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As the main component of silicon (Si)-based Optic Electronics Integrated Circuit (OEIC) chip, Si-based infrared photodetector operating at communication wavebands is very important. In this paper, we report a kind of chromium (Cr)-hyperdoped black Si material fabricated using femtosecond laser pulses irradiation. The concentration of the Cr atoms in the black Si layer exceeds 1020 cm−3 and the Cr-hyperdoped Si has a large sub-bandgap absorptance (~60% for $1.31 \boldsymbol {\mu }\text{m}$ ). The deep-energy level introduced by Cr impurity is 0.39 eV below the bottom of conduction band and thus the ionized electron concentration is very low (~1015 cm−3). Owing to the excellent sub-bandgap absorption of Cr-hyperdoped Si, face-to-face black Si photodiodes are fabricated. Under illumination of $1.31 \boldsymbol {\mu }\text{m}$ light, the responsivity of the photodiodes based on N+-N junction reaches 0.57 A/W at 4.3 V bias. In addition, the rise and delay time of the device to the infrared light are on the order of milliseconds.

Blazed gratings are widely used in optical detection devices with the unique property of concentration of light energy to a desired diffraction order. However, traditional substrates for fabricating blazed gratings are easily damaged with the wear and tear in long-term usage under harsh conditions. Here, we propose the fabrication of blazed gratings on sapphire with high mechanical stability by femtosecond laser lithography combined with subsequent reactive ion etching (RIE). Various sapphire blazed gratings with periods from 2 μm to 10 μm and heights from 260 nm to 2 μm were realized to concentrate light energy (wavelengths of 405 nm, 532 nm and 633 nm) to different diffraction orders (1st, 2nd, and 3rd). The results provide great insights for the construction of micro-optical devices that have potential applications under harsh conditions.

Femtosecond laser additive manufacturing based on two-photon polymerization performs a useful technique for fabricating high-precision 3D structures. However, poor mechanical strength and low processing efficiency brought by near polymerization threshold processing to achieve high accuracy are still urgent problems. In this work, a definition-reinforcement-solidification (DRS) processing strategy is proposed to solve the current problems, in which DRS processing includes three steps: utilize a near-threshold femtosecond laser to accurately define the surface profile of 3D structures, perform enhanced scanning on the above structure's inner surface with a high-power femtosecond laser to increase the mechanical strength, and rapidly solidify the inner unpolymerized resin through one exposure of ultraviolet light to improve the processing efficiency. Compared with conventional near-threshold point-by-point direct writing, microstructures fabricated by the DRS strategy for a given geometry and polymer have hardness and Young's modulus values increase to 154% and 199%, respectively, and exhibit a 10000% improvement in machining efficiency without the loss of processing accuracy. Arbitrary complex 3D microstructures can be implemented rapidly via this strategy. This work will inject new vitality into two-photon polymerization additive manufacturing.

In recent years, femtosecond laser direct writing technology has made great progress in integrated quantum photonic circuits due to its advantages of applicability to an extensive range of materials and true 3-D ability. However, a waveguide prepared via a femtosecond laser shows a non-circular cross section and high birefringence, which seriously restricts the development of polarization encoded quantum photonic integrated chips towards greater integration and higher functions. Here, we propose an amplitude-phase double shaping method to reduce waveguide birefringence, which involves using a cylindrical lens and slits. A waveguide prepared using this method shows a circularity cross-section that reaches up to 97.6% and a birefringence that is as low as 1.49 × 10−6. Based on such an ultralow birefringence waveguide, a polarization independent Hong-Ou-Mandel quantum interferometer was fabricated. Interference visibilities for identical photon pairs in different polarization states were found to be more than 95% with a standard deviation of 0.6%. The ultra-low birefringence single-mode waveguide and the polarization-independent interferometer realized using this approach will play an important role in large-scale polarization encoding integrated quantum photonic chips.

We propose a machine vision-based focus detection method (MVFD) for femtosecond laser machining. By analyzing the laser focus pattern, the defocus direction and distance are obtained simultaneously. The proposed technique presents high precision with an average error of 0.047 µm and a root mean square error (RMSE) of 0.055 µm. Moreover, the method is robust and is less affected by the tilted sample. For the curved surface sample, the average error and RMSE are 0.093 and 0.145 µm, respectively. Thus, the proposed focus detection method can be easily combined with laser processing equipment, which is widely used in large-range and high-precision femtosecond laser processing.

This Letter reports a novel helical sapphire fiber Bragg grating (HSFBG) in a single crystal sapphire fiber with diameter of 60 µm fabricated by a 515 nm femtosecond laser. Due to the large refractive index modulation region and high structural symmetry of the HSFBGs, high-reflectivity and high-quality spectra can be prepared and additionally have good bending resistance. The spectral properties of HSFBGs with different helical diameters are studied. When the helical diameter is 30 µm, the reflectivity of HSFBG is 40%, the full width at half-maximum is 1.56 nm, and the signal-to-noise ratio is 16 dB. For the HSFBG bending test, the minimum bending radius is 5 mm, which can still maintain relatively good spectral quality. In addition, the HSFBG array with different periods has been successfully cascaded in a sapphire fiber. The experimental results of the HSFBG high-temperature test show that this HSFBG can work reliably at 1600°C, and the temperature sensitivity in the high-temperature range can reach 35.55 pm/°C. This HSFBG can be used in high-temperature and harsh environments, such as metal smelting and aeroengine structural health monitoring.

Natural compound eyes provide the inspiration for developing artificial optical devices that feature a large field of view (FOV). However, the imaging ability of artificial compound eyes is generally based on the large number of ommatidia. The lack of a tunable imaging mechanism significantly limits the practical applications of artificial compound eyes, for instance, distinguishing targets at different distances. Herein, we reported zoom compound eyes that enable variable-focus imaging by integrating a deformable poly(dimethylsiloxane) (PDMS) microlens array (MLA) with a microfluidic chamber. The thin and soft PDMS MLA was fabricated by soft lithography using a hard template prepared by a combined technology of femtosecond laser processing and wet etching. As compared with other mechanical machining strategies, our combined technology features high flexibility, efficiency, and uniformity, as well as designable processing capability, since the size, distribution, and arrangement of the ommatidia can be well controlled during femtosecond laser processing. By tuning the volume of water injected into the chamber, the PDMS MLA can deform from a planar structure to a hemispherical shape, evolving into a tunable compound eye of variable FOV up to 180°. More importantly, the tunable chamber can functionalize as the main zoom lens for tunable imaging, which endows the compound eye with the additional capability of distinguishing targets at different distances. Its focal length can be turned from 3.03 mm to infinity with an angular resolution of 3.86 × 10-4 rad. This zoom compound eye combines the advantages of monocular eyes and compound eyes together, holding great promise for developing advanced micro-optical devices that enable large FOV and variable-focus imaging.

Microlens array has been demonstrated to be an effective method for laser beam homogenization. However, the homogenization of high-fluence laser beam is still a great challenge due to the serious damage to the microlens-array-based homogenizer. Here, an ultra-smooth sapphire concave microlens-array-based homogenizer, which is fabricated by dry-etching-assisted femtosecond laser machining, is proposed for shaping high-fluence pulsed laser beam to a flat-top profile intensity distribution. By taking advantages of high transmittance (>70%) and low surface roughness (1.1 nm), high-fluence (5 J/cm2) and wide-band (266 nm, 532 nm and 808 nm) laser beams homogenization is successfully realized by the sapphire concave microlens arrays.

In graphene oxide (GO)-based compound photocatalysts, where GO is a novel cocatalyst, the mainly photophysical processes are the charge separation/transfer between GO and other nanocatalysts. Howev...

Here, we report embedded spiral zone plates (SZPs) processed by tightly focused femtosecond pulses, inducing a refractive index change in a sapphire crystal. The change in the index is investigated both experimentally and theoretically and found to be 0.93% lower than that before the laser irradiation. Benefiting from the investigation of the photorefraction, a high diffractive efficiency of up to 78% is achieved for the SZPs. In addition, the SZPs are embedded under the surface of the sapphire, which ensures that the components possess stable optical properties in the case of external refractive index changes. The high-performance elements having a high diffractive efficiency and stable optical performance will have tremendous applications in optical communication and optical manipulation.

How to overcome the diffraction barrier of light in the far-field region to obtain subwavelength processing resolution has always been an important issue in advanced optical manufacturing. The traditional strategy to achieve this goal is to use the nonlinear threshold effect of materials, such as femetosecond laser induced two-photon polymerization (TPP) [1] . By introducing the stimulated radiation loss mechanism, the resolution of TPP can further reach tens of nanometers [2] . However, for solid materials, there is still no such a universal method that can realized robust and controllable nanoscale resolution for programable patterning. Here, we report an optical far-field-induced near-field breakdown technology [3] , which we abbreviate it as optical FIB, that in principle can be applied to any solid materials. The core idea of this technology is to invoke the initial optical damage created by ultrafast laser as a near-field probe (usually a nanohole, see Fig. 1 ), to trigger the subsequent subwavelength light confinement around the seed. Then, the far-field energy can be efficiently transferred to the near-field hotspot which is not restricted by the diffraction limit ( Fig. 1 ,left), thereby permitting a deep subwavelength direct writing resolution (18 nm, 1/40 λ for 800 nm pulse). The orientation of this near-field hotspot is always perpendicular to laser polarization due to the constraint of the electrical displacement continuity condition. By a simple polarization control of the incident light for steering nano-groove writing along the designed pattern, free-form nanowriting can be achieved while all the advantages of far-field optical direct writing can be maintained.

Herein, a vector scanning subtractive manufacturing technology is proposed to rapidly fabricate smooth micro-optical components, which is based on the vector scanning method and wet etching. Compared with the raster scanning method, the vector scanning method increases processing efficiency by nearly two orders and mitigates a buildup of stress around the laser processed region, avoiding the generation of cracks. The Letter demonstrates the fabrication of three-dimensional (3D) micro-structures with various sizes and morphologies. For example, micro-concave lenses with diameters of 20 µm to 140 µm, heights of 10 µm to 70 µm, and surface roughness of 29 nm are flexibly fabricated on sapphire by vector scanning subtractive manufacturing technology. The results indicate that the technology has broad prospects in the field of monolithic integrated 3D all-solid-state micro-optics.

Remote manipulation of a micromachine under an external magnetic field is significant in a variety of applications. However, magnetic manipulation requires that either the target objects or the fluids should be ferromagnetic or superparamagnetic. To extend the applicability, we propose a versatile optical printing technique termed femtosecond laser-directed bubble microprinting (FsLDBM) for on-demand magnetic encoding. Harnessing Marangoni convection, evaporation flow, and capillary force for long-distance delivery, near-field attraction, and printing, respectively, FsLDBM is capable of printing nanomaterials on the solid-state substrate made of arbitrary materials. As a proof-of-concept, we actuate a 3D polymer microturbine under a rotating magnetic field by implementing γ-Fe2O3 nanomagnets on its blade. Moreover, we demonstrate the magnetic encoding on a living daphnia and versatile manipulation of the hybrid daphnia. With its general applicability, the FsLDBM approach provides opportunities for magnetic control of general microstructures in a variety of applications, such as smart microbots and biological microsurgery.

Direct optical ferroelectric switching (FE switch) has the advantage of being ultrafast over the traditional FE switch, which relies on domain nucleation and growth. However, how to realize nonvolatility in such an optical FE switch poses a serious challenge. Time-dependent density-functional theory molecular dynamics study reveals that subpicosecond nonvolatile FE switches can be realized in GeTe and ${\mathrm{PbTiO}}_{3}$. While optical tuning of the transition barrier and initiation of a directional atomic motion are crucial, the dephasing of the excited state holds the key for the realization of nonvolatility.

An active surface with an on-demand tunable topography holds great potential for various applications, such as reconfigurable metasurfaces, adaptive microlenses, soft robots and four-dimensional (4D) printing. Despite extensive progress, to achieve refined control of microscale surface structures with large-amplitude deformation remains a challenge. Moreover, driven by the demand of constructing a large area of microstructures with increased complexity&mdash, for instance, biomimetic functional textures bearing a three-dimensional (3D) gradient&mdash, novel strategies are highly desired. Here, we develop an active surface with a dynamic topography and three-tier height gradient via a strain-tunable mismatching-bonding process. Pneumatic actuation allows for rapid, reversible and uniform regulation of surface microstructures at the centimeter scale. The in-situ modulation facilitates large-amplitude deformation with a maximum tuning range of 185 &mu, m. Moreover, the structural gradient can be modulated by programming the strain value of the bonding process. With our strategy, another two types of surfaces with a four-tier gradient and without gradient were also prepared. By providing active modulation and design flexibility of complicated microstructures, the proposed strategy would unlock more opportunities for a wealth of novel utilizations.

The past decades have seen growing research interest in developing efficient fabrication techniques for preparing bioinspired graphene surfaces with superwettability. Among the various fabrication methods, laser fabrication stands out as a prominent one to achieve this end and has demonstrated unique merits in the development of graphene surfaces with superwettability. In this paper, we reviewed the recent advances in this field. The unique advantages of laser fabricated graphene surfaces have been summarized. Typical graphene surfaces with superwettability achieved by laser fabrication, including superhydrophobic graphene surfaces, oil/ water separation, fog collection, antibacterial surfaces, surface enhanced Raman scattering (SERS), and desalination, have been introduced. In addition, current challenges and future perspectives in this field have been discussed. With the rapid progress of novel laser physical/ chemical fabrication schemes, graphene surfaces with superwettability prepared by laser fabrication may undergo sustained development and thus contribute greatly to the scientific research and our daily life.

Superior performances, such as high processing speed and resolution, make galvano-mirror-based fabricating strategy widely applied, particularly for micro/nano-scale femtosecond laser direct writing (FsLDW). However, the optically limited processing area restricts its applications. Here, we report a simple, low-cost, and universal pre-compensation method that corrected the off-axis optical aberrations to considerably expand the processing area of galvano-mirror-based nano-FsLDW with 3D nano-resolution maintained. A high-quality continuous-surface Fresnel lens was one-step fabricated with a 550- $\mu \text{m}$ diameter, which surpassed the effective range (~150- $\mu \text{m}$ ) of the high-numerical aperture objective lens used for high resolution. It provides a significant approach for novel high-speed/efficiency micro/nano-FsLDW of diverse micro/nano-elements/systems.

In this letter, a sapphire fiber Bragg grating (SFBG) is fabricated by a femtosecond laser line-by-line scanning method. A third-order fiber Bragg grating is obtained in a single crystal sapphire fiber with a diameter of 60 μ m. Compared to the SFBG written by a point-by-point method, the SFBG written by the line-by-line method has a higher reflectivity and grating with about 15% reflectivity is achieved when the track length is about 40 μ m. The temperature sensing characteristics of this SFBG from a room temperature to 1600 °C are studied, and the temperature sensitivity of SFBG is 34.96 pm/°C from 1000 °C to 1600 °C. The strain characteristics are also tested at the temperature of 26 °C, 500 °C, 1000 °C, and 1600 °C, and the strain sensitivities are 1.42, 1.42, 1.44, and 1.45 pm/μϵ, respectively. These characteristics show that this SFBG has potential applications in a harsh environment structural health monitoring.

We propose UV–IR femtosecond laser hybrid lithography for the efficient printing of complex on-chip waveguides, which offers good performance in terms of processing efficiency and accuracy. With this three-dimensional printing technology, waveguides with complex cross-section shapes, such as owls and kittens, can be easily fabricated with an efficiency increased by 1500% (for 6 µ m × 6 µ m ). In addition, a circular cross-section waveguide with an extremely low birefringence and complex 8 × 8 random walk networks were quickly customized, which implies that in the design and preparation of the large-scale optical chips, the proposed maskless method allows for the preparation of highly customized devices.

A crystalline silicon (Si) surface was modified using nanosecond laser pulses in an argon atmosphere. The laser-modified Si (M-Si) samples have a higher performance and thermostable absorption in the broadband range (400–2400 nm) than conventional Si. The concentration of carrier electrons in the M-Si layer is at least five orders of magnitude greater than the carrier concentration of the Si substrate. Using the N+–N− junction formed between the M-Si layer and the Si substrate, visible and near-infrared (VIS-NIR) M-Si photodetectors are made. The N+–N− photodiode has good rectification characteristics and a high photoresponse to the subbandgap NIR light at 1310 nm. At the same time, the M-Si photodetector at a low reverse bias shows a large gain to the VIS-NIR light above the bandgap. By comparing the response time of the M-Si photodetector to the light of 900 and 1310 nm, the response speed of the device to the photon above-bandgap energy is faster.

The combination of surface-enhanced Raman spectroscopy (SERS) technology with microfluidics makes it possible to diagnose genetic disease through label-free on-chip DNA detection. However, open problems including the integration of SERS substrate with microfluidic devices, controllable trapping and releasing of target molecules are still challenging. Here we demonstrate a facile laser scribing method to fabricate silver nanoparticles (AgNPs) and graphene oxide (GO) based biochips as a reusable SERS sensor for DNA detection. Programmable laser scribing of the AgNPs@GO composite film enables direct patterning of sensitive SERS channels that consist of graphene supported AgNPs by exfoliating the composites into hierarchical porous structures. Integrating the SERS-active patterns with a microfluidic chip forms a biochip for allowing SERS detection of DNA. The noncovalent interactions between DNA and graphene mediated controllable trapping and releasing of DNA sequences, enabling efficient on-chip SERS detection and the regeneration of the biochip. The simple, green and cost-effective fabrication of the SERS-active biochips reveals great potential for biomolecular sensing and genetic engineering applications.

Micro-ripple and micro-bead structures are formed on a silicon (Si) surface after irradiation with femtosecond laser pulses in nitrogen (N2) atmosphere. Simultaneously, supersaturated nitrogen (N) atoms, with a concentration above 1020 cm−3, are doped into the textured black Si layer via laser ablation. The N-doped Si exhibits strong below-bandgap infrared absorption from 1.1 to $2.5~\mu \text{m}$ , which remains nearly unchanged after annealing for 30 min at 873 K. The mechanism of this thermally stable infrared absorption is analyzed by first-principles calculations. According to the transmission electron microscopy results, multiple phases (including single crystalline, nanocrystalline, and amorphous phases) are observed in the laser-irradiated layer. Hall Effect measurements prove that N-dopants induce a low background free-carrier concentration ( $\sim 1.67\times 10^{16}\,\,\text {cm}^{-3}$ ). Finally, a Schottky-based bulk structure photodiode is made. This broadband photodiode exhibits good thermal stability and a photo-responsivity of 5.3 mA/W for $1.31~\mu \text{m}$ at a reverse bias of 10 V.

The design and fabrication of devices that based on adaptive soft matter with the autonomous transduction of environmental and field signals is an interesting area of material science and device engineering. Additive manufacturing, also known as 3D printing, has gained great attention as it allows the creation of complex 3D geometries with precisely prescribed microarchitectures, which enable new functionalities or improved performance. Here, we report on poly(ethylene glycol) diacrylate hydrogel microstructures with excellent humidity responsiveness by 3D printing of two-photon photopolymerization. The voxels of fabricated hydrogel microstructures have controllable crosslinking density because adjusting fabrication parameters, therefore controllable humidity-driven swelling ability can be achieved. Using the proper parameters, we present an array of microstructures which can realize the function of nano-interconnected network and a hydrogel microstructure with pores to mimic the open and close of the stomata of plants. Based on a flexible two-steps fabrication method and the combination of active and inert materials, binary encoding micropillar arrays and joint-like cantilever microstructure have been easily fabricated. The humidity-responsive actuation of hydrogel microstructures is repeatable and stable over 10000 cycles. This kind of composite hydrogel microstructures may lead to great promise for the diverse applications such as sensors, actuators or construction of soft robots.

In this letter, we report the design and fabrication of an aplanatic zone plate, whose phase distribution is described by a fourth-order non-spherical function. Its optimal coefficients are determined by an iterative calculation based on the ray tracing method. The special zone plate, with a diameter of 10 mm, can significantly reduce the spherical aberration. The focal spot diameter is $43.4~\mu \text{m}$ , which is less than that of spherical lens, i.e., $153.6~\mu \text{m}$ . In addition, the zone plate is buried inside a z-cut sapphire crystal by femtosecond laser direct writing technology. This ensures that the zone plate possesses stable optical properties in complex and harsh environments. The novel embedded zone plate has an important application in optical aberration balance system. It improves the system’s integration and stabilization in a high temperature environment, especially in a refractive index changing environment.

Color centers are widely used in quantum information, quantum sensing, micro-nano optics and other relevant fields. In addition to the traditional ways that can generate color centers, for instance, ion beam implantation, direct laser writing (DLW) technology has recently emerged as an appealing alternative to induce color centers because it enables true three-dimensional and high precision machining. Particularly, DLW can induce color centers near/on the surface or inside the crystals with a homogeneous and pure surrounding environment, which permits subsequent integration with other components. In this paper, the recent advances in laser-induced color centers in different crystals are comprehensively reviewed, including diamond, silicon carbide, alkali halide crystals and others. Meanwhile, cutting-edge applications of laser-induced color centers are introduced. Lastly, current challenges and future perspective of this field have been discussed.

Femtosecond (fs-) laser induced subwavelength and deep-subwavelength periodic structures have attracted attention due to their sub-diffraction feature size and rich physics of laser-matter interaction. However, the formation mechanisms of fs-laser induced deep-subwavelength structures on organic materials have not been reported nor systematically studied. Herein, based on the degree of laser induced free-carrier excitation, the formation of deep-subwavelength structures by fs-laser ablation was systematically studied on popular materials: negative tone resists SU8 and conductive polymer poly-3, 4-ethylenedioxythiophene: poly-(styrenesulfonate) (PEDOT: PSS). A weak propensity to form deep-subwavelength structures was found on poly-methylmethacrylate and polyvinyl alcohol. The photo-excited electrons forming the surface plasmonic wave contributed to energy localization and absorption, which led to the imprinting of deep-subwavelength structures on polymers. It has been found that materials with $\pi $ -bonds and benzene rings were most susceptible to deep-subwavelength structure formation. Based on a laser-induced surface plasmonic model, the period of regular patterns was estimated and was in a good accordance with experimental results. The proposed formation mechanism of the deep-subwavelength structures on organic materials extends an application field of fs-laser micro/nanomachining of polymers.

External electric fields can be used to manipulate the electronic properties of two-dimensional (2D) materials. 2D InSe semiconductors possess high electron mobility and wide band gap tunability. Therefore, they have been proposed for use in ultrathin electronic devices. Here, using first-principles calculations, we study the charge polarization, structure, electronic structure, and gas adsorption of an InSe monolayer under vertical electric fields. We find that both the structural evolution and charge polarization rely on the directions of the electric fields. The hole effective mass at the valance band maximum can be decreased by fields that offer a possible route to increase mobility. In contrast, the fields have little impact on the effective mass of electrons at the conduction band minimum. Therefore, high electron mobility in InSe is retained under the fields. Besides, electric fields could alter the absorption intensity for gas molecules. Therefore, gas sensors could be an expected application. More importantly, this work systematically points out some key steps for setting up electric-field calculations in the popular VASP code, such as the cancellation of the symmetrisation of the charge density, avoiding electrons spilling out into the vacuum under high fields.

Nitrogen-vacancy color centers (NVs) in diamond have several potential applications ranging from quantum computing to data storage. However, artificial NVs are often close to the surface, which limits their spatial density and applicability. Here we demonstrate an effective and precise method for preparing deep single NVs in diamond. The method is based on a spatial-shaped femtosecond laser to overcome laser defocus in high-refractive materials, and realizes the preparation of single NVs at 95 µm. In addition, owing to the good energy distribution of the shaped laser focus, the single NVs exhibit a statistic yield of 56 % ± 11 % with excellent qualities. This processing method will contribute to the integration of color centers with emerging optical elements and high-density data storage.

First-principles calculations reveal a Mexican-hat potential energy surface (PES) for two-dimensional (2D) In2Se3. This unique PES leads to a pseudo-centrosymmetric paraelectric β phase that resolves the current controversy between theory and experiment. We further show that while the α-to-β (ferroelectric-to-paraelectric) phase transition is fast and coherent, assisted by an in-plane shear phonon mode, a random distribution of the atoms in the trough of the PES acts as an entropy barrier against the reverse β-to-α transition. This will be the origin of the speed limitation of current In2Se3 ferroelectric devices. However, if one orders the β phase (due to the formation of in-plane ferroelectric domains), the reverse transition can take place within tens of picoseconds in the presence of a perpendicular electric field. Finally, the Mexican-hat PES is a general feature for the entire family of 2D III2-VI3 materials. Our finding offers a critical physical picture in controlling the ultrafast reversible phase transition in 2D In2Se3 and other III2-VI3 materials, which will benefit their practical industrial development for advanced ferroelectric devices.

GeSbTe alloys have the ability of rapidly transforming between amorphous and crystalline phases. Therefore, they can be used in the non-volatile phase change memory. Recently, a vacancy-ordered cubic Ge 2 Sb 2 Te 5 ( VOC GST) phase change material where the vacancies are highly ordered in the (111) plane, has been experimentally demonstrated by STEM. However, studies are mainly on the structural characterization, rather than on the phase change behavior and possible applications of the VOC GST. Here, using first-principles molecular dynamic simulations, we study the melt-quenched amorphization process and its possible applications. We find that the VOC GST exhibits a quasi-two-dimensional amorphization process that is triggered by the diffusion of Ge atoms but not others. A partial amorphous ( P-amor ) phase is obtained, which can act as an intermediate state between the pure amorphous and pure crystalline phases for possible ternary-state data storage.

Optical microcavities have been paid enormous attentions as a basic integrated element in photonic devices including micromodulators, microfilters, and microsensors. In particular, the microcavities that can produce unidirectional and single-mode lasing emissions are greatly demanded to meet the challenge of integrating high-efficiency and high-sensitivity optical functional systems. Herein, a three-dimensional polymer microlaser composed of stacked circular-ring-shaped and spiral-ring-shaped microcavities is fabricated directly on a narrow bandpass filter substrate by the femtosecond laser processing technique. The on-chip polymer microlaser provides a room-temperature, low-threshold, unidirectional, and single-mode laser output, resulting from the coupling between the two stacked microcavities. The fabrication of the on-chip low-threshold polymer microlaser opens up a possibility toward the integration of a variety of polymer microcavities for organic optoelectronic devices.

Gold (Au)-doped-textured silicon (Si) material with a thermostable absorption below bandgap (>50%) is obtained by femtosecond laser irradiation. Although the concentration of Au impurity (1019 cm−3 ) in textured Si is at least four orders of magnitude greater than the solid solubility of Au in crystalline Si, the sheet carrier density (approximately 1010 cm−2) in Au-doped Si is very low due to a self-compensation effect of Au impurity in Si material. The infrared absorption of Au-doped Si is related to laser-induced-structural defects and sub-band absorption of deep energy levels of Au in Si, which is determined by temperature-dependent Hall Effect measurement. Besides supersaturated doping of Au, a gold silicide phase is formed at textured Si surface.

Femtosecond (fs) laser annealing has been applied to improve the crystalline quality and absorptance below bandgap of ion implanted silicon (Si) with sulfur (S). The doping concentration of S is up to $10^{20}$ atoms/cm3, which is at least four orders of magnitude higher than the solid solubility of S in crystalline Si. According to the Raman spectra, after fs laser irradiation with appropriate laser energy, the crystal quality is evidently better than primary ion implanted sample. Moreover, the optical absorption coefficient at wavelengths of 1100~2400 nm is up to $1.54 \times 10^{4}$ cm $^{\mathrm {-1}}$ , which is much larger than the contribution of free carriers. Excessive laser energy will induce serious ablation effect and cause the removing of doping layer. We consider that the high absorption is a combination of sub-bandgap transition of S-related localized states, free carrier absorption, ion implantation induced defect absorption and fs laser irradiation induced defect absorption. In the end, a photo-response of 8.4 mA/W is obtained for the photodiode for 1310 nm detection light.

Nanoscale surface texturing, drilling, cutting, and spatial sculpturing, which are essential for applications, including thin-film solar cells, photonic chips, antireflection, wettability, and friction drag reduction, require not only high accuracy in material processing, but also the capability of manufacturing in an atmospheric environment. Widely used focused ion beam (FIB) technology offers nanoscale precision, but is limited by the vacuum-working conditions; therefore, it is not applicable to industrial-scale samples such as ship hulls or biomaterials, e.g., cells and tissues. Here, we report an optical far-field-induced near-field breakdown (O-FIB) approach as an optical version of the conventional FIB technique, which allows direct nanowriting in air. The writing is initiated from nanoholes created by femtosecond-laser-induced multiphoton absorption, and its cutting “knife edge” is sharpened by the far-field-regulated enhancement of the optical near field. A spatial resolution of less than 20 nm (λ/40, with λ being the light wavelength) is readily achieved. O-FIB is empowered by the utilization of simple polarization control of the incident light to steer the nanogroove writing along the designed pattern. The universality of near-field enhancement and localization makes O-FIB applicable to various materials, and enables a large-area printing mode that is superior to conventional FIB processing., Nanotechnology: Better writing with light An optical version of Focused Ion Beam technology (FIB) allows nanoscale “writing” such as surface texturing, drilling and sculpting of materials to be performed in air, avoiding the need for a vacuum which limits the application of conventional FIB. The “Optical Far-field-Induced near-field Breakdown” (O-FIB) approach has been developed by Hong-Bo Sun of Tsinghua University and colleagues at Jilin University in China and Swinburne University of Technology in Austrilia. It works by creating nanoholes with a femtosecond laser, which is controlled by sophisticated optical effects. The process can cover larger areas than conventional FIB, and with a spatial resolution below 20 nanometres. The ability to be performed in an open atmosphere offers new possibilities for nanoscale writing. These range from working on industrial scale materials such as ship hulls, down to living tissues and cells.

Femtosecond laser-induced periodic surface structures have opened broad prospects in the aspect of high-efficient and low-cost nanotextured patterning, yet defined great challenges on how to keep the periodicity in a macro area. Herein, we report a transition from non-periodicity to periodicity as the scan strategies changing. By suppressing the transition from the initial structures to the nanogratings with long-range order, arbitrary high-resolution direct writing patterns have been obtained in a large area. We attribute this phenomenon to the dynamic evolution of the near-field energy deposition around the pre-existing structures. This approach paves another way to high-precision laser processing.

Laser-induced periodic surface structures (LIPSS) have gained lots of attention for the rich physics and potentials in subdiffraction nanostructuring. Herein, we report new aspects of LIPSS to uniformly extend the periodicity to macro, or conversely suppress the periodicity to obtain freeform nanostructures. We have focused on the electron excitation, effective surface permittivity modifications, and plasmonic standing wave ablation for the structure origination and evolution. A plasmonic nanoimprinting model in long range and a nanohole-based light field enhancement in the nearfield are proposed, which are in good accord with the experiments. The nanotextured surface is obtained in a large area by light tailoring method with a cylindrical lens focusing and scanning. Besides, a critical power control method to confine the light field in nanoregion are conducted to obtain the freeform nanostructures, which have potential applications in birefringent optics and nanoscience.

Birefringence of 3 &times, 10 - 3 is demonstrated inside cross-sectional regions of 100 &mu, m, inscribed by axially stretched Bessel-beam-like fs-laser pulses along the c-axis inside sapphire. A high birefringence and retardance of &lambda, / 4 at mid-visible spectral range (green) can be achieved using stretched beams with axial extension of 30&ndash, 40 &mu, m. Chosen conditions of laser-writing ensure that there are no formations of self-organized nano-gratings. This method can be adopted for creation of polarization optical elements and fabrication of spatially varying birefringent patterns for optical vortex generation.

A dry-etching-assisted femtosecond laser lithography technology is proposed to in-site fabricate micro-optical components with an ultra-smooth three-dimensional continuous profile on a non-planar substrate. Owing to the nanometric resolution of femtosecond laser multi-photon polymerization and dry etching, smooth micro-optical components can be realized on hard materials with surface roughness of approximately 1.5 nm. With flexible and arbitrary designability of femtosecond laser lithography, various high-quality micro-optical components are realized on sapphire. These results indicate that dry-etching-assisted femtosecond laser lithography has promising potential for versatile fabrication of arbitrary ultra-smooth micro/nanostructures on hard materials.

A series of single-phase CaAlBO4: Eu3+ powder samples were synthesized by high-temperature solid-phase method, the main factors are temperature, time, concentration of rare-earth ion, etc. The results show that the maximum emission peak of the sample is located in the wide band spectrum of 467 nm, and belongs to the 4f65d to 4f7 transition of Eu3+. The maximum absorption peak is located at a narrow band of 678 nm. by a study of the relationship between the doping amount of Eu3+ and the luminescence property of the sample, The optimum doping content of Eu x 3+(x = 0.0025)

The K2MgSiO4:xMn4+ phosphor was synthesized by high temperature solid-p hase method and its luminescence characteristics were explored. The X-diffraction patt ern measured by the X-ray diffractometer matched well with the international standard card. The synthesized sample is a pure phase crystal, indicating that the doping of Mn 4+ has not changed The crystal structure of K2MgSiO4. Through the excitation and emi ssion spectra measured by the fluorescence spectrometer, it can be seen that the sample has 4 excitation peaks at 368nm, 422nm, 451nm and 534nm, and the maximum emissi on peak of the sample is at 654nm. By changing the doping concentration of Mn4+ ion s, it is found that as the Mn4+ concentration increases, the luminescence intensity of the sample increases, and finally the concentration quenching occurs after the concentrati on exceeds 1%. The chromaticity coordinates of the emission of the sample were meas ured to prove its role in the market. The chromaticity coordinates of the sample are loc ated in the red light zone and are close to the standard red light. The fluorescence lifeti me of Mn4+ transition on the D layer in the sample is about 0.2ms.

In this paper, a high-temperature solid-phase method was used to synthesize Pr3+ ion-doped Li2CaSiO4 matrix phosphor. An X-ray diffractometer and a fluorescence transient spectrometer were used to characterize the crystal structure and luminescence properties of the prepared phosphors. The results show that the prepared sample is a single phase of Pr3+-doped Li2CaSiO4; it exhibits a good orange light emission under the excitation of blue light, and is expected to be used as white light LED lighting

Calcium acuminate matrix (CaAlBO4) was prepared at temperatures 1160°C by soild state reaction, a spectroscopy analysis of Cr3+ doped CaAlBO4 based on excitation spectrum and emission spectra was performed. Broad band excitation spectra are observed with 414 nm and 553 nm. respectively owing to the 4A2→4T1 and 4A2→4T2 transition of Cr3+ ion, and emission spectra with the strongest emission peak 694 nm owing to the 2E2→4A2 transition of Cr3+ ion. Also, the influences of the concentration of Cr3+ ion on the luminescent properties in CaAlBO4 compounds were investigated, which the optimal concentration is 0.5mol%.

In emerging optoelectronic applications, such as water photolysis, exciton fission and novel photovoltaics involving low-dimensional nanomaterials, hot-carrier relaxation and extraction mechanisms play an indispensable and intriguing role in their photo-electron conversion processes. Two-dimensional transition metal dichalcogenides have attracted much attention in above fields recently; however, insight into the relaxation mechanism of hot electron-hole pairs in the band nesting region denoted as C-excitons, remains elusive. Using MoS2 monolayers as a model two-dimensional transition metal dichalcogenide system, here we report a slower hot-carrier cooling for C-excitons, in comparison with band-edge excitons. We deduce that this effect arises from the favourable band alignment and transient excited-state Coulomb environment, rather than solely on quantum confinement in two-dimension systems. We identify the screening-sensitive bandgap renormalization for MoS2 monolayer/graphene heterostructures, and confirm the initial hot-carrier extraction for the C-exciton state with an unprecedented efficiency of 80%, accompanied by a twofold reduction in the exciton binding energy. Light-matter interaction in atomically thin transition metal dichalcogenides is dominated by excitonic effects and hot-carrier relaxation/extraction mechanisms. Here, the authors report that the C exciton in two-dimensional MoS2exhibits a slower hot-carrier cooling than band-edge excitons.

Annealing-insensitive black silicon with high absorption below the silicon bandgap has been achieved by femtosecond laser direct writing. Spike microstructures with sizes ranging from 4 to 25 μm are formed on the surface layer of silicon substrate, and a large amount of phosphorous impurities (1021 cm-3) is doped during the resolidification process. The infrared absorption of phosphorus-doped black silicon decreases slightly with both the annealing temperature and duration. Excitingly, the largest decrease is less than 10% at 2 μm (annealing 240 min at 873K). This thermostable infrared absorption is related to free carrier absorption. After laser irradiation, the phosphorus-doped layer maintains a relatively high crystallinity that can be improved further during thermal annealing. The density of the electrically activated impurities is approximately 1019 cm-3.

We report sapphire-based Dammann gratings (DGs) for ultraviolet (UV) beam (266 nm) splitting, which is fabricated via femtosecond laser direct writing assisted with subsequent wet etching. By applying 400-nm-wavelength laser processing followed by wet etching, smooth surface morphology, together with well-tailored geometry, was obtained. These DGs generated 2 × 2, 3 × 3, 4 × 4, and 5 × 5 spot sources in the fan-out as designed and exhibited diffraction efficiency of 59.26%, 39.53%, 44.68%, and 55.37%, respectively, comparable with theoretical values. Such sapphire-based DGs show great potential in UV beam shaping, UV beam splitting, and laser parallel microprocessing.

We have investigated the strong coupling interaction between excitons of CdSe quantum dots (QDs) and surface plasmon polaritons (SPPs) of gold nanohole array by steady-state spectroscopic method and transient absorption measurements. Numerical and experimental steady-state measurements demonstrate that the SPP-QD system can indeed undergo strong coupling, characterized by a Rabi splitting up to 220 meV. In particular, it is found that in the transient absorption spectra, under resonant excitation, the 1S transition bleaching band from uncoupled CdSe QDs is completely separated into two distinctive bleaching bands, remarkably fingerprinting the hybrid SPP-QD state. It was also found that the lifetime of these hybrid bands is just slightly shorter than the lifetime of bare CdSe QDs, possibly caused by the phonon bottleneck effect due to the large Rabi splitting. These results could open a new avenue toward the development of novel nanoplasmon devices with strong SPP-QD interaction.

We demonstrate a novel mode-selecting microcavity laser composed of gratings and a microdisk and fabricated by femtosecond-laser direct-writing technology. The microcavity laser shows good directivity and a single longitudinal mode, resulting from the mode coupling between the microdisk and gratings. The lasing wavelength can be regulated by adjusting the grating period. The properties of the laser were investigated and show good agreement with theoretical calculation and simulation. Based on the behavior and properties, this novel microcavity laser demonstrates good application prospects in integrated microoptics devices.

Herein, by using maskless and noncontact femtosecond laser direct writing (FsLDW) form protein aqueous ink, protein-based Y-junction optical micro/nano-splitters (PYOMs) have been readily customized with environmental-stimulus-actuated light-splitting adjustments for the first time to our knowledge. Bio/eco-compatible protein-based biopolymer successfully acted as the ideal alternative of artificial polymers for optical waveguide devices. Based on flexibly programmable “one-step” FsLDW, applicable shape-symmetric PYOMs were facilely fabricated with tailorable light-power-splitting ratios (from ∼1:1 to ∼3:1 in air). Significantly, via environmental responses and sensitivity of protein hydrogels, another type of “heterogeneous” PYOMs exhibited “smart” dynamic adjustments of light-power-splitting ratios by simply tuning surrounding chemical stimuli for example of pH value (∼1:1 in air, ∼1.35:1 in pure water, and 1.48:1–1.85:1 under pH 2.0–6.0), showing their application promise for optical sensing and environment-signal-actuated tunable micro/nano-optics.

Suspended structures have attracted a great deal of attention in the field of micro-technology and nanotechnology for their important functions. However, the fabrication of the suspended structures is typically cumbersome and time-consuming and requires complicated processes, such as multiple deposition, photolithography, and etching. Here, we report a new method of fabricating flexible suspended structures by femtosecond laser direct writing followed by wet chemical alkaline (KOH) etching. Our proposed method will enable convenient and flexible fabrication of suspended structures for a wide variety of applications in the field of micro-technology and nanotechnology.

Here, we report a sapphire-based Fresnel zone plate (FZP), which is fabricated by femtosecond laser direct writing assisted with subsequent wet etching. With this method, we solved the problem of high surface roughness caused by ultrafast femtosecond laser processing. We have obtained $\sim 12$ -nm average surface roughness smaller than 1/25 of the optical working wavelength. As-formed sapphire FZP also exhibited a well-defined geometry. More importantly, ultraviolet (UV) light focusing and imaging can be easily achieved. Due to the high material hardness, thermal and chemical stabilities of sapphire, such sapphire FZP, may have great potential in UV imaging and focusing under some harsh environments.