plethora of scientific investigations in the research field of photocatalysis. In particular, the variety of materials that could be employed to efficiently enhance the procedure, is extensively studied. One of the most widely used materials is titania (TiO 2 ) due to its efficiency in photocatalysis [1] , while maintaining and other notable properties such as non-toxicity, chemo-stability, enhanced electronic and optical characteristics.

The detection of vapours of organic solvents at low concentrations impacts significant market sectors such those of chemical processing, safety, and security. The interaction of organic molecules in the gas phase with optical surfaces mostly refers to physisorption processes, with typical adhesion monolayers in the scale few nm’s or lower; the transduction mechanism for tracing those vapours using evanescent field interactions is a significant challenge. Few gas sensing probes have been realised using planar micro-ring resonators (MRRs), while being used for detecting inert gas pressure changes or vapours of organic molecules using oxide layers.

Welcome and Introduction to SPIE Photonics West LASE conference 11675: Synthesis and Photonics of Nanoscale Materials XVIII

Multiphoton lithography allows the high resolution, free-form 3D printing of structures such as micro-optical elements and 3D scaffolds for Tissue Engineering. A major obstacle in its application in these fields is material and structure autofluorescence. Existing photoresists promise near zero fluorescence at the expense of poor mechanical properties, and low printing efficiency. Sudan Black B is a molecular quencher used as a dye for biological studies and as means of decreasing the autofluorescence of polymers. In our study, we report the use of Sudan Black B both as a photoinitiator and as a post-fabrication treatment step, using the zirconium silicate SZ2080 for the development of a non-fluorescent composite. We use this material for the 3D printing of micro-optical elements, and meso-scale scaffolds for mesenchymal stem cell cultures. Our results show that the Sudan Black B photosensitive hybrid can be used for the fabrication of high resolution, highly transparent, autofluorescence-free microstructures.

A ring resonator device developed onto an optical fiber taper, using multi-photon laser lithography, while operating as ethanol vapor sensor is presented. This sensor readily measures ethanol vapor concentrations of 0.5ppm, with Q-factor of 1.9x103.

Multiphoton lithography allows the high resolution, free-form 3D printing of structures such as micro-optical elements and 3D scaffolds for Tissue Engineering. A major obstacle in its application in these fields is material and structure autofluorescence. Existing photoresists promise near zero fluorescent in expense of poor mechanical properties, and low printing efficiency. Sudan Black B is a molecular quencher used as a dye for biological studies and as means of decreasing the autofluorescence of polymers. In our study we report the use of Sudan Black B as both a photoinitiator and as a post-fabrication treatment step, using the zirconium silicate SZ2080™ for the development of a non-fluorescent composite. We use this material for the 3D printing of micro-optical elements, and meso-scale scaffolds for Mesenchymal Stem Cell cultures. Our results show the hybrid, made photosensitive with Sudan Black B, can be used for the fabrication of high resolution, highly transparent, autofluorescence-free microstructures.

Arrays of hierarchical microstructures are considered nowadays as an effective method to create hydrophobic surfaces. Herein, we use femtosecond 3D printing to manufacture microstructures in different geometric patterns. Direct laser writing and, in particular, multiphoton polymerization lithography (MPL) with ultrafast laser pulses has taken additive manufacturing all the way down to the sub-micrometer scale. MPL is a 3D nanoscale manufacturing tool offering great potential for rapid prototyping and the manufacture of photonic devices, tissue scaffolds and biomechanical parts. In this study, we demonstrate the tuning of the wetting performance of surfaces via trichomes designs of 3D microstructures.

We are presenting a model for a quantitative description of the polymerization process in 3D-laser microfabrication. With aim to assist in estimating the necessary power threshold to obtain certain feature size, particularly the line characteristics, depending on the laser power and writing speed. The focal distribution as well as the photoresist is taken into account. We do not try to gain any chemical insight into the processes involved, and restrict us to a quantitative study of a multi-photon process. Machine learning is used to classify the input SEM images providing a look-up table as a custom field for optimized parameter selection.

EUR was partially supported by Grant of Russian Ministry of Science and Education (Grant No. 18-15-00172). Multimode high-power laser diodes suffer from inefficient beam focusing, leading to a focal spot 10-100 times greater than the diffraction limit. This inevitably restricts their wider use in 'direct-diode' applications in materials processing and biomedical photonics. We report here a 'super-focusing' characteristic for laser diodes, where the exploitation of self-interference of modes enables a significant reduction of the focal spot size. This is achieved by employing a conical microlens fabricated on the tip of a multimode optical fibre using 3D laser nano-printing (also known as multi-photon lithography). When refracted by the conical surface, the modes of the fibre-coupled laser beam self-interfere and form an elongated narrow focus, usually referred to as a 'needle' beam. The multiphoton lithography technique allows the realisation of almost any optical element on a fibre tip, thus providing the most suitable interface for free-space applications of multimode fibre-delivered laser beams. In addition, we demonstrate the optical trapping of microscopic objects with a super-focused multimode laser diode beam thus rising new opportunities within the applications sector where lab-on-chip configurations can be exploited. Most importantly, the demonstrated super-focusing approach opens up new avenues for the 'direct-diode' applications in material processing and 3D printing, where both high power and tight focusing is required. Publisher PDF

We demonstrate the fabrication of 3D microstructures which display motion under the influence of a magnetic field. This is achieved by forming a coating of iron, known for its ferromagnetic properties, on 3D microstructures fabricated by Multiphoton Lithography. Pulsed Laser Deposition is the technique used to produce the iron coating. It is a simple and fast method that can be employed using a variety of materials. Movement of magnetic microstructures inside a liquid in response to a magnetic field has been observed.

Ultrashort ring-Airy laser beams with tunable characteristics are experimentally generated and employed for the advanced fabrication of large 3D structures with high resolution using multiphoton polymerization. These beams can be adjusted to abruptly autofocus over an extended range of working distances while keeping almost invariant their voxel shape and dimensions. This striking property together with the real-time controlled focus tuning, through a spatial light modulator, make them ideal candidates for long range multiphoton polymerization. Moreover, the paraxial ring-Airy beams can approach the wavelength limit when scaling down, while observing a counterintuitive, strong enhancement of their focal peak intensity. Using numerical simulations, we show that this behavior is a result of the coherent constructive action of paraxial and nonparaxial energy flow.

The development of dynamically responsive 3D photonic elements, which is crucial for the design of active integrated photonic circuits, requires the incorporation of material systems with fast and tunable response. To this end, semiconductor quantum dots have been widely used to perform as the active material system to be integrated; nonetheless, multiple-step processing is usually required for the active functions to be preserved, thereby restricting functionality of integrated 3D quantum photonic elements mostly to the infrared. Here, we report a simple scheme for the realization of visible light active 3D photonic devices by combining direct laser writing with two-photon absorption and in situ synthesis of cadmium sulfide (CdS) nanoparticles. The novel active 3D printable hybrid material is synthesized by crosslinking precursors of CdS quantum dots into a photo-structurable organic–inorganic zirconium–silicon hybrid composite integrating functional properties of both high spatial resolution and high third-order nonlinearity into the photonic matrix. As a proof-of-demonstration for 3D printed active photonic devices, woodpile photonic crystals with an inlayer periodicity down to 500 nm are successfully fabricated showing clear photonic stop bands in the visible spectral region, while for the first time, evidence of an ultrafast dynamic response in the visible is also demonstrated.

A Fabry–Perot optical sensing microresonator, fabricated by direct laser writing on the endface of a standard telecom fiber, is demonstrated as a microsensor for the specific detection of common chlorinated organic solvent vapors. The device operates within the 1550-nm spectral region, while the spectra recorded in the reflection mode correlate to the refractive index and absorption changes due to the different vapors trapped inside the microcavity. The operation of the microresonator sensing probe is explained in terms of standard physisorption and molecule packing mechanisms of organic vapors onto the porous sites of the photopolymerized reflection surface. The sensing of traces of three different chlorinated organic solvents vapors at concentrations down to 4 ppm and their discrimination through their spectral and temporal evolution is demonstrated and discussed, while the chlorinated volatile organic compound identification potential is also considered.

We demonstrate that paraxial ring-Airy beams can approach the wavelength limit, while observing a counterintuitive, strong enhancement of their focal peak intensity. Using numerical simulations, we show that this behavior is a result of the coherent constructive action of paraxial and nonparaxial energy flow. A simple theoretical model enables us to predict the parameter range over which this is possible.

A Fabry–Perot micro-optical sensing resonator fabricated by direct laser writing on the endface of a standard telecom fiber is demonstrated. This endface optical fiber sensing probe has been tested for tracing the vapors of common organic solvents. The device operates in the spectral region lying between 1440 and 1660 nm, while the spectra recorded in reflection mode correlate to the refractive index changes due to the different vapors trapped inside the microcavity. The performance of the device operation with respect to the reflecting surface porosity of the fabricated microstructure is presented, while the sensing of ethanol traces down to 4 ppm concentrations was achieved.

Since 3D printing became widely available for a variety of applications, the demand for three-dimensional structures with high resolution has grown. Direct laser writing by multiphoton polymerization, due to its unique, nm-scale resolution, has proven to be an indispensable tool for high-accuracy 3D printing. Here, we will discuss the basic principles of direct laser writing by multiphoton polymerization, the equipment used, and the most commonly employed materials. Finally, we will discuss its application in the field of tissue engineering.

Tunable abruptly autofocusing ring Airy beams enable advanced multiscale photo-polymerization. Scaling down to the paraxial regime, these beams can approach the wavelength limit while presenting a strong enhancement of their focal intensity.

A novel three-dimensional (3D) metallic metamaterial structure with asymmetric transmission for linear polarization is demonstrated in the infrared spectral region. The structure was fabricated by direct laser writing and selective electroless silver coating, a straightforward, novel technique producing mechanically and chemically stable 3D photonic structures. The structure unit cell is composed of a pair of conductively coupled magnetic resonators, and the asymmetric transmission response results from interplay of electric and magnetic responses; this equips the structure with almost total opaqueness along one propagation direction versus satisfying transparency along the opposite one. It also offers easily adjustable impedance, 90° one-way pure optical activity and backward propagation possibility, resulting thus in unique capabilities in polarization control and isolation applications. We show also that scaling down the structure can make it capable of exhibiting its asymmetric transmission and its po...

Display Omitted A review on multiphoton direct laser writing (DLW) for scaffold fabrication.We present the basic principles of DLW by multi-photon polymerization.We describe the most commonly used materials.Finally, we discuss the prospects of the technology. For a great variety of research fields extending from photonics to tissue engineering applications, the requests for the construction of three-dimensional structures with high resolution grow more and more imperative. Towards this aim, the direct laser writing technique by multi-photon polymerization, due to its unique properties and characteristics, has proven to be an indispensable tool to high accuracy structuring and has been put on the map as an emerging technology for scaffold 3D printing. In the present review, the basic principles of multi-photon polymerization are presented, the experimental set-up requirements are described and the employed materials demands are thoroughly mentioned as well as the most representative examples of the recent developments in the field.

Plasmonic metamaterials for biosensing were designed as artificial materials, composed of gold/silver nanostructured blocks forming a nanolattice, which can provide improved sensing response in optical transduction compared to classical materials and additional sensing functionalities. 2D plasmonic nanoperiodic structures, including nanohole and nanodot arrays are prominent examples of such metamaterials, which can offer a series of novel functionalities, including size selectivity, spectral tuneability, drastical field enhancement etc., although spectral sensitivity of these structures is limited by spatial periodicity related to diffraction nature of plasmon coupling. Here, we consider metamaterials based on 3D plasmonic crystals and show the possibility of a delocalized plasmon mode, which can provide a drastic gain in spectral sensitivity (> 2600 nm/RIU compared to 200-400 nm/RIU for 2D structures). Combined with larger surface for bioimmobilization provided by the 3D matrix, the proposed metamaterial structure promises the advancement of plasmonic biosensing technology.

A three-dimensional (3D) holographic focal volume engineering method is proposed and employed for advanced multiphoton polymerization. A large number of foci are closely positioned in space according to a designed geometry, avoiding undesired interference effects by phase engineering. Through all-optical micro-displacements in space, the discrete foci bundle leads to the realization of complete 3D arbitrary structures. The microstructures are fabricated by direct laser writing without additional optical or mechanical motion support. We report a 20-times faster fabrication time in comparison to point-by-point laser polymerization techniques.

An introduction is provided to the feature issue of Optical Materials Express on laser materials.

In this work, we present our most recent results on the fabrication of 3D high-resolution woodpile photonic crystals containing an organic-inorganic silicon-zirconium (Si-Zr) composite and cadmium sulfide (CdS) quantum dots (QDs). The structures are fabricated by combining 3D Direct Laser Writing by two-photon absorption and in-situ synthesis of CdS nanoparticles inside the 3D photonic matrix. The CdS-Zr-Si composite material exhibits a high nonlinear refractive index value measured by means of Z-scan method. 3D woodpile photonic structures with varying inlayer periodicity from 600nm to 500nm show clear photonic stop bands in the wavelength region between 1000nm to 450nm.

We explore the excitation of plasmons in 3D plasmon crystal metamaterials and report the observation of a delocalized plasmon mode, which provides extremely high spectral sensitivity (>2600 nm per refractive index unit (RIU) change), outperforming all plasmonic counterparts excited in 2D nanoscale geometries, as well as a prominent phase-sensitive response (>3*104 deg. of phase per RIU). Combined with a large surface for bioimmobilization provided by the 3D matrix, the proposed sensor architecture promises a new important landmark in the advancement of plasmonic biosensing technology.

We present our investigations into the fabrication of three-dimensional microoptical elements by the direct femtosecond laser writing of a germanium–silicon photosensitive hybrid material. Germanium glass composites are very interesting for optical applications as they are photosensitive, and maintain high optical transparency in the visible and near-infrared bands of the spectrum. Here, we have used a germanium containing hybrid material to make nanophotonic structures and microoptical elements such as photonic crystal templates, prisms and spatial polarization plates, both on flat surfaces and fiber tips. Our results show that this germanium silicate composite is an excellent material for microoptics fabrication.

Single ultra-short pulses from Gaussian and vortex beams have been used for the fabrication of complex micro-structures via multi-photon polymerization. The complexity of the resultant micro-structures stems from the modification of both transverse intensity and phase profiles of these single pulses to create modulated scaffolds and hollow cylinders. Experimental results are compared to theoretical models, and good agreement is shown.

The fabrication of fully three-dimensional photonic crystals with a bandgap at optical wavelengths is demonstrated by way of direct femtosecond laser writing of an organic-inorganic hybrid material with metal-binding moieties, and selective silver coating using electroless plating. The crystals have 600-nm intralayer periodicity and sub-100 nm features, and they exhibit well-defined diffraction patterns.

We present our investigations into the direct laser writing of a novel germanium-containing hybrid sol–gel photosensitive material for optical applications at micro scale. We employ this material in the fabrication of photonic micro-structures, such as aspheric lenses and prisms; these are well-shaped and provided good optical performance. The material exhibits good transparency and structurability, and three-dimensional structures with sub-100 nm resolution are achieved. We demonstrate the suitability of the direct laser writing method for the rapid production of custom shaped microoptical components. Since germanium glasses are widely used in fiber optics, the combination of direct laser writing with this specially designed, functional material opens an interesting way in fabricating structures for controlling light flow.

The combination of materials with targeted optical properties and of complex, 3D architectures, which can be nowadays obtained by additive manufacturing, opens unprecedented opportunities for developing new integrated systems in photonics and optoelectronics. The recent progress in additive technologies for processing optical materials is here presented, with emphasis on accessible geometries, achievable spatial resolution, and requirements for printable optical materials. Relevant examples of photonic and optoelectronic devices fabricated by 3D printing are shown, which include light‐emitting diodes, lasers, waveguides, optical sensors, photonic crystals and metamaterials, and micro‐optical components. The potential of additive manufacturing applied to photonics and optoelectronics is enormous, and the field is still in its infancy. Future directions for research include the development of fully printable optical and architected materials, of effective and versatile platforms for multimaterial processing, and of high‐throughput 3D printing technologies that can concomitantly reach high resolution and large working volumes.

In this work, we have synthesized and characterized a novel, titanium-containing hybrid material that can be structured three-dimensionally using two-photon polymerization. We investigate the effect on the structurability of the increase of titanium isopropoxide and methacrylic acid in this photosensitive composite. We show that while it is possible to make transparent thin films with a titanium isopropoxide molar content as high as 90%, three-dimensional structures can be made only when the titanium isopropoxide molar content is less than 50%. We measure the refractive index of films with different titanium isopropoxide: methacrylic acid concentrations and we show that while the refractive index increases linearly with the titanium isopropoxide, the increase of the methacrylic acid content does not affect the refractive index of the material.

Two-photon polymerization of photosensitive materials has emerged as a very promising technique for the fabrication of photonic crystals and devices. We present our investigations into the structuring by two-photon polymerization of a new class of photosensitive sol-gel composites exhibiting ultra-low shrinkage. We particularly focus on two composites, the first containing a zirconium alkoxide and the second a nonlinear optical chromophore. The three-dimensional photonic crystal structures fabricated using these materials demonstrate high resolution and clear bandstops in the near IR region.

Direct laser writing by two-photon polymerization of photosensitive materials has emerged as a very promising technique for rapid and flexible fabrication of photonic crystals. In this work, a photosensitive silica sol-gel containing the nonlinear optical chromophore Disperse Red 1 is synthesized, and the two-photon polymerization technique is employed to fabricate three-dimensional photonic crystals with stop-gaps in the near-infrared. The composite material exhibits minimal shrinkage during photopolymerization, eliminating the need for shrinkage compensation or the fabrication of support structures.

Multiphoton Lithography is a technique that allows the fabrication of three-dimensional structures with sub-100 nm resolution. It is based on multi-photon absorption; when the beam of an ultra-fast laser is tightly focused into the volume of a transparent, photosensitive material, polymerization can be initiated by non-linear absorption within the focal volume. By moving the laser focus three-dimensionally through the material, 3D structures can be fabricated. The technique has been implemented with a variety of materials and several components and devices have been fabricated such as photonic crystals (Fig. 1a), biomedical devices (Fig. 1b), and microscopic models (Fig. 1c).

Laser-induced forward transfer has been used for the deposition of photoactive biotin in micron-scale patterns. The process uses a 500 fs pulsed KrF laser beam to transfer small amounts of a liquid solution target as micron-size droplets to a substrate placed parallel and in close proximity to it. The biomolecules remain active after the transfer; this is demonstrated through fluorescence assays. In addition to the laser parameters, those regarding the target composition and the receiving surface for the miniaturization of the transferred patterns have been studied and optimized. Droplets as small as 5 μm have been obtained by reducing the target thickness and transfer energy; by increasing the percentage of glycerol added in the biomolecules solution and by using hydrophobic surfaces as receiving substrates. The influence of the glycerol addition and the hydrophobicity of the receiving surfaces on the activity of the transferred biomolecules have also been studied.

We have demonstrated micromachining of bulk 3C silicon carbide (3C- SiC) wafers by employing 1028nm wavelength femtosecond laser pulses of energy less than 10 nJ directly from a femtosecond laser oscillator, thus eliminating the need for an amplified system and increasing the micromachining speed by more than four orders of magnitude.

We have investigated the ablation behaviour of single crystal SrTiO3 with focus on the influence of the pulse duration at a wavelength of 248 nm. The experiments were performed with KrF-excimer lasers with pulse durations of 34 ns and 500 fs, respectively. Femtosecond-ablation turns out to be more efficient by one order of magnitude and to eliminate the known problem of cracking of SrTiO3 during laser machining with longer pulses [1],[2]. In addition, the cavities ablated with femtosecond pulses display a smoother surface with no indication of melting and well-defined, sharp edges. These effects can be explained by the reduced thermal shock effect on the material by using ultrashort pulses.

Three different designs of Fabry-Perot optical sensing microresonators fabricated by direct laser writing on the endface of a standard telecom fiber using a zirconium-silicon, organic-inorganic hybrid photosensitive material, are demonstrated. These endface optical fiber sensing probes are used for the detection of common organic alcohols and chlorinated solvents vapors. The devices operate in the spectral region lying between 1440 nm and 1660 nm, while the spectra recorded in reflection mode correlate to refractive index or absorption changes due to different vapors trapped inside the microcavities. A sensitivity of 1503nm/RIU, for a concentration of 4ppm ethanol vapors was succeeded. The microresonator sensing probe is explained in terms of standard physisorption and molecule packing mechanisms of organic vapors onto porous surfaces.

Many applications of high-power laser diodes demand tight focusing. This is often not possible due to the multimode nature of semiconductor laser radiation possessing beam propagation parameter M2 values in double-digits. We propose a method of 'interference' superfocusing of high-M2 diode laser beams with a technique developed for the generation of Bessel beams based on the employment of an axicon fabricated on the tip of a 100 μm diameter optical fiber with highprecision direct laser writing. Using axicons with apex angle 1400 and rounded tip area as small as similar to 10 μm diameter, we demonstrate 2-4 μm diameter focused laser ` needle' beams with approximately 20 mu m propagation length generated from multimode diode laser with beam propagation parameter M2= 18 and emission wavelength of 960 nm. This is a few-fold reduction compared to the minimal focal spot size of ∼11 μm that could be achieved if focused by an 'ideal' lens of unity numerical aperture. The same technique using a 1600 axicon allowed us to demonstrate few-μm-wide laser 'needle' beams with nearly 100 μm propagation length with which to demonstrate optical trapping of 5-6μm rat blood red cells in a water-heparin solution. Our results indicate the good potential of superfocused diode laser beams for applications relating to optical trapping and manipulation of microscopic objects including living biological objects with aspirations towards subsequent novel lab-on-chip configurations. Publisher PDF

We report two-photon polymerization of an acrylate composite using a femtosecond laser at 1028 nm. The composite consists of an acrylate monomer, a free-radical co-initiator and a photo-sensitizer. The material is transparent to infrared laser radiation and absorbs strongly in the visible. By scanning the tightly focused laser beam, we employ two-photon absorption to polymerize and selectively solidify the material. Two photo-polymerization of organic composites permits the construction of complex-shaped three-dimensional structures of sub-micron resolution. Due to their versatile optical and chemical properties and the ability to mix them with active molecules, the materials described in this work are particularly useful for a variety of applications such as photonic devices, actuators and micro-fluidic devices. In addition, as both the single photon and the two-photon wavelengths are not in the ultraviolet part of the spectrum, this technique is particularly promising for incorporation into the photo-polymer of active molecules that are sensitive to UV radiation.

In the current paper, a study is made of the manufacture of three-dimensional structures of micron resolution using two- and three-photon polymerization. A femtosecond laser operating at a wavelength of 1028 nm is employed for the multi-photon polymerization processes. For the component manufacture, two different materials are used. The first material, used in two-photon polymerization, is an acrylate-based photo-polymer that polymerizes by employing green radiation. The second material, used in three-photon polymerization, is an ultraviolet (UV) -photopolymerizable acrylate composite.

We have performed a comparative study of UV laser ablation of SrTiO3 with nanosecond- and sub-picosecond sources, respectively. The experiments were performed with lasers at a wavelength of 248 nm and pulse durations of 34 ns and 500 fs. Femtosecond ablation turns out to be more efficient by one order of magnitude and eliminated the known problem of cracking of SrTiO3 during laser machining with longer pulses. In addition, the cavities ablated with femtosecond pulses display a smoother surface with no indication of melting and well-defined, sharp edges. These effects can be explained by the reduced thermal shock effect on the material by using ultrashort pulses.

We demonstrate surface micromachining of bulk 3C silicon carbide (3C-SiC) wafers by employing tightly focused infrared femtosecond laser pulses of energy less than 10 nJ directly from a femtosecond laser oscillator, thus eliminating the need for an amplified system and increasing the micromachining speed by more than four orders of magnitude. In addition, we show that high aspect ratio through-tapered vias can be drilled in 400 µm thick wafers using an amplified femtosecond laser.

The plasmonic version of a 3D chiral meta-atom which consists of a loop-wire structure, namely the so-called twisted omega particle, is experimentally realized. The structure is fabricated by direct laser writing and subsequent electroless silver plating, a novel technique capable of producing truly 3D photonic nanostructures. In this case, the metallic wire of finite length supports an electric dipole resonance, whereas the loop acts as a split-ring resonator which exhibits a magnetic dipole resonance, leading to the separation of right-handed circularly polarized light and the left-handed one. The arising optical activity is discussed in terms of a single oscillator model system used classically to describe the generation of natural optical activity in chiral media, and it is shown that the twisted omega particle acts as its exact plasmonic analogue.

Recent work in three-dimensional microstructuring of photosensitive materials by femtosecond lasers is reviewed. The applications of nonlinear and quenching phenomena allow one to overcome both surface absorption and the diffraction limit to produce 3D microstructures with sub-diffraction limit resolution. Potential applications in the emerging fields of photonics and microfluidics are discussed.