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1.
Opt Lett ; 45(9): 2580-2583, 2020 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-32356821

RESUMO

Here a continuous axial-spiral phase microplate (CAsPP), based on combining a logarithmic axicon and a spiral phase plate, was proposed for generating high-quality higher-order Bessel vortex beams. The novel optical component implemented via femtosecond laser direct writing possesses compact geometry and unique optical properties. The CAsPP with a diameter of 80 µm possesses a controllable long focus ranging from 50 to 600 µm and exhibits a good self-healing ability after free transmission of about 45 µm. Unique optical properties were demonstrated in both experiments and simulations, which were well matched to each other. This Letter provides new opportunities for applications in integrated optics, optical trapping, laser machining, and information reconstruction.

2.
Opt Lett ; 45(9): 2684-2687, 2020 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-32356847

RESUMO

We propose a precise diamond micromachining method based on ultraviolet femtosecond laser direct writing and a mixed acid heating chemical treatment. The chemical composition of the attached clusters generated during laser ablation and their effects on morphologies were investigated in experiments. The averaged roughness of pristine and processed regions reduced to 0.64 nm and 9.4 nm from 20.5 nm and 37.4 nm, respectively. With this method, spiral zone plates (SZPs) were inscribed on a high-pressure high-temperature diamond surface as micro-optical vortex generators. The optical performances of the diamond SZPs were characterized in both experiments and simulations, which were very consistent with each other. This chemical auxiliary processing method will contribute greatly to the wide application of integration and miniaturization of diamond surface optical components.

3.
ACS Appl Mater Interfaces ; 12(9): 10107-10117, 2020 Mar 04.
Artigo em Inglês | MEDLINE | ID: mdl-32046483

RESUMO

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.

4.
Opt Lett ; 45(3): 636-639, 2020 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-32004271

RESUMO

We report fabrication of silica convex microlens arrays with controlled shape, size, and curvature by femtosecond laser direct writing. A backside etching in dye solution was utilized for laser machining high-fidelity control of material removal and real-time surface cleaning from ablation debris. Thermal annealing was applied to reduce surface roughness to 3 nm (rms). The good optical performance of the arrays was confirmed by focusing and imaging tests. Complex 3D micro-optical elements over a footprint of $100 \times 100\;\unicode{x00B5}{{\rm m}^2}$100×100µm2 were ablated within 1 h (required for practical applications). A material removal speed of $120\;\unicode{x00B5}{{\rm m}^3}/{\rm s}$120µm3/s ($6 \times {10^5} \;{{\rm nm}^3}/{\rm pulse}$6×105nm3/pulse) was used, which is more than an order of magnitude higher compared to backside etching using a mask projection method. The method is applicable for fabrication of micro-optical components on transparent hard materials.

5.
Opt Lett ; 44(21): 5149-5152, 2019 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-31674953

RESUMO

We demonstrate a versatile method for fast and flexible fabrication of either one or an array of microlenses. Multi-foci axial intensity distribution generated by a phase pattern displayed on a spatial light modulator irradiates silica, causing ablation and its internal modification. The following wet etching step defines the diameter r, while the radius of curvature R (hence, the focal length f) is maintained the same. As a result, the numerical aperture NA=r/f changes from 0.2 to 0.4 for the same pulse energy (but different number of multi-foci) during ablation. An isotropic wet etching of silica becomes highly anisotropic for the initial stages of etching following the irradiated pattern. Subsequent evolution of the shape is governed by an isotropic silica etch and forms a spherical lens. This method can be extended to other materials and geometries of micro-optical elements.

6.
Nanomaterials (Basel) ; 9(10)2019 Oct 03.
Artigo em Inglês | MEDLINE | ID: mdl-31623407

RESUMO

Birefringence of 3 × 10 - 3 is demonstrated inside cross-sectional regions of 100 µ m, inscribed by axially stretched Bessel-beam-like fs-laser pulses along the c-axis inside sapphire. A high birefringence and retardance of λ / 4 at mid-visible spectral range (green) can be achieved using stretched beams with axial extension of 30-40 µ 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.

7.
Opt Lett ; 44(10): 2454-2457, 2019 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-31090705

RESUMO

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.

8.
ACS Nano ; 13(4): 4041-4048, 2019 04 23.
Artigo em Inglês | MEDLINE | ID: mdl-30677287

RESUMO

Strategies that can make general materials smart are highly desired for developing artificial shape-morphing systems and devices. However, at present, it still lacks universal technologies that enable designable prototyping of deformable 3D micro-nanostructures. Inspired by natural automation systems, for instance, tendrils, leaves, and flowers deform dynamically under external stimuli by varying internal turgor, we report a dual-3D femtosecond laser processing strategy for fabricating smart and deformable 3D microactuators based on general photopolymers. By programming the size and distributions of voxels at the nanoscale, both the 3D profile and the 3D internetwork of a general photopolymer could be tailored in a controlled manner; thus, 3D microstructures encoded with precisely tailored networks could perform predictable deformations under certain stimuli. Using this dual-3D fabrication approach, energetic 3D microactuators, including a smart microflower, a responsive microvale, and an eight-finger microclaw, that permit controllable manipulation have been successfully developed.

9.
Adv Mater ; 31(5): e1806386, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-30536794

RESUMO

Muscles and joints make highly coordinated motion, which can be partly mimicked to drive robots or facilitate activities. However, most cases primarily employ actuators enabling simple deformations. Therefore, a mature artificial motor system requires many actuators assembled with jointed structures to accomplish complex motions, posing limitations and challenges to the fabrication, integration, and applicability of the system. Here, a holistic artificial muscle with integrated light-addressable nodes, using one-step laser printing from a bilayer structure of poly(methyl methacrylate) and graphene oxide compounded with gold nanorods (AuNRs), is reported. Utilizing the synergistic effect of the AuNRs with high plasmonic property and wavelength-selectivity as well as graphene with good flexibility and thermal conductivity, the artificial muscle can implement full-function motility without further integration, which is reconfigurable through wavelength-sensitive light activation. A biomimetic robot and artificial hand are demonstrated, showcasing functionalized control, which is desirable for various applications, from soft robotics to human assists.

Assuntos
Materiais Biomiméticos/química , Grafite/química , Ouro/química , Luz , Modelos Anatômicos , Nanotubos/química , Polimetil Metacrilato/química , Robótica , Condutividade Térmica
10.
Opt Lett ; 43(13): 3116-3119, 2018 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-29957793

RESUMO

In this Letter, we report mirror-rotation-symmetrical single-focus spiral zone plates (MS-SZPs) fabricated by femtosecond laser direct writing. The novel optical element can generate a single-focus vortex beam, owing to the element's complicated continuous surface. The MS-SZP surface possesses reverse mirror-rotation symmetry, which ensures that the transfer element has the same surface morphology as the original element. Both the transfer element and original element have good optical properties. The single-focus behavior was investigated by a microscopic imaging system and found to be in good agreement with theoretical simulation results. The innovative optical component is expected to be widely used in optical communication, quantum computation, optical manipulation, and other fields.

11.
Langmuir ; 34(20): 5712-5718, 2018 05 22.
Artigo em Inglês | MEDLINE | ID: mdl-29706078

RESUMO

Reported here is a high-efficiency preparation method of amorphous nickel phosphide (Ni-P) nanoparticles by intense femtosecond laser irradiation of nickel sulfate and sodium hypophosphite aqueous solution. The underlying mechanism of the laser-assisted preparation was discussed in terms of the breaking of chemical bond in reactants via highly intense electric field discharge generated by the intense femtosecond laser. The morphology and size of the nanoparticles can be tuned by varying the reaction parameters such as ion concentration, ion molar ratio, laser power, and irradiation time. X-ray diffraction and transmission electron microscopy results demonstrated that the nanoparticles were amorphous. Finally, the thermogravimetric-differential thermal analysis experiment verified that the as-synthesized noncrystalline Ni-P nanoparticles had an excellent catalytic capability toward thermal decomposition of ammonium perchlorate. This strategy of laser-mediated electrical discharge under such an extremely intense field may create new opportunities for the decomposition of molecules or chemical bonds that could further facilitate the recombination of new atoms or chemical groups, thus bringing about new possibilities for chemical reaction initiation and nanomaterial synthesis that may not be realized under normal conditions.

12.
Nanomaterials (Basel) ; 8(5)2018 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-29710764

RESUMO

We report a systematical study on the liquid assisted femtosecond laser machining of quartz plate in water and under different etching solutions. The ablation features in liquid showed a better structuring quality and improved resolution with 1/3~1/2 smaller features as compared with those made in air. It has been demonstrated that laser induced periodic structures are present to a lesser extent when laser processed in water solutions. The redistribution of oxygen revealed a strong surface modification, which is related to the etching selectivity of laser irradiated regions. Laser ablation in KOH and HF solution showed very different morphology, which relates to the evolution of laser induced plasma on the formation of micro/nano-features in liquid. This work extends laser precision fabrication of hard materials. The mechanism of strong absorption in the regions with permittivity (epsilon) near zero is discussed.

13.
Opt Lett ; 43(8): 1710-1713, 2018 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-29652346

RESUMO

Non-doped black silicon (b-Si) is fabricated on the surface layer of a near-intrinsic Si substrate by nanosecond (ns) laser direct writing in an argon (Ar) atmosphere. The non-doped samples exhibit a near-unity sub-bandgap (1100â¼2500 nm) absorptance of more than 50%. Amazingly, the resistivity of the ns laser irradiated b-Si layer is about five orders of magnitude lower than that of the unprocessed Si substrate. The carrier density of the b-Si layer is about 1×1018 cm-3, according to the Hall effect measurement. Temperature-dependent Hall effect measurements show that the non-doped b-Si layer exhibits an energy level of 0.026 eV below the conduction band minimum (CBM). At last, Si infrared photodiodes are made based on the difference of carrier concentration between the ns laser-processed b-Si layer and the high-resistivity Si substrate. The responsivity of the b-Si photodiode for 1310 nm is up to 256 mA/W at a 10-V reverse bias, which is much higher than that of the reported pure Si bulk-structure photodiodes.

14.
Opt Lett ; 43(4): 831-834, 2018 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-29444005

RESUMO

This work developed a method of femtosecond laser (fs-laser) parallel processing assisted by wet etching to fabricate 3D micro-optical components. A 2D fs-laser spot array with designed spatial distribution was generated by a spatial light modulator. A single-pulse exposure of the entire array was used for parallel processing. By subsequent wet etching, a close-packed hexagonal arrangement, 3D concave microlens array on a curved surface with a radius of approximately 120 µm was fabricated, each unit lens of which has designable spatial distribution. Characterization of imaging was carried out by a microscope and showed a unique imaging property in multi-planes. This method provides a parallel and efficient technique to fabricate 3D micro-optical devices for applications in optofluidics, optical communication, and integrated optics.

15.
Phys Chem Chem Phys ; 20(10): 6945-6950, 2018 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-29465118

RESUMO

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.

16.
Opt Lett ; 42(21): 4446-4449, 2017 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-29088184

RESUMO

Formation of ripples by ablation of surfaces of laser-irradiated materials is an example of ultrafast energy delivery. Herein, we report on fs-laser optical imprinting of periodic nano-grooves on silica substrate at only 25% of the laser ablation threshold via an interface plasmonic light localization at the ZnS film (top) interface with silica (bottom) by plasmonic surface wave. The nano-grooves were formed throughout ZnS with the same period and orientation imprinted onto the underlying silica. Based on a detailed account of the multi-photon and avalanche ionization using the Drude model, laser-induced plasmonic ablation describes quantitatively the energy deposition from the top ZnS to the substrate of silica.

17.
Opt Lett ; 42(19): 3832-3835, 2017 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-28957140

RESUMO

Herein, we report a kinoform phase-type lens (KPL), which is fabricated by femtosecond (fs)-laser-induced refractive index change inside sapphire crystal. By fabricating volume phase gratings in sapphire and measuring the energy ratio of the grating's first and second diffraction orders, the refractive index change in sapphire induced by fs-laser modification was obtained. Then a four-level KPL was designed and fabricated inside sapphire following the experimentally established scaling of the refractive index change and fs-laser power. Importantly, the KPL has unique UV focusing and imaging capability as well as a stable optical performance in different refractive index environments. The KPL embedded in sapphire has the same optical performance after a high-temperature (1050°C) annealing for 30 min. The KPLs in sapphire have great potential to increase light extraction efficiency in GaN blue-UV light-emitting diodes and can be used in micro-optical sensor applications in chemically harsh and high-temperature environments.

18.
Phys Chem Chem Phys ; 19(36): 24735-24741, 2017 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-28861554

RESUMO

Femtosecond lasers (fs) can cause a disparity between electronic and lattice temperatures in the very short period after irradiation. In this relatively cool lattice regime, the material properties can differ drastically from those under thermal equilibrium. In particular, first-principles calculations reveal two general mechanical effects on semiconductors. Firstly, the excitation can induce a negative pressure on the lattice, causing a >10% expansion, even for superhard diamond. Secondly, it induces inhomogeneous local forces on the atoms, for both perfect and distorted lattices. In the case of phase-change-memory for Ge2Sb2Te5 and GeTe alloys, such random forces cause a simultaneous phase transition from crystalline to amorphous, which enables faster data writing. These excitation effects are further supported by the time-dependent density functional theory. This work could be an important step in advancing fs laser techniques for the atomic-level control of structures, rather than relying on traditional melting or ablation approaches which often apply to much larger and non-atomic scales.

19.
Opt Lett ; 42(8): 1572-1575, 2017 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-28409801

RESUMO

In this Letter, we report a suspended whispering gallery mode microdisk with a hole pierced through its surface. The novel disk is made up of Rhodamine B-doped resin, which is fabricated by femtosecond laser direct writing technology. The pierced microcavity achieves highly directional emission of single-mode lasing with a far field divergence angle of about 10 deg, and its high Q factor exceeds 2.6×103. The excellent properties are confirmed by numerical simulation based on the finite-difference time-domain method. The effect of the pierced hole on the microcavity performance is discussed in detail. The method is easy to implement and has a guiding significance for improving the characteristics of an existing microcavity by simple modification.

20.
Appl Opt ; 56(8): 2157-2161, 2017 Mar 10.
Artigo em Inglês | MEDLINE | ID: mdl-28375300

RESUMO

In this paper, a maskless, high efficiency, and flexible technology is developed to fabricate three-dimensional (3D) microstructures on a silicon wafer, which is based on the combination of femtosecond laser modification and subsequent dry etching. The silicon atoms in 2D patterned areas were insufficiently oxidized after femtosecond laser irradiation. Complex 3D structures can be fabricated on the silicon wafer after etching, such as micro gears, comb drive actuators, and micro cantilevers applied in microelectromechanical systems (MEMS) and micro Fresnel zone plates applied in micro optics. What is more, surface roughness of the laser structured wafer can be improved with increased etching time in the dry etching process. This technology shows its unique capacity to fabricate various 3D microstructures for applications in MEMS and micro optics.